Looking at sanitation systems rather than sanitation technologies - Outcomes of Workpackage 3 of NETSSAF
Prepared by Chris Zurbrugg (Mr.) Eawag / Sandec
Most sub-Saharan African countries are not on track to reach the sanitation target as stated in the Millennium Development Goals, which is to half the number of people with access to adequate sanitation. Despite numerous efforts and campaigns the reality is, that sanitation projects which were implemented often do not show the desired effect and have not been replicated in large-scale across the regions of need. One explanation for the marginal improvements is the prevailing assumption that the conventional (centralised) water-based sewer system can be the solution in all contexts, and to all sanitation problems in urban and peri-urban or even rural areas irrespective of the differences in the physical and socio-economic conditions. It is only quite recently that research and development have targeted alternative approaches and solutions to the increasing environmental sanitation problem.
One of the challenges for improving sanitation in rural West-Africa involves acquiring a sound knowledge of the feasible sanitation systems and technologies which in the site specific context can achieve the intended objectives of health hygiene and well-being.
Activities and Products of Workpackage 3
The objective of Workpackage 3 of the NETSSAF program was to assess existing low cost, conventional and innovative sanitation technologies, in order to determine their feasibility and sustainability for implementation in rural and peri-urban areas of West Africa that lack access to improved sanitation.
The final document compiled by the workpackage partners defines and systematizes distinct sanitation systems as well as assesses and evaluates the specific technologies. The various systems are briefly described and for each system the relevant flowstreams are explained. Then a description of the technology components follows. The technologies are categorized according to the processes: User Interface, On-site Collection, Storage and Treatment, Transport, Off-site Treatment Technologies, Reuse, and Disposal. The document finally also contains a qualitative assessment of technology components using an approach of expert judgement and is structured according to flowstreams, using a methodology developed within the framework of the NETSSAF project.
Systematizing Sanitation Systems
A “good” sanitation system minimizes or removes health risks, is economically viable, and avoids negative impacts on the environment. Ensuring good sanitation systems for the protection of public health and of environment is of public interest and, therefore, a key duty of the public sector. This duty includes the provision of an enabling framework as well as control and supervision to ensure that these conditions are met for all users. “Sustainable” sanitation however goes a step further. Sustainable systems take into account economic aspects (financial capital investments required as well as recurring operation and maintenance costs, affordability), institutional aspects (organisational set-up, opportunities for public-private partnership), environmental aspects (minimum energy requirements, opportunities for resource recovery and reuse, environmental impact, health aspects) and finally social aspects (convenience, dignity, acceptability, and willingness to pay or operate).
A sanitation system - contrary to a sanitation technology - considers all components required for the adequate management of human wastes. Each system represents a configuration of different technologies that carry out different processes on specific products (wastes). The sequence of process-specific technologies through which a product passes is a flowstream. Each system therefore, is a combination of product- and process-specific technologies designed to address each flowstream from origin to disposal. Technology components exist at different spatial levels, each with specific management, operation and maintenance conditions. Starting at the household level with waste generation, a system can include storage and potentially also treatment and reuse of all products such as urine, excreta, as well as greywater, rainwater/stormwater or even solid waste. However, problems can often not be solved at the household level alone. The household “exports” waste to the neighborhood, town, or downstream population. In such cases, it is crucial that the sanitation system boundary be extended to include these larger spatial sections; those that take into account technology components for storage, collection, transport, treatment, discharge or reuse at these levels.
The consensus of the consortium in NETSSAF was to focus the work on 7 main sanitation systems. Two main criteria for subdividing the systems are WET <--> DRY as well as the various degrees of separating waste flowstreams. “Wet” and “Dry” indicate the presence of flushing water for the transport of excreta. This however only gives a certain indication of how wet or dry the collected waste materials will be. Although flushing water might not be used (and would not therefore qualify as a “Dry system”) a system may nevertheless contain anal cleansing water, urine flushing water, or even greywater. Also, Wet systems are characterized by the production of a parallel product: faecal sludge. In wet systems then, the faecal sludge flowstream must be taken into account and treated accordingly with its own set of process- and product-specific technologies until the point of ultimate disposal. It is important to note also the similarity in naming convention between products and flowstreams. For example, blackwater is a product, but the entire process of collecting, treating and disposing of blackwater is referred to as the blackwater flowstream. Similarly, greywater can be managed separately as an independent product, but when it is combined and treated along with blackwater, the flowstream is referred to as the ‘blackwater mixed with greywater’ flowstream.
|1||Wet mixed blackwater and greywater system with offsite treatment||§ blackwater mixed with greywater flowstream§ faecal sludge flowstream|
|2||Wet mixed blackwater and greywater system with onsite treatment||§ blackwater mixed with greywater flowstream§ faecal sludge flowstream|
|3||Wet blackwater systems (blackwater separated from greywater)||§ blackwater flowstream§ faecal sludge flowstream§ greywater flowstream|
|4||Wet urine-diversion system||§ urine flowstream/ yellowwater§ brownwater mixed with greywater flowstream§ faecal sludge flowstream|
|5||Dry greywater-separate system||§ excreta flowstream§ greywater flowstream|
|6||Dry urine- and greywater-diversion system||§ urine flowstream§ faeces flowstream§ greywater flowstream|
|7||Dry all mixed systems||§ excreta mixed with greywater flowstream|
In this system, all wastewater that is created by households, institutions, industries and commercial establishments are collected, transported and treated without stream separation. There are different user interface technologies available for the collection of blackwater. These can be by high- or low-volume cistern-flush toilets, or pour-flush toilets. After collection, blackwater is mixed with household greywater as it leaves the house; the mixture (referred to as ‘wastewater’ for simplicity) is transported to a centralized (offsite) treatment plant. There a wide array of technology options for wastewater treatment. Transport technologies may be pipes with gravity flow, pressure flow, or using vacuum systems.
