university of nairobi school of...
TRANSCRIPT
1
UNIVERSITY OF NAIROBI
SCHOOL OF ENGINEERING DEPARTMENT OF ENVIRONMENTAL AND BIOSYSTEMS ENGINEERING
REPORT
PROJECT TITLE: DESIGN OF AN AQUAPONIC SYSTEM
CANDIDATE NAME: WAMBUA LYDIA WAYUA
CANDIDATE NO: F21/1731/2010
SUPERVISOR’S NAME: MR. S.C ONDIEKI
DATE OF SUBMISSION: 29Th
MAY, 2015
A Report Submitted in Partial Fulfillment of the Requirements of the Degree of Bachelor of
Science in Environmental and Bio Systems Engineering of
University of Nairobi
FEB 540: ENGINEERING PROJECT
2014/2015 ACADEMIC YEAR
2
DECLARATION
I declare that this project is my original work and has not been submitted for a degree in any
other University.
Sign ………………………………….. Date…………………………………………..
(Wambua Lydia Wayua)
This project report has been submitted for examination with my approval as University
supervisor.
Sign …………………………………… Date…………………………………………
(MR. S.C ONDIEKI)
Supervisor
3
DEDICATION
I dedicate this project to my family, for their never ending support throughout; to my friends for
their assistance, to my supervisor, Mr. Ondieki for his understanding and guidance. I finally
dedicate it to the prospect farmer in Kamulu, for her inspiration to me to carry out this project.
4
ACKNOWLEDGEMENT
First and foremost, I extend my gratitude to God, for His ever presence and success.
Much esteem goes to my supervisor, Mr. Ondieki for his support and his tremendous knowledge
and skill toward my project till the end.
I also acknowledge the rest of the supervisors for their advice in class, and my friends for their
encouragement and support.
I acknowledge Mr. Daniel Kimani, an aquaponist, for his contribution to my project.
To all I say thank you and God bless you.
5
ABSTRACT.
This report entails the designing of an aquaponic system. This is a system of simultaneously
growing crops and rearing fish on the same piece of land, whereby the fish and crops live in a
symbiotic relationship; the fish supplies nutrients to the crops while the crops clean the water for
the fish by removing ammonia (produced by the fish), which would otherwise accumulate to
toxic levels for the fish survival.
The design focus is to optimize the use of agricultural resources of land, water, as well as labour,
to make farming more sustainable. It addresses two issues; (1) the issue of limited land for
farming in the city and its outskirts and (2) low yields associated with inconsistent water and
nutrient supply.
Functional decomposition and synthesis method was applied for the conceptual design of the
system as a logical approach that describes the transformation between initial and final states of
the system, relying on restructuring the design task to a more abstract and comprehensive level to
promote greater access to the understanding of the system.
The alternatives produced by the functional decomposition were analyzed through a decision
matrix that facilitated the selection of the most suitable and customized system for the problem at
hand. The analysis and prioritization conducted for the alternatives was in accordance to the
ranking of the engineering characteristics obtained from the House of Quality.
Design criteria for aquaponic systems successfully applied to similar systems, especially by the
pioneers of aquaponic systems from the University of Virgin Islands have been applied in the
design. The engineering principles of fluid mechanics were used to determine the correct water
velocity and flow rate for fish swimming and fish tank self-cleaning, the required settling
velocity for sediments in the sedimentation tank, the required pressure to supply water to the
towers and the associated system head, head losses and pumping requirements. Material
selection was used to select the most suitable materials for the tanks and pipes. The layout of the
system and associated detailed drawings were drawn using AutoCAD.
For further up-scaling of the project and for environmental and financial sustainability, it was
recommended that solar or wind power should be enhanced as part of the energy source. Rain
water could also be harvested as an alternative source of water. Automatic fish feeding system
and mobile phone-control of the system is also recommended as steps toward automation of the
system as much as is acceptable. Other hydroponic design alternatives apart from vertical tower
system could also be applied for a given locality and project.
6
Table of Contents
DECLARATION ............................................................................................................................ 2
DEDICATION ................................................................................................................................ 3
ACKNOWLEDGEMENT .............................................................................................................. 4
ABSTRACT. ................................................................................................................................... 5
CHAPTER 1 ................................................................................................................................... 9
INTRODUCTION ...................................................................................................................... 9
1.1 PROBLEM STATEMENT AND PROBLEM ANALYSIS ............................................ 9
Problem statement .................................................................................................................. 9
Hypothesis ............................................................................................................................... 9
Problem Analysis and justification ......................................................................................... 9
Converging point of aquaponics and the current soil farming ................................................. 13
1.2 SITE ANALYSIS AND INVENTORY ......................................................................... 14
1.2.1 Location ....................................................................................................................... 14
1.2.2 Climate ......................................................................................................................... 15
1.2.3 Water supply ................................................................................................................ 16
1.2.4 Electricity supply ......................................................................................................... 16
1.2.5 Farming........................................................................................................................ 16
1.2.6 Significance of the site ................................................................................................. 16
1.3 OVERALL OBJECTIVE ............................................................................................... 17
1.3.1 SPECIFIC OBJECTIVES........................................................................................ 17
1.4 STATEMENT OF SCOPE............................................................................................. 18
CHAPTER 2 ................................................................................................................................. 19
LITERATURE REVIEW AND THERORETICAL FRAMEWORK ..................................... 19
2.1 Literature Review................................................................................................................ 19
2.1.3 Nutrient source for hydroponics and aquaponics ........................................................ 19
2.1.4 System design ............................................................................................................... 20
2.1.5 Overview of unit operation ..................................................................................... 21
2.2 Theoretical framework ........................................................................................................ 32
2.2.1 Sizing the hydroponic growing area ............................................................................ 32
2.2.2Sizing and design of the fish rearing tanks ................................................................... 32
7
2.2.3 Tower development ..................................................................................................... 35
2.2.4 Settling basin design details ......................................................................................... 35
2.2.5 Aeration requirements .................................................................................................. 36
2.2.6 Pump sizing .................................................................................................................. 36
2.2.7 Piping ........................................................................................................................... 37
CHAPTER 3 ................................................................................................................................. 41
GENERATION OF CONCEPT DESIGN ................................................................................ 41
4.1. Overall Functional decomposition and synthesis .............................................................. 41
4.2 Functional decomposition and synthesis for this project .................................................... 42
4.3 Generation and analysis of alternative solutions ................................................................ 43
4.3.1 Selection of a hydroponic system ................................................................................ 44
4.3.2 Selection of the solids removal devices ....................................................................... 45
4.3.3 Selection of the fish culture tank ................................................................................. 47
4.3.4 Selection of an aeration device .................................................................................... 47
4.4 Generated conceptual design .............................................................................................. 48
CHAPTER 4 ................................................................................................................................. 49
METHODOLOGY ....................................................................................................................... 49
CHAPTER 5 ................................................................................................................................. 54
RESULTS ................................................................................................................................. 54
CHAPTER 6 ................................................................................................................................. 71
6.1 CONCLUSION ................................................................................................................... 71
6.2 RECOMMENDATION .......................................................................................................... 74
6.3 REFERENCES .................................................................................................................. 75
APPENDICES .............................................................................................................................. 77
Appendix A ............................................................................................................................... 77
Appendix B ............................................................................................................................... 80
8
List of figures
Figure 1: Bar chart showing Hydroponic vs. Conventional Farming ........................................... 11
Figure 2: Maps showing project location in Kamulu area, Nairobi, Kenya ................................. 14
Figure 3: Chart showing Kamulu average temperature ranges from 2000-2013.......................... 15
Figure 4: Graph showing the average temperature and the rainfall pattern of Kamulu ............... 16
Figure 5: Photo of commercial aquaponic farming using vertical towers .................................... 19
Figure 6: Optimal arrangement of aquaponic system components ............................................... 21
Figure 7: Common rearing tank shapes ........................................................................................ 21
Figure 8: Settling basin ................................................................................................................. 24
Figure 9: Radial flow separator..................................................................................................... 25
Figure 10: NFT System ................................................................................................................. 27
Figure 11: Raft system .................................................................................................................. 28
Figure 12: Aeroponic system ........................................................................................................ 29
Figure 13: Ebb and flow system ................................................................................................... 29
Figure 14: Vertical system ............................................................................................................ 30
Figure 15: Growing area 15 x 8 m ................................................................................................ 55
Figure 16: Front and side view of a single tower.......................................................................... 56
Figure 17: Drawing of one fish tank layout .................................................................................. 61
Figure 18: Sketch of a settling tank .............................................................................................. 63
Figure 19: Sedimentation tank layout ........................................................................................... 64
Figure 20: System layout .............................................................................................................. 70
Figure 21: Moody chart ................................................................................................................ 78
Figure 22: House of quality most complete configuration ........................................................... 78
Figure 23: Data collection photos ................................................................................................. 80
Figure 24: Google earth map showing the elevation of the farm ................................................. 80
List of Tables
Table 1: Cost-Benefit Analysis ..................................................................................................... 13
Table 2: Exclusion screen sizes .................................................................................................... 35
Table 3: Circulation- drains/pumped return line ........................................................................... 38
Table 4: Decision matrix for a hydroponic system ....................................................................... 45
Table 5: Decision matrix for a solids removal device .................................................................. 46
Table 6: Analysis of fish tanks...................................................................................................... 47
Table 7: Bill of Quantities............................................................................................................. 73
Table 8:The aquaponic House of Quality streamlined configuration Rooms 1,2,3,4 and 5 ......... 79
9
CHAPTER 1
INTRODUCTION
1.1 PROBLEM STATEMENT AND PROBLEM ANALYSIS
Problem statement
The project is designed to addresses two major issues; (1) The issue of limited land for farming
in the city and its outskirts and (2) Low yields associated with inconsistent water and nutrient
supply.
Hypothesis
An aquaponic system can grow 90% more food on 90% less land.
It optimizes agricultural resources of land, water, nutrients and labour, consequently optimizing
yields, income, and the selection of the best enterprise for a potential farmer.
Problem Analysis and justification
Significance of Agriculture to Kenyan economy
Agricultural sector in Kenya is the largest employer in the economy, accounting for 60% of the
total employment. It directly contributes 24%of the GDP and indirectly contributes 27% through
linkages with manufacturing, distribution and other service related sectors. 45% of government
revenue is derived from agriculture. It contributes over 75% of industrial raw materials and 60%
of export earnings. About 80% of the population living in the rural areas derives their livelihoods
mainly from agricultural activities.1 Yet agriculture still faces a number of challenges.
Current challenges in agricultural development in Kenya
The key challenges include:
o Agriculture is the mainstay of the economies but is practiced at subsistence scale
with low levels of commercialization
o Low adoption of improved technologies/innovations leading to low productivity
and fragile resource base
o Overreliance on labour intensive and low productive agricultural technologies
1 http://www.amshaafrica.org/projects-and-clients/current-projects/aquaponics-in-rural-kenya.html
10
o Overreliance on rain fed agriculture, famines being a common problem due to
droughts
o Biotic and abiotic stresses for crops and livestock, leading to yields losses due to
pests, diseases, drought, natural resource degradation, etc
o Socio-cultural orientation among some communities where agriculture as viewed
as a non-commercial venture, and
o Reduced focus and /or low investments in agricultural ventures and training
Opportunities for development of agricultural sector
There is interest to make agricultural sector more competitive due to globalization. One of the
opportunities from the Kenyan vision 2030 is its interest in making agriculture a commercial
undertaking and creating development impact by recognizing that market driven and private
sector-led growth transforms agriculture. There are thus numerous opportunities from the
increased need to conserve and sustainably utilize natural resources to the need of adopting
technologies.
Adoption of Aquaponics
This is a system of farming that is independent on the soil type, and whose scale can be increased
on a limited land. It can thus be well applied in existing or upcoming urban settings, such as
Kamulu town in Kenya.
Aquaponics is a farming technique that combines the production of crops through hydroponics
and the rearing of fish though aquaculture. In aquaponics, any of the two systems can either be
the primary or the secondary component depending on the needs of the user.
