Tool and Guideline # 9. Practical Technical Information on Low-cost Technologies such as Composting Latrines and Rainwater Harvesting Infrastructure

Transcription

1 Tool and Guideline # 9 Practical Technical Information on Low-cost Technologies such as Composting Latrines and Rainwater Harvesting Infrastructure Rwanda Environment Management Authority Republic of Rwanda Kigali, 2010

2 PREFACE In 2010, REMA prepared 11 practical technical tools intended to strengthen environmental management capacities of districts, sectors and towns. Although not intended to provide an exhaustive account of approaches and situations, these tools are part of REMA s objective to address capacity-building needs of officers by providing practical guidelines and tools for an array of investments initiatives. Tools and Guidelines in this series are as follows: # TOOLS AND GUIDELINES 1 Practical Tools for Sectoral Environmental Planning : A - Building Constructions B - Rural Roads C - Water Supply D - Sanitation Systems E - Forestry F - Crop Production G - Animal Husbandry H - Irrigation I - Fish Farming J - Solid Waste Management 2 Practical Tools on Land Management - GPS, Mapping and GIS 3 Practical Tools on Restoration and Conservation of Protected Wetlands 4 Practical Tools on Sustainable Agriculture 5 Practical Tools on Soil and Water Conservation Measures 6 Practical Tools on Agroforestry 7 Practical Tools of Irrigated Agriculture on Non-Protected Wetlands 8 Practical Tools on Soil Productivity and Crop Production 9 Practical Technical Information on Low-cost Technologies: Composting Latrines & Rainwater Harvesting Infrastructure 10 Practical Tools on Water Monitoring Methods and Instrumentation Practical Tools on Solid Waste Management of Imidugudu, Small Towns and Cities : Landfill and Composting Facilities 11.2 Practical Tools on Small-scale Incinerators for Biomedical Waste Management These tools are based on the compilation of relevant subject literature, observations, experience, and advice of colleagues in REMA and other institutions. Mainstreaming gender and social issues has been addressed as cross-cutting issues under the relevant themes during the development of these tools. The Tool and Guideline # 9 provides practical information on low-cost technologies such as composting latrines and rainwater harvesting infrastructure. These tools could not have been produced without the dedication and cooperation of the REMA editorial staff. Their work is gratefully acknowledged. Dr. Rose Mukankomeje Director General, Rwanda Environment Management Authority 2

3 TABLE OF CONTENT 1. INTRODUCTION OVERVIEW PURPOSE LOW-COST SANITATION FACTORS THAT HINDER SANITATION COVERAGE STRATEGIES FOR HYGIENE AND SANITATION PROMOTION Awareness Ecological Sanitation COMPOSTING LATRINES ADVANTAGES OF COMPOSTING LATRINES DESIGN CONSIDERATIONS Composting Pit Latrines Skyloo Latrines Ventilated Improved Pit Latrines RAINWATER HARVESTING INFRASTRUCTURE CURRENT STATUS SYSTEM COMPONENTS Catchment Areas Collection Devices Conveyance Systems ADVANTAGES OF RAIN WATER HARVESTING SAFETY CONSIDERATION DESIGN CONSIDERATIONS Brick Jar Plastic Tube Tank Ferro-cement Jar GENDER AND SOCIAL ISSUES IN WATER SUPPLY AND SANITATION ANNEX 1: REFERENCES AND USEFUL RESOURCES TABLES TABLE 1: COMPARISON COMPOSTING LATRINES TABLE 2: SIMPLE RAINWATER HARVESTING JARS

4 Tool and Guideline # 9 Practical Technical Information on Low-cost Technologies such as Composting Latrines and Rainwater Harvesting Infrastructure 1. INTRODUCTION 1.1 Overview Water supply may be obtained through protected or improved water sources, for instance from private vendors, protected springs and public standpipes, which usually must be purchased. Whereas urban areas have greater access to improved water sources, almost half of the rural population of Rwanda in 2005 remained dependent on unprotected water sources, such as unprotected springs, open wells, and surface water (rivers, streams, lakes, etc.). As reported in the 2009 Rwanda State of the Environment and Outlook, domestic water consumption accounted for approximately 24% of total water withdrawals in In terms of available water supplies, the estimated volume of drinking water in 2005 was 85 million m³ per year. Despite its abundant water resources, Rwanda experiences water scarcities due to inefficiencies and limitations in water supply accessibility. It is estimated that water demand over the next decade will double in Kigali and rural areas and more than double for the semiurban settlements. Groundwater is an important source of potable water in Rwanda, which is obtained primarily through pumps, wells and boreholes by local communities. Until recently, groundwater exploration by drilling has been limited, mainly due to relatively easy access to surface waters and springs. However, the government is currently supporting projects to increase water supply by drilling boreholes, with reportedly good results. Surface outlets of localised aquifers give rise to Rwanda s numerous springs. There are approximately 22,300 identified springs, mainly located in the north-western part of the country. Springs are especially important for maintaining the minimum flow of rivers mainly in the north and west of the country and are important sources of drinking water for local communities. Despite having abundant and good quality water supplies, Rwanda faces a number of challenges in the water sector. Water stress is likely to be accentuated by projected increases in water demand across all sectors. Projected water demand will increase to 1,016 million m 3 per year in 2020 from the 2005 demand of million m 3 per year. The most significant increase in water demand is clearly from the agricultural sector. Given the country s substantial water resource base, Rwanda s water predicament can be readily tackled with an appropriate combination of governance, technological, ecosystem restoration and market-based responses. Rwanda s drinking water problem is essentially one of improving access efficiency. Resolving this challenge does not necessarily require major infrastructure investments. While 71 percent of the Rwandan population currently has access to safe drinking water, this figure drops significantly in rural areas. Access issues are linked to the limited water distribution 4

