providing sanitation in peri-urban slums of nairobi, kenya

5/21/2018 Providing Sanitation in Peri-Urban Slums of Nairobi, Kenya

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Providing Sanitation in Peri-Urban Slums of Nairobi, Kenya

Lance M. Langer, Rahul Gogia, Amanda Caldwell-Jacques, Reggie Jansen, Bill ChengWEF-AWWA Joint Student Chapter Design Team

University of Illinois Urbana-Champaign

August 2014



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CONTENTS1. Introduction .......................................................................................................................................................... 3

1.1 Sanergy - Current Situation in Nairobi, Kenya .............................................................................................. 3

1.2 Anaerobic Digestion - Background ............................................................................................................... 4

2. Evaluation of Alternatives ..................................................................................................................................... 5

2.1 Wet Anaerobic Digester ............................................................................................................................... 6

2.2 Dry Anaerobic Digester ................................................................................................................................ 7

3. Gas Production ...................................................................................................................................................... 7

4. Economic analysis ................................................................................................................................................. 9

4.1 Wet Anaerobic Digester ............................................................................................................................... 9

4.2 Dry Anaerobic Digester .............................................................................................................................. 10

4.3 Payback Period ........................................................................................................................................... 10

5. Recommendations .............................................................................................................................................. 11

Works Cited ................................................................................................................................................................. 12

Appendix ...................................................................................................................................................................... 13

Biogas Production Calculations ............................................................................................................................... 13

Concrete Calculations .............................................................................................................................................. 14

Steel Bar Reinforcement Calculations ..................................................................................................................... 16

Team MembersPaper Contributions ....................................................................................................................... 22



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1.INTRODUCTION The world today is comprised of many countries that lack basic needs such as clean drinking water and

sanitation. Without the proper guidance and necessary resources these countries are forced to live an

impractical lifestyle that makes the environment unsafe. The city of Nairobi, home to around 3 million,

is located in the East African country of Kenya. Unfortunately, this city has been plagued with the lack of

essential sanitation infrastructure. However, Nairobi is currently working towards building a working

sanitation system, and cleaning up their environment, with the help of the non-government

organization (NGO), Sanergy.

FIGURE 1-1 SLUMS OF NAIROBI, KENYA

1.1 SANERGY -CURRENT SITUATION IN NAIROBI, KENYASanergy has a plan to supply the city of Nairobi with a sustainable sanitation system while still turning a

profit through their Build-Franchise-Collect-Convert-Transfer operational plan.

FIGURE 1-2 SANERGY 'S OPERATIONAL PLA N



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Sanergy engineers design and manufacture Fresh Life Toilets which focus on hygiene, accessibility and

affordability. Once the toilets are ready for use, Sanergy sells the toilets to locals who become part of

the franchise. They assume the role of Fresh Life Operatorsand receive training, access to financial

assistance, and marketing. It is their responsibility to make sure that the toilets are operational on a

daily basis. When the toilets are in full operation, they consist of a waste separated collection cartridge

system and provide a hand washing station. The waste is collected at the end of each day and the

cartridges are replaced with fresh ones. After the waste is collected, it is transported by wheelbarrows

to the Sanergy facility where it is converted to an organic fertilizer. Finally, Sanergy supplies local

farmers with the organic fertilizer.

FIGURE 1-3MICHAEL AZZARELLO NEXT TO AN OPERATIONAL FRESH LIFE TOILET(CEE449TRIP TO NAIROBI,KENYASPRING 2014)

Sanergy currently serves a roughly four square kilometer area in which approximately 500,000 people

have access to this sanitation system. The toilets are accessible at a cost of 5 Kenyan Shillings per use,

equivalent to 6 cents in the U.S., and there are a little more than 325 toilets in operation which are each

used from 150 to 200 times daily. It is estimated that 3 metric tons of waste is being produced per day at

30% total solids content. The toilets are not yet found in the poorest regions of Nairobi, but Sanergy is

looking to expand to these regions after they have experience in the field.

1.2 ANAEROBIC DIGESTION - BACKGROUNDAnaerobic digestion is a process for which organic matter is converted to methane and carbon dioxide in

the absence of oxygen. This biological process is characterized into four steps: hydrolysis, acideogenesis,

acetogenesis and methanogenesis. Hydrolysis is when the organic matter is broken down into sugars

and amino acids. Acideogenesis is when everything is reduced to simple acids. Acetogenesis is where

materials are broken down into acetate, carbon dioxide and hydrogen gas. Finally, methanogenesis is

when the formation of carbon dioxide and methane occur.



