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Alternative sanitation options for households and communities 

The resource-intensive wastewater collection and treatment systems found in many parts of the developed world are not feasible for meeting the sanitation[1] needs of the less developed regions still lacking or having poor sanitation.  Establishment and maintenance costs are high and large amounts of energy are required to operate these systems.  In fact, it can be questioned whether such systems are even desirable because of the precious resources that are wasted in the process -  considerable volumes of water are used just as a transport medium and nutrients are often taken out of the food cycle. 

Alternative sanitation systems can be found which consume less resources and focus on recycling the nutrients and energy found within human excreta.

In order to have a sanitation system that is effective and beneficial, it should address the five criteria of sustainability identified by the Sustainable Sanitation Alliance[2], namely: health and hygiene, environment and natural resources, technology and operation, financial and economic issues, and socio-cultural and institutional aspects (SuSanA, 2008a).  Moreover, the assessment of the sanitation system should consider the possible components of the complete flow chain, starting from the collection, to the storage, transport, treatment, reuse and/or disposal mechanisms.  

This article gives an overview of three reuse-oriented alternative sanitation options which can be implemented at the household or community level.  These are the double-vault urine-diverting dehydration toilet system, the fixed-dome biogas sanitation system and the constructed wetland wastewater treatment system.  The UDDT and biogas systems focus on toilet waste streams; greywater is collected and treated separately and is not discussed here.  The constructed wetland system processes the complete wastewater produced by a household. 

The article first describes each sanitation system and the treatment mechanisms for the waste streams.  It then tells about the ‘products’ which result from the treatment processes and have a reuse value.  Here it should be noted that the ‘products’ utilisable for agriculture are not completely pathogen-free after treatment; rather, a multi-barrier approach is used to protect health and treatment is one step in this approach.  Other barriers include following WHO[3] application guidelines for excreta reuse (WHO, 2006) and maintaining good personal hygienic practices when using the products, such as, wearing protective boots and gloves and washing hands after handling the products.  Finally, a general list of criteria for implementation is recommended for each system, which should help to ensure the sustainability of the system.    

[1] In this article sanitation refers to wastewater related aspects only.

[2] The Sustainable Sanitation Alliance (SuSanA) is an open network on sustainable sanitation (www.susana.org).

[3] World Health Organisation.

Content Table

Urine Diverting Dehydration Toilet (Double-vault) System

Description

A urine-diverting dehydration toilet (UDDT[2]) is a dry sanitation system in which excreta waste streams are separated at source (through the use of multiple outlets in the toilet seat/squatting pan) and collected, treated and reused separately.  In a washer culture, three separate material streams are produced from the toilet - faeces, urine, and cleansing water respectively, and in a non-washer culture, only the first two waste streams are produced. 

The UDDT consists of an above-ground substructure in which excreta are collected and a superstructure on top of that which houses the user-interface.  Faecal matter (and toilet paper or loam, if used) is deposited directly through a hole into a faeces collection chamber below.  Absorbents such as lime, ash, or dry soil are added to the chamber after each defecation to absorb excess moisture, make the pile less compact and make it less unsightly for the next user. The addition of absorbents also reduces flies and bad odours. Moreover, depending on the additive, the pH may also be increased due to this addition, and hence enhance bacterial pathogen die-off.  As breakdown of organic material in dehydrating conditions is slow, toilet paper or similar objects placed in the chamber will not disintegrate quickly[3]. 

Nad1.jpg

Figures 1 - 2: A schematic of two side-views of a double-vault UDDT showing the two faeces collection chambers and separate urine collection (source: Tilley et al., 2008). (Diversion of anal cleansing and hand washing water is not shown here).

two squatting pans/toilet seats or designing two drop holes for faeces in the floor of the superstructure.  The collection chambers have doors at the sides to be able to remove the dried faecal material.  A ventilation pipe leads out from the faeces collection chambers and extends above the highest point of the roof of the superstructure, in order to dry the material and help reduce smell in the toilet.