5 infrastructure as well as the high costs of paying for safe drinking water. Access issues are accentuated by problems of drinking water contamination. The main problem is biological contamination of drinking water sources. Sanitation and facilities remain inadequate in both rural and urban areas throughout the country. The majority of the population (80%) relies on pit latrines, which are inadequately constructed or maintained, increasing the risk of ground and surface water contamination. Water contamination due to poor sanitation is likely to be a growing problem for small towns because of increased population densities. Only 10 percent of the population have sanitation facilities within required norms. As part of the decentralisation process, districts now have authority over the development of water infrastructure within their jurisdiction and can encourage private sector investment. Furthermore, Community Development Committees provide a mechanism for increased community participation in local water governance. These committees are responsible for the coordination of water-related activities, including implementation of community water projects. Community Development Committees can have women as members, thus enhancing their potential role in improving water resources management and conservation. Decentralisation offers a good opportunity to make water resource management more responsive and adaptive to local needs and priorities, as well as facilitate a more coordinated approach across different sectors. 1.2 Purpose Low-cost technologies for water and sanitation are suggested and a possible solution. The objective of this guide is to provide practical technical information on low-cost technologies such as composting latrines and rainwater harvesting infrastructure. Although not intended to provide an exhaustive account of approaches and situations, this tool is intended to address capacity-building needs of officers by providing information on lowcost water and sanitation technologies. This tool can be used as field guides or as checklists of elements for discussion during training and during implementation of low-cost water and sanitation investments. This document was produced to address REMA s proposed policy action to strengthen the resource capacity of environmental and related institutions at national and district level for environmental assessment, policy analysis, monitoring, and enforcement. 5

6 2. LOW-COST SANITATION 2.1 Factors that Hinder Sanitation Coverage The main motivation to build latrines is to increase health and hygiene awareness, and education about disease. Households prefer sanitation technologies that are affordable, inexpensive to maintain, clean and hygienic, use locally available materials, easy to replicate, offer safety, privacy, and convenience. The main problems that hinder sanitation coverage are: Limited financial ability: The inability of a household to raise sufficient funds to construct sanitation facilities is the main hindrance to the construction of better facilities than those currently used. Financial capability not merely as a lack of resources but as an opportunity cost amidst other competing needs. A household would find it more useful to dispatch its able members to pursuits that will lead to the acquisition of other basic necessities as opposed to concentrating their resources (money, time and energy) towards sanitation facilities. Lack of awareness of sanitation and hygiene: There is a positive relationship between improvements in education, health and hygiene awareness and the demand for sanitation facilities. Households with members who had a higher level of literacy are most likely to demand and adopt safer methods of excreta disposal than those with low levels of literacy. The higher level of literacy is also associated with a high premium placed on health status, which will lead to a demand for safer sanitation technologies. Lack of knowledge on how to construct and maintain pit latrines within households: This can resulted in poor quality construction, basic design faults, unsafe pits and poor maintenance. There is a general demand for technologies that employ locally and easily available construction materials. Adverse geo-hydrological conditions cause a number of problems: o Weak soil structure leading to collapse of latrines especially during the rainy season; o High water table resulting in shallow pit latrines; o High basement rock resulting in shallow pits. Flooding in low lying areas: Flooding is a major constraint as latrines fill-up and overflow during the rainy season. Quite often the latrines collapse making it difficult and expensive to rebuild after the rains. In such cases, family members prefer to use the bush. Cultural factors: Cultural factors such as restrictions on sharing sanitary facilities between adults and children, men and women and in-laws, and outsiders in general are constraints. 2.2 Strategies for Hygiene and Sanitation Promotion Awareness People mostly learn about sanitation technologies from their neighbours, public health workers, public meetings and community workers. One of the best channels for the promotion 6

7 of hygiene and sanitation are public meetings, religious organizations, schools and women groups. Promotion strategies should include: Creation of health awareness and training of community leaders; Construction of demonstration facilities; Provision of construction materials; Provision of construction equipment; Enforcement of the Rwanda Public Health Act in the event of epidemics Ecological Sanitation Ecological sanitation, or ecosan, is a new concept. It is based on the principle that pollutants or waste can be useful resources. Ecosan can be tailored to the needs of the users and local conditions. Ecosan incorporates the following principles: A conscious effort to conserve resources in the management of sanitation and wastewater Recycling and reuse of waste matter Pollution Prevention Rendering recyclables from waste (human and animal excreta, gray water) safe for reuse The main objectives of ecosan are to reduce health risks related to sanitation, improve the quality of surface and groundwater, improve soil fertility, and optimize the management of nutrients and water resources. An essential step in this process is the appropriate hygienization and handling of the materials throughout the entire treatment and reuse process. This is done to ensure a satisfactory 7