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The factors that dictate the design of anaerobic digesters and gas production include the following:

Temperaturemust remain in either the mesophilic range of 20-45 C (68-113 F) or the thermophilic

range of 50-65 C (122-149 F).

Solids Retention Time (SRT)the typical range for mesophilic treatment is 15-30 days and the typical

range for thermophilic treatment is 12-14 days.

Total Solids Contentthe total solid contents can range from 10-15% to meet the conditions needed for

a wet digestion process and can range from 22-40% to meet the conditions needed for a dry digestion

process.

Carbon to Nitrogen ratio (C:N)must remain within the ideal range of 20-30. If this range is exceeded,

the result will be a lower biogas production. If this range is not met, the result will be potential failure of

the reactor.

pHmust remain within the ideal range of 6.5-7.

2.EVALUATION OF ALTERNATIVES In proposing feasible designs for anaerobic digesters in Nairobi, the team had to step back and consider

the design challenges that we could potentially face in this region. The team determined that the key

design challenges would include space and operation limitations, shortage of materials and funding, lack

of expertise and volume of incoming waste.

FIGURE 2-1 DESIGN CHALLENGES IN NAIROBI, KENYA

After considering these challenges and limitations, it was decided that design goals would be to keep

costs at a minimum while providing a simple operation and maintenance plan. Two different digesters,

wet and dry, which took the form of two different reactor types, Continuously Stirred Tank Reactor

(CSTR) and Plug Flow Reactor (PFR), were investigated. However, both structures share many similarities

to conform to the feasibility study.



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2.1 WET ANAEROBIC DIGESTERThe wet anaerobic digesters are continuously stirred tank reactors (CSTR) with proposed 10% total solids

content. With 3 metric tons of waste being produced per day at 30% total solids content, the diluted

influent would be around 9 metric tons per day (9 m/day). It is assumed that the solids retention time

(SRT) would be 30 days bringing the total required internal volume to 270 cubic meters. At this size,having just one reactor that could handle this volume would be hard to build and maintain, thus the

team spread this volume out among three reactors. Each reactor is designed to be about three meters in

height, half below ground and half above, and three and a half meters in radius, all constructed out of

steel bar reinforced concrete. With these dimensions, each reactor would contain a total of 115 cubic

meters of usable storage volume providing a factor of safety of 1.28. To note, the usable storage does

not include the dome for which will be elevated half a meter at its peak.

This design will operate on the principle of conservation of mass. With an influent chute a meter above

ground, and an effluent discharge one half meter above ground regulated by a plug valve, the goal is to

use this principle to keep the reactors closed to the atmosphere and exploit the property that gas rises,in order to collect the production at an intake at the top of the dome. The gas will travel up and through

a hose, regulated by a check valve, which will be connected to the top of the dome. Each reactor will be

equipped with four long plastic oars, evenly spaced from each other and connected at the dome, which

will be used to manually stir the contents of the reactors.

The team determined that it would not be necessary to provide heating to our digesters, as

conventional digesters need, because Nairobi is located right below the equator. With this in mind, the

team theorizes that the digester will naturally receive enough heat from the sun to achieve mesophilic

temperatures. To add, the influent will be naturally heated by the sun and will provide extra heat

needed to meet the assumed SRT.

FIGURE 2-2 BASIC LAYOUT OF WET ANAEROBIC DIGESTERS



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2.2 DRY ANAEROBIC DIGESTERThe dry anaerobic digester is a plug flow reactor (PFR) with proposed 30% total solids content. With 3

metric tons of waste being produced per day at 30% total solids content, the influent would be around 3

metric tons per day (3 m/day). Again assuming that the SRT would be 30 days, the total required

internal volume is 90 cubic meters. Applying a 5:1 length to width ratio, the length should be 20 metersand the width to be four meters while providing a height of one and a half meters, all above ground and

constructed with steel bar reinforced concrete. With these dimensions, the reactor would contain a

total of 120 cubic meters of usable storage volume providing a factor of safety of 1.33. To note, the

usable storage does not include the dome for which will be elevated half a meter at its peak.

