The MicroUtility will provide modern utility services to rural sub-Saharan Africa at a low capital and operating cost, using easily maintained, low-tech equipment. The services that the MicroUtility provides are: (1) wastewater treatment; (2) potable water supplies; (3) high-protein animal feed; (4) fertilizer; and (5) gas service for lighting and cooking. The MicroUtility utilizes solar energy and biomass recycling as the sustainable inputs for the system. Wastewater treatment is a key function of the MicroUtility. Animal waste, food waste and human waste are collected and mixed together to form a slurry. The slurry is delivered to one or more anaerobic digesters. The anaerobic digesters are made of low-cost components. The main tanks are rugged plastic. A solar oil heater provides the heat necessary to maintain the tanks at operating temperature. In the anaerobic digester, bacteria convert the slurry into a gas, a solid and a liquid. The gas (“biogas) is a combination of 60% methane and 40% carbon dioxide. Biogas can be used as a renewable fuel for biogas appliances. The non-volatile solids from the digester have a relatively high concentration of nitrogen and phosphorus and can be applied as a fertilizer to the soil.
The digester liquid is drained into a duckweed pond. Duckweed removes excess nitrogen and phosphorus and, together with solar energy and photosynthesis, produces a high-protein animal feed for domesticated fowl. In sub-Saharan climates, yields of 5 tons of duckweed per acre per year can be anticipated.
In order to supply potable water for the community, water from the duckweed pond is recycled. To remove any harmful pathogens remaining in the water, the water is heated to at least 150F in a parabolic solar trough. The solar trough uses an evacuated tube solar collector filled with oil as the collector element and can reach temperatures of 300F with one hour of morning sun at tropical latitudes. The water is thereby pasteurized and harmful bacteria and rotoviruses (the main cause of severe diarrhea in children) are rendered inert. To the extent needed, primarily at night, the heated oil is pumped into a heat exchanger in the anaerobic digesters to maintain a constant temperature. Thus, the MicroUtility’s parabolic solar trough serves two purposes: potable water supplies for the community and anaerobic digester temperature maintenance.
The introduction of biogas for cooking in sub-Saharan Africa communities provides a convenient means of food preparation without the use of traditional fuels, such as firewood and charcoal. Local deforestation, which is associated with wood gathering, can be greatly minimized with biogas service being provided by the MicroUtility. A good biogas lamp produces a light intensity comparable to a 25-75W electric light bulb. In addition to cooking and lighting, biogas from the MicroUtility can be utilized for a wide array of conventional utility applications, such as a gas-powered refrigerator or a chicken incubator. While the MicroUtility is primarily a public health measure, it has the added benefit of providing wide array of basic utility services for the community.
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