8 sanitization of the excrement. Therefore, unlike conventional sanitation systems, ecosan systems not only control the direct hygienic risks to the population but also protect the natural environment. In practice, the commonly applied ecosan strategy of separately collecting and treating feces, urine and gray water minimizes the consumption of valuable drinking water. At the same time, it enables treatment of the separate wastewater flows at low cost for subsequent reuse in soil amelioration, as fertilizer, as service or irrigation water or for groundwater recharge. For example, the recycling of one person s faecal and urine nutrients can provide up to 85% of the nutrient requirements to grow 250 kilograms of cereals. Excreta is re-used by applying as soil conditioner on the farm. Fruit trees such as bananas, avocados, papayas, mangoes can be grown on abandoned pit sites. The fertilising effect of urine is similar to that of a nitrogenrich chemical fertiliser. This means that urine is best utilized to fertilise crops and vegetables which thrive on nitrogen. Appropriate technologies for the rural area include composting latrines. Introduction of ecosan to communities will need to be supported by intensive education to correct practices of managing excreta and materials. Particularly for communities accustomed to traditional sanitation systems, significant retooling and possibly, retrofitting of existing facilities will be required. 2.3 Composting Latrines A composting latrine is a structure (usually small, holding a single person, and freestanding) for defecation and urination. Composting latrines allow for safer and more hygienic disposal of human waste than open defecation. They are used in rural areas and lowincome urban communities. Many Figure 1: Arborloo variations exist, but at its simplest, the reason for using a composting latrine is that waste is controlled and decomposed into safer by-products. Many forms of composting latrine technology have been used in the past, from utterly simple to more sophisticated, while newer developments show promise using ecological sanitation. Some different types and technologies regarding latrines are: Figure 2: Fossa Alterna - Pit toilets or pit latrines: These are the simplest and cheapest type, minimally defined as a hole in the ground. The most basic improvement is installation of a floor plate. A dry pit does not penetrate the water table, while a wet pit does. Composting variations of the pit toilets are: o Arborloo is a portable superstructure with no urine diversion. A tree can be o planted in the filled pit (figure 1). Fossa Alterna has dual pits and is a portable superstructure. Digested contents of pit not in use can be emptied after a year (figure 2). Fossa Alterna and Arborloos work best when quantities of soil, wood ash and leaves are added periodically to produce balanced compost. 8

9 - Skyloo: The Skyloo (figure 3) is a raised latrine with urine diversion and separate collection of urine and faeces. Skyloo technology is seen as an alternative to the use of pit latrines in areas where the water table is high and the community relies on shallow wells for their water needs. In hilly areas with thin soil cover under hard rock, the Skyloo eco-san composting latrine is a good option. The Skyloo latrine is a permanent feature that requires periodic (6-12 months) emptying of the receptacle and transportation to a composting site. Not only is it constructed at ground level, it also turns human waste into compost. The Skyloo composting latrine consists of two brick pits, constructed above ground level with a latrine squatting Figure 3: Skyloo slab and superstructure on top. Human waste drops through a hole into the vaults and ash is thrown on top, increasing alkalinity to a level that kills pathogens. The temperature in the vaults is raised by the sun beating down on metal vault covers and the decomposition of the faeces. This also neutralizes pathogens. After several months the first pit is dug out and the fertile compost is used to grow crops. The second pit is then used until it becomes full and the process is repeated. The hygienic latrines generate free compost and pose no threat to groundwater resources. Hygienic latrines that generate free compost and pose no threat to groundwater resources are a real benefit to the community. - A Ventilated Improved Pit (VIP) Latrine: This latrine reduces two of the most common problems with a simple pit latrine: odour and fly/mosquito breeding. Adding a ventilating pipe is the key improvement of the ventilated improved pit latrine. The Doublevault Ventilated Composting Latrine (figure 4) is currently the most advanced, free-standing latrine. Apart from offering significant reduction in risk from waterborne disease, this type of ecological sanitation provides the closure of some nutrient cycles by allowing the safe, composted waste to be used as a "free" soil treatment in agriculture. Figure 4: Ventilated Improved Pit Single vault composting latrine: The first makes use of anaerobic bacteria to decompose the excreta, with two vaults alternatively storing excreta and a separate 9

10 receptacle for storing urine. The urine should be diluted with 3-6 parts water before being used. This can be done by pouring a small amount of water on to the urine collection area (squatting plate, or specific part of the pedestal) after use. In many applications the urine is then diverted directly to a plot of land where it acts as a soil conditioner for plants and/or crops. Control of moisture content in the stored excreta is vital for correct operation of the latrine. Such latrines are therefore not appropriate Figure 5: Double-vault composting latrine where water is used for anal cleansing. An advantage of this type of latrine is that since the vault contents are kept dry, there is no pollution to the surrounding ground provided the system is correctly operated and maintained. Double-vault composting latrine: The second type is a continuous composting latrine, which makes use of aerobic bacteria to break down the excreta. These tend to be more commercially manufactured systems that incorporate the full functioning of the latrine into a single unit, or can be built using local materials under good supervision and with experienced builders. The method of separating the urine from the faeces at the squatting plate or pedestal is something of a technical challenge and a number of designs have been tried and tested. Composting latrines consist of a single or double vault construction (figure 5). Some systems are also designed to ensure that urine is kept separate from faeces. This aims to reduce the odour. The urine is an effective fertiliser, while the faeces contain most of the disease-causing micro-organisms. The faeces are collected in the vault and need to be mixed regularly with earth, wood ash or other organic waste material to deodorize them and to control the moisture content. The accumulated compost waste needs to be left at least a year in order to ensure that all pathogenic organisms have died off. In some cases, it may be recommend that the excreta be left to compost for 2 years, to ensure the material is safe to handle. The collection box can be constructed either above or below ground and so in theory the system is suitable for regions with shallow groundwater or risk of flooding. 2.4 Advantages of Composting Latrines The advantages of ecological sanitation such as composting latrines are given as: - Nutrients in human excreta can be reclaimed and used in plant/crop growing when composted; - Urine can be used as a soil conditioner / fertilizer; - Treating and handling human waste on-site protects the environment from the pollution potential from untreated waste, or waste that is transported off-site and then treated; and 10