This design would utilize a 20 meter long stainless steel auger that would move the influent through the

length of the reactor in a plug flow fashion. The auger would be mounted at both ends and would be

equipped with a hand crank which would be manually cranked from both ends in unison. A similar

convention for influent addition and effluent removal will be applied to this reactor. The influent chute

will be one meter above ground at one end of the reactor while the effluent discharge, regulated by aplug valve, a half a meter above ground will be located at the other end. The exact same method for gas

collection and heating that was used for the wet anaerobic digester will be used for this digester.

FIGURE 2-3 BASIC LAYOUT OF DRY ANAEROBIC DIGESTER

3.GAS PRODUCTIONThe choice of the reactor configuration had a significant impact on determining biogas production. For

the CSTR, assumptions made include ideal mixing occurring with minimal concentration gradients inside

the reactor volume. For this to be reasonable, the reactor contents must be mixed thoroughly in regular

intervals, as the biomass will aggregate and settle to the bottom of the tank as it is processed. The first

step in determining gas production was determining the solids retention time (SRT), which is the optimal

retention time for biomass digestion. For many systems, it can be difficult to decouple the solids



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retention time from the hydraulic retention time (HRT), especially if the stream is high in solids content

and/or there is a recycle stream present. However, since this is not the case with the current design, the

SRT can be set equal to the HRT.

Method #1: Volatile Suspended Solids Reduction

The first of the methods used to calculate biogas production was the empirical method developed by

Metcalf & Eddy (2003), in which the volatile suspended solids (VSS) reduction is calculated as a function

of the SRT. The empirical equation used assumes no characteristics about the waste being used, and as

such provides more of a ballpark estimate of the biogas production. The VSS reduction was calculated

and used to determine the VSS removed from the total VSS in the feed stream. Finally, biogas

production was calculated from dimensional analysis with the total VSS removed and common design

criteria.

Vd= 13.7 ln + 18.9

Where Vd= percentage VSS reduction, = SRT (days)

Assumptions:

- 10% solids loading = 0.9 tonne/day of suspended solids = 900 kg solids/day

- 25% VSS present in human waste

- Typical design criteria for biogas production is 0.75 - 1.12 m3biogas / kg VSS removed

- Biogas is 60% methane by volume, as a conservative estimate.

The biogas production was estimated to be 111 - 165 m3/day. When the biogas is assumed to be

composed of approximately 60% methane, the methane production is 66 - 99 m3/day.

Method #2: Chen & Hashimoto equation

A more accurate method of determining biogas and methane production was by taking into account the

waste characteristics. The following empirical equation was developed by Chen & Hashimoto (1978):

Where v= methane production rate (m3gas/m3digester day)

B0= ultimate methane yield per gram of VSS added (L/g VSS)

S0= influent VSS concentration (g/L)

m= bacterial growth rate parameter (day-1)

K = kinetic parameter (dimensionless)

The parameters can be estimated as follows:



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m= 0.013T - 0.129, where T is in C

K = Assumptions:

- For mesophilic conditions: m= 0.013(35C) - 0.129 = 0.326 day-1

- Because the total solids concentration is 10% with 25% VSS content assumed, S0= (100 g/L)(0.25) = 25

g/L

- K = - For a single pass CSTR, HRT = SRT = 30 days

- B0= 367 m3/tonne VSS (for municipal human waste) = 0.367 L/g VSS

was calculated to be 0.284

using these parameters. When scaled by the total reactor

volume of 270 m3, the overall methane and biogas production were determined to be 77 and 128

m3/day, respectively.

4.ECONOMIC ANALYSIS

4.1 WET ANAEROBIC DIGESTERBelow is a line by line break-down of the CSTR wet anaerobic digester. The check and plug valves are

needed to regulate the flow of gas and effluent. The ladders are necessary for employees to stir the

sludge with the plastic oars. Excavation is necessitated by the partially below grade design. This forcesthe total cost to $24,681.15 USD (2,175,643 Kenyan Shillings). Details about concrete and steel rebar

calculations and costs can be found in the Appendix.