Urine flows through the urine outlet in the squatting pan/toilet seat and via a pipe underneath into a urine collection container placed within or outside the substructure.  The urine containers have to be closed at all times to prevent odour and loss of ammonia into the air.   Cleansing water (which can be combined with hand washing water) is directed via a pipe underneath into an infiltration bed outside the UDDT. 

The excreta and water streams are separated at source for several reasons: the treatment of each stream is carried-out efficiently with minimal losses of nutrients, odours in the toilet are easy to control, and the reuse of the materials can be targeted to get maximum benefits from the nutrient content. 

[1] This section has been written based on information from Winblad and Simpson-Hebert (2004) and lecture notes of the 2008 Summer course on Sustainable sanitation- decentralised, natural and ecological wastewater treatment, at UMB, Norway. 

[3] Owing to the slow disintegration of toilet paper, toilet paper can be collected separately and burnt or composted.

Treatment Processes

In the double-vault UDDT, the out-of-use faeces collection chamber serves as the treatment chamber. Factors that kill pathogens in faeces include temperature, ultra-violet radiation, moisture reduction, alkalinity, and just time itself.  Within the faeces treatment chamber, the moisture content is reduced to about 25% or less, the alkalinity is increased if lime or ash are used as the dehydrating and cover materials, and the vaults are designed to hold the faeces for a sufficient length of time to kill off most of the pathogens.

The treatment design parameter that is used for faeces in a UDDT is storage time.  According to the World Health Organisation’s guidelines for the safe reuse of excreta, in warm environments (20°C - 35°C) storage times of less than one year, and in ambient temperatures (2°C - 20°C) storage times of 1.5 - 2 years, will be sufficient to eliminate most bacterial pathogens and substantially reduce viruses, protozoa and parasites. Some soil-borne ova (e.g. Ascaris lumbricoides) may persist (Muench, 2009a).  The dried faeces can also be further treated off-site through co-composting with organic matter.

The factors that kill pathogens in urine are alkalinity from the rapid conversion of urea to ammonia, increased ammonia concentration together with the increase in pH, and time.

As with faeces, the design parameter used for treatment of urine is storage time.  The WHO guidelines adopted for reuse of urine in agriculture recommend a storage time of 1 - 6 months, depending on the temperature and type of crop to be fertilised (Schönning & Stenström, 2004).  Urine treatment and handling can be avoided by piping it directly from the UDDT to non-consumable plants or trees and using it in a system of fertigation.

Products

The UDDT system produces two products- dehydrated faeces and urine- which are valuable inputs for agriculture. The product from the faeces dehydration process, a crumbly, powdery material, is not compost but rather a kind of powder which is rich in carbon and fibrous material, phosphorus and potassium.  This is used as a soil conditioner which increases the organic matter of the soil, and hence improves soil structure and water-holding capacity, and acts as a slow release fertiliser (Muench, 2009a). 

Urine is a quick acting, nitrogen-rich fertiliser which also contains the macro-nutrients P, K and S (phosphorus, potassium and sulphur[1]) as well as sodium and chloride.  The fertilising effects of these nutrients in urine are the same as those of artificial mineral fertiliser if the same amount of N, P and K is applied. The composition of urine makes it well suited as a fertiliser for crops thriving on nitrogen (such as maize) and especially for crops also enjoying sodium, such as chard (similar to spinach). Care should be taken when applying it for crops sensitive to chloride (e.g. potatoes and tomatoes), although yields of these crops can also be much improved by appropriate urine application[2].

Criteria for Implementation

The following criteria should be met by households wanting to implement a UDDT:  

  • Space for the construction of a two-chamber UDDT structure.
  • Commitment to proper use and maintenance of the UDDT.
  • Ability to manage the volumes of urine, from collection to storage to reuse (or make necessary arrangements).
  • Commitment to reuse of products for agriculture.
  • Use of WHO guidelines for excreta reuse in agriculture and application of hygienic practices.