Hydroponics has been recognized as a viable method of producing vegetables: tomatoes, lettuce,
cucumbers, peppers and strawberries as well as ornamental crops such as herbs, roses, freesia
and foliage plants. Aquaponics, which mimics the natural dynamics of all of earth's water ways,
is the only organic hydroponic method that has proven to be commercially viable. And, as an
added bonus, one produces two crops - fish and vegetables. The fertilizer in an aquaponic system
comes from the fish waste. Microbial activity converts the waste into nutrients that the plants
need and, as the plants consume the nutrients, they help to purify the water the fish live in. This
all happens in a recirculating system that uses less water than traditional agriculture.
11
Why Aquaponics?
Aquaponics is the solution to many of the global problems faced today. Here are just some of the
environmental, social, and financial reasons why:
Population Growth: The World Health Organization estimates that one-third of the world goes
hungry. If we are to feed the world sustainably, now and in the future, we need to grow food
closer to where it will be consumed in an efficient and sustainable way. If we don't, vital
ecosystems worldwide will have to be replaced with farmland needed to feed our growing
population.
Economy: Every cent spent locally generates twice as much income for the local economy.
When consumers buy imported goods, money leaves the community at every transaction.
Closing the loop makes good economic sense: by supporting local agriculture we will keep our
money re-circulating in the local economy. In addition, local food is fresher, tastes better, and
makes us more secure than relying on imported food.
Due to increased energy costs, importing food is becoming cost prohibitive. Demand for high-
quality fish products is also increasing as importation costs increase.
Figure 1: Bar chart showing Hydroponic vs. Conventional Farming
(Hydroponic represented by the color orange)
The above chart shows the relative amounts of resources it takes to produce equal amounts of
food using these two farming practices. Compared with conventional field agriculture,
12
hydroponics (low impact method of growing plants in nutrient solutions without using soil) is
sustainable, efficient, and requires no pesticides.
Additionally, hydroponic produce is picked ripe, and is thus fresher and tastier than
conventionally farmed produce, which is typically picked prematurely, transported hundreds or
thousands of miles, and then "gas blasted" with ethylene hormone to ripen artificially.
Energy: Food produce travels huge distances from farm to consumers. With consumers'
increasing awareness of „food miles' and the 'true cost' it takes to produce their food, preference
is shifting towards local, sustainable agriculture.
Water: 70% of all available freshwater is used for agriculture. Global water problems, already at
crisis proportions, are already a source of conflict in many areas and could escalate into full-
blown war in the future. The time has come for us to become better stewards of this most
precious of natural resources. Representing less than 1% of all water on Earth, freshwater is
essential to all life, and we can no longer afford to waste it.
Kenya has not yet become autonomous in food as evidenced in parts of the country facing severe
famine and continued importation of food into the country from our neighboring countries. As
one way to attain food self-sufficiency as well as agricultural commercialization, adoption of
aquaponic systems would be one of the best ways forward.
Currently very few farmers have adopted this technology, a technology that optimizes
production components of water, land, time and all the farm inputs such as fertilizers. For
instance, in the production of strawberries which is the main crop in this design project, most
farmers are cultivating the crop on soil. Strawberries are exceptionally suited for hydroponic
cultivation and adoption of this technology, when well implemented, would offer more benefits of
higher and sustainable yields, less soil-borne pests and diseases, less usage of water, easier
cultivation and picking due to the elevated height of crops, production of more crops on less land
and increased source of food and income from the production of fish.
The payback to be gained from practicing crop farming within an aquaponic system can be
analyzed in a cost-benefit analysis:
13
Table 1: Cost-Benefit Analysis
C0ST-BENEFIT ANALYSIS
Category Costs Benefits
Economic
(tangible)
Capital Bigger yields
Knowledge (agronomy: fish and crop health) Quicker yields
Training Lower water and nutrient costs (recycling and
water usage efficiency)
Maintenance of components Elimination of soil borne diseases and insects
Water and electricity reliability Almost any land is suitable (from poor soils to
paved areas)
No weeding or cultivation required
Crop rotation/fallowing is unnecessary
Job creation: is labor intensive especially
during peak season
Intangible
Record keeping: of fish and crop growth,
health, harvesting and replacement seasons More control; nutrient content, Ph, growing
environment
More attention and observation of parameters
e.g, Ph
Better working conditions: crops can be lifted
from ground level, less fatiguing, and suitable
for rural as well as urban areas
High level of sanitation by people and within
the system to minimize pathogen attacks Preserves the pace of farming technology
advancement
Healthier and bigger crops and fish
Sustainable yields: thus sustainable food
production and/or entreprise
No soil testing or use of farm equipment
Converging point of aquaponics and the current soil farming
The converging point for taking up this technology would be for prospective farmers in the
production of some vegetative and fruiting crops and herbs that are well suited in an aquaponic
system to adopt the technology or/and for current „soil‟ farmers to whom this technology would
be more feasible in terms of production components and sustainability.
Aquaponics is an appropriate technology that is socially acceptable because it creates necessary
labour for handling the crops and fish and removes the major farming bottlenecks; economically
viable because it has proved to be financially rewarding in terms of costs v benefits; and
technically feasible because the technology is readily available and easy to adopt.
14
Through the diffusion of technology, it is necessary to preserve the pace of farming technology
advancement by conducting a project such as aquaponic farming.
1.2 SITE ANALYSIS AND INVENTORY
1.2.1 Location
The proposed site selected for the system is Kipawa area at Kamulu sub-location, Njiru district,
Nairobi County, Kenya. Its geographic coordinates of the site was obtained from a GPS on
21/04/15 at 4pm; S 01016.323‟ , E 037
O02.982‟
Figure 2: Maps showing project location in Kamulu area, Nairobi, Kenya
15
1.2.2 Climate
The climate is warm and temperate in Kamulu. In winter there is much less rainfall in Kamulu
than in summer. According to Köppen and Geiger climate is classified as Cwb (temperate
highland tropical climate with dry winters)2. The average annual temperature in Kamulu is 19.7
°C (range between 15-30 º C). The area receives low rainfall with an average of annual rainfall
of 720 mm. The altitude of the area is 1483 meters.
Figure 3: Chart showing Kamulu average temperature ranges from 2000-2013
(Source: weather online data 2000-2013)
2 http://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classification
29
31 31 30
29 28
27 27
29 30
28 27
18 18 19 19
18
15 15 15 16
17 18 18
0
5
10
15
20
25
30
35
jan feb mar april may june july aug sep oct nov dec
Tem
peraure ( C )
Months
Average High/Low Temperature for Kamulu, Kenya
Average high temperature Average low temperature
16
Figure 4: Graph showing the average temperature and the rainfall pattern of Kamulu
1.2.3 Water supply
Piped water supply to the area exists though it is inadequate to meet current city demand and
reticulation (network) does not cover the whole area. The Kamulu area is mostly serviced by
private boreholes. Developers adopt coping strategies such as sinking of boreholes or allowing
for underground reservoir tanks to tap intermittent water inflows. (NEMA, EIA)
1.2.4 Electricity supply
The Kenya Power and Lighting Co. (KPLC) currently supplies Grid power to the Kamulu area
though neighbours claim it is of low reliability (frequent interruptions and/or low voltage). The
timelines for KPLC proposals to increase bulk power supply to the area are unclear and measures
to mitigate this have to be put in place. A common back-up power supply generator is proposed
for the common areas coupled with battery-inverter systems for each houses emergency power
supply. The power supply will be augmented by solar water heating systems in each house for
energy conservation. ( NEMA, EIA)
1.2.5 Farming
Currently there exists no strawberry faming in the area. The commonly grown crops are one in
small scale and include tomatoes, capsicums and mushrooms.
1.2.6 Significance of the site
The temperature condition of the site will offer a major advantage for the application of the
aquaponic system. Tilapia thrive in the temperature range of 21.11° C to 29.44° C while the
17
recommended temperature for strawberries is 15-30°C. Thus these two fall exactly within the
temperature range in Kamulu. This is advantageous because it eliminates the need and expense
of designing and installing auxiliary heaters or coolers.
On the other hand, the area receives an annual rainfall of about 720mm; typical of a rather
semiarid area (semiarid areas receive annual rainfall of about 700mm)3. Given that water is
available at the proposed site of project installation, the aquaponic system will be profitable to
the owner of the system because these systems extend water usage and use water at least 10
times more efficiently compared to field farming. The available rainfall could also be harvested
and stored for use in the system. With electricity supply to the area, the project is viable and a
back-up-power system may be installed to increase electricity reliability.
Strawberries require maximum sunlight exposure while presence of rain is undesirable on the
leaves of strawberries. Because of these factors a greenhouse shade cloth will be used; single-
layered around the walls and double-layered roof. This will bar most of the rain from getting into
the structure while allowing diffused sunlight (which is better than direct sunlight for crops) from
the roof and walls. This will avoid the risk of overheating which is highly likely in the area due
to the high temperatures. The shade cloth will also be significant in keeping off birds and insects.
1.3 OVERALL OBJECTIVE
The overall objective of the design project is to design a system that integrates crop and fish
farming for a farmer in Kamulu area, Nairobi. The design is aimed at optimizing the use of land
and water to make the project cost-effective and sustainable.
1.3.1 SPECIFIC OBJECTIVES
The specific objectives are to:
1. Evaluate and select the most suitable design alternative from the available options
2. Design of:
a. A strawberry hydroponic system
b. Circular fish tanks and a sump (water reservoir).
c. Filtration devices namely a settling basin and filtration tanks
3 http://www.iisd.org/casl/asalprojectdetails/asal.htm
18
d. A water recirculating system that consists of pumps, piping, and fittings
for the aquaponic system
1.4 STATEMENT OF SCOPE
The scope of the project covers the design of the basic components that ensure the complete
operation of the aquaponic system and these include the fish rearing components, the hydroponic
component, pump and the solids removal components. The design will not include the structural
design of the components, aeration, the abstraction of water from the source and the electricity
back-up systems, all of which have been mentioned as recommendations.
19
CHAPTER 2
LITERATURE REVIEW AND THERORETICAL FRAMEWORK
2.1 Literature Review
The concept behind aquaponics is that fish and crops can be mutually raised in one recirculating
system that uses relatively small volumes of water whereby the crops and fish co-exist in a
symbiotic relationship: the crops clean/purify the water for the fish by taking up ammonia in the
form of nitrates, while the fish provide a constant supply of nutrients in form of nitrates and other
elements to the crops. Thus an aquaponic system is the combination of a hydroponic component
that involves soilless cultivation of crops and an aquaculture system that involves the rearing of
fish.
A handful of studies have documented the productivity of research-scale aquaponics operations
(Rakocy, 2012, Rakocy et al., 2006 and Watten and Busch, 1984), and in 2013 the United States
Department of Agriculture (USDA) began collecting aquaponics production data as part of the
Census of Aquaculture, which was last published in 2006 (USDA, 2006). Results from research
facilities and other factors, such as expanding interest in sustainable agriculture and producing
food closer to urban centers, have stimulated interest and involvement from a small but growing
aquaponics industry. However, research is still being conducted on commercial-scale aquaponics
production.
Figure 5: Photo of commercial aquaponic farming using vertical towers
2.1.3 Nutrient source for hydroponics and aquaponics
Hydroponic supplies plants with the actual water and nutrient requirements allowing plats to
reach their genetic potential (producing highest yields), 3-4 times more fruitful than conventional
soil farming. Because there is no soil, the nutrients are modified to be in their broken down form
20
so that the crops will not use up energy breaking down the nutrients. Saving this energy is
another reason why the crops are very fruitful. The challenge for hydroponics, especially in
Kenya, is the local availability of hydroponic nutrients. With the recent adoption of this system
in the country, there are now a few distributors of the nutrient solution. The main manufacturer
and supplier is Mr. Chege Peter from Zambezi area in Kikuyu and the nutrient solution is named
„hydropeter‟.
In an aquaponic system, the nutrients supplied to the crops come from the water received from
the aquaculture. Plants grow rapidly with dissolved nutrients that are excreted directly by fish or
generated from the microbial breakdown of fish wastes. In closed recirculating systems with very
little daily water exchange (less than 2 percent), dissolved nutrients accumulate in concentrations
similar to those in hydroponic nutrient solutions.