CSTR Cost Analysis

Item Quantity Units Cost/Item Total Cost

Check Valve 3 UNIT $ 54.23 $ 162.69

Plug Valve 3 UNIT $ 54.51 $ 163.53

Wall Concrete 87.39 CUB MET $ 138.64 $ 12,115.75

Base Concrete 136.8 SQ MET $ 20.80 $ 2,845.44

Steel Bar Reinforcement 4,828 KG $ 1.59 $ 7,676.63

Extra Base Thickness 6.15 PER 150 MM $ 18.18 $ 111.81Ladders 3 UNIT $ 49.99 $ 149.97

Plastic Oar 12 UNIT $ 19.99 $ 239.88

Excavation 267.72 CUB MET $ 2.84 $ 760.33

Spread Dirt On Site 267.72 CUB MET $ 1.70 $ 455.12

Total $ 24,681.15TABLE 4-1WET ANAEROBIC DIGESTER COST ANALYSIS



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4.2 DRY ANAEROBIC DIGESTERWhile the plug flow reactor requires neither plastic oars nor excavation, the stainless steel auger adds

significantly to the price. Also, as this design only calls for a single digester, fewer check and plug valves

are needed, in addition to requiring less concrete. The total cost is $19,470.87 USD (1,716,357 Kenyan

Shillings). Details about concrete calculations and costs can be found in the Appendix.

PFR Cost Analysis

Item Quantity Units Cost/Item Total Cost

Check Valve 1 UNIT $ 54.23 $ 54.23

Plug Valve 1 UNIT $ 54.51 $ 54.51

Wall Concrete 39.54 CUB MET $ 170.45 $ 6,739.59

Base Concrete 96.22 SQ MET $ 25.57 $ 2,460.35

Extra Base Thickness 2.05 PER 150 MM $ 18.18 $ 37.27

Steel Bar Reinforcement 6,367 KG $ 1.59 $ 10,124.92

Stainless Steel Auger 1 UNIT $ - $ -

Total $ 19,470.87TABLE 4-2DRY ANAEROBIC DIGESTER COST ANALYSIS

4.3 PAYBACK PERIODUsing our calculations for biogas production, we were able to come up with project payback periods for

both designs. According to Charles Banks, a speaker at the University of Southampton, every mof

biogas produced can be expected to yield 10 kWh. For our project, we scaled this down to 2 kWh to

factor in ideal yield, inefficiencies, malfunctions and methane concentration. With our range of 110-

165 m of biogas per day, we were able to come up with a range of 88,000 to 130,000 kWh/year of

energy production in our digesters. According to Regulasweb.com, the current rate for commercial

electricity in Kenya is $0.18 (16 Kenyan Shillings). We applied this going rate to estimate anywhere from$15,600 to $23,200 of return value per year if Sanergy were to decide and invest in a combustion engine

and generator. In covering the costs of the digester construction, these biogas yields would produce

payback periods of less than two years. Table 4-3 below summarizes the payback calculations.

Metcalf/Eddy Method Metcalf/Eddy Method Chen/Hashimoto Method

Amount Units Amount Units Amount Units

Design Criteria 1.12 mof biogas/kg VSS 0.75 m of biogas/kg VSS N/A

Biogas Production 165 m 111 m 128 m

kWh/day 353 kWh/day 238 kWh/day 274 kWh/day

kWh/year 128,882 kWh/year 86,702 kWh/year 99,981 kWh/year

Return value/year $ 23,198.67 $ 15,606.38 $ 17,996.54

Wet Digester Cost $ 24,681.15 $ 24,681.15 $ 24,681.15

Payback period 1.06 Years 1.58 Years 1.37 Years

Dry Digester Cost $ 19,470.87 $ 19,470.87 $ 19,470.87

Payback period .84 Years 1.25 Years 1.08 YearsTABLE 4-3PAYBACK PERIODS



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5.RECOMMENDATIONS Our team took into account a number of factors when considering which recommendation to make to

Sanergy. Cost, performance, maintenance and practicality all played a part in our decision. After

weighing different options, our team recommends Sanergy use the Wet Anaerobic Digester design

because it is economically viable, practical and a proven technology. With 3 smaller digesters as

opposed to the Dry designs singular tank, it allows for continued use in case of a malfunction or

maintenance issue. Its 2 year payback period is a realistic length for Sanergy to have to wait before

turning a profit. Most importantly, wet anaerobic digesters are used all over the world and have been a

proven energy-producing technology for decades, so issues with maintenance and future upgrades will

be simplified and minimal.

