Water for small-scale biogas digesters in sub-Saharan Africa
Water for small-scale biogas digesters in sub-Saharan Africa
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DOI：
10.1111/gcbb.12339
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发表时间：
2017-02-01
影响因子：
5.6
通讯作者：
Smith, Jo U.
中科院分区：
文献类型：
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作者：
Bansal, Vamini;Tumwesige, Vianney;Smith, Jo U.
沼气可以为撒哈拉以南非洲的农村家庭提供比木材燃料更可持续的能源。然而，沼气池的功能在水可用性低的地区可能受到限制。每头奶牛需水量约为每天50dm(3)(-1)，每头向沼气池提供粪便的猪需水量约为每天10dm(3)(-1)，或使用沼气池体积为1.3 (+/- 0.3)m(3)人均（-1），家庭中每人需水量约为25 (+/- 6)dm(3)天（-1）。在这里，我们考虑了在撒哈拉以南非洲不同国家，国内水循环利用、雨水收集和水产养殖提供消化所需水的潜力。每个国家的家庭用水回收都很重要，但通常不足以满足沼气池的要求，72%的国家的家庭需要收集额外的水。屋顶雨水收集也有重要的作用，铁屋顶在收集水方面比茅草屋顶更有效。然而，即使使用铁屋顶，撒哈拉以南非洲地区常见的屋顶尺寸（15至40米(2)）也太小，无法收集足够的水，每个人（R/100） （R为降雨量，单位为毫米）需要额外的面积（m(2)）。如果当地有鱼的市场，在一个池塘里饲养罗非鱼，以在沼气池的生物浆上生长的浮游生物为食，可以提供一个重要的额外收入来源，并保持沼气池所需的水。在降雨量少和季节性的地区，鱼塘可能只在雨季放养，使池塘在干旱期间被覆盖，以减少蒸发。如果蒸发损失（E单位毫米）超过降雨量，则需要额外的集水区来维持池塘的水位，相当于家庭中每个人大约（1.5x(E-R)/R） m(2)。
Biogas could provide a more sustainable energy source than wood fuels for rural households in sub-Saharan African. However, functioning of biogas digesters can be limited in areas of low water availability. The water required is approximately 50dm(3)day(-1) for each cow and 10dm(3)day(-1) for each pig providing manure to the digester, or 25 (+/- 6)dm(3)day(-1) for each person in the household, using a digester volume of 1.3 (+/- 0.3)m(3) capita(-1). Here, we consider the potential of domestic water recycling, rainwater harvesting, and aquaculture to supply the water needed for digestion in different countries of sub-Saharan Africa. Domestic water recycling was found to be important in every country but was usually insufficient to meet the requirements of the digester, with households in 72% of countries need to collect additional water. Rooftop rainwater harvesting also has an important role, iron roofs being more effective than thatched roofs at collecting water. However, even with an iron roof, the size of roof commonly found in sub-Saharan Africa (15 to 40m(2)) is too small to collect sufficient water, requiring an extra area (in m(2)) for each person of (R/100) (where R is the rainfall in mm). If there is a local market for fish, stocking a pond with tilapia, fed on plankton growing on bioslurry from the digester, could provide an important source of additional income and hold the water required by the digester. In areas where rainfall is low and seasonal, the fishpond might be stocked only in the rainy season, allowing the pond to be covered during the dry period to reduce evaporation. If evaporative losses (E in mm) exceed rainfall, an extra catchment area is needed to maintain the water level in the pond, equivalent to approximately (1.5x((E-R)/R))m(2) for each person in the household.