11 - Ecological composting sanitation latrines can be easier to empty than other on-site options (such as pit latrines). When promoting the use and philosophy of ecological composting latrines, the arguments must include technical, social, cultural, health and cost aspects. Handling human excreta is not acceptable in many cultures, for a variety of reasons which could be linked to cultural beliefs. Although fully composted excreta is relatively safe to handle, incorrect handling or handling excreta that has not been left long enough under the right conditions introduces a significant health risk. This is of particular concern in situations where those handling excreta are likely to also be affected by HIV/AIDS and therefore have a lower immunity to disease. The composting latrine has caused a good deal of controversy and discussion amongst experts around the world and there are many arguments against using the system. In particular, health risks are associated with poorly managed composting latrines and there is also a low level of user acceptance in many countries and cultures. It is not therefore recommended that composting latrines are constructed unless there is a proven track record of operation and acceptance in the project area or region. Composting latrines are an improvement on open pit latrines because they yield a useable fertilizer after a few years. Several of types also have passive solar ventilation for better air circulation and fewer doors. The next Table provides with the major advantages of each design. Table 1: Comparison Composting Latrines CRITERION COMPOSTING PIT LATRINES Arborloo Fossa Alterna SKYLOO LATRINES VENTILATED IMPROVED PIT (DOUBLE OR SINGLE) Easy construction using local materials yes yes yes no Costs low low medium high Water requirements low low low low Odour medium medium medium low Maintenance cost low low low medium Likelihood of ground water contamination low low low low Space requirement high low low medium Suitable in areas with impermeable no no yes no underground Suitable in hilly areas yes yes yes yes Urine diversion no no yes yes Both financial and economic costs need to be taken into account. Composting latrines require more user time to operate and maintain in terms of adding ash to the pit, keeping the pedestal or squatting plate clean, handling the collected urine and emptying vaults. This has economic implications where time has a financial dimension. Financial gains derived from increased crop production have to be balanced against these other costs. Consideration should also be given to the fact that the costs and benefits may not accrue to the same person. As composted excreta and urine are intended to be collected and used, there needs to be a place for application of these end products. Where households have their own small gardening plots, direct application at the household level is possible, with no transport or third-party handling involved. If this is not the case, some form of household- or community-level collection by farmers, or a commercial user of compost, is needed. Without such a collection system, households will not be in a position to dispose of the composted excreta and the latrine will fill up and become unusable. Without a suitable disposal point for the urine, this could also become a problem to dispose of and may end up polluting adjacent watercourses. 11

12 Use of ecological sanitation is often promoted on the basis that it is a better option than pit latrines, as it is reported to deal more effectively with smells, flies and end use of excreta. Pit latrines are a safe and effective system of excreta management if correctly designed, built, operated and maintained. They should not be dismissed on the basis of incorrect, or poor, operation. Similarly for urine-diversion composting latrines, there are situations where the use of these are more appropriate than other forms of sanitation, however it should be offered as a way to achieve improved sanitation as one of a range of options - from a simple hole in the ground with a sanitary platform on top to a more advanced water-borne system, if this is appropriate. 2.5 Design Considerations The next sections provide technical information on Composting Pit Latrines, Skyloo Latrines and Ventilated Improved Pit Latrines Composting Pit Latrines Description: Pit toilets, or pit latrines, are the simplest and cheapest type, minimally defined as a hole in the ground. A pit latrine consists of a hole in the ground covered with either a squatting plate or a slab provided with riser and seat. A housing or toilet room is built over the pit. A pit latrine operates without water. Liquid portion of the excreta soaks away into the soil. The most basic improvement is installation of a floor plate. A dry pit does not penetrate the water table, while a wet pit does. Composting variations of the pit toilets are: Arborloo is a portable superstructure with no urine diversion. A tree can be planted in the filled pit. The arborloo is the simplest type of latrine and similar to the conventional pit latrine. It is used like a regular pit latrine but with the addition of soil and ash after each use. In four to nine month a layer of soil is added to the full pit and a sapling placed into the soil. The tree grows and utilizes the compost to produce large, succulent fruit. After a few years of latrine movement the result is an orchard that is producing fruit with a real economic value. Fossa Alterna has dual pits and is a portable superstructure. Digested contents of pit not in use can be emptied after a year. Design: The Arborloo and Fossa Alterna volume is given by the product of: Sludge accumulation rate X Number of people X Filling time 1. Sludge accumulation rate = 20 liters/person/year or rate decreased to 10 liters/person/year if pit is seasonally flooded or water from washings is added to the pit. Increase rate by 50% to allow bulky materials for anal cleansing. 2. Design use of single pit (filling time) = 9 months 3. Pit bottom not lined to enable liquid to soak away Applications: The Arborloo and Fossa Alterna latrines are suitable for use in rural areas where the soil is deep and space is available to construct succeeding pits. These latrines can be used in areas where there are no on-site water supplies; however, water is needed for hand washing. Components: Pit; squatting plate or wooden seat & cover; cover slab; and a movable housing or toilet room. Capacity: Minimum pit volume = 0.5 m 3 for household of 6 persons for use in about 9 months Operating Principles: Two important actions take place in the pit which reduce the rate at which it fills: 12