The main reason our team did not further pursue the dry digester option was due to the need for a

stainless steel auger and the complications that would arise during construction. Because of the high

solids content in the dry digester, a strong material was needed for mixing. When looking at similar

models, it was consistently found that augers were used to mix the waste, and we chose this as our

design point. However, when consulting with mentor Professor Jeremy Guest, who works in research

with Sanergy, our team learned that constructing and installing an auger would be an expensive and

non-practical option. Sanergy does not employ anyone who is licensed to work with stainless steel. In

order to install the auger, Sanergy would have to either train an existing employee or bring in someone

outside of the company to make the design work. The team decided that both of these options were

too costly and inconvenient, especially when considering that in addition to cost, the dry digester did

not have any significant advantages over the wet design.

Hopefully with our detailed design and research, we can begin to build towards a better future for the

residents of Nairobi, Kenya. Our model, if expanded upon and further developed, has the potential to

become widespread throughout developing nations in need of proper sanitation systems. If Sanergy

does indeed move forward with our design, it could be a pivotal moment for the community and the

wastewater industry as a whole.



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WORKS CITED1. Khanal, S. K. Anaerobic Biotechnology for Bioenergy Production: Principles and Applications.

Wiley-Blackwell Publishing, 2008, pg. 93-97.

2. Kigozi, R. Biogas Production Using the Organic Fraction of Municipal Solid Waste as Feedstock.

International Journal of Research in Chemical, Metallurgical, and Civil Engineering, 2014, 1, 107.

3. Gebremedhin, K. G. Biogas Production Model for Plug-Flow Anaerobic Digesters.ASABE Annual

International Meeting, July 2006.

4. Chen, Y.R. and A.G. Hashimoto. A substrate utilization kinetic model for biological treatment

processes. Biotechnology and Bioengineering, 1980, 22(10), 2081-2095.

5. Surendra, K. C.; Takara, D.; Hashimoto, A. G.; Khanal S. K. Biogas as a sustainable energy source

for developing countries: Opportunities and challenges. Renewable and Sustainable Energy

Reviews. March2014, 31, 846-859.

6. Feasibility of Generating Green Power through Anaerobic Digestion of Garden Refuse from the

Sacramento Area. N.p.: RIS International Ltd., Apr. 2005. PDF

7.

Monnet, Fabien.An Introduction to Anaerobic Digestion of Organic Waste. N.p.: Remade

Scotland, Nov. 2003. PDF.

8. "The Sanergy Model." Sanergy. 1 Jan. 2013. Web. 10 Aug. 2014. .

9.

Anaerobic Digestion and Energy Recovery Project. N.p.: CDM, Oct. 2009. PDF.

10.Banks, Charles. University of Southhampton (20): n. pag. 20. Web.

11."Regulus." Electricity Cost in Kenya. N.p., n.d. Web. 13 Aug. 2014.

12.British Standards Institution (2005) BS 8110-1:1997: Structural use of concrete. London, BSI.

13.

Nyakiongora, M. A. Current Construction Cost Handbook. Ministry of Public Works, 201214.KS Code (2009) Building Code of the Republic of Kenya.



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APPENDIX BIOGAS PRODUCTION CALCULATIONS

Method #1 calculations: Volatile suspended solids reduction

VSS reduction: Vd= 13.7 ln(30 days) + 18.9 = 65.5% reduction

VSS removed: (900 kg solids/day)(0.25)(0.655) = 147.4 kg VSS removed

Lower estimate of biogas production: (0.75 biogas / kg VSS removed)(147.4 kg VSS removed) = 111 m3

biogas

Upper estimate of biogas production: (1.12 biogas / kg VSS removed)(147.4 kg VSS removed) = 165 m3

biogas

Lower estimate of methane production: (110.6 m3biogas)(0.6) = 66 m3methane

Upper estimate of methane production: (165.1 m3biogas)(0.6) = 99 m3methane

Method #2 calculations: Chen & Hashimoto equation

Methane production rate:

Methane production:

Biogas production:



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CONCRETE CALCULATIONS

WET ANAEROBIC DIGESTER

WALL THICKNESS = 1.0ft

BASE THICKNESS = 1.5ft

DOME THICKNESS = .50ft

RI= 3.5m = 11.5ft

RO= (RI+ WALL THICKNESS) = 12.5ft

RD= (RI+ DOME THICKNESS) = 12ft

HDOME= 1.65ft H = 3m = 9.85ft

CONCRETE BASE:

CONCRETE WALLS:

PROJECTED BOX DOME:

EXCAVATION:

CALCULATIONS FOR ONE DIGESTER

TOTAL COSTS: (VIBRATED REINFORCED CONCRETECLASS 20/20)