Aquaponic systems offer several benefits compared to hydroponic systems. Dissolved waste
nutrients are recovered by the plants, reducing discharge to the environment and extending water
use (i.e., by removing dissolved nutrients through plant uptake, the water exchange rate can be
reduced). Minimizing water exchange reduces the costs of operating aquaponic systems. The
daily application of fish feed provides a steady supply of nutrients to plants and thereby
eliminates the need to discharge and replacement of depleted nutrient solutions or adjustment of
the nutrient solutions as in hydroponics. Aquaponic systems require substantially less water
quality monitoring than separate hydroponic or recirculating aquaculture systems. Savings are
also realized by sharing operational and infrastructural costs such as pumps, reservoirs, heaters
and alarm systems. In addition, the intensive, integrated production of fish and plants requires
less land than ponds and gardens.
2.1.4 System design
The design of aquaponic systems closely mirrors that of hydroponic systems in general, with the
addition of an aquaculture component (or vice versa) and the possible elimination of a separate
biofilter and devices (foam fractionators) for removing fine and dissolved solids. Fine solids and
dissolved organic matter generally do not reach levels that require foam fractionation if
aquaponic systems have the recommended design ratio. The essential elements of an aquaponic
21
system are the fish-rearing tank, a settleable and suspended solids removal component, a
biofilter, a hydroponic component, and a sump.
Figure 6: Optimal arrangement of aquaponic system components
Effluent from the fish-rearing tank is treated first to reduce organic matter in the form of
settleable and suspended solids. Next, the culture water is treated to remove ammonia and nitrate
in a biofilter. Then, water flows through the hydroponic unit where some dissolved nutrients are
taken up by plants and additional ammonia and nitrite are removed by bacteria growing in the
media. Finally, water collects in a reservoir (sump) and is returned to the rearing tank.
2.1.5 Overview of unit operation
a. Rearing Tank
Sizing of fish tanks is based upon the density of fish, the primary controller of system stability.
The fish density also ultimately controls the feed application rate. There are three common tank
shapes as shown below.
Figure 7: Common rearing tank shapes
22
Circular tanks
The dominance of circular tanks in the RAS industry stems from their inherent structural and
hydrodynamic nature. The walls of a circular tank are maintained in tension by water pressure,
i.e., they are self-supporting. This allows them to be constructed out of relatively thin
polyethylene plastic or sturdier fiberglass materials. The hydrodynamics of a circular tank
facilitate the rapid removal of suspended solids. A circular tank with a center drain is naturally
good at solids removal. Even a small circulation will tend to accumulate solids in the center
where radial velocities are the lowest.
Rectangular tanks
These tanks are often seen with a 45 degree bevel providing some rounding of the tank corners.
The rectangular tank is prone to poor solids movement but about 20 percent more efficient in
floor space utilization and is more easily harvested than circular tanks. The inherent structural
weakness of a square or rectangular design can be overcome by careful engineering when tanks
are fabricated out of concrete or fiberglass. Earth reinforcement by partial burial can also
alleviate most structural concerns presented by a rectangular tank design. As a result rectangular
tanks are widely used in ornamental fish, baitfish, soft crab, and tilapia industries.
Solids movement in any rectangular tank requires consideration. Serious water quality problems
can occur if solids accumulate in the bottom of a long rectangular tank. Water movement
induced by recirculating water or aeration systems can be used to accelerate solids movement to
the clarifier.
Raceway Tanks
Raceway tanks blend the advantages of the circular and rectangular tanks and are most often
seen in marine culture. A third wall is centered along the tanks length to facilitate controlled
circulation of water. This circulation is highly effective at movement of solids with natural
collection points occurring just downstream of the center panel ends. The rounded ends are
generally compatible with quick moving species that have difficulty navigating sharp corners.
Although raceway tanks would appear to be the perfect compromise between circular and rectan-
gular, the third wall adds cost and can interfere with the ease of harvesting.
23
b. Solids Removal
Waste solids are produced in an aquaculture system as uneaten feed, feed fines, fish fecal
matter, algae, and sloughed biofilm cell mass from biological filters. Waste solids influence
the efficiency of all other unit processes in the recirculating system. They are a major source of
carbonaceous oxygen demand and nutrient input into the water and can directly affect fish health
within recirculating systems. Therefore, solids removal is considered one of the most critical
processes in aquaculture systems. Optimally, solids need to be removed from the fish culture
tank as soon as possible, with minimum turbulence and mechanical shearing. If the solids are not
effectively removed, problems with waste build-up will arise which will cause toxicities in the
water and clogging of the plumbing and coating the roots with fine solids which inhibits the
nutrient uptake ability of the plants.
Solids are generally classified into three categories: settleable, suspended and fine or dissolved
solids. In recirculation systems, the first two are the primary concern, while dissolved organic
solids can become a problem in systems with very little water exchange. Waste solids can be
removed by either settling within the culture unit or through the use of a solids removal unit
following the rearing tank. Several unit process options/clarifiers are currently being used in
aquaculture: settling basins, radial flow clarifiers, mechanical filters, granular media filters, and
floatation or foam fractionation.
Since it is advantageous to allow the suspended solids to remain in the system for a period of
time, while the waste is converted to valuable elements and trace metals, most aquaponic system
designs do not usually incorporate equipment to immediately remove the suspended solids.
There are two typical styles of clarifiers, a conical design and a settling basin. The conical
clarifier has been utilized in UVI (University of Virgin Islands), the main pioneers and
developers of aquaponic systems with a proven effectiveness. Some smaller systems use a
settling basin. The idea of both designs is the same, to allow the solids to settle out of the water
column, where they can be easily removed.
In a conical filter, the waste-laden water enters the top of the filter. It is forced down, by a baffle
or series of baffles and, as it rises around the baffle, the solids fall to the bottom of the cone. To
24
completely remove the solids, a valve at the base of the filter is emptied, quickly and efficiently
removing the fish wastes and uneaten fish food.
A settling basin is simply a tank that provides a quiet, non-turbulent area, where the flow rate is
slowed and the solids allowed to settle out of suspension by gravity. In an attempt to increase
sedimentation, tube or plate settles are often used, consisting of a sequence of inclined tubes or
plates that are stacked several centimeters apart. This increases the effective settling area per unit
volume and reduces the depth to which a particle must settle to contact a surface. Advantages of
settling basins are the simplicity of operation, low energy requirements and their low
construction costs. Disadvantages include the relatively large size of settling basins, their low
removal efficiencies of small or low density particles, and leaching of nutrients from the settled
solids back into the system while the solids are stored in the settling basin.
Figure 8: Settling basin
Over the years, settling basins have gotten a bad rap, mostly because they have been improperly
designed and managed. In the radial flow clarifier, water flows directly from the drain in the
tanks to a small diameter ring suspended in the center at the top of the settling cone. It then
flows down this ring, turns the corner and very slowly moves upward over a discharge weir. The
slow velocity of the water upward, allows the solids to settle out quickly. The system is easy to
clean by flushing the solids out of a bottom drain.
Another method to increase sedimentation rate is through the use of swirl separators or
hydrocyclones. The effluent water from the culture tank is injected at the outer radius of a
conical tank, so that the water spins around the tanks center axis. The spinning creates a
centrifugal force that moves the particulates towards the wall, where they settle and can be
removed continuously. These have most often been used in aquaculture recirculating systems to
concentrate the solids from the dual-drain culture tank systems. These are very effective in
removing large, easily settable solids and can be manufactured in almost any size or flow range.
25
The glass swirl separators on the right have the additional advantage that during feeding when
uneaten feed particles start appearing you know the fish are satiated.
Figure 9: Radial flow separator
Suspended solids from an aquaculture viewpoint are that fraction of total solids that will not
settle out of the water column in a reasonable amount of time (30 to 60 minutes). Most of this
fraction of the solid wastes needs to be removed from the culture tank water because of its
potentially high oxygen demand and the increased rate of ammonia-nitrogen production from
mineralization. They are more difficult to remove and usually some form of mechanical
mechanism is used. Two types of mechanical filters are commonly used in aquaculture to
remove suspended solids: screen filters and expandable granular media filters.
c. Biofilter
A bio-filter is simply a place for the bacteria to colonize. It provides large surface areas, proper
temperature, pH and dissolved oxygen levels. In raft and media-filled bed aquaponic systems, a
separate bio filter is not usually used because the rafts, media, tank walls and all other surfaces in
the system provide sufficient area for the bacteria. In an NFT (Nutrient Film Technique) system,
a separate bio filter is required because the NFT channels do not provide adequate surface area.
Another reason some growers will add a separate bio filter to an aquaponic system is so that, if
for some reason they are not using the plant grow bed but are still running the fish tanks, there
will not be a lack of biofilter. A bio filter is usually a canister, tank or barrel of some sort that
holds a porous media that is heavily aerated. The water from the fish tank runs through this bio
filter where the ammonia will be efficiently converted to nitrite and then to nitrate (nitrification
process).
26
The ammonia removal capacity of biological filters is largely dependent upon the total surface
area available for biological growth of the nitrifying bacteria. For maximum efficiency, the
media used must balance a high specific surface area (i.e. surface per unit volume) with
appreciable voids ratio (pore space) for adequate hydraulic performance of the system. The
media used in the biofilters must be inert, non compressible and not biologically degradable.
Typical media used in aquaculture biofilters are sand or some form of plastic or ceramic material
shaped as small beads, or large spheres, rings or saddles. Biofilters must be carefully designed to
avoid oxygen limitation or excessive loading of solids
Moving bed bioreactors (MBBR) have been introduced over the last several years and appear to
be one of the most competitive of all the biofilter types. The media remains in suspension as the
water flows through the biofilter, which is actively aerated. The high turbulence and aeration
provides good mixing and contract with the media
Each biofilter has advantages and disadvantages that need to be taken in consideration during the
early design phase. One of the chief advantages of both the trickling biofilter and the MBBR is
that they both add oxygen to the water flow during normal operation. In contrast the submerged
biofilters, floating bead filters, microbead filters and fluidized-bed biofilters are all net oxygen
consumers and must rely solely on the oxygen in the influent flow to maintain aerobic conditions
for the biofilm. If for whatever reason, the influent flow is low in dissolved oxygen or the
incoming flow to the biofilter is too low, anaerobic conditions will be generated within the
biofilter.
The application of low specific surface area media is a distinct disadvantage for both the
trickling biofilters and the MBBR. Since the capital cost is proportional to the total surface area
of the filters, the result is physically large and more costly filters. In contrast, floating bead filters
and especially fluidized-bed filters and downflow microbead filters use media with high specific
surface area resulting in reduced cost and space requirements for the equivalent surface area.
Dissolved oxygen is the first limiting factor in intensive aquaculture systems. Minimum
dissolved oxygen concentrations of from 4 to 6 mg/l are required for optimal growth and survival
of most aquaculture species. At densities up to 45 kg/m3, aeration with atmospheric oxygen is
27
adequate to maintain this level, and is commonly referred to as aeration. At higher stocking
densities, pure oxygen is required and is usually referred to as oxygenation.
Ideally an aquaponic system should be designed to eliminate the expense of a separate biofilter.
d. Hydroponic systems
Hydroponic systems can either be liquid or aggregate. Liquid systems have no supporting
medium for the plant roots; whereas, aggregate systems have a solid medium of support.
Liquid Hydroponic System
Nutrient Film Technique (NFT): NFT consists of many narrow plastic troughs 10 to15
cm wide (4 to 6 inches) in which plant roots are exposed to a thin film of water that flows
down the troughs, delivering water, nutrients, and oxygen to the roots of the plants. The
troughs are lightweight, inexpensive, and versatile. Troughs can be mounted over rearing
tanks to efficiently utilize vertical greenhouse space.
Water absorbs oxygen by diffusion, but dense plant roots and associated organic matter
can block water under flow and create anaerobic zones, which precludes the growth of
nitrifying bacteria and further necessitates the installation of a separate biofilter. Thus
aquaponic systems utilizing NFT require effective solids removal to prevent excess solids
accumulation on roots, which can lead to root death and poor plant growth.