13 1. The liquid portion of the excreta soaks away into the soil. 2. The solids in the excreta are broken down into simpler compounds by biological digestion. Soluble products are carried into the soil by the liquid portion of the excreta. Fossa Alterna and Arborloos work best when quantities of soil, wood ash and leaves are added periodically to produce balanced compost. Maintenance: 1. Regular cleaning. 2. Use of a little bleach or disinfectant to wash the floor slab. 3. Where there is standing water in the latrine pit, small quantities of special oils, kerosene, and old engine oil can be added to the pit to prevent mosquitoes from breeding. 4. Stop use of pit when level of solids reaches 0.5 m from the underside of the slab. Fill the pit immediately with soil. Construction Materials: 1. Indigenous materials bamboo, stabilized soil blocks, stone bricks, etc. could be used for the pit or housing structure. 2. Reinforced concrete for the pit cover slab. Costs: Options for the construction of a Arborloo and Fossa Alterna latrines are: Use of construction materials like concrete for slab, galvanized iron sheet for roofing and walls. Use local available construction material. Utility & Efficiency: 50% reduction of solids by digestion. Can be single pit or double pit. Reliability: Can be relied upon to maintain protection with limited supervision for long periods of time. Flexibility: Flexible in the use of construction materials. Regulatory/Institutional Issues: Compliance with the Rwanda Sanitation Code. Advantages: 1. Easy construction using local materials. 2. The costs are the same as ordinary pit latrines. 3. Minimal water requirement. 4. Low annual cost. 5. Simple maintenance. 6. For the Arborloo, fruit trees can be grown on abandoned pit sites. 7. Latrines are shallow; there is less likelihood of ground water contamination or collapse during the rainy season. Disadvantages: 1. Lack of space for relocating the Arborloo in dense areas. 2. Not suitable in areas with high groundwater table, due to possible infiltration with leachate. 3. Not suitable in areas with impermeable, rocky underground, due to limited infiltration capacity. 4. Arborloo and Fossa Alterna latrines do not divert urine and no one needs to handle the faeces. Figure 6: Arborloo Figure 7: Inside the Fossa Alterna 13

14 2.5.2 Skyloo Latrines Description: Skyloo technology is seen as an alternative to the use of pit latrines in areas where the water table is high and the community relies on shallow wells for their water needs. In hilly areas with thin soil cover and hard rock, the Skyloo eco-san composting latrine is a good option. The Skyloo latrine is a permanent feature that requires periodic (6-12 months) emptying of the receptacle and transportation to a composting site. Not only is it constructed at ground level, it also turns human waste into compost. The Skyloo composting latrine consists of two brick pits, constructed above ground level with a latrine squatting slab and superstructure on top. Human waste drops through a hole into the vaults and ash is thrown on top, increasing alkalinity to a level that kills pathogens. The temperature in the vaults is raised by the sun beating down on metal vault covers and the decomposition of the faeces. This also neutralizes pathogens. After several months the first pit is dug out and the fertile compost is used to grow crops. The second pit is then used until it becomes full and the process is repeated. The hygienic latrines generate free compost and pose no threat to groundwater resources. Hygienic latrines that generate free compost and pose no threat to groundwater resources are a real benefit to the community. Design: The Skyloo volume is given by the product of: Sludge accumulation rate X Number of people X Filling time 1. Sludge accumulation rate = 20 liters/person/year or rate decreased to 10 liters/person/year if pit is seasonally flooded or water from washings is added to the pit. Increase rate by 50% to allow bulky materials for anal cleansing. 2. Design use of single pit (filling time) = 9 months 3. Pit elevated Applications: Skyloos require some ash to dry the faeces and increase pathogen destruction. Components: pit; squatting plate or wooden seat & cover; cover slab; and a movable housing or toilet room. Capacity: 1. Minimum pit volume = 0.5 m 3 for household of 6 persons for use in about 9 months Operating Principles: Two important actions take place in the pit which reduce the rate at which it fills: 1. The liquid portion of the excreta soaks away into the soil. 2. The solids in the excreta are broken down into simpler compounds by biological digestion. Soluble products are carried into the soil by the liquid portion of the excreta. Maintenance: 1. Regular cleaning. 2. Use of a little bleach or disinfectant to wash the floor slab. 3. Where there is standing water in the latrine pit, small quantities of special oils, kerosene, and old engine oil can be added to the pit to prevent mosquitoes from breeding. 4. Stop use of pit when level of solids reaches 0.5 m from the underside of the slab. Fill the pit immediately with soil. Construction Materials: 1. Indigenous materials bamboo, stabilized soil blocks, stone bricks, etc. could be used for the pit or housing structure. 2. Reinforced concrete for the pit cover slab. Costs: Options for the construction are: 1. Use of construction materials like concrete for slab, galvanized iron sheet for roofing and walls. Utility & Efficiency: 50% reduction of solids by digestion. Can be single pit or double pit. 14