BASE (INCLUDES 150MM THICKNESS):

EXTRA THICKNESS: WALLS: = $12,115.75

EXCAVATION: = $760.33

DIRT SPREAD: = $455.12



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DRY ANAEROBIC DIGESTER

STORAGE:

WALL THICKNESS = 1.0ft

BASE THICKNESS = 1.5ft

PROJECTED DOME:

DOME THICKNESS = .50ft

L = 20m = 65.62ft

H = 3m = 4.92ft

STORAGE:

CONCRETE BASE:

2 FACES:

2 SIDES:

PROJECTED DOME:

TOP:

2 FACES:

2 SIDES:

TOTAL COSTS: (VIBRATED REINFORCED CONCRETE

CLASS 30/20)

BASE (INCLUDES 150MM THICKNESS):

EXTRA THICKNESS:

WALLS: = $6,739.59



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STEEL BAR REINFORCEMENT CALCULATIONS

BS 8110

Table 3.1 strength of reinforcement

Hot Rolled Mild Steel = 250 N/mm2

Table 3.4 Nominal cover for all reinforcement

Severe- 40mm (concrete surfaces exposed to severe rain, alternate wetting and

drying or occasional freezing or severe condition)

3.12.7.4 Horizontal bars for support of small amounts of compression

reinforcement

a) fy= 250 N/mm2: min. 0.30% of concrete area

max. 2% of concrete area

3.3.1.3 Nominal maximum size of aggregate

Nominal cover > nominal max aggregate size

For most work, 20mm aggregate is suitable (any larger and flow of concrete may becompromised)

Table 3.28- Clear Distance between bars according to percentage redistribution

Distance between primary rebar should not be below the greater of three times theaggregate size or 100mm

Distance between secondary rebar should not be greater than 300mm

3.12.11.2.7- Slab

In no case should the clear spacing between bars exceed the lesser of three times theeffective depth or 750mm



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Calculations- Primary Steel Rebar

Dome- Number of primary steel rebar per m2

Material:Hot Rolled Mild Steel = 250 N/mm2Reinforcement Ratio:1% (steel area to concrete area)

Primary Steel Diameter: 10mmCover:40mm

Asn=0.01A

cr n=0.1*1m*0.1524m / ((0.005m)2

)=19.35 ~ 20 rebar/m2

100mm distance between rebar OK

two rows, top and bottom, with 10 rebar per 1m row at a distance of 100mm betweeneach rebar

Base- Number of primary steel rebar per m2

Material:Hot Rolled Mild Steel = 250 N/mm2Reinforcement Ratio:1% (steel area to concrete area)Primary Steel Diameter: 10mmCover:40mm

Asn=0.01A

cr n=0.1*1m*0.4572m / ((0.005m)2 ) =58 ~ 60 rebar/m2

33.3mm distance between rebar NOT OK100mm distance between rebar OK

two rows, top and bottom, with 30 rebar per 1m row at a distance of 33.3mm betweeneach rebar is bellow minimum of 100mm requirement

Wall- Number of primary steel rebar per m2

Material:Hot Rolled Mild Steel = 250 N/mm2Reinforcement Ratio:1% (steel area to concrete area)Primary Steel Diameter: 10mmCover:40mm

Asn=0.01A

cr n=0.1*1m*0.3048m / ((0.005m)2 ) =38.8 ~ 40 rebar/m2

50mm distance between rebar NOT OK100mm distance between rebar OK

two rows, top and bottom, with 20 rebar per 1m row at a distance of 50mm between

each rebar is bellow minimum of 100mm requirement

Conclusion:

Use Y10 100 for primary steel rebar on top and bottom



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FIGURE 1CROSS SECTION OF CONCRETE DOM E



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Calculations- Secondary Steel Rebar

Dome- Number of secondary steel rebar per m2Material:Hot Rolled Mild Steel = 250 N/mm2Reinforcement Ratio:0.2% (steel area to concrete area)

Primary Steel Diameter: 10mmCover:40mm

Asn=0.002A

cr n=0.002*1m*0.1524m / ((0.005m)2 )=3.8 ~ 4 rebar/m2

500mm distance between rebar NOT OK250mm distance between rebar OK

two rows with 2 rebar per 1m row would equate to a distance of 500mm between eachrebar. This is greater than the maximum distance of 300mm between each rebar. Thus use4 rebar per 1m row at a distance of 250mm between each rebar.

