Difference between revisions of "Sanitation Systems & Technology Options"
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Contents
1. Introduction: the need for a systems approach
Technology choice should be based on determining the best possible and most sustainable solution within an urban or rural context. There is often a prevailing assumption that centralised water-based sewer system can be the solution in all urban and peri-urban contexts. Site specific considerations such as the scarcity of fresh water, farmers’ demand for treated wastewater or excreta-based fertiliser, or lack of technical skill and institutional or socio-economic barriers to such centralised sewer systems are often neglected (Luethi et al., 2011).
The options: to change the basic design or to consider alternative sanitation technologies to take into account the specific on site conditions are often overlooked or not investigated. As a result, in spite of significant investments, a number of latrines are found to be either dysfunctional or malfunctioning and the unsatisfied users have reverted to open defecation or the use of unsanitary pits latrines. In addition, the focus is often on the construction of toilets alone with little consideration given to the management of the generated faecal sludge, including its collection, transport, treatment and possible reuse or disposal.
There is a great need for sanitation practitioners to plan sanitation from a more holistic perspective, for example by considering the entire municipal area and the sanitation chain in order to come up with an overall sanitation concept. A holistic perspective includes components such as technical, (socio-) economic, institutional and financial feasibility studies, consultation with the users in which the whole life cycle of different sanitation options are presented and discussed, quality assurance during implementation, and ongoing institutional support during the O&M phases. Training is another very crucial aspect as even the most inexpensive or sophisticated technologies eventually fail if they are not accompanied by a trained service provider.
One of the challenges for improving sanitation in low and middle income countries involves acquiring a sound knowledge of the wide range of sanitation options to ensure informed decision making. The most feasible sanitation systems and technologies - for the different habitats in urban and rural areas, which can achieve the objectives of improved health, changed hygiene practices, minimal impact on the environment, improved quality of life, and are best suited to the site specific context - can be chosen when decision making is informed.
2. Systemising sanitation systems
The main objective of a sanitation system is to protect and promote human health by providing a clean environment and breaking the cycle of disease transmission, as well as to preserve the dignity of users - particularly women and girls. In order to be sustainable, a sanitation system has to be not only economically viable, socially acceptable, and technically and institutionally appropriate, it should also protect the environment and the natural resources (SuSanA, 2008).
A sanitation system - contrary to a sanitation technology - considers all components required for the adequate management of human excreta. Each system represents a configuration of different technologies that carry out different functions on specific waste inputs or waste products. The sequence of function-specific technologies through which a product passes is called a “Flowstream”. Each system is therefore a combination of inputs, function-specific technologies, and products designed to address each flowstream from origin to reuse or adequate disposal.
Technology components exist at different spatial levels, each with specific management, operation and maintenance conditions as well as potential implications for a range of stakeholders. A system can include waste generation, storage, treatment and reuse of all products such as urine, excreta, greywater, organic solid waste from the household and agricultural activities such as manure from cattle at or near the source of waste generation. However, the requirement to effectively contain the wastes and prevent the spread of diseases and the pollution of the environment can often not be solved at the household level alone.
Sanitation systems can be distinguished by:
- being water-reliant or non-water reliant for the transport of excreta and wastewater (Cruz et al., 2005) (Tilley, Zurbruegg, 2007)
- on-site and off-site treatment
- various degrees of separation of incoming wastes.
In the following table seven distinctly different sanitation systems are described based on the categorisation from the EU-funded NETSSAF project (Network for the development of Sustainable approaches of large-scale implementation of Sanitation in Africa). They all have their place and application, and not one of them is perse better than the other.
| Sanitation system | Description |
|---|---|
| a) Wet mixed blackwater and greywater system with offsite treatment | In this system, all wastewater which is created by households and institutions, also partly industries and commercial establishments is collected, transported through gravity sewers or pumping mains, and treated without stream separation. There are different user interface technologies available for the collection of blackwater. These can be cistern-flush toilets or pour-flush toilets. |
| b) Wet mixed blackwater and greywater system with semi-centralised treatment | This system, like the previous one, is characterised by flush toilets (cistern flush, pour flush or vacuum toilets) at the user interface. Here however, the treatment technology is located closer to the source of wastewater generation. Depending on the plot size, the treatment technology will be appropriate for one house, one compound or a small cluster of homes or an entire settlement. |
| c) Wet blackwater system | In this system, urine, faeces and flushing water (together called blackwater) are collected, transported and treated together. However, greywater is kept separate. Since greywater accounts for approximately 60% of the wastewater produced in homes owning flush toilets, this separation simplifies blackwater management. A common 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. Another technology option is anaerobic treatment for blackwater with biogas production. |
| d) Wet urine diversion system | 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 diversion toilet. Urine can be either collected with or without flushing water (see von Muench and Winker, 2011, for a detailed description of this concept). The objective of the urine separation is to keep the urine free of pathogens and to ultimately facilitate its reuse in agriculture. |
| e) Dry excreta and greywater separate system | Here excreta, a mix of urine and faeces, are discharged at the user interface without using any flushing water. Greywater is collected separately. Generally, the system is characterised by “drop and store” latrines that are emptied or abandoned when full. The separate greywater should be treated close to where it is generated (on-site-treatment). The faecal sludge may be further treated off-site. |
| f) Dry urine, faeces and greywater diversion system | This system is characterised 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 separately managed in terms of its volumetric flow, nutrient and pathogen content and handling characteristics. This diversion can facilitate more targeted treatment and end use for the different fractions. |
| g) Dry excreta and greywater mixed system | Urine, faeces and greywater are mixed in the same on-site collection, storage and treatment technology. Although this type of system with a simple soak pit for excreta and greywater together can be found in rural and peri-urban areas of many developing countries, it is not considered to be good practice in densely populated areas, or areas with high groundwater tables or unfavourable soil conditions |
3. Description and evaluation of technology components
In all the recent publications that have described sets of typical sanitation systems (Cruz et al., 2005), (IWA, 2005), (Tilley, Zurbruegg, 2007), (Tilley et al., 2008), (DWA, 2010) a certain procedure was applied to characterise technologies: along with the description of the sanitation system, each technology (or technological component) is discussed and described. The technology is grouped according to its role in the process (i.e. the function that it serves) while on the other hand it is also sub-divided according to the flowstreams that it deals with. The technological components and the complete sanitation systems need to be discussed and evaluated with respect to specific sustainability criteria. Examples for such criteria are given in Table 2.
| Health issues | |
| reduces exposure(and thus health risks) | of users |
| of waste workers | |
| of resource recoverers /reusers | |
| of “downstream” population | |
| hygienisation rate | |
| increases health benefits | |
| Impact on 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 on the environment | surface water and groundwater |
| ground water | |
| soil / land | |
| air | |
| noise, smell, aesthetics | |
| good possibilities for recovering resources | nutrients |
| water | |
| organic matter | |
| energy | |
| Technical Characteristics | |
| allows simple construction and low level of technical skills required for construction | |
| has high robustness and long lifetime/high durability | |
| enables simple operational procedures and maintenance; low level of skills required | |
| Economical and financial issues | |
| has low construction costs (unit cost per household) and low operation and maintenance costs | |
| provides benefits to the local economy (business opportunities, local employment, etc.) | |
| 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 of issues for women, children, elderly and people with disabilities | |
4. Acknowledgements
SuSanA factsheet: Capacity development for sustainable sanitation. April 2012. susana.org
