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Low-cost on-site sanitation systems

Pedro Quintalo Guerreiro Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1

Master student in Envitonmental Engineering

E-mail: pedro.q.guerreiro@ist.utl.pt

Abstract

According to the UNO, there are one billion people without access to sanitation (UN

Secretariat, 2013), practicing open defecation, mostly in rural areas in developing countries

where financial recourses are not abundant. The implementation of low-cost on-site sanitation

systems is a strategy to mitigate this situation, with this dissertation being focused on the

creation of a simplified guide in order to facilitate the implementation of this type of systems.

The dissertation starts by describing the different types of low-cost on-site sanitation systems,

followed by the analysis of the effluent discharge quality criteria and the analysis of the major

constraints to the implementation of these systems. With this information in mind, two formulas

meant to support the decision-making process were created, one allowing for the separation of

“dry” and “wet” solutions, and another for the selection of the type of final disposal of the

effluents.

This dissertation managed to increase the amount of scientific literature in Portuguese,

allowing for communities without sanitation in places like Brazil or some African countries to

have more available information about this type of sanitation systems. Another important aspect

of this dissertation relates to the application of simplified formulas capable of optimizing the

decision-making process and hence making it easier, allowing for faster decisions to be made.

Key-words: rural sanitation, developing countries, decision-making support guide, optimization.

1. Introduction

The millennium development goals set by the UN in 2000 predict a reduction by half of

the proportion of people living without sanitation by 2015 (UN Secretariat, 2013). Currently,

more than 1 billion people don’t have access to sanitation, with most of them living in rural areas

in developing countries with limited incomes. Low-cost on-site sanitation systems present a way

of mitigating this situation and meeting some of the UN goals. However, the implementation of

these systems is prevented by a difficult decision-making process, which requires the

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knowledge of different characteristics of several sanitation systems, as well as knowing the

site’s own characteristics.

In order to facilitate the implementation of these systems the main goal of this

dissertation is to create formulas able to speed the decision-making process. This dissertation

will analyse the characteristics of the different types of low-cost on-site sanitation systems, as

well as the effluent discharge quality criteria that should be met to safeguard the environment,

as well as the local populations’ health. The major constraints to the implementation of these

systems, which are related to the sites characteristics, will also be analysed, allowing for the

creation of formulas which will generate a sanitation option given the site’s characteristics.

2. Methods

The first goal was to characterize the major different low-cost on-site sanitation

systems, which was achieved through the compilation of data from the most relevant sources,

namely the American EPA (EPA, 2006) and the latest draft of ISO/TC 224/WG 8 available in

March 2013 (ISO/TC 224/WG 8, 2012). The environmental quality criteria were compiled from

the European Directive 91/271/EEC (Directive 91/271/EEC) and from EPA regarding the

pollution removal performance for the different systems. The constraints regarding the

implementation of the low-cost on-site sanitation systems were analyzed in order to allow a

clear understanding of which systems are impacted by each one of the different constrains. The

formulas were created using the Excel software, one allowing the user to separate the “wet”

form the “dry” systems and another one enabling the user to choose between different

treatment and final disposal options for the effluents.

3. Results

3.1. Sanitation systems’ characterization

The different types of collection, transportation, treatment and final disposal systems are

briefly summarized in Table 1. This allows for a faster understanding of the major differences

between the on-site sanitation systems.

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Table 1: Characterization of the different collection, transportation, treatment and final disposal systems

Type of system Description Pre-requisites Advantages Disadvantages

Ventilated

improved pit

latrine (VIP)

Ventilated

superstructure over a pit

Low ground

water table

Sludge removal

No bad odours and

flies

Creates untreated

sludge

Urine diversion

latrine (UD

Latrine)

Ventilated

superstructure with

separation of

urine/faeces

None Creates compost

fertilizer

More difficult to

use

Pour flush toilet

Ventilated

superstructure with flush

toilet

Water supply

needed

Effluent needs

treatment

More user-friendly Generates

untreated effluent

Cistern flush

toilet

The same as before with

flush toilet connected to

a cistern

The same as

before

The most user

friendly

Creates high

volumes of

untreated effluent

Septic tank

A dug pit to collect

domestic effluents, can

be impermeable or not

Low water table Removes solids

from effluent

Risk of water table

pollution

Only for domestic

effluents

Seepage pit

A dug pit enabling the

effluent to infiltrate

trough the walls

Low ground

water table

Permeable soil

Generates quality

effluent

Risk of water table

pollution

Infiltration trench

Underground perforated

plumbing, with effluent

purified by the trench

medium

The same as

before The same as before

The same as

before

Risk of clogging

Buried sand filter

Parallel underground

impermeable filtration

trenches, effluent

treated by filter medium

Low water table The same as before

The same as

before

Superficial sand

filter

The same as above but

above ground

Used when

buried sand

filter are not

used

The same as before

Low risk of water

table pollution

Risk of clogging

Evapotranspiratio

n bed (ET bed)

