USING USING BIOGAS TECHNOLOGY TO SOLVE PIT LATRINE WASTE DISPOSAL PROBLEMS PROBLEMS
Introduction Introduction
This technical brief looks at the option of using biogas units to reduce the waste produced by standard pit latrines. Waste is removed from the pit and transported to a biogas system where treatment takes place. As populations grow and urban migration places further strain on towns, problems surrounding the applicability of on-site sanitation facilities such as pit latrines (Figure 1) and how they were originally supposed to operate are increasing. Using a pit to retain the faeces underground for approximately two years making it less harmful requires space, which densely populated regions such as slum areas do not have, and there are cost implications of repeated construction. Therefore users must empty their latrines and reuse them whenever possible. This has been the subject of much research over the past few years, but what is then done with the emptied waste has received little attention. Figure 1: Pit latrines in the Kibera informal settlement The need to collect sludge from an on-site system, (slum) in Nairobi, Kenya. Photo: transport it to a treatment facility and dispose of it Karen Robinson / Practical Action. hygienically was given the term Faecal Sludge Management (FSM) by the Department of Water and Sanitation in Developing Countries (SANDEC) in Switzerland. Figure 2 shows that the first step to solving disposal issues is to implement a structured procedure that defines how waste should be managed. Without it pollution of the environment will occur earlier (i.e. during a transportation stage). Biogas Biogas technologies Biogas is the by-product of anaerobic digestion, the breaking down of organic material in the absence of air. The gas is rich in methane and can be used as a fuel for cooking, lighting and generating electricity. Anaerobic digestion takes place in what is known as a digester. Traditionally digesters have been directly linked to the latrine so the fresh faeces are subjected to digestion immediately. Little work has been done to see if using mature, partially digested waste from a pit latrine is feasible in producing biogas.
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Using biogas technology to solve the disposal issues surrounding latrine waste
Practical Action
Figure 2: Faecal Sludge Management Cycle - (Boot N. , 2007)
Possible Possible Digester options
The aim of the digester is to provide a sealed vessel that allows input of feedstock and removal of gas whilst being built of locally available construction materials. The options of digester design are described in the Practical Action Technical brief Biogas. The most common types of digester are the floating dome or Indian digester and the fixed dome or Chinese digester. Other digesters include the bag or balloon digester, a type of Plastic Bio-Digester and the plug flow digester which is a type of Earth-pit plant. Both of these are more suitable in emergencies or situations where a digester is needed quickly or only for a short period of time because of their small life span in comparison to the above.
Assessing Assessing the technology
Technological Technological barriers The issues regarding technology can be split into collection, haulage, disposal and treatment.
Figure 3: A diagram explaining the problem of soiling up Collection: Collection: the sludge will be partially degraded upon emptying therefore decreasing the maximum methane yield. This means, to make the system feasible the frequency of pit emptying will have to increase. Pit emptying frequency is inversely proportional to the
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Using biogas technology to solve the disposal issues surrounding latrine waste
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operational life of the pit. Dismantling often required when emptying a pit. A solution proposed is to fit an in-situ pipe to the pit that has an exit outside the super structure (Figure 4). This addition will limit the disruption caused by emptying as well as making the whole process more hygienic because the hose will no longer have to be dropped into the faeces. The addition will also help deal with the problems regarding viscosity and soiling up in pits (3) because emptying will happen from the bottom and water can be added through the pipe to decrease the viscosity. aulage: Haulage: for sustainability reasons and to limit costs the push is to combine the system with manually operated emptying technologies (Boot N., 2006). These technologies are also more feasible in urban settings where access is an issue for vacuum pumps. When using these technologies it is not the distance from the latrine to the disposal point that is the defining factor but the time it takes. In this situation a cost/time benefit calculation should be used working backwards from the costs that must be covered for the system to work which will give the number of empties per day required. Using this information and the average working day a suitable haulage distance can be calculated. Disposal: Disposal essentially the placement of the digester which is governed by three main factors: • Space and land tenure; in slum areas space is sparse and they live on land they do not own so improving sanitation facilities is not high on their priority list • Not in my back yard (NIMBY); people do not want waste dumped where they live however this is a very context specific area • Use of the gas; whether it be a communal facility or private household Logistic issues also affect the placement as outlined above. Treatment: there are essentially two main issues regarding treatment. Figure 4: A diagram The first is problems surrounding pressure of the gas. One solution conveying the use of an in would be to ensure that the digester is correctly maintained. Another situ pipe. physical solution, highlighted by Kossmann (1999), is the use of a separate gas holder. Floating drum digesters allow the user to alter the pressure of the gas by applying weight and pushing the moving “drum” down. Research has highlighted maintenance issues surrounding these digesters and that fixed dome digesters provide better results. Therefore a possible solution is to take the benefits from both technologies and use them to their full advantage by using the fixed dome design for the batched digester setup while connecting a floating drum design in series to act as storage, so when/if the user does experience pressure complications they can apply an amount of weight to the top of the drum and increase the pressure.