15 Reliability: Can be relied upon to maintain protection with limited supervision for long periods of time. Flexibility: Flexible in the use of construction materials. Regulatory/Institutional Issues: Compliance with the Rwanda Sanitation Code. Advantages: 1. Easy construction using local materials. 3. Minimal water requirement. 2. Low annual cost. 3. Simple maintenance. 4. Suitable in areas with high groundwater table. 5. Suitable in areas with impermeable, rocky underground, due to limited infiltration capacity. 6. Suitable in hilly areas. 7. The Slyloo diverts urine and no one needs to handle the faeces. Disadvantages: 1. The costs are higher than Arborloo and Fossa Alterna latrines. Figure 8: Skyloo 15

16 2.5.3 Ventilated Improved Pit Latrines Description: A pit latrine consists of a hole in the ground covered with either a squatting plate or a slab provided with riser and seat. A housing or toilet room is built over the pit. A pit latrine operates without water. Liquid portion of the excreta soaks away into the soil. The VIP is a pit latrine with a screened vent installed directly over the pit. The vent provides odour control and the screen on top of the vent prevents entry of insects attracted by the smell. Filled pits are covered with soil for composting. There are two types of VIP latrines: single pit and alternating-pit. For the latter, there are two adjacent pits below the toilet room and one pit is used at any given time. When one pit becomes full, it is closed and the other pit is used. By the time the second pit becomes full; the first has fully decomposed and becomes innocuous. Materials in the filled pit are removed and the pit can then be returned to service till it becomes full. Single vault construction: The first makes use of anaerobic bacteria to decompose the excreta, with two vaults alternatively storing excreta and a separate receptacle for storing urine. The urine should be diluted with 3-6 parts water before being used. This can be done by pouring a small amount of water on to the urine collection area (squatting plate, or specific part of the pedestal) after use. In many applications the urine is then diverted directly to a plot of land where it acts as a soil conditioner for plants and/or crops. Control of moisture content in the stored excreta is vital for correct operation of the latrine. Such latrines are therefore not appropriate where water is used for anal cleansing. An advantage of this type of latrine is that since the vault contents are kept dry, there is no pollution to the surrounding ground provided the system is correctly operated and maintained. Single vault VIPs can be abandoned after filling as they were made of concrete elements that could not be moved or re-used. They also more expensive than the traditional pit latrines that are always built with locally available materials. As a result the price of a latrine doubles when a household opts for a conventional VIP five meters deep instead of a simple pit latrine of similar depth. This explains why VIP latrines are not more numerous since communities are unable to replicate project VIPs even after initial material assistance. The VIP are simply too expensive to be adopted by some rural communities. The Double-vault Ventilated Composting Latrine is currently the most advanced, free-standing latrine. Apart from offering significant reduction in risk from waterborne disease, this type of ecological sanitation provides the closure of some nutrient cycles by allowing the safe, composted waste to be used as a "free" soil treatment in agriculture. Design: The pit volume is given by the product of: Sludge accumulation rate x Number of people x Filling time 1. Sludge accumulation rate = 40 liters/person/year or rate decreased to 20 liters/person/year if pit is seasonally flooded or water from washings is added to the pit. Increase rate by 50% to allow bulky materials for anal cleansing. 2. Design use of single pit (filling time) = period of 2 years. 3. Pit bottom not lined to enable liquid to soak away. Applications: Single-pit VIP latrines are suitable for use in rural areas where the soil is deep and space is available to construct succeeding pits. Alternating double-pit VIP latrines are appropriate for urban areas where people can afford a permanent latrine that does not require relocating after every few years. VIP latrines can be used in areas where there are no on-site water supplies. Water is needed for hand washing. 16