Fixed-Dome Biogas Sanitation System

Description

In a fixed-dome biogas sanitation system, blackwater from low-flush toilets or excreta from dry toilets is collected and treated in a ‘biogas digester’[3].  In this system, microorganisms break down the organic matter in excreta under anaerobic (without air) conditions, producing a methane-rich biogas and a digested organic matter slurry in the conversion process (Kossmann et al., 1999). 

While the main aim of installing this system is to contain and treat toilet waste, the secondary aim is to provide biogas which can partially replace cooking energy needs of the household and thus be an incentive for the upkeep of the system.  The biogas digester, as a single household sanitation system attached to toilets alone, produces little biogas.  In comparison, as an approximation, one cow equals 17 people with respect to biogas production from excreta (Muench, 2008).  Therefore, it is suggested that households should have a few cows to make this system economically viable.  Additionally, kitchen organic waste can also be added to the system if available. 

The organic input stream must have a water content of at least 50% for the digestion process to take place (Muench, 2008).  However, with too much dilution, the biogas production reduces significantly and digester volumes increase greatly in order to achieve the retention time required for hygienisation.  Therefore, greywater is excluded from the system.

The fixed-dome plant model is constructed below ground.  It consists of a rigid digester structure in which the liquid matter is digested in the lower part (the hydraulic part) and the gas generated is stored in the upper part (in the gasholder).  When gas production starts, the slurry is displaced into an attached expansion chamber. Gas pressure increases with the volume of gas stored and the height difference between the slurry level in the digester and the slurry level in the expansion chamber.  When gas is consumed, slurry enters back into the digester from the expansion chamber.  Excess slurry exits the system from an overflow in the expansion chamber (Kossmann et al. 1999). 

nad2.jpg

Figure 3: A schematic of a household, fixed-dome biogas digester.  As gas is produced in the digester, slurry is pushed up into the expansion chamber at the right side.  When the gas is consumed, the slurry flows back into the digester (source: Tilley et al., 2008).

[1] Sulphur is an important macro-nutrient, needed in approximately the same amount as phosphorus, and often lacking.

[2] The benefits of treated urine and faeces as a fertiliser and its application methods have been well documented in SuSanA (2008b), PuVeP (2008), Morgan (2007), WHO (2006), Jönsson et al. (2004) and EcoSanRes (2008).

[3] It is also possible to use a urine-diverting flush toilet and use the urine separately as a liquid fertiliser (Mang and Li, 2009).

Treatment Processes

The treatment result of anaerobic digestion can be summarised as follows.  The organic matter is broken down into simpler molecules.  There is a high level of organic matter removal[1], but some organic matter remains in the digestate.  There is no removal of the nutrients nitrogen and phosphorus and there is no removal of heavy metals.  The digestate also has reduced odour (Muench, 2008).       

The inactivation of pathogens during the treatment process depends on temperature and retention time.  Pathogens die easily in thermophilic conditions in any system (i.e. > 50°C for several days).  In the typical lower-temperature psychrophilic (< 20°C) operating conditions of a household digester, retention time plays a critical role.  Mang and Li (2009) report findings from Zhang Wudi in China that a retention time of 60 days in a psychrophilic biogas unit reduces pathogens significantly.  The main pathogens are largely killed off during this time period; only Ascaris eggs remain persistent.

Products

The biogas sanitation system generates two products in the treatment process - biogas and digestate (slurry) – which have to be managed as a part of the system.  These products contain the energy and nutrients of the system input materials and therefore have a high reuse value.  Biogas is a fuel, and at the small-scale household level, the biogas produced can be used directly in gas stoves for cooking or in gas lamps for lighting.  The digestate contains organic matter and the macro-nutrients N, P, K (nitrogen, phosphorus and potassium) and thus it is a fertiliser and soil conditioner for agriculture (Mang & Li, 2009).  The digestate can be applied directly as slurry or treated further before application by co-composting with organic matter or by separating solids and liquids in a drying bed.