Figure 5: Possible digester setup to deal with pressure issues. The other treatment issue that needs to be assessed is the concentration of nitrogen in the feedstock. Mang & Li (2009) describes how urea from urine will be toxic to the bacteria (selfintoxification) involved in digestion. In practice, Mang & Li(2009) stress it is important to
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Using biogas technology to solve the disposal issues surrounding latrine waste
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maintain, by weight, a Carbon/Nitrogen (C/N) ratio between 20-30:1. The C/N ratio can be manipulated by combining materials low in carbon with those that are high in nitrogen, and vice versa (The United Nations, 1979). “If the C/N ratio is very high the biogas production will
be low; if the C/N ratio is very low, the pH value will increase, and will have a toxic effect on bacteria” (Mang & Li, 2009).
cultural Social and cultural issues The first area of concern regarding social and cultural issues is tackling problems regarding the community’s willingness to use the technology. There are three main areas that must be dealt with to ensure a successful implementation. First the implementer must keep the public well informed. It is “extremely difficult to achieve
change in excreta disposal practices as they are part of the basic behavioural pattern of a community and are not readily modified” (Faechem & Cairncross, 1978). Chaggu et al (2002)
identify in Dar-es-Salaam that there is a lack of understanding why the disposal system has to be changed because of the “lack of perceived benefits” (IRCWD, 1982) biogas technology has. The low education level results in “inadequate financial resources” (Chaggu et al, 2002) so the priority is not a good excreta disposal when there is competition for financial resources. This poor education level leads a low level of involvement (Strauss et al 2002) and without involvement, construction and maintenance skills cannot be passed on. This lack of knowledge can lead to an unwillingness to use the by-products, (Strauss & Montangero, 2002) the second area of concern. When assessing the willingness to use the residual as a soil conditioner the critical factor is land to use the conditioner on. If people do not have gardens or areas to use compost, like in urban areas, then they are not going to want it. One solution suggested is for farmers and other industries that have use for soil conditioner to collect the treated sludge. This will be dependent on a number of factors including sufficient access for the farmer’s haulage vehicle to collect the soil conditioner, the collection being more beneficial for the farmers (i.e. quicker and cheaper) than collecting from their normal supplier and also the dependability of the agreement. Gas should be more acceptable than the residual because of the lack of direct contact with consumables that soil conditioner has. However the reasons why people do not like the use of digestion by-products cannot always be attributed to a straight forward misunderstanding. Often these decisions are difficult to understand. The final concern when dealing with willingness to use the technology is religious issues over human excreta. Night soil workers carry a stigma, Eales (2005) explains that in Kibera residents see the job as illegal and it is therefore “legitimate to assault those who haul stinking buckets and drums through narrow alleys”. This leads to emptying taking place at night because there is less chance they will be robbed or beaten. The idea is to make the process as less obtrusive as possible, which implementing manually operated systems will do. This will limit the disruption to the customer and therefore their opinion of emptying will improve. Regarding cultural taboos research could only come back to the use of education programmes put in place to help people understand the benefits of the practice, but once again this factor is very context specific. Another area of concern is the effect of increasing the emptying frequency. There are two ways the user can be affected, the increase in frequency of payments and, the inconvenience to the occupant. The inconvenience to the user can be limited through improved emptying practices as outlined throughout this brief. Regarding the former point, currently, the occupant will relate the pit being full to emptying time. The challenge the implementer faces is to remove that link and in its place put in an ideology that instead of waiting for the pit to fill, have it emptied on a more regular basis so the user has more control over payments. The burden households face when saving up for one large payment is often too much and can often leave them in financial disarray. A smaller more frequent payment will be easier to manage removing the cash flow risk large payments carry. It is important that these smaller more frequent payments do not leave users worse off financially. If you can incentivise the setup by
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Using biogas technology to solve the disposal issues surrounding latrine waste
Practical Action
decreasing the emptying costs because the implementer is benefiting from the by-products generated from the sludge, then the technology is more likely to get unified backing. This theory of incentivising can also be applied to the emptier, making it beneficial for them to dispose of the waste in the correct area by paying them per load. In this situation care must be taken that loads are not bulked up with water from a surface water source in order get more empties per day. The final point regarding social and cultural issues is the importance of educational programmes. Firstly, as with so many social factors, educational programmes are context specific based on culture and current practices and therefore the implementer should deal with issues on a case by case nature. The second point is the need for education in improving community awareness. This is important for preventing situations where technologies are refused due to radical changes in sanitation practices. Thirdly, the public need confidence in the procedure to aid acceptance, so educational programs will be used to give training to the service providers to improve processes therefore improving the experience for the customer. Regarding the organisation of these programmes the initial step, as with any new implementation is the organisation of a piloting scheme to see how effectively the process works. It is at this point acceptability of the process must be achieved, with one solution being incentivising decisions once again by making the fuel much cheaper than the alternatives, so the community use it and see the benefits. What a piloting scheme also helps to do is create a sense of “keeping up with the Jones’” so implementation in neighbouring communities is easier. After analysis, if a piloting scheme is successful and the funds are available to grow then the technology can be implemented on a larger scale. The first area of a good educational programme is promotion at home. This not only regulates practice but also helps to install a sense of ownership with the householder that not only helps with maintenance issues but also helps acceptability because people will feel in control of their own practices and not dictated to. Promotion at home will often require visits, usually conducted by “hygiene teams” whose job it is to outline any change in practice and promote it and address any issues the household has. As well as hygiene team visits, visual materials should be used around the community to keep the public informed, for example directions to solid waste disposal points. As well as hygiene and process education there is also construction education which will involve passing down skills to local workmen so the whole process becomes more sustainable. Figure 6 outlines where education will be needed and why. The dashed outline signifies those tasks carried out by a hygiene team and the solid outline the more technical education.
Figure 6: Need for education at each process stage
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