Vegetated sand bed built

above ground, effluent

treated by the medium

and plants

The same as

above The same as above

The same as

before

Constructed

wetlands

Artificial vegetated

wetland, effluent treated

by plants and medium

High space

required

The same as before

Aesthetically

pleasant

Very expensive

Risk of clogging

Evaporation pond

Impermeable

constructed pond, with

effluent being

evaporated

The same as

above

Aesthetically

pleasant

Low risk of water

table pollution

Risk of bad odours

and flies

Very expensive

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Data collected from: (DWAF, 2002), (EPA, 2006), (Morais, 1962), (EPA, 1980), (SFSDG

Team, 2009), (WaterAid, 2011) and (UNEP, 2000).

3.2. Effluent discharge quality criteria

The effluent discharge quality criteria are compiled from the European Union directive

91/271/EEC. This directive states that for populations corresponding to less than 2000

population equivalent (p.e.), effluents must be subjected to appropriate treatment. The directive

defines 1 p.e. as “the organic biodegradable load having a five-day biochemical oxygen demand

(BOD5) of 60 g of oxygen per day” (Directive 91/271/EEC).

On Table 2, the performance evaluation for the final disposal systems is presented. These

performance values compare the reduction occurring in the effluent since it enters the septic

tank, until it leaves the final disposal system do the natural environment. These data allow for a

better understanding of the potential of each final disposal system.

Table 2: Performance evaluation for the different final disposal systems, including a septic tank.

Type of final disposal

(including a septic tank)

BOD COD TSS TN TP FC

Infiltration trench ++ ND ++ + + ++++

Seepage pit ND +++ +++ +++ ++++

Sand filters +++ ND +++ + ++ ++++

CW Superficial Flow ++ + +++ + + +++

CW Horizontal Flow ++ + + + + +++

Evapotranspiration bed +++ ND +++ + ++ ++++

Evaporation pond + ND + + + +

Data collected from: (EPA, 1980), (EPA, 2006), (ISO/TC 224/WG 8, 2012), (Morais, 1962),

(SFSDG Team, 2009) and (UNEP, 2000).

3.3. Constraints impacting the choice of possible solutions

3.3.1. Water supply condition

The water supply condition is a very important constraint since it allows the decision-maker

to realize if the site can support “dry” and/or “wet” systems, choosing between dry latrines and

flush toilets (Figure 1). UD Latrines are suitable also for people with water supply because these

people might also want to benefit from the urine and faeces reutilization. Flush toilets are

applicable only when there is water supply. Pour flush toilets don’t need a constant water

source but cistern flush toilets need.

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Figure 1: Organogram simplifying the problematic regarding the choice between “dry” and “wet”

systems.

3.3.2. Available space, size and density of the population

Available space is an important factor since many final disposal systems require large areas

to be implemented, like the evaporation pond system or the constructed wetlands. In rural areas

in the developing countries lack of available land is not common, with most of the land

composed by natural ecosystems. Therefore, this criterion is not usually a serious constraint.

The population size is important because on-site systems have a limited operation capacity

to only a few hundred people. This dissertation focuses only on rural areas with maximum 250

inhabitants, which can be easily served by the on-site systems already described. Population

density poses a considerable constraint to the decision-making process, on the other hand,

when people live in communities very close to each other. An area is considered densely

populated if there are more than 200 inhab/ha, with lower figures being declared as sparsely

populated. For densely populated areas, the final disposal systems should be collective, serving

several houses simultaneously (Figure 2).

Water supply condition

Existence of plumbing

Cistern flush toilet

UD Latrine

Well access in the garden

Pour flush toilet UD Latrine

No domestic water supply

VIP

UD Latrine

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Figure 2: Organogram depicting the existing options for high and low population density.

3.3.3. Cultural and hygienic habits and climate

Cultural habits can be a constraint on two ways: requiring a certain toilet shape or

preventing urine and faeces reutilization. The first constraint does not limit the choice between

“dry” and “wet” systems, since all of them can easily include a western type toilet or a Turkish

type, complying with the local costumes. The second constraint however is very important since

it prevents the implementation of the UD Latrine, one of the most cost-effective systems.