With NFT, a disruption in water flow can lead quickly to wilting and death. Water is
delivered at one end of the troughs by a PVC manifold with discharge holes above each
trough and collected at the opposite, down-slope end in an open channel or large PVC
pipe.
Figure 10: NFT System
28
Floating Hydroponics; Raft System: A floating or raft hydroponic subsystem is ideal for
the cultivation of leafy green and other types of vegetables. Long channels with closed-
cell polystyrene sheets support vegetables at the water surface with roots suspended in
the culture water. The floating sheets can provide sufficient biofiltration if the plant
production area is large enough. The system provides maximum exposure of roots to the
culture water and avoids clogging, although suspended solids captured by the roots can
cause root death if concentrations are high. The sheets shield the water from direct
sunlight and maintain lower than ambient water temperatures.
A disruption in pumping does not affect the plant‟s water supply as in gravel, sand, and
NFT subsystems. The sheets are easily moved along the channel to a harvesting point
where they can be lifted out of the water and placed on supports at an elevation that is
comfortable for the workers.
Figure 11: Raft system
Aeroponic System: It is probably the most high-tech type of hydroponic gardening. Plant
roots remain suspended in an enclosed growing chamber, where they are sprayed with a
mist of nutrient solution at short intervals, usually every few minutes. (Appendix A,
Figure 3). A timer controls the nutrient pump much like other types of hydroponic
systems, except the aeroponic system needs a short cycle timer that runs the pump for a
few seconds every couple of minutes.
29
Figure 12: Aeroponic system
Aggregate Hydroponic System
3. Ebb and flow system: Media-based hydroponic subsystems are common in small
operations. To ensure adequate aeration of plant roots, the beds have been operated
in a reciprocating (ebb and flow) mode, where they are alternately flooded and
drained. During the draining phase, air is brought into the media. The high oxygen
content in air (compared to water) speeds the decomposition of organic matter in the
media. Beds are inoculated with worms which improve bed aeration and assimilate
organic matter.
The media is subject to clogging with suspended solids, microbial growth, and the
roots that remain after harvest, thus the beds require tilling between planting cycles
to allow organic matter to be dislodged and discharged. The resulting reduction in
water circulation together with decomposition of organic matter due to clogging
leads to the formation of anaerobic zones, which impairs or kills plant roots.
Figure 13: Ebb and flow system
4. Vertical farming: This system is the best known for allowing many plants to be
grown on a small plot of ground; if one is planting in the ground, (s) he can grow
30
exactly one strawberry plant in one square foot of the ground while if a tower is
used, (s) he may grow many plant, even upto 100 plants on one tower.
The vertical towers have nutrient rich fish water pumped up to the top of the tower
and then trickle down through the gravel (or any other media used) in the towers
feeding each plant. In this system, getting the flow just right is critical for success.
Too much water causes the tower to flood and the water will cascade down the side
while too little water starves the plant of nutrients. Water can be supplied in several
ways such as having a number of drippers that trickle the fish water in each tower.
On tap fitting can then be used to adjust the water pressure to each grow bed. The
maximum water head must be determined according to the height of the towers so
that the correct pump size may be selected.
The towers may need frequent cleaning in an aquaponic system because of the
heavier amount of fish solids that will get deposited in the tops of the towers, with a
possibility of clogging the flow if a solids removal is not used.
Figure 14: Vertical system
e) Sump
Water flows by gravity from gravel, sand and raft hydroponic subsystems to a sump, which is the
lowest point in the system. The sump contains a pump or pump inlet that returns the treated
culture water to the rearing tanks. There should be only one pump to circulate water in an
aquaponic system.
31
The sump should be the only tank in the system where the water level decreases as a result of
overall water loss from evaporation, transpiration, sludge removal and splashing. An electrical or
mechanical valve is used to automatically add replacement water from a storage reservoir or
well. A water meter should be used to record additions. Unusually high water consumption
indicates a leak. The sump is a good location for the addition of base to the system. Soluble base
such as potassium hydroxide causes high and toxic pH levels in the sump. However, as water is
pumped into the rearing tank, it is diluted and pH decreases to acceptable levels.
f) Circulation
The aquaponic system is connected by water recirculating from the tank through the filtration
loop and hydroponic system. Generally, the water pumps or air blower, if incorporated, that
drives the circulation loop is the major source of energy consumption. Failure of the circulation
system leads to a rapid deterioration in fish tank water quality, and drying of roots in the
hydroponic system thus, the method selected must be cost effective and reliable. Two common
types of pumping systems are centrifugal and axial flow.
Centrifugal pumps
Typically, a centrifugal pump is used to circulate aquaponic waters. These pumps operate from
the thrust generated when water in the pump head is spun at high speed. The design of most
centrifugal pumps is optimized for moderate to high pressure operation. In most cases, the pump
will be placed outside the tank, but in some smaller systems a submersible pump may be used.
Centrifugal pumps are readily available for virtually any flow range and salinity.
Axial flow pumps
Axial flow pumps are used on larger scale systems because they have better pumping efficiencies
than centrifugal pumps under low lift conditions (<10 feet or 3 m). Axial flow pumps are driven
by a propeller mounted on a motor shaft within a vertical pipe. These pumps are robust and
highly resistant to clogging. In recirculating applications, the propeller is submerged so pumping
can be initiated without priming. Axial pumps tend to be more expensive than the more common
centrifugal pump, and are rarely used unless the system recirculation rates reach several hundred
gallons per minute (>2,500 lpm). In these larger systems, lower operation costs may offset higher
initial capital expense.
32
2.2 Theoretical framework
The main engineering principles to be applied in this design project are fluid mechanics with
regard to irrigating the crops, flow rates, velocity, pump head and piping; structural design with
regard to dual-drain tank design, settling basin design, tower design, mechanical filter design and
biofilter design; material science in the selection of the materials to be used, and machinery with
regard to pump. The design project also entails natural science because of the biological aspect
concerning strawberry crop and fish characteristics and requirements.
2.2.1 Sizing the hydroponic growing area
The size of the hydroponic area for growing strawberries will be based on the scale required by
the owner of the system.
2.2.2Sizing and design of the fish rearing tanks
Ratio between hydroponic component and fish rearing
To ensure effective waste treatment, it is recommended (Timmons and Ebeling ) for media based
hydroponic systems that a volume ratio of 1ft3 of fish rearing tank to 2ft
3 of media (
to
in
diameter).This ratio requires that the tilapia be raised to a final density of 0.5 pound/gallon
(=0.0599kg/l) and fed appropriately.
With the volume of fish rearing area determined from this ratio, the number and size of tanks can
then be determined such that fish can be raised to the final density of 0.5pounds/gallon.
Number and type of fish tanks
For economic sense of the aquaponic system it is necessary that the pumps (for water and
aeration) be utilized at maximum capacity at all times. This may be affected by the following
factor: fish stocking method which ultimately affects the number and type of fish tanks to be
used.
The maximum biomass of fish (density of reared fish) a system can support without restricting
fish growth is called the critical standing crop. Operating a system near its critical standing crop
uses rearing space efficiently, maximizes production and reduces variation in the daily feed input
to the system, an important factor in sizing the hydroponic component. In general;
33
Critical standing crop in aquaponic systems should 0.5 pounds/gallon (Rakocy, Masser and Losordo, 2006)
Predicting fish growth:
Weight = function (length)
Wt lbs = CF.
…………………………………equation 1
Whereby CF tilapia = 760
Growth = F (temp)
=
=
whereby for tilapia, T base=65, TU base = 15, and Tmax =
85……………………………………..equation 2
The number and type of fish tanks to be used depends on the fish stocking method. Multiple
rearing units is the type of fish stocking method that will avoid underutilization of the rearing
capacity of the tank and the water conditioning equipment associated with the system. It requires
that each rearing tank contain different age groups and these numbers will be used to size the
flow rates and pumps. With this method, any fish movement is avoided because fish movement
leads to loss of growth and additional mortality due to the stress experienced by the fish.
Engineering design details: Dual-drain self-cleaning fish tanks
Factors to be considered during design:
Diameter and depth
Optimum water velocity
Radial velocity (self-cleaning action)
Flow injection
Outlet flow structure
Exclusion screen
Design suggestions (Ebeling and Timmons, (2012)):
Diameter: depth = 3:1 to 6:1
15 – 25 % of flow through center drain
75 – 85 % of flow through sidewall discharge
Orientation of inlet jets is critical for mixing and solids flushing
Inlet impulse force; F = ρ. Q. (V orifice –V rot)………………………..equation 3
34
Where ρ = density of water
Q = inlet flow rate
V orifice = velocity of orifice
V rot = velocity of rotation
The impulse force can be adjusted by either flow rate Q, or the number of openings.
Area of orifice is obtained from the equation: Q = KA√ ……………..equation 4
Where Q = flow rate
K = Coefficient of orifice
H = Head across orifice
g = Gravitational constant
Design 0.6 – 1.2 m water pressure behind inlet jets
Size centre drain 0.d 10% tanks
Size open area for centre and side drains to provide 15 – 30 cm/s velocity
Choice of centre drain flow should be the largest of
o 6 lpm/m2 of floor
o 10-15 % of total tank flow
Equation to predict safe non-fatiguing water velocities:
V safe < 5.25 / (L) 0.37
……………………………….equation 5
Where V safe is the maximum design velocity (about 50% of the critical swimming
speed) in fish lengths s-1
and where L is the fish body length in cm.
Rotational velocity can be controlled by design of the water inlet structures, so water flow does
not have to be increased beyond that required for the fish‟s culture environment.
Corrosion resistance screening materials, such as perforated sheets of aluminum, stainless steel,
fiberglass, or plastic are used to cover drain outlets.
35
Table 2: Exclusion screen sizes
Theoretically, media-based and NFT systems should have a daily feeding rate ratio that is
approximately (Rakocy, Losordo, 2006) 25% of the recommended ratio for raft hydroponics.
The recommendation for raft hydroponic is 60-100g/m2 plant area/day.
25% of 60 = 15
Hence the feeding rate ratio for the media-based hydroponic system is 15-25g of fish feed/day
2.2.3 Tower development
For supporting thin-stemmed plants like strawberries, each tower may have
inch holes 3inches
apart4. Suitable recommended tower diameter is 6 inches.
Determination of water flow rate
In aquaponics systems, it is generally required (Zipgrow, 2014) that for a highly porous media, 7
gallons (26.50 Liters) of water be run through each tower every hour. Using this, the flow rate
for the system can be determined using the empirical formula:
( )
= GPH aquaponics………………………………………equation 6
2.2.4 Settling basin design details
With an existing bottom drawing centre drain (Timmons and Ebeling 2012)
Length: Width = 3:1 to 8:1
Basin floor area of 1 ft2 per 1 gpm of flow (40 lpm/m
2 of flow)
250-410 lpm per meter width of weir for outflow
Submerge inlet weir 15% of basin water depth
4 http://www.instructables.com/id/Save-500-Make-your-own-vertical-hydroponicsaquapon/all/?lang=es
Exclusion screen
slot size (mm) Fish size, g
1.6 x 3.2 fingerlings to 0.45g
3.2 x 6.4 0.45 to 2.3 g
6.4 x 12.7 2.3 to 15 g
12.7 x 19.1 15g and larger
36
Use 25 cm wide weirs with rounded edges
1 Lb of feed 0.30 lbs of solids
Settling basin design is based on overflow rates which are the flow rate being treated
divided by the effective settling surface area:
Overflow rate = (
)
………………………..equation 7
2.2.5 Aeration requirements
(Aeration with atmospheric oxygen)
Oxygen requirements
Metabolism/respiration: 0.25 lbs O2 / lb feed
Nitrifying bacteria : 0.40 lbs O2 / lb feed
Total : 0.65 to 1.00 lbs of O2 / lb feed (proportionality constant)
Rule of thumb: 1 kg feed about 1 kg oxygen
Estimation of oxygen demand
RDO = Biomass system. r feed . a DO………………………………………equation 8
Where a DO = average DO consumed per kg of feed (proportionality constant)
r feed = feed rate
Biomass system =total biomass of the system
RDO = average DO consumption rate (kg DO consumed by fish/day)
2.2.6 Pump sizing
As a general rule in aquaponic systems, a pump should circulate all of the water in the system at
least every hour. The two factors to be considered in sizing a pump for an aquaponic system or
any other water system are:
The flow rate (check tower development), and
The head height
Every water system has pipes, valves and fittings that create resistance to flow. This resistance
makes up what is referred to as the friction head. On the other hand, the height which the water
37
needs to be pumped from the lowest level at the pump to the highest level of the water system is
referred to as the static head. The total head is computed as follows:
ΔHp (q) = ΔHf (q) + ΔHEQ (q) + ΔHv (q) + ΔHTS……………………………equation 9
The Total Static head is constant and the friction head, equipment head and velocity head are
flow dependent. The calculation of pump power requirements is calculated from the formula
P =
Where E m = E p = 0.3 (for small pumps): motor and pump efficiencies respectively
2.2.7 Piping
Primary factors involved in aquaponics plumbing system are internal pipe diameter (and the
resulting fluid velocity), materials of construction and pipe routing. The design flow rates are
based on system demands that are normally established in the process design phase of a project,
as has been done in tower development.