17 Components: pit; squatting plate or wooden seat & cover; cover slab; and a housing or toilet room. Capacity: 1. Minimum pit volume = 1 m 3 for household of 6 persons for use in about 2 years. 2. Increase in capacity can be achieved by making the pit at least 0.5 m deeper than the minimum since the latrine cannot be used after the sludge surface gets close to the slab cover. Operating Principles: Two important actions take place in the pit which reduce the rate at which it fills: 1. The liquid portion of the excreta soaks away into the soil. 2. The solids in the excreta are broken down into simpler compounds by biological digestion. Soluble products are carried into the soil by the liquid portion of the excreta. 3. Gases (foul air) produced by the digestion are pushed out through the vent by fresh air entering the pit hole. Maintenance: 1. Regular cleaning and repairs. 2. Periodic inspection of the fly screens and signs of erosion around the edges of the slab. 3. Use of a little bleach or disinfectant to wash the floor slab. 4. Where there is standing water in the latrine pit, small quantities of special oils, kerosene, and old engine oil can be added to the pit to prevent mosquitoes from breeding. 5. Stop use of pit when level of solids reaches 0.5 m from the underside of the slab. Fill the pit immediately with soil. Construction Materials: 1. Indigenous materials like rot-resistant wood, bamboo, nipa, stabilized soil blocks, stone bricks, etc. could be used for the pit or housing structure. 2. Permanent materials like concrete hollow block (CHB), cement mortar, stone or bricks, metal sheets, etc. could be used for the pit or housing. 3. Reinforced concrete for the pit cover slab or flooring. 4. PVC pipe for the vent pipe. Costs: Options for the construction of a VIP Latrine are: 1. Use of permanent construction materials like concrete for slab, blocks for walls and galvanized iron sheet for roofing. 2. Use of indigeneous materials like wood and hay for walls and roofing for the housing. Utility & Efficiency: 50% reduction of solids by digestion. Can be single pit, double pit or multiple pits. Reliability: Can be relied upon to maintain protection with limited supervision for long periods of time. Flexibility: Flexible in the use of construction materials particularly indigenous materials. A toilet room in the house could be used in lieu of a separate structure. Regulatory/Institutional Issues: Compliance with the Rwanda Sanitation Code. Advantages: 1. Easy construction using local materials. 2. Minimal water requirement. 3. Low annual cost. 4. Easy maintenance. 5. All kinds of anal cleansing materials may be used. Disadvantages: 1. Much more expensive that composting pits. 2. Potential for groundwater pollution. 3. Does not dispose of large quantities of sewage water. 4. Not suitable in areas with high groundwater table, due to possible infiltration with leachate. 5. Not suitable in areas with impermeable, rocky underground, due to limited infiltration capacity. 17

18 Figure 9: Ventilated Improved Pit Latrines Figure 10: Details - Ventilated Improved Pit Latrines 18

19 3. RAINWATER HARVESTING INFRASTRUCTURE 3.1 Current Status Rainwater harvesting is a technology used for collecting and storing rainwater from rooftops, the land surface or rock catchments using simple techniques such as jars and pots as well as more complex techniques such as underground check dams. Rainwater harvesting is the gathering, or accumulating and storing, of rainwater. Rainwater harvesting has been used to provide drinking water, water for livestock or water for irrigation. Rainwater collected from the roofs of houses and local institutions can make an important contribution to drinking water. In some cases, rainwater may be the only available, or economical, water source. Rainwater systems are simple to construct from inexpensive local materials, and are potentially successful in most habitable locations. Roof rainwater is usually of good quality and does not require treatment before consumption. Household rainfall catchment systems are appropriate in areas with an average rainfall greater than 200mm per year, and no other accessible water sources. The rate at which water can be collected from either system is dependent on the plan area of the system, its efficiency, and the intensity of rainfall. 3.2 System Components Commonly used systems are constructed of three principal components; namely, the catchment area, the collection device, and the conveyance system Catchment Areas Rooftop catchments In the most basic form of this technology, rainwater is collected in simple vessels at the edge of the roof. Variations on this basic approach include collection of rainwater in gutters which drain to the collection vessel through down-pipes constructed for this purpose, and/or the diversion of rainwater from the gutters to containers for settling particulates before being conveyed to the storage container for the domestic use. As the rooftop is the main catchment area, the amount and quality of rainwater collected depends on the area and type of roofing material (see figure 11). Figure 11 Rooftop Catchment Systems 19

20 Reasonably pure rainwater can be collected from roofs constructed with galvanized corrugated iron, aluminum or asbestos cement sheets, tiles and slates, although thatched roofs tied with bamboo gutters and laid in proper slopes can produce almost the same amount of runoff less expensively. However, the bamboo roofs are least suitable because of possible health hazards. Similarly, roofs with metallic paint or other coatings are not recommended as they may impart tastes or colour to the collected water. Roof catchments should also be cleaned regularly to remove dust, leaves and bird droppings so as to maintain the quality of the product water. Land surface catchments Rainwater harvesting using ground or land surface catchment areas is less complex way of collecting rainwater. It involves improving runoff capacity of the land surface through various techniques including collection of runoff with drain pipes and storage of collected water. Compared to rooftop catchment techniques, ground catchment techniques provide more opportunity for collecting water from a larger surface area. By retaining the flows (including flood flows) of small creeks and streams in small storage reservoirs (on surface or underground) created by low cost (e.g., earthen) dams, this technology can meet water demands during dry periods. There is a possibility of high rates of water loss due to infiltration into the ground, and, because of the often marginal quality of the water collected, this technique is mainly suitable for storing water for agricultural purposes. Various techniques available for increasing the runoff within ground catchment areas involve: i) clearing or altering vegetation cover, ii) increasing the land slope with artificial ground cover, and iii) reducing soil permeability by the soil compaction and application of chemicals (see figure 12). Figure 12: Ground Catchment System Variations in components of the land surface catchments are suggested: Clearing or altering vegetation cover: Clearing vegetation from the ground can increase surface runoff but also can induce more soil erosion. Use of dense vegetation cover such as grass is usually suggested as it helps to both maintain a high rate of runoff and minimize soil erosion. Increasing slope: Steeper slopes can allow rapid runoff of rainfall to the collector. However, the rate of runoff has to be controlled to minimise soil erosion from the catchment field. Use of plastic sheets, asphalt or tiles along with slope can further increase efficiency by reducing both evaporative losses and soil erosion. 20