Criteria for Implementation

The recommended criteria for households interested in implementing a biogas sanitation system are the following:

  • More than one cow or buffalo in the compound.
  • Sufficient space to construct the biogas system underground and for management of the digestate.
  • Commitment to proper operation and maintenance of the system.
  • Commitment to reuse of the biogas (i.e. not letting it escape into the atmosphere) and the digestate.
  • Use of guidelines for digestate reuse in agriculture and application of hygienic practices.

Constructed Wetland Wastewater Treatment System

Description

A constructed wetland treatment system is used to treat combined wastewater.  It is an engineered system that copies the purification functions of a natural wetland to treat contaminants in wastewater.  IWA (2000) describe a wetland as “a complex assemblage of water, substrate, plants (vascular and algae), litter (primarily fallen plant material), invertebrates (mostly insect larvae and worms) and an array of microorganisms (most importantly bacteria)”.  Numerous and often interrelated mechanisms take place in this set-up to treat wastewater (IWA, 2000). 

While the essence of the system is the wetland structure, the system includes pre-treatment or primary treatment measures to reduce the level of solids in the effluent that can cause blockages in the wetland and reduce its purification capacity (Muench, 2009b).  The pre-treatment aspect is not looked at in this article.

There are two main types of constructed wetlands: Free water surface (FWS) and Subsurface flow (SSF). The description of these two types here is taken as excerpts from Muench (2009b).   In FWS constructed wetlands, water flows on top of the soil medium (with a “free surface”), whereas SSF systems are designed to keep the water level below the top of the soil or gravel substrate.

A typical FWS constructed wetland has emergent macrophytes and is a shallow, lined basin or sequence of basins, containing 20-30 cm of rooting soil, with a water depth of 20-40 cm. They are similar in appearance to natural marshes. The wastewater flows above the ground, exposed to the atmosphere. Incoming wastewater containing particulate and dissolved pollutants slows and spreads through a large area of shallow water and emergent vegetation.

nad3.jpg

Figure 4: Schematic cross-section of a free water surface constructed wetland (source: Morel and Diener, 2006).

The SSF constructed wetlands are further classified according to the direction of water flow -  horizontal or vertical.  Water flows inside a layer of sand, gravel or soil (60-80 cm).  In contrast to the FWS wetlands, the substratum contributes to the treatment processes by providing a surface area for microbial growth and supporting adsorption and filtration processes. This effect results in a lower area demand and generally higher treatment performance per area than FWS constructed wetlands. Furthermore, no mosquito breeding is expected by avoiding surface ponding.

nad4.jpg

Figures 5 - 6: Schematic cross-section of a horizontal flow subsurface flow constructed wetland (left) and a vertical flow subsurface flow constructed wetland (right) (source: Morel and Diener, 2006).

Some requirements are necessary to be able to use constructed wetlands to treat domestic wastewater.  Constructed wetlands are low-rate treatment systems and therefore have a high space requirement.  They need enough incident light to allow photosynthesis to take place because plants play an essential role in the system.  Temperatures should not be too low as biological activity reduces significantly with lower temperatures; however, designs can be adjusted for cold climates (Muench, 2009b). 

[1] 40 – 60 % of the organic matter in faeces is converted to biogas.

Treatment Processes

The constructed wetland systems are usually designed for removal of suspended solids, organic matter and nutrients (nitrogen and phosphorus).  The general treatment mechanisms in the systems include (IWA 2000):

  • settling of suspended particulate matter,
  • filtration and chemical precipitation through contact of the water with the substrate and litter,
  • chemical transformation,
  • adsorption and ion exchange on the surfaces of plants, substrate, sediment and litter,
  • breakdown and transformation and uptake of pollutants and nutrients by MOs and plants, and
  • predation and natural die-off of pathogens.

Products

Constructed wetlands treat wastewater to a standard fit for discharge to surface water or fit for various reuse applications according to WHO guidelines (WHO, 2006).  The most common type of reuse is for irrigation.  Nitrogen and phosphorus nutrients remaining in the effluent from the treatment system have a fertilising effect for crops.