Before the determination of the minimum inside diameter can be made, service conditions must
be reviewed to determine operational requirements such as recommended fluid velocity for the
application and liquid characteristics such as viscosity. This information is then used to
determine the minimum inside diameter of the pipe for the network.
For normal liquid service applications, the acceptable velocity( Engineer‟s Edge 2000-2015) in
pipes is 2.1 ± 0.9 m/s (7 ± 3 ft/s) with a maximum velocity limited to 2.1 m/s (7 ft/s) at piping
discharge points including pump suction lines and drains. This translates to 1.5 inch pipes. For
commercial scale aquaponic systems, 6 inch diameter drain pipes are recommended. Numerous
tables have been designed for various pipe diameters and type, such as PVC pipes, that display
the flow rate, fluid velocity and friction head for each pipe size.
38
Table 3: Circulation- drains/pumped return line
Maximum Flow (gpm) Pipe
Diameter Drain line Pumped Return
(inches) (1 to 2 fps) (< 5 fps)
0.5 1 5
3/4 2 10
1 5 15
1.5 10 30
2 20 50
3 45 125
4 75 200
6 150 500
As a general rule of thumb the pipes removing water from the hydroponic system may be larger
than those taking the water to them in order to ensure that the towers can drain properly and not
overflow, or at least able to adequately handle the volume of water being delivered to them.
Over time debris may build up on the inside of the pipes and this will affect the rate of flow in
the pipes. Pipes may need to be cleaned every few months in order to ensure a constant and
unimpeded flow of water. The necessity to clean some sections of your plumbing should also
influence the decision as to whether one need to glue the pipes together or the piping can be
pushed together firmly enough to avoid the need for glue.
Pressure drop, or head loss, is caused by friction between the pipe wall and the fluid, and by
minor losses such as flow obstructions, changes in direction, changes in flow area, etc. Fluid
head loss is added to elevation changes to determine pump requirements. General equation for
pressure drop, known as Darcy's formula expressed in meters of fluid is:
hf =
.
…………………………..equation 10
Where is: hL - head loss due to friction in the pipe;
f - Friction coefficient;
L - Pipe length;
v - Velocity;
39
D - Internal pipe diameter;
g - Acceleration of gravity;
The friction factor, f, is a function of the relative roughness of the piping material and the
Reynolds number, Re .
Re =
=
……………………………equation 11
Where:
Re = Reynolds number
D = inside pipe diameter, m (ft)
V = fluid velocity, m/s (ft/s)
v = kinematic viscosity, m2/s (ft
2 /s)
u = dynamic viscosity
If the flow is laminar (R < 2,100), then f is determined by:
Where: Re = Reynolds number
f = friction factor|
When flow is turbulent and Reynolds number is higher than 4000, the friction factor depends on
pipe relative roughness as well as on the Reynolds number. Relative pipe roughness is the
roughness of the pipe wall compared to pipe diameter e/D. Since the internal pipe roughness is
actually independent of pipe diameter, pipes with smaller pipe diameter will have higher relative
roughness than pipes with bigger diameter and therefore pipes with smaller diameters will have
higher friction factors than pipes with bigger diameters of the same material.
Most widely accepted and used data for friction factor in Darcy formula is the Moody diagram.
(Appendix A, Figure 9). On Moody diagram friction factor can be determined based on the value
of Reynolds number and relative roughness.
40
The method of equivalent lengths accounts for minor losses by converting each valve and fitting
to the length of straight pipe whose friction loss equals the minor loss. The equivalent lengths
vary by materials, manufacturer and size. The other method uses loss coefficients. This method
must be used to calculate exit and entrance losses. The coefficients can be determined from
Estimated Pressure Drop for Thermoplastic Lined Fittings and Valves.
41
CHAPTER 3
GENERATION OF CONCEPT DESIGN
For the generation of a concept design, a systematic method was applied to help the designer
consider the broadest possible set of feasible conceptual designs and a structured problem
solving approach for the design of the aquaponic system. Description of any product that acts
sequentially on some kind of material flowing through it is well defined by a function structure
(Dieter and Schmidt, 2009). Thus Functional Decomposition and Synthesis method has been
applied for this design project. Functional analysis is a logical approach that describes the
transformation between initial and final states of a system and relies on restructuring a design
task to a more abstract level to promote greater access to potential solution.
4.1. Overall Functional decomposition and synthesis
Using this method, the aquaponic system to be designed has been represented into its broadest
functional blocks with standard flow classes (energy, material and signal) and functional names
having been used for the representation as shown below. The functional diagram represents a
comprehensive aquaponic system for a high organic loading density with reference to the 2012
Aquaponic Association Conference (Timmons and Ebeling, 2012).
Figure 10: Function Structure of an Aquaponic System
Material
Energy
Set.S – Settable solids
Sus.S – Suspended solids
Dis.S – Dissolved solids
Water HP – Water Horsepower
Water – The term water refers to the circulating water and it contains considerable traces of nutrients, dissolved
oxygen, nitrates and sometimes pathogens.
42
CO2
Water Water
Set. S Sus.S Water Water Sus. S Dis.S Dis.S Ammonia Ammonia
Dis.S Water HP Nutrients
Ammonia Ammonia Gases Water HP
Water HP Water HP nutrients
Water HP Sludge Sludge water HP
Water with
nutrients
& nitrates
Disinfected Water with Water Water
water base Base Water HP
Water HP Water HP Water hp
Electrical energy clean water & base
4.2 Functional decomposition and synthesis for this project
With the main objective of the system being to grow strawberry crops, the hydroponic
component of the aquaponic system is the primary (main) component while the aquaculture
component is the secondary component. Hence the design is expected to have a large growing
area and a relatively smaller number of fish that are enough to provide the required nutrients.
This will result to a design of medium organic loading that leads to a simplified overall system.
W
ater
wit
h D
O , b
ase,
nit
rate
s
Fish
culture
Settable
solids
removal
Suspended
solids
removal
Degassing
Biofiltration
Dispose Dispose
Hydroponic
crop
growing
Water
Reserve
Pumping
UV ozone
system
disinfection
Aeration
Power
back-up
Water &
supplement
replenishing
CO2
stripping
43
For instance, moderately efficient solids removal devices are applicable rather than costly highly
efficient counterparts, while other components such as the CO2 stripping chamber that is used to
remove excess CO2 associated with high loading densities are entirely eliminated. The resulting
design is as illustrated below:
Figure 11: Specified functional decomposition and synthesis
Water Water
Set. S Sus.S Water
Sus. S Dis.S Ammonia
Dis.S Water HP Ammonia Ammonia nutrients
Water HP Water HP
Sludge Sludge
water HP
Water HP Water with nutrients & nitrates
Water Water Water
Base Water HP
Water HP Water hp
Electrical energy clean water & base
4.3 Generation and analysis of alternative solutions
The various alternatives associated with the functional units were generated from known existing
systems and/or components. For instance, the hydroponic crop growing functional unit has its
alternatives as the NFT system, raft system, ebb and flow system or vertical growing systems.
The diagram below depicts the available options generated for the main functional units.
Wat
er w
ith
DO
, b
ase,
nit
rate
s Dispose Dispose
Hydroponic
crop growing
Water
Reserve
Pumping
Aeration
Power
back-up
Water &
supplement
replenishing
Fish
culture
Settable
solids
removal
Suspended
solids
removal
Biofiltration
44
Figure 12: Generation of alternative solutions
The generated alternatives were then analyzed for the purpose of selecting the most suitable
option. The analysis and prioritization conducted for the alternatives was in accordance to the
ranking of the engineering characteristics obtained from the House of Quality. (Appendix A,
Table 1). The ranking was to facilitate the designer in the preliminary determination of the
engineering characteristics that were deemed to be the most important for the user of the system.
The house of quality translates the voice of the customer input as customer requirements in room
1 into target values in room 8. Decision matrix was used for further analysis of the engineering
characteristics.
4.3.1 Selection of a hydroponic system
The selection of the most suitable hydroponic system for this design was conducted as shown in
the table shown below. Vertical growing was selected as the most suitable hydroponic system
due to its suitability for growing strawberries, cost effectiveness, maximum growing space
Fish culture
(Tanks)
Circular
Rectangular
Raceway
Settable solids removal
Settling basin
Clarifier
Microscreen-
drum filter
Mineralization
tank
Suspended solids removal
Screen filters
Expandable
granular media
filters
Biofilter
Trickling
Submerged
Floating bed
Fluidized
bed
Moving bed
bioreactors
Pumping
Axial
Centrifugal
Water reserve
Hydroponic
NFT System
Raft system
Ebb and flow
Vertical
growing
Power back-up system
Automatic transfer switch
Automatic phone alarm system
Water reserve replenishing
Base addition
Aeration
Submerged air stone
Diffuser hose
Airlifts
Surface aerator
45
utilization and applicability for commercial application, among others. The main advantage of
this growing system is that it caters for the biofiltration process thus eliminating the need for a
separate biofilter device.
Table 4: Decision matrix for a hydroponic system
4.3.2 Selection of the solids removal devices
Solids removal is the most important function for effective performance of any aquaponic
system. This was conducted as shown in the table below.
Decision Matrix For Evaluating The Most Suitable Hydroponic System For The Aquaponic System
Criteria
Weight
%
Raft
system NFT Ebb and Flow
Vertical
growing
1 Efficiency in operation(nitrification, mineralization & aeration) 15 8 6 9 9
R x Weight 120 90 135 135
2 Suitability to strawberries 20 3 9 5 9
R x Weight 60 180 100 180
3 Efficiency in space utilization 5 3 9 1 9
R x Weight 15 45 5 45
4 Maintainability (clogging) 5 7 7 4 4
R x Weight 35 35 20 20
5 Dependence in Power (electricity) 5 8 2 2 2
R x Weight 40 10 10 10
6 Possibility for commercial application 5 7 9 1 8
R x Weight 35 45 5 40
7 Ergonomics (Does it fit 99% of the people who use it?) 5 8 8 7 8
R x Weight 40 40 35 40
8 Cost (elimination of a separate biofilter) 25 7 0 9 9
R x Weight 175 0 225 225
9 Strength analysis & durability (effects of shocks/loading over the life of the product) 10 7 6 8 7
R x Weight 70 60 80 70
10 Ease of adaptation, fabrication and assembly 5 6 9 6 5
R x Weight 30 45 30 25
100 620 550 645 790
46
Table 5: Decision matrix for a solids removal device
Decision matrix for evaluating the most suitable solids removal device
Criteria
Weight
%
Settling
basin Clarifier
Micro-
screen
drum filter
Mineralization
tank
1 Organic loading (suitable for medium organic loading densities) 15 6 1 1 5
R x Weight 90 15 15 75
2 Mineralization 20 5 5 4 8
R x Weight 100 100 80 160
3 Efficiency (solids removal) 25 7 9 9 5
R x Weight 175 225 225 125
4 Solids retention time 10 7 7 6 8
R x Weight 70 70 60 80
5 Water consumption rate 5 3 4 6 5
R x Weight 15 20 30 25
6 Effluent characteristics (both solid waste and treated water) 10 6 6 6 5
R x Weight 60 60 60 50
7 Cost 15 7 3 2 7
R x Weight 100 105 45 30 105
615 535 500 620
After the analysis it was concluded that the mineralization tank was the most efficient in the
mineralization process which supplies nutrients to the crops. But for medium organic loading
densities the mineralization tank would pose technical problems in solids removal as more
aeration would be needed to enhance the mineralization process, consequently causing the
settable solids to be highly dispersed and cause excessive clogging of the filters and the
hydroponic component. As mentioned before, this would be undesirable.