Therefore, the local inhabitants should be made fully aware of all the potential of this system in

order to overcome any cultural biases (Figure 3).

Figure 3: Organogram illustrating the options available according to the cultural perspective on

urine and faeces reutilization.

The climate is important because some final disposal systems’ performance depend on

the type of climate. These systems, namely de evaporation pond, the evapotranspiration bed

and the constructed wetlands all need dry climates to have good performances, since it is the

evapotranspiration rate that is responsible for the removal of most of the effluent from these

systems (Figure 4). For wet climates these systems are not applicable, with the underground

systems being more suitable for this type of weather.

Population density

>200 inhab/ha

Collective final disposal systems

≤200 inhab/ha

Individual final disposal systems

Cultural position and other constraints

Favors urina /eces reutilization

UD Latrine

Objects urine/feces reutilization

VIP Flush toilets

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Figure 4: Organogram depicting the impact of the type of climate on the choice of a final disposal

system.

3.3.4. Income and willingness to pay

Income is a very important constraint since low-income families will prefer the adoption of

more affordable sanitation systems even if they underperform or require more maintenance

compared to more expensive systems. There should be considered two levels of income: high

and low. High income corresponds to families that can afford to pay more expensive systems

without jeopardizing their financial stability. Medium-income families can afford more expensive

systems but they become too vulnerable to financial shocks if they do so, while low income

families cannot afford any of the more expensive systems. With Table 3, it is easier to decide

which types of systems are more affordable to the low income families.

Table 3: Costs for the different on-site sanitation systems.

Type of final disposal

system

Costs(1)

including

septic tank (€)

Type of “wet” or “dry”

system Costs

(2) (€)

Seepage pit 2800 VIP 250 - 450

Infiltration trench 2200 - 14000 UD Latrine 250 - 560

Sand filters 4800 Pour flush toilet 235 - 410

Evapotranspiration bed 7400 Cistern flush toilet 150 - 375

Evaporation pond <34000

Constructed wetlands 50000 - 90000

(1) – Costs compiled for USA$ values.

(2) – Costs compiled from South-African Rand.

Data collected from: (DWAF, 2002), (EPA, 1999), (EPA, 2006), (EPA, 2000), (EPA, 1999)

and (EPA, 2000).

Another important aspect is the willingness to pay (WTP) that is transmitted by the local

inhabitants. The WTP should be taken in consideration only for the medium and low-income

families. Therefore, it should not be asked for a family to pay for a more expensive system if it

Type of climate

Wet

Seepage pit Sand filters Infiltration trench

Dry

All systems are possible

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puts the family at risk from financial shocks. Only high income families should be asked to pay

for more expensive sanitation types (Figure 5). The definition of high, medium and low-income

families should not be universal because different countries have different income inequalities,

purchasing power and poverty level definition. Therefore, high, medium and low-income families

should be defined for the country where the site is located.

Figure 5: Organogram depicting the existing options for a given Income and WTP.

3.3.5. Capacity and competence for the operation

This constraint relates to the ability of the local inhabitants to perform the tasks required to

maintain a system properly functioning. The final disposal systems which require more

elaborate tasks are the ET beds and the constructed wetlands. These systems have vegetation

growth inside them, increasing the likelihood of reckless vegetation growth, which could

damage the system and lower the performance rates. Therefore, future user will have to be able

to maintain a proper vegetation growth, since these systems’ performance depends on it. For

sand filters and infiltration trenches potential users will need to know when to substitute the

sand so that clogging is prevented. The other final disposal systems have simpler maintenance

tasks, such as emptying the pit for the seepage pit solution (Figure 6). “Dry” Latrine and “wet”

toilet systems are not impacted by this constraint since maintenance tasks are very similar,

mainly regarding the cleansing of the installations.

Income and WTP

High

Evaporation pond

Constructed wetlands

Medium

Infiltration trench

Sand filters

ET bed

Low

Seepage pit

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Figure 6: Organogram illustrating the diverse options suitable for each level of future user

competence.

3.3.6. Soil type and receptor medium

The soil type is one of the major constraints to the implementation of o-site sanitation

systems because of two soil characteristics: groundwater level or water table and permeability.

The groundwater lever specifies if a system can be implemented into the soil or, instead, has to

be constructed over the soil. Places with low water tables (>1,5 meters from surface) are proper

places to build sanitation systems underground, since there is little risk of contamination of the

groundwater resources by the effluent percolating the soil. For high water table places (≤1,5

meters from surface) the opposite occurs, with high risks of groundwater contamination.