This system, like the previous one, is characterised by flush toilets (full, low, vacuum or pour flush toilets) at the user interface. Here however, the treatment technology is located close to the source of waste generation. Depending on the plot size, the treatment technology will be appropriate for one house, one compound or a small cluster of homes. Accordingly, transport before treatment is limited to short distances mostly by gravity sewers. There are various low-cost technology options for on-site wastewater treatment, which differ from those typically used as centralised, off-site technologies. Examples include septic tanks, filters, constructed wetlands, anaerobic baffled reactors, and biogas plants, among others. Although it is commonly practiced, pits should not be used.
In this system, urine, faeces and flushing water (blackwater) are collected, transported and treated together however, greywater is kept separate. Since greywater accounts for approximately 60% of the wastewater produced in homes, this separation simplifies blackwater management. The most common and frequently practiced example of this system is the double-pit pour flush toilet; this technology allows users to have the comfort of a pour-flush toilet and water seal, without the trouble of having to pump out the sludge, since it is removed only once it has matured into a solid, humic-like substance. To avoid overloading the pits, a separate system for greywater management must be implemented. However, since separated greywater contains few if any pathogens, and usually low concentrations of nitrogen and phosphorus, it does not require the same level of treatment as blackwater or mixed wastewater. Greywater can be recycled for irrigation, toilet flushing, exterior washing, and other water-conservation measures.
In this system faeces, flushing water and greywater are collected, transported and treated together but urine is kept separate. The diversion of urine from the other flowstreams requires a specific user interface, known as a urine-diverting flush toilet, which, due to the intricate plumbing and construction, is available only as a pedestal. The objective of the urine separation is (usually) to keep the nutrient rich urine free of pathogens and to ultimately facilitate its reuse. In this wet urine diverting system, the faeces are flushed with water (brownwater) to an off-site treatment facility. Sometimes the urine is mixed with a small amount of flushing water, in which case the product is referred to as yellowwater. Because of the novelty of user interface and the complicated infrastructure (plumbing) required for this type of system, it is appropriate only to more experimental settings at this point.
Excreta is a mix of urine and faeces; there is no flushing water. In this system the greywater is collected separately. So although the mixture of urine and faeces may be slightly wet, the system is referred to as ‘dry’ simply because there is no flushing water. Depending on the cultural habits, beigewater (or anal cleansing water) may or may not be included although smells and flies are minimized if the mixture is kept as dry as possible. This is particularly true for the composting-type systems (Arbor loo, Fossa alterna) that can become flooded/anaerobic if too much water is added. Generally, the system is typically characterised by “drop and store” latrines that can be emptied, reused, or capped and filled. The separate greywater should be treated as close to where it is generated (on-site-treatment) as possible. The excreta may be further treated off-site. Generally, off-site treatment is only performed to improve hygienisation (especially in the case of single pits that are emptied before the contents can be completely digested). Proper operation and maintenance significantly influence the performance of these facilities. It is possible to either reuse the recovered resources (greywater and/or treated excreta sludge) or to dispose of them when interest in resource recovery and reuse is lacking.
This system is characterized by the separation of urine, faeces and greywater into three different flowstreams, and where anal cleansing water is used, a fourth flowstream. In this way, each flowstream can be more appropriately managed in terms of its volumetric flow, nutrient and pathogen content and handling characteristics. This diversion facilitates more targeted treatment and end use for the different fractions. This system requires a urine-diverting user interface. Urine is collected through the front outlet and conveyed to a collection vessel (a tank in larger, more expensive systems or a jerry can in smaller, simpler systems), a garden or possibly a soak pit, if the urine is not brought to use. Through the rear outlet the faeces are collected in a container located underneath the toilet. Dry cleansing material (such as toilet paper) can be dropped through the rear outlet, although it is often kept separate. Some urine-diverting squat pans are also equipped with an additional outlet for anal cleansing water (beigewater), which is then treated, in a separate flowstream.
Dry excreta and greywater mixed system
In this system, urine, faeces and greywater are mixed in the same On-site Collection, Storage and Treatment technology. Although this type of system can be frequently observed in rural and peri-urban areas of West Africa, it is not considered to be good practice. The difference between this system and System 5 ‘Dry excreta and greywater separate system’ is the inclusion of greywater.
Description and Evaluation of Technology components
Following the sanitation system descriptions, each technology is described briefly when possible with a reference. The technology components are grouped according to process (i.e. the function that they serve) and sub-divided according to flowstream. Furthermore the technologies are then evaluated with respect to specific criteria as listed below:
|reduces exposure||of users|
|of waste workers|
|of resource recoverers /reusers|
|of “downstream” population|
|increases health benefits|
|Impact to environment / nature|
|use of natural resources||needs low land requirements|
|needs low energy requirements|
|uses mostly local construction material|
|low water amounts required|
|low emissions and impact to the environment||surface water|
|soil / land|
|noise, smell, aesthetics|
|good possibilities for recovering resources||nutrients|
|allows simple construction and low level of technical skills required for construction|
|has high robustness and long lifetime/high durability|
|enables simple and low operational procedures and maintenance and low skills required|
|Economical and financial issues|
|has low construction costs (unit cost per household)|
|provides benefits to the local economy (business opportunities, local employment, etc.)|
|has low operation and maintenance costs|
|provides benefits or income generation from reuse|
|Social, cultural and gender|
|delivers high convenience and high level of privacy|
|requires low level of awareness and information to assure success of technology|
|requires low participation and little involvement by the users|
|takes special consideration issues of women, children and elderly|