The settling basin was thus more preferred because it was more efficient in solids removal and
also good enough for the mineralization process. The rest of the devices were efficient but costly
for the size and purpose of the design project.
With this as the sole method of solids removal, large quantities of solids would be discharged to
the hydroponic component. Therefore another treatment stage is required to remove re-
suspended and fine solids. Apart from preventing the suspended solids from getting into the
hydroponic system and the dissolved solids from causing filamentous bacteria growth along
drain lines and the tanks, the accumulation of these solids on the filters serves as growing areas
47
for anaerobic bacteria and this enhances the denitrification process. This process involves
converting nitrates to nitrogen gas and is very paramount to fruiting crops (as opposed to
vegetative crops) and thus needs to be regulated for maximum productivity for the strawberry
crop. This regulation is simply determined by the frequency of cleaning the filter used, which
could be orchard netting or multiple screen tanks.
4.3.3 Selection of the fish culture tank
Fabricated fish tanks were deemed more suitable relative to ground fish culture due to aspects
concerning solids waste removal and connection to the settling basin such that water movement
induced by recirculating water or aeration systems can be used to accelerate solids movement to
the settling basin. The available fish tank types were analyzed as follows:
Table 6: Analysis of fish tanks
Analysis of the three available fish rearing tank types
Circular tank Rectangular tank Raceway tank
Walls are self supporting: This
allows them to be constructed out
of thin materials such as
polyethylene plastic or sturdier
fiberglass
20% more efficient in floor space
utilization and are more easily
harvested than circular tanks
are a compromise between the
circular and rectangular tanks
Hydrodynamics of a circular tank
facilitates the rapid removal of
suspended solids
Inherent structural weakness of a
rectangular (or square) design
requires use of more and stronger
material, such as concrete or
fiberglass, and reinforcements
The third wall centered within is
facilitates controlled circulation of
water but is an added cost and can
interfere with the ease of
harvesting
Is prone to poor solids movement
From the above considerations, the circular tank, which is also the most commonly used type,
was selected as the most suitable.
4.3.4 Selection of an aeration device
While most commercial aquaponic systems use pure oxygen systems for aeration to meet the
high dissolved oxygen (DO) levels required, other commercial systems and all medium and
small-scale systems use blown air systems that involves blowing air rather than pure oxygen into
the water to meet the DO requirements.
Of the alternative aeration devices generated, the diffuser hose has been selected as the most
suitable device because the hoses are suitable for multiple tanks, are efficient, flexible and easier
48
to clean. Air lift aeration device is more suitable for a single large open tank, while surface
aerators are usually used to supplement blown air systems during periods of peak loading or high
temperature. Air stones are also efficient and operate just like the diffusion hose but the later are
superior in terms of cleaning and maintenance.
4.4 Generated conceptual design
The overall conceptual design was finally converted to a design suitable for adoption as per the
objectives of the design project, as shown below:
Figure 13: Generated conceptual design
Water Water
Set. S Sus.S Water Sus. S Dis.S Ammonia
Dis.S Ammonia Water HP
Ammonia Water HP Nutrients
Water HP
Sludge Sludge
water HP
Water HP Water with nutrients & nitrates
Water Water
Water HP Base
Water hp
Electrical energy clean water & base
Wat
er w
ith
DO
, b
ase,
nit
rate
s Dispose
Water
Reserve
(Tank)
Pumping
(Centrifugal)
Aeration
(Diffuser hose)
Power back-up
(Automatic transfer
switch)
Water &
supplement
replenishing
(Base addition
tank)
Fish
culture
(Circular fish
tank)
Settable solids
removal
(Settling basin)
Suspended
solids
removal
(Filter tank)
Hydroponic &
Biofiltration
(Vertical growing
system)
Dispose
49
CHAPTER 4
METHODOLOGY
The aquaponic system design was undertaken using the following design steps:
1) Design of a vertical strawberry farming system
Farm dimensions
The farm dimensions were measured with a tape measure and the elevation profile
obtained using a GPS and Google earth.
Number of towers
The number of towers to be used was then determined as follows:
Taking the tower spacing as; (Zipgrow, 2014)
Side to side (across the width spacing) =55 cm
( )
+ 1 = Y towers along the width
Front to back (along the length spacing) =45 cm
( )
+ 1 = X towers along the length
Total number of towers = X.Y towers
Number of crops per tower
The number of crops to be grown on each tower was determined by dividing the
length of the tower with the recommended spacing of 10 cm between the crops.
(Zipgrow, 2014)
The total number of crops was then taken as the product of the number of towers
and the number of crops per tower.
50
2) Calculation of the fish tanks volume
This was calculated using the crop to fish rearing area ratio 1 ft3 of fish rearing to 2 ft
3 of
media, (Rakocy, Masser and Losordo, 2006), whereby the media is the total volume of the
towers.
The number of fish to be kept was calculated using a design criterion of critical standing
crop, a value of 0.5 pounds per gallon recommended fish density.
3) Calculation of the flow rate
The system water flow rate was calculated using the empirical equation 5:
( )
= GPH aquaponics
4) Design of the inlet and outlet water structures for the fish tanks.
The inlet structure was designed to bring in water into the fish tanks using a
vertical and horizontal pipe at 90 o configuration. (Timmons, Summerfelt and
Vinci, 1998). The pipes were designed to have orifices. The velocity of the
orifices was related to the recommended tank velocity.
V orifice= Φ V rotation Where Φ ranges from 0.15-0.20
The number of orifices to be used was determined using the equation
V orifice =
A= Q/V orifice K
Where Q = system flow rate
K= coefficient of orifice
A = total cross-sectional area of all orifices
Area of one orifice =
Calculation of the fish tank inlet pipe diameter:
Relationship between water velocity in inlet pipe and velocity out of orifice
51
V orifice=
A pipe=
;
r =√
d=2 r , where d is the fish tank inlet pipe diameter.
Calculation of the fish tank outlet pipe diameter:
Q center drain = 0.15*10.93960642m3 =1.64094096m
3/hr
Q side drain =0.85*10.93960642m3/hr =9.298665457m
3/hr
A=Q/V
A=∏r2; r =√ ; d=2r
5) Design of the settling basins.
The settling basin was designed for over flow rate, also called the surface load of the
basin, Q/A:
To achieve settling in a basin the condition Vs > Q/A, must be achieved, where,
Vs =Sinking Velocity of particle (m/h)
A=surface area of the basin (m2)
Q=water flow through the basin (m3/h)
The sinking velocity VS of the particle is given by stoke‟s law;
Vs = ( )
Where;
Vs =sinking velocity
52
ρ p =density of particle
ρ w = density of water =1g/cm3
g=acceleration due to gravity =98m
dp = diameter of particle
u=dynamic viscosity of the water
When the condition Vs> Q/A has been achieved, the area of the basin to be used is then
calculated as
A> Q/Vs =Q center drain/ Vs
The dimension of the basin was then calculated with a selected design ratio for maximum
settling efficiency, length: width = 3:1 to 8:1 3 (Timmons and Ebeling 2012).
6) Design of the piping network.
The pipe sizes for the aquaponic system were determined using the fluid flow
continuity equation Q = AV
Whereby Q = flow rate in the pipe, (m3/s)
A = cross section area of the pipe (m2)
V = the flow velocity through the pipe (m/s)
From which,
A=Q/V
A=∏r2; r =√ ; d=2r, where d is the pipe diameter.
The head loss in the pipes is determined as:
hf =
.
Whereby L = pipe length (m)
D = internal pipe diameter (m)
53
V = velocity through the pipe (m/s)
g = acceleration due to gravity (m2/s)
f = pipe friction
The pipe friction is dependent on the value of the Reynold‟s number.
If Re < 2000 flow is lamina and f = 64/Re, and if Re > 4000 flow is turbulent and
f is obtained from the moody chart. (Appendix 1)
7) Selection of a suitable pump for the system. This will involve:
8) Hs = H s t + H f
Determination of the system head (which will include determination of the Total
Static head [constant] and the friction head, equipment head and velocity head
which are flow dependent using equation 9.
With these data, pump power requirement will be obtained using the equation
P =
Where E m = E p = 0.3 (for small pumps): motor and pump efficiencies
respectively
54
CHAPTER 5
RESULTS
Data that was collected physically included the size of land and elevation of the potential farm in
Kamulu area:
Total area: 30 x 7 m
Elevation: Geographic coordinates of the site was obtained from a GPS on 21/04/15 at 4pm; S
01016.323‟ , E 037
O02.982‟
Design data was obtained primarily form literature review and through personal contacts, such as
phone calls.
Material selection was determined by the local availability and suitability of the material.
Though fiberglass would have been sturdier, polyethylene tanks were selected because they were
cost-effective yet efficient as well. Polyethylene (PE) pipes were selected for piping because
most of the pipes would be exposed and PE pipes are more suitable in sunlight. Material selected
for tower design was standard 6 inch PVC pipes which are locally available and easily
fabricatable. The material selection was based from existing systems of University of Virgin
Islands Aquaponic System and Mr. Daniel Kimani‟s aquaponic farm that was in Kinangop early
this year.
1. Design of the strawberry farm
Size of growing area: Measured as 15 x 8 m
Area = 15 x 8 = 120 m2
Number of towers
1500 cm
800 cm
Taking; (Zipgrow, 2014)
Spacing between the towers across the width of the growing area (Side to side
spacing) =55 cm
( )
+ 1 = Y
( )
+ 1 = 15 rows
Strawberry growing
area
55
Spacing between the towers along the length of the growing area (Front to back
spacing) =45 cm
( )
+ 1 = X
( )
+ 1 = 34 columns
Number of towers = X.Y = 15 X 34 = 510 Towers
Figure 15: Growing area 15 x 8 m
Size of each tower:
A Standard size of 6 inch diameter and length of 1.8m5 was selected for the towers. The size is
suitable because strawberries have a shallow root system of 5-6 inches, making them sensitive to
water deficit and excess. On the other hand, the height is the average height that an adult can
ergonomically plant and harvest the berries.
Number of crops per tower:
56
Taking a spacing of 4” (≈10 cm) from opening to the next6, and that the strawberries will be
grown at a height of 30 cm from below, the effective tower length is 1.8 – 0.3 = 1.5 m = 150 cm.
And thus each tower has 15 x 2 = 30 crops on both sides of each tower.
Total number of strawberries to be grown = 510 towers x 30 strawberries = 15, 300 strawberries.
Figure 16Front and side view of a single tower
2. Design of fish tanks
2.1: Fish rearing area
The volume of water for fish rearing was obtained from the ratio criterion of 1 ft3 of fish rearing
to 2 ft3 of media (Ebeling and Timmons, (2012).
Volume of media:
1 tower dimensions; 1.8 by 6” =5.9 ft by 0.5 ft
Volume = ∏ r 2 h= ∏ x (
)
6 http://www.instructables.com/id/Save-500-Make-your-own-vertical-hydroponicsaquapon/all/?lang=es
57
For 510 towers = 510 x = 590.835 ft 3
Ratio
295.4175 ft 3 = 8.365292 m
3 = 8365.292 L = 2209.87623 gal
2.2: Number of tanks to be used
One large tank could suffice as a fish tank but for staggered growth and additional margin of
safety in terms of a sustainable nutrient supply, 2 tanks will be used. From first principles, if the
volume of water is divided equally between the two tanks, when fish from one tank is harvested
and replaced with fingerlings, the overall nutrient content in the water would be insufficient. For
this reason the two tanks have an equal amount of water with each tank having two-thirds so that
at any particular time after harvesting the system will have an acceptable level of nutrients.