Therefore, only superficial systems can be implemented in places with high groundwater tables

(Morais, 1962). These systems are the evaporation pond, the ET bed and the superficial sand

filter. When the water table is low, underground systems are the more appropriate systems.

These are the buried sand filter, the constructed wetlands, the infiltration trench and the

seepage pit (Figure 7).

Permeability is an important factor for places with low water table, since some of the

underground systems use the soil’s purification mechanisms to treat the effluent. These

systems are the seepage pit and the infiltration trench, which can only be adopted in places with

permeable soils. The other underground systems, like the constructed wetlands and buried

sand filter, are more appropriate for soils with low permeability. This is possible because these

two systems are built on an impermeable layer, preventing effluent leakage. The soil

permeability is related to the proportion of sand composing the soil. Soils with more than 70% of

sand are considered permeable, while the opposite is true for less than 70% (Figure 7).

Future user competence

High

ET bed

Constructed wetlands

Medium

Sand Filters

Infiltration trench

Low

Seepage pit

Evaporation pond

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Figure 7: Organogram portraying the most appropriate options for different water table and

porosity levels.

3.4. Simplified proposal to support the decision-making process

With all the information gathered in sections 3.1 and 3.2, together with the information

analyzed in section 3.3, it is now possible to create formulas that can optimize the decision-

making process. Using the Excel software, it was possible to create two formulas: one to allow

the user to separate de “dry” and “wet” solutions and a second one to enable the user to choose

the final disposal solution for the effluents. Figure 8 displays an example of the application of

Formulary one.

Figure 8: Illustration of an application of the formulary one.

Water table

>1,5 meters from surface

Evaporation pond

ET bed

Superficial sand filter

<1,5 meters from surface

≤70% sand

Buried sand filter

Constructed wetland

>70% sand

Seepage pit

Infiltration trench

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On this example, the site is characterized by no water supply and for a local culture

receptive to the idea of urine and faeces reutilization, with the most suited on-site sanitation

system being the UD Latrine.

With Formulary 2 more constraints are considered because final disposal systems

require more information prior to their implementation than “dry” latrines or “wet” toilets. On this

example (Figure 9), the water table is low, distancing more than 1.5 meters from the surface.

The example also illustrates that the site has a dry climate type, while the future users have low

income and WTP. Since the site’s permeability is high, with the soil presenting sandy

characteristics, the most appropriate final disposal system is the seepage pit.

Figure 9: Illustration depicting an example of the application of Formulary 2.

4. Conclusion and recommendations

Nowadays there are still one billion people without access to sanitation worldwide (UN

Secretariat, 2013). Stronger action from governments, NGO and others is needed in order to

halve the proportion of people without access to sanitation by 2015. This dissertation

characterized the different collection, transportation, treatment and final disposal systems for

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both the human excreta and the domestic effluents. The effluent discharge quality criteria were

analyzed, as well as the major constraints to the implementation of local sanitation. The

analysis of all this information enabled the creation of formulas that are capable of facilitating

the decision-making process.

The realization of this dissertation enabled the increase in the number of scientific

papers available in Portuguese related to the topic of on-site low-cost sanitation systems. This

is important because there are several populations without sanitation in developing countries

which have Portuguese as their mother tongue, especially in Brazil and Africa. Therefore,

scientific papers that are able to increase the available literature in Portuguese should be

promoted, in order to allow a higher number of people to have access to reliable information,

through the diminishing of the gap between the available literature in English and Portuguese.

Another important aspect this dissertation has achieved relates to the creation of

simplified formulas to support the decision-making process, allowing for a faster and more

simplified choice of the type of latrine, the type of treatment and the final disposal to be

implemented in the desired community. This is possible through the optimization of the

decision-making process. However, this process might be too standardized, risking evaluating

different situations as being the same, when those differences are too difficult to be detected.

Therefore, these two simplified functions should be seen as starting points for future

improvements and developments that will allow the functions to evaluate a higher number of

constraints, making them more precise and their application more trustworthy.

With the end of this dissertation, it is hoped that it corresponds to a contribution for

organizations working throughout the world promoting local sanitation among the poorest and

most isolated people on the developing countries to do their job in a more effective way.

Nevertheless, this dissertation should be further completed in the future, in order to

make it more useful and trustworthy, especially regarding the functions that simplify the

decision-making process. These functions should incorporate more variables and constraints,

be more precise and detailed, mainly respecting the unitary costs of the components of the

different “dry” and “wet” sanitation solutions.

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