21 Soil compaction by physical means: This involves smoothing and compacting of soil surface using equipment such as graders and rollers. To increase the surface runoff and minimize soil erosion rates, conservation bench terraces are constructed along a slope perpendicular to runoff flow. The bench terraces are separated by the sloping collectors and provision is made for distributing the runoff evenly across the field strips as sheet flow. Excess flows are routed to a lower collector and stored. Soil compaction by chemical treatments: In addition to clearing, shaping and the compaction of a catchment area, chemical applications with such soil treatments as sodium can significantly reduce the soil permeability. Use of aqueous solutions of a silicone-water repellent is another technique for enhancing soil compaction technologies. Though soil permeability can be reduced through chemical treatments, soil compaction can induce greater rates of soil erosion and may be expensive. Use of sodium-based chemicals may increase the salt content in the collected water, which may not be suitable both for drinking and irrigation purposes Collection Devices Storage tanks Storage tanks for collecting rainwater harvested using guttering may be either above or below the ground. Precautions required in the use of storage tanks include provision of an adequate enclosure to minimise contamination from human, animal or other environmental contaminants, and a tight cover to prevent algal growth and the breeding of mosquitoes. Open containers are not recommended for collecting water for drinking purposes. Various types of rainwater storage facilities can be found in practice. Among them are cylindrical ferro-cement tanks and mortar jars. The ferro-cement tank consists of a lightly reinforced concrete base on which is erected a circular vertical cylinder with a 10 mm steel base. This cylinder is further wrapped in two layers of light wire mesh to form the frame of the tank. Mortar jars are large jar shaped vessels constructed from wire reinforced mortar. The storage capacity needed should be calculated to take into consideration the length of any dry spells, the amount of rainfall, and the per capita water consumption rate. Rainfall water containers As an alternative to storage tanks, battery tanks (i.e., interconnected tanks) made of pottery, ferro-cement, or polyethylene may be suitable. The polyethylene tanks are compact but have a large storage capacity (ca to l), are easy to clean and have many openings which can be fitted with fittings for connecting pipes. Jars of earthen materials or ferro-cement tanks are commonly used. The use of rainwater catchment technologies, especially roof catchment systems, expanded rapidly in a number of regions in the world. Early problems with the jar design were quickly addressed by including a metal cover using readily available, standard brass fixtures. The immense success of the jars is that the technology met a real need, was affordable, and invited community participation. It can also capture the imagination and support of not only the citizens, but also of government at both local and national levels as well as community based organizations, small-scale enterprises and donor agencies. The introduction of Bamboo reinforced tanks, however, are less successful because the bamboo can be attacked by termites, bacteria and fungus. 21

22 3.2.3 Conveyance Systems Conveyance systems are required to transfer the rainwater collected on the rooftops to the storage tanks. This is usually accomplished by making connections to one or more downpipes connected to the rooftop gutters. When selecting a conveyance system, consideration should be given to the fact that, when it first starts to rain, dirt and debris from the rooftop and gutters will be washed into the down-pipe. Thus, the relatively clean water will only be available some time later in the storm. There are several possible choices to selectively collect clean water for the storage tanks. The most common is the down-pipe flap. With this flap it is possible to direct the first flush of water flow through the down-pipe, while later rainfall is diverted into a storage tank. When it starts to rain, the flap is left in the closed position, directing water to the down-pipe, and, later, opened when relatively clean water can be collected. A great disadvantage of using this type of conveyance control system is the necessity to observe the runoff quality and manually operate the flap. An alternative approach would be to automate the opening of the flap as described below. A funnel-shaped insert is integrated into the down-pipe system. Because the upper edge of the funnel is not in direct contact with the sides of the down-pipe, and a small gap exists between the down-pipe walls and the funnel, water is free to flow both around the funnel and through the funnel. When it first starts to rain, the volume of water passing down the pipe is small, and the *dirty* water runs down the walls of the pipe, around the funnel and is discharged to the ground as is normally the case with rainwater guttering. However, as the rainfall continues, the volume of water increases and *clean* water fills the down-pipe. At this higher volume, the funnel collects the clean water and redirects it to a storage tank. The pipes used for the collection of rainwater, wherever possible, should be made of plastic, PVC or other inert substance, as the ph of rainwater can be low (acidic) and could cause corrosion, and mobilization of metals, in metal pipes. In order to safely fill a rainwater storage tank, it is necessary to make sure that excess water can overflow, and that blockages in the pipes or dirt in the water do not cause damage or contamination of the water supply. The design of the funnel system, with the drain-pipe being larger than the rainwater tank feed-pipe, helps to ensure that the water supply is protected by allowing excess water to bypass the storage tank. A modification of this design is possible with a simple overflow/bypass system. In this system, it also is possible to fill the tank from a municipal drinking water source, so that even during a prolonged drought the tank can be kept full. Care should be taken, however, to ensure that rainwater does not enter the drinking water distribution system. 3.3 Advantages of Rain Water Harvesting These are some of the major advantages of rain water harvesting facilities: Provides self-sufficiency to your water supply. Reduces the cost for pumping of ground water. Provides high quality water, soft and low in minerals. Improves the quality of ground water through dilution when recharged to ground water. Reduces soil erosion in urban areas. The rooftop rain water harvesting is less expensive. Rainwater harvesting systems are simple which can be adopted by individuals. Rooftop rain water harvesting systems are easy to construct, operate and maintain. In hilly terrains, rain water harvesting is preferred. 22