Size of one tank: 8.365292 m 3 x
= 5.576861333 m
3
Taking diameter: depth ratio of 3:1 -6:1, (Ebeling and Timmons, (2012),
Volume = ∏ r 2h
= ∏ r
2 x 1m = 5.576861333 m
3
R = 1.332355094m
D = 2.664710188 = 2.7 m
Fish tank diameter = 2.7 m
2.3: Number of fish per tank
For 1512.530898 gal /tank
Taking critical standing crop = 0.5 pounds/gal
1 gal=0.5 pounds
1512.530898 756.2654489 Pounds of fish per tank
1 Nile tilapia weighs 4.324kg = 9.532787586 pounds and 60cm length
media fist tank
2 ft 3 1 ft
3
590.835
ft 3
=295.4175 ft 3
58
Number of fish =
=79.333 fish = 80 fish per tank
Total number of fish=160 fish for the two tanks
2.4: Sizing of inlet structure
Water inlet &outlet structures are engineered to; Reduce labor requirements for fish handling,
obtain uniform water quality, obtain rotational velocities and to obtain uniform solids removed.
For tilapia an upper current speed of 20-30 cm/s is recommended for maintaining fish health,
muscle tone &respiration. On the other hand, velocities required to drive settable solids to the
tanks center drain be greater than 15-30cm/s, (Timmons, Summerfelt and Vinci, 1998).
Taking the current speed to be 20cm/s = 0.2m/s
V orifice= Φ V rotation =
=1m/s
Where Φ ranges from 0.15-0.20
Recommended values of velocity are below 1.5m/s in the inlet pipe, while the velocity in the
orifice should be below 1.2m/s……….* (Timmons, Summerfelt and Vinci, 1998).
1m/s < 1.2m/s, so value of velocity is acceptable and V jet >> V circulating so ok as well
V orifice =
A= Q/V orifice.K
Area of one orifice =
Relationship between water velocity in inlet pipe and velocity out of orifice
V orifice=
From *, taking inlet pipe velocity to be 1.2 m/s
A pipe=
;
59
r =√
d=2r
In aquaponics, it is required to run 7 gallons of water through each tower every 2 hours.
( )
= GPH aquaponics
( )
= 2889.938115 gph =10,939.60642 l/h =10.93960642m
3/h
Thus for A= Q/V orifice K, we have
=0.004901257335 m2
A orifice=49.0125735 cm2
Taking the radius of each orifice to be 1 cm,
Area =∏r2
= ∏*12= ∏
Therefore number of orifices
49.01257335cm/ ∏
=15.60118669 = 16 orifices
2.5: Sizing outlet structure
Taking 15% of total tank flow rate to pass through the center and 85% of the total tank flow rate
to go through the side drain
Q center drain = 0.15*10.93960642m3 =1.64094096m
3/hr
Q side drain =0.85*10.93960642m3/hr =9.298665457m
3/hr
The outlet pipe should be designed for water velocities above 0.3m/s to ensure no setting of
solids.
60
Velocities above 1.5 m/s in the outlet will result in rough treatment of the particle which may
break up making later filtration of the outlet water more difficult, (Timmons, Summerfelt and
Vinci, 1998).
Taking outlet velocity =0.3m/s for both center &side drain; lower values of flow rate and
velocity in an aquaponic system are recommended to enhance the mineralization process that
supplies nutrients to the crops (breakdown of wastes to produce nutrients) , (Rakocy, Masser and
Losordo, 2006)
2.6: Center drain outlet pipe diameter
A=Q/V
=
= 0.00151938978m
2 =15.1938978cm
2
A=∏r2
r = √ =√ = 2.199174364
Diam=4.398348727cm
2.7: Side drain outlet
A=Q/V
= 0.00860987542 m
2 = 86.0987542cm
2
A=IIr2
R=√ = 5.235082106 cm
Diam=10.47016421 cm
In a correctly designed flow through a tank with inlet and outlet a circular flow pattern. The best
water exchange rate should be 2 exchanges / hr.
Q=10,939.60642l/h
Tank size=5,725.552611 l
61
= 1.910663854 ex /hr = 2ex/hr so ok.
Figure 17: Drawing of one fish tank layout
3: Design of Filters
3.1: Settling basin
Settling basin is designed for over flow rate of the setting basin. The equation to achieve setting
Vs > Q/A
Vs =Sinking Velocity of particle (m/h)
A=surface area of the basin (m2)
Q=water flow through the basin (m3/h)
Where Q/A is called the surface load or over flow rate for through settling basin.
The sinking velocity VS of the particle is given by stoke‟s law;
62
Vs = ( )
Where;
Vs =sinking velocity
ρ p =density of particle
ρ w = density of water =1g/cm3
g=acceleration due to gravity =98m
dp = diameter of particle
u=dynamic viscosity of the water
Experiments have shown that the predominant particle size in the outlet water from fish farming
is less than 30-40 um. Density of faces from fish farming varies report densities are above 1 from
1.005-1.2 which means that the faces will settle in water. Surface water temp in many water
bodies (streams) will likely increase 2-30c as air temp increases 3-5
0c, (Timmons, Summerfelt
and Vinci, 1998).
Air temp in Kamulu is 19.70c, thus the water temp is estimated as 10.7
0c
Dynamic viscosity of water at 10 0c = 1.307 x 10
-3kg/m
2
Taking ρ p =1.1 g/cm; d p 30 um
(
) ( )
( = 0.00003752869 m/s
=0.135103284m/h
Vs> Q/A
A> Q/Vs=Q center drain/ Vs
=1.640940963m3/h / 0.135103248m/h =12.14582588m2
Therefore the surface area of basin needs to be more than 12.15m2 to allow proper setting.
63
If length ratio of 3:1 is chosen for the basing the exterior measurements of the basin will be about
5.7 x1.8 x 1.2m .Two setting basins are needed so that one can be running while purification and
sludge removal can be done in the other.
25cm wide weirs with rounded edges will be used in the settling basin. The inlet weir will be
submerged 15% of basin water depth.
Outlet design is much simpler, only requiring a weir spanning the entire width of the basin
ensuring a uniform discharge across the entire weir length
Figure 18: Sketch of a settling tank
64
Figure 19: Sedimentation tank layout
3.2: Sizing of filter tank
Q=M3/h
Taking a residence of 5 min and the system flow rate of 10.9396642m3/h through the tank,
60min=10.9396642m3
5min= (10.93960642m3 x 5min) / 60min = 0.9116338683m
3
=1m3
Thus the size of the filter tank should be 1by1by1m (1m3).
The selected size was taken to be 2 x 1 x 1m (=2m3) as an additional factor of safety and to allow
each tank to be able to allow the flow of the other tank through it during cleaning and sludge
removal.
65
It was noted that in the tank, in which the fluid is constantly moving, there are rarely a define
residence time, but it is important to prevent the occurrence that no part of the volume has an
„external‟ residence time, i.e., a part of volume is not moving. A complete turn over can be
achieved by locating the inlet &outlet at different levels vertically.
3.3: Sizing degassing tank
Volume =∏r2 h=2m
3
Taking h=1.5m
d =√ ( ) 1.3m
3.4 Sizing of sump tank
The sump tank contains the water that is re-circulated from the towers to the fish tank as well as
the additional water added to the system to replace any water losses.
Volume =∏r2 h=3m
3
Taking h=2m
d =√ ( ) 1.4m
4: Piping
The towers require 7 gal every 2hrs = 3.5 gal/hr = 3.248942l/h
Select a button dripper of 12 l/hr of which operating pressure is 0.6-3.5bar (Irrico Ltd catalog)
For 15 laterals and 34 drippers
Flow rate in the mainline = 15*34 * 12l/h =6 120l/h = 6.120m3/h
= 0.0017m3/s
Diameter determination:
Q=AV
66
Taking V=1.2m3/s
A=Q/V=0.0017m3/s / 1.2 m/s =0.00141666666 m
2
D=2* √
=2 x √
= 0.04247m = 4.247cm
Available PE size close to 4.247cm is 0.041m or1.5 inches
Head loss determination in the main line;
HL = F
Re =ρVD/u
Actual velocity
V=Q/A=
(
)
= 1.2876 m/s
RE=
= 37643.4538
If Re < 2000 flow is lamina and if Re > 4000 up to even more than 50,000 flow is turbulent
Pipe roughness of pipes=3.0 x10-6
m
= 0.00007
From moody chart for RE = 3.7643 X 10-4
and e/d = 0.00007
F = 0.023
HL= 0.023 X
= 0.7110m
Flow rate in the Lateral
Q= 6.120m3/l / 15 laterals =0.408m3/h per lateral = 0.00011333333m
3/s
67
A pressure of 0.6 bar=6m should be the allowable pressure along the length of the lateral for the
drippers to give out water at their designed flow rate.
P=ρ g h
H=P/ρ g=6 / ( 100*9.81) =0.00611620m
Thus the head loss should not go beyond 0.00061162079m
Taking V=0.1
A=q/v =0.00011333333/0.1 =0.0011333333
d=2*A/II = 0.0109658744 =1.0966 cm
Re =
=2906.419486 =2.9 x 10
3
e/d =3 x10-6
/ 0.03798690268 =0.00007897458
Flow is in the lamina and thus
F=
=
0.02206896552
HL=0.044416m
The above achieved head loss has exceeded the limit head loss of 0.00061162079m by 0.0438m.
Since from the head loss equation we see that head loss is indirectly propotional to the dimeter,
increasing the pipe diameter would further decrease the head loss to the required limit.
By taking a diameter of 1.27 cm (0.5 inches), the head loss = 0.02209 X
=
0.000625m. The difference in the head loss became 0.000014m = 0.014mm which is negligible.
Drainage pipe size determination
The average crop water requirements for strawberry in an open field is 500mm (FAO)
68
Since each tower is supplied with 0.01325m3/h, the drained water to be obtained from the bottom
of the tower will be of lesser volume because of water uptake by the crops and
evapotranspiration as well.
Assuming that the strawberries will have exactly 500mm water needs in the hydroponic system,
the volume of water that is lost is
Volume = cross-section area of tower (15.24 cm diameter) x water depth
= 3.142 x
x 0.5 m = 0.1197102m
3
This would be used to determine how much water to add to the system at any particular time.
Taking the flow rate through pumice to be 7.64m3/m
2h (esearch gate, 2003), the drainage flow
rate through the tower of 0.2394 m2 was 1.829 m
3/h. The water drained from the towers is
collected in gravel beds of 0.9 x 15m sloped at 1 inch for 3.5 m for water flow into the drainage
pipe.