Criteria for Implementation

The following criteria should be met by a household wanting to participate in the system:  

  • Sufficient land for the constructed wetland.
  • Commitment to maintaining the pre-treatment structure and the wetland and associated parts in the long-term (e.g. plants, pipes, pumps).
  • Use of WHO guidelines for effluent reuse in agriculture and application of hygienic practices.

References

1) EcoSanRes (2008) Guidelines on the Use of Urine and Faeces in Crop Production. EcoSanRes Factsheet 6. Stockholm Environment Institute, Stockholm, Sweden.

2) IWA (2000) Constructed Wetlands for Pollution Control- Processes, Performance, Design and Operation.  Scientific and Technical Report No. 8.  IWA Specialist Group on Use of Macrophytes in Water Pollution Control, IWA Publishing, London, UK.

3) Jönsson, H., Richert Stintzing, A., Vinnerås, B. and Salomon, E. (2004) Guidelines on the use of urine and faeces in crop production, EcoSanRes Publications Series, Report 2004-2. 

4) Kossmann, W., et al. (1999) Biogas Digest. Volume I: Biogas Basics. Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), Eschborn, Germany. 

5) Mang, H.-P. Li, Z. (2009) Biogas sanitation for black water, or brown water or excreta treatment and reuse in developing countries. Draft version. Technology Review “Biogas sanitation”. Sustainable Sanitation – ecosan program, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), Eschborn, Germany.

6) Morel A., Diener S. (2006) Greywater Management in Low and Middle-income Countries- Review of Different Treatment Systems for Households or Neighbourhoods.  Swiss Federal Institute of Aquatic Science and Technology (Eawag). Dübendorf, Switzerland. 

7) Morgan, P. (2007) Toilets That Make Compost - Low-cost, sanitary toilets that produce valuable compost for crops in an African context, Stockholm Environment Institute, EcoSanRes Programme, Stockholm, Sweden 

8) Muench, E.v.  (2008) Anaerobic treatment processes. Course 2, Unit 4. UNESCO-IHE on-line ecosan course.   Institute for Water Education, Delft, The Netherlands.

9)  Muench, E. v.  (2009a) Basic Description of Urine-diversion Dehydration Toilets (UDDTs), Draft version. Technology Review “Urine-diversion Dehydration Toilets”. Sustainable Sanitation – ecosan program, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), Eschborn, Germany.

10) Muench, E. v. (2009b) Constructed Wetlands for Greywater and Domestic Wastewater Treatment in Developing Countries. Draft . Technology Review “Constructed wetlands”. Sustainable Sanitation – ecosan program, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), Eschborn, Germany.

11)  PUVeP (2008) Philippine allotment garden manual with an introduction to ecological sanitation. Periurban Vegetable Project (PUVeP), Xavier University College of Agriculture, Cagayan de Oro City, Philippines. 

12) Schönning, C. & Stenström, T. A. (2004) Guidelines for the Safe Use of Urine and Faeces in Ecological Sanitation Systems. Report 2004-1. EcoSanRes, Stockholm Environment Institute, Stockholm, Sweden (new version).

13) SuSanA (2008a) SuSanA: Towards more sustainable sanitation solutions. Version 1.2, February 2008

14) SuSanA (2008b) Food security and productive sanitation systems. Fact sheet of Sustainable Sanitation Alliance.

15) Tilley et al. (2008) Compendium of Sanitation Systems and Technologies. EAWAG, Switzerland.

16) WHO (2006) WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater. Volume 4: Excreta and Greywater Use in Agriculture. World Health Organisation, Geneva, Switzerland. 

17) Winblad, U. & Simpson-Hebert, M. (2004) Ecological Sanitation.  Revised and Enlarged Edition.  Stockholm Environment Institute, Stockholm, Sweden.

Resources

This article was written by:

Nadira Khawaja

Advisor in Sanitation, Urban Water Supply Improvement in Afghanistan (GTZ).

The article was adapted from the paper, Assessment of Alternative Sanitation Systems in the Navin Well-Field Project Area, Herat , Afghanistan, for the GTZ Sustainable Sanitation Ecosan project.

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