Wall- Number of secondary steel rebar per m2Material:Hot Rolled Mild Steel = 250 N/mm2Reinforcement Ratio:0.2% (steel area to concrete area)Primary Steel Diameter: 10mmCover:40mm

Asn=0.002A

cr n=0.002*1m*0.3048m / ((0.005m)2 )=7.76 ~ 8 rebar/m2

250mm distance between rebar OK

two rows with 4 rebar per 1m row would equate to a distance of 250mm between eachrebar

Wall- Number of secondary steel rebar per m2Material:Hot Rolled Mild Steel = 250 N/mm2Reinforcement Ratio:0.2% (steel area to concrete area)Primary Steel Diameter: 10mmCover:40mm

Asn=0.002A

cr n=0.002*1m*0.4572m / ((0.005m)2 ) =11.6 ~ 12 rebar/m2

166.7mm distance between rebar OK

two rows with 6 rebar per 1m row would equate to a distance of 166.7mm between each

rebar

Conclusion:

Use Y10 100 primary steel rebar for top and bottom and Y10 250 for secondary steelrebar top and bottom.



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Wet Anaerobic Digester- Amount of Steel Rebar

Steel Density: 8050 kg/m3

Total Concrete Volume: 20.85 + 21 + 8.13 = 49.98m3

Primary Steel Rebar: 49.98 * 0.01 = 0.4998m3

Secondary Steel Rebar: 499.98 * 0.002 = 0.09996m3

Total Steel Rebar Volume: 0.4998 + 0.09996 = 0.6m3

Total Steel Weight: 0.6 * 8050 = 4,828 kg

Wet Anaerobic Digester- Cost of Steel Rebar

Round Mild Steel Bars Reinforcement10 mm Diameter Bars: 140 shillings (USD $1.59) per kg

4,828 * 1.59 = $7,676.63

For one wet anaerobic digester the total amount of steel rebar in weight is 4,828 kg andthe total material cost for the steel rebar is $7,676.63



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Dry Anaerobic Digester- Amount of Steel Rebar

Steel Density: 8050 kg/m3

Total Concrete Volume: 43.43 + 4.21 + 18.28 = 65.92m3

Primary Steel Rebar: 65.92 * 0.01 = 0.6592m3

Secondary Steel Rebar: 65.92 * 0.002 = 0.1318m3

Total Steel Rebar Volume: 0.6592 + 0.1318 = 0.791m3

Total Steel Weight: 0.791 * 8050 = 6,367.87 kg

Dry Anaerobic Digester- Cost of Steel Rebar

Round Mild Steel Bars Reinforcement10 mm Diameter Bars: 140 shillings (USD $1.59) per kg

6,367.87 * 1.59 = $10,124.92

For one dry anaerobic digester the total amount of steel rebar in weight is 6,36.87 kgand the total material cost for the steel rebar is $10,124.92



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TEAM MEMBERS PAPER CONTRIBUTIONS

Lance M. Langer contributed to the design team by meeting with

faculty advisor Jeremy Guest and leading weekly design teammeetings from idea inception through the completion of this

paper. Specifically, Lance completed the introduction, evaluation

of alternatives and the calculations/costs of the wet and dry

anaerobic digesters.

LANCE M. LANGER

Rahul Gogia contributed to the design team by attending and

participating in weekly design team meetings from idea

inception through the completion of this paper. Specifically,

Rahul completed the gas production calculations and analysis.

RAHUL GOGIA

Amanda Caldwell-Jacques contributed to the design team by

attending and participating in weekly design team meetings

from idea inception through the completion of this paper.

Specifically, Amanda reviewed and edited this paper to help it

attain a more professional and coherent quality, in addition to

assisting with Trimble SketchUp modeling and providing general

support throughout the entire process.

AMANDA CALDWELL-JACQUES



23

Bill Cheng contributed to the design team by attending and

participating in weekly design team meetings

from idea inception through the completion of this paper.

Specifically, Bill completed all of the steel bar reinforcement

calculations.

BILL CHENG

Reggie Jansen contributed to the design team by meeting with

faculty advisor Jeremy Guest and participating in weekly design

team meetings from idea inception through the completion of

this paper. Specifically, Reggie assisted with biogas calculationsand completed the payback period and final recommendations.

REGGIE JANSEN

Other members of the team include Namrata Logishetty, Nick Domalewski, Joseph Chang and Theodore

Chan.

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