Using the Darcy head loss formula the head loss in each pipe was calculated in excel:
Pipe flow rate
(m3/h) diameter(cm) diameter
(inches) velocity
(m/s) length
(m)
Head loss
per unit
length(m)
Total
head
loss(m)
Pump to junction
between rearing tanks 21.86 14.42 5.677165354 0.335 7.7 0.0008 0.00616
junction to rearing
tanks 10.93 7.211 2.838976378 0.671 3 0.006 0.018
Rearing tanks to
sedimentation tank 1.641 4.3983 1.731614173 0.213 1 0.001 0.001
Rearing tank to filter
tank 9.299 10.47 4.122047244 0.366 13.4 0.001 0.0134
Between filter tanks 10.93 7.2211 2.842952756 0.671 8.4 0.006 0.0504
Filter tank to degassing
tank 10.93 7.2211 2.842952756 0.671 4 0.006 0.024
Degassing to mainline
and mainline 6.12 4.247 1.672047244 0.884 10.7 0.016 0.1712
laterals 0.408 1.27 0.5 0.701 120 0.042 5.04
drainage from towers 0.094 2.54 1 0.244 120 0.006 0.72
Drainage to Sump tank 1.8291 2.54 1 0.823 2.7 0.008 0.0216
69
5. Pump sizing
The power of the pump required to deliver the water from a tank to a discharge point in the
aquaponic system was give as
Pump 1
Given that for a pump, the power requirement is given by the equation:
P =
Where E m = E p = 0.3 (for small pumps): motor and pump efficiencies respectively
Given;
Static suction head = 3m (depth of sump tank)
Delivery head = 4m (from sump to top of fish tanks)
Pipeline friction head = 0.00616 + 0.018 + 0.001 + 0.0134+ 0.0504 + 0.0024 = 0.11296
Other losses (due to bends, elbows, etc) = 0.5m
Total head = 7.61296m
Taking Q = 21.86m3/h = 0.0060722m
3/s
P = =
= 5038.79w
= 5.038 Kw
Pump 2
Given;
Static suction head = 3m (depth of degassing tank)
Delivery head = 2m (depth on top of hydroponic towers)
Pipeline friction head = 0.008 + 0.032 + 5.04 = 5.08
Other losses (due to bends, elbows, etc) = 0.5m
70
Total head = 10.58m
Taking Q = 6.12m3/h = 0.0017m
3/s
P =
= 1960.47w
= 1.960 Kw
Figure 20: System layout
71
CHAPTER 6
6.1 CONCLUSION
The following expected results were obtained:
1. A designed vertical tower hydroponic farm structure with an incorporated biofilter.
2. A designed aquaculture system constituting of circular rearing tanks and sumps.
3. Settling basins and filter tanks
4. A designed piping network and water-pump for the given flow rate and system head.
The system consists of 510 PVC pipes designed as towers (6 inches diameter, about 1.8m long)
in which plant roots are exposed to water that flows down the towers, delivering water, nutrients
and oxygen to the roots of the plants. The towers are lightweight, inexpensive, and versatile and
use vertical farming space efficiently providing highest plant density possible. Water is delivered
to the towers from the top of the towers by 0.5 inch PE pipes, collected from the bottom of the
towers into slanted 4 by 3 by 0.5 m gravel beds (slanting at 1 inch for 3.5 m)that drain to 1 inch
drainage pipes before being re-circulated to the fish tanks.
Each circular rearing tank has a water volume of 5752 liters with an internal water recirculating
velocity of 20 cm/s. The flow rate to the two tanks is 21.86 m3/h but the flow rate to individual
tanks is apportioned so that tanks receive a higher flow rate as the fish grow. The water exchange
rate for each tank is 2 exchanges per hour.
The estimated annual production from the system:
Estimated annual production (kg)
Aquaponic Land cover 30 X 9 m
Strawberry land cover 120 sq. meters
Fish
Weight of adult tilapia 250 kg
Annual fish production 320 fish
Total annual weight (kg) 80000
Strawberries
Maturity period 70 days, approx 3
months
Each plant produces (Ministry of agric.) 2 kg annually
72
Number of crops 10200 berries
Total annual weight produced (kg) 20400
Case Study Comparison
A strawberry farmer (on soil) in
Machakos: Mr. Alexendar Mwangi's farm
Strawberry Land cover: eighth of an acre 505.8571 sq. meters
Weekly Production 15 kg per week
Annual production (kg) 780
Farmer in Nyeri, Mr. Robert (on soil)
Strawberry Land cover: three quarter of
an acre 3035.142 sq. meters
Weekly Production 147
Annual production (kg) 7644
Thus, this aquaponic farm shows that it can produce more crops on lesser land and thus proving
the hypothesis, as illustrated using Robert‟s farm below:
73
The logistics of working with both fish and plants can be challenging. If multiple units are used,
fish may be stocked and harvested as frequently as once a week. Similarly, staggered crop
production requires frequent seeding, transplanting, harvesting and marketing. Therefore, the
goal of the design process was to reduce labor wherever possible and make operations as simple
as possible. For example, incorporating two fish-rearing tanks adds extra expense. One larger
tank could be purchased instead and partially harvested and partially restocked every 6 weeks.
However, this operation requires additional labor, which is a recurring cost and makes
management more complex. In the long run, having several smaller tanks in which the fish are
not disturbed until harvest (hence, less mortality and better growth) will be more cost effective.
Labour reduction was also enhanced by designing a self-cleaning tank and incorporating
filtration devices which function to prevent solids from reaching the hydroponic system. With
the high potential of the growing media to clog, frequent bed tillage or periodic media
replacement would be required, especially considering that the design uses of vertical towers.
Hence, the fish tank and filters are significant in minimizing clogging and reducing the
aforementioned labour since it is much easier to clean the filters than it would have to clean the
medium.
The costing of the system was approximated as:
Table 7: Bill of Quantities
74
6.2 RECOMMENDATION
Management of the system
Out of the three stocking methods that can maintain fish biomass near the critical standing crop,
multiple rearing units are recommended for fish management. In this method, each rearing tank
contains a different age group of fish, but they are not moved during the production cycle. This
system does not use space efficiently in the early stages of growth, but the fish are never
disturbed and the labor involved in moving the fish is eliminated. A system of four multiple
rearing tanks has been used successfully with tilapia in the UVI commercial scale aquaponic
system.
By using multiple rearing method, production will be staggered so one of the rearing tanks is
harvested every 6 weeks. At harvest, the rearing tank will be drained and all of the fish are
removed. The rearing tank is then refilled with the same water and immediately restocked with
fingerlings for a 12-week production cycle.
Sustainability and automation
For further up-scaling of the project and for environmental and financial sustainability, it was
recommended that solar or wind power should be enhanced as part of the energy source. Rain
water could also be harvested as an alternative source of water. Automatic fish feeding system
and mobile phone-control of the system is also recommended as steps toward automation of the
system as much as is acceptable. Other hydroponic design alternatives apart from vertical tower
system could also be applied for a given locality and project.
75
6.3 REFERENCES
AMEDI .D.M. and KENYANI .A.I. (2014), Engineering Design project Guide, University of
Nairobi (unpublished)
DAHA.M. (1999), Easy Gardening With Hydroponics, copyright, Foothill Hydroponics
Department of Agriculture, Forestry and Fisheries, Republic of South Africa, (2011),
Hydroponic Vegetable Production
DIETER .G.E and SCHMIDT .L.C. (2009), Engineering Design, 4th
Ed, McGraw-Hill
Companies Inc., New York
Engineers Edge (2000-2015) Pipe friction calculations within pipe for fluid flow,
http://www.engineersedge.com/fluid_flow/pressure_drop/pipe-friction-calculation.htm
JIM. E. WYATT, EMILY W. GATCH, MITCHELLE V. HATCHETT AND CRAIG H.
CANADAY. (2002), Greenhouse production of off-season, Hydroponic Strawberries, West
Tennessee Experiment
KHANDANI .S. (2005), Engineering Design Process, Industry Initiatives for Science and Math
Education (IISME), California
KIARIE LILIAN, (Tuesday, November 5th
2013 article), The Rich Pickings in Strawberry
Farming,
LOSORDO.T.M, MASSER.M.P and RAKOCY.J, (1998), Recirculating Aquaculture Tank
Production System: An overview of critical considerations, SRAC Publication No. 451, New
York.
LYNX.T. (March 26th
, 2011) Pump Sizing, Accessed by: http://www.aquaponiclynx.om/pump
sizing
MAINA WILSON, (October 2010 article), Strawberry Gardening.
MALONE .R. (2013), Recirculating Aquaculture Tank Production System: A review of
current design practice, Southern Regional Aquaculture Centre (SRAC) Publication No. 453
MASSER .M.P, RAKOCY.J and LOSORDO .T.M, (1999), Recirculating Aquaculture Tank
Production System: Management of Recirculating Systems, SRAC Publication No. 452, New
York.
MKULIMA YOUNG, (Article May 13th
2014), Strawberry Flavored Cash for Farmers.
76
MICHAEL.C (August 21, 2013). Choosing a pump for your aquaponic system for an
aquaponics or hydroponics, Accessed by: http://solarhomestead.com/choosing-a-pump-for-
your-acquaponics-system
NELSON .R.L (2008), Aquaponics Equipment, The Biofilter, Nelson and Pade, Inc
Nema/PR/5/2/10931, July 2013, Environmental Impact Assessment Full Study Report, Kamulu,
Nairobi county
RAKOCY .J, MASSER .M.P. and LOSORDO .T.M. (2006), Recirculating Aquaculture Tank
Production System: Integrating fish and plant culture, SRAC Publication No. 454, New York
SEN.C. ME 402 Workshop; Functional Modeling, Clemson University (unpublished)
TIMMONS .M.B and EBELING J.M. (2012), An Engineer’s View of Recirculating
Aquaculture and Aquaponics System, Aquaponics association conference
World Weather Online, Data from year 2000-2013,
file:///C:/Users/Standard%20user/Desktop/Anaa%20clutter/Kamulu,%20Kenya%20WeatherYES
%20Averages%20_%20Monthly%20Average%20High%20and%20Low%20Temperature%20_
%20Average%20Precipitation%20and%20Rainfall%20days%20_%20World%20Weather%20O
nline.htm
77
APPENDICES
Appendix A
78
Figure 21: Moody chart
Figure 22: House of quality most complete configuration
Room 1
Customer Requirements
(CRs)
“whats”
Room 4
Relationship Matrix
“whats” related to “hows”
Room 2
Engineering characteristics
(ECs)
“hows”
Units for ECs
Improvement direction
Room 3
Correlation
matrix
Room 6
Customer assessment of
competing products
(Rating competitors “whats”)
Room 5
Importance rating
Room 7
Technical assessment
Room 8
Target values
79
Table 8:The aquaponic House of Quality streamlined configuration Rooms 1,2,3,4 and 5
Engineering Characteristics
Improvement direction
Units m n/a n/a n/a n/a n/a m2 m/s s °C kW n/a n/a n/a
Customer
Requirements
Imp
ort
ance
wei
gh
t fa
ctor
Ex
tern
al &
in
tern
al d
imen
sion
s
Geo
met
ry/s
hap
e
Mat
eria
l o
f th
e co
mp
onen
t
Pip
ing
Net
work
Typ
e &
Siz
ing
of
pum
p
Aer
atio
n
Con
fig
ura
tion
and
type
of
hyd
ropo
nic
com
ponen
t
Pre
sence
&W
eig
ht o
f m
edia
To
tal ar
ea c
over
ed
Wat
er f
low
rat
e
Wat
erin
g in
terv
al &
tan
k w
ater
exch
ang
e in
terv
al
Wat
er a
nd
air
tem
per
atu
re
Lig
hti
ng
/ill
um
inat
ion
in
ten
sity
Use
of
elec
tric
ity
/so
lar
So
lids
rem
ov
al c
om
po
nen
t: t
yp
e an
d
sizi
ng
Eas
e o
f op
erat
ion
and
rep
air
Det
ecti
on
s &
mea
sure
men
ts
Correct component
ratio and sizing 5 9 9 9 9 1 9 9 9
Minimize power failure 5 9 9
Cost effective 5 9 3 9 3 3 1 9 3 9 1 9 9 9 9 9 9
Stability of structure 4 3 3 3 1 1 3 1
Minimize clogging 4 3 3 1 1 9 3 1 9 9 9 9 1
Optimal watering frequency and
timing 4 3 3 3 1 3 3 3 3
Improve water quality adjustments 4 1 9 1 3 9 9 3 9 3
Minimize leakage 4 3 1 9 1 1 3 9
Maximize lighting
and temperature 3 9 9 9 9
Maximize aeration 3 9 9 1 3 1 3 9
Maximize wind effect 3
Warning alarms 2 3 1 3 3 3 3
Ease of disassembling 2 9 3 3 3 9 9 9
Raw score 144 43 63 122 125 78 156 100 58 151 144 90 72 120 243 99 133
Relative weight % 7.42 2 3.2 6.3 6.4 4 8.03 5.2 2.9 7.8 7.4 5 4 6.2 12.5 5 6.9
Rank order 4 17 15 8 7 13 2 10 16 3 4 12 14 9 1 11 6
+
+
+
+
+
+
+
+
+
+ +
++ Strong positive
+ Positive
None
80
Appendix B
Figure 23: Data collection photos
Photo 1: Measuring the size of land photo 2: Recording of GPS data
Figure 24: Google earth map showing the elevation of the farm
Map 1
81
Map 2