Potential of biogas production to reduce firewood consumption in remote high-elevation Himalayan communities in Nepal

Abstract

Abstract. Remote communities in the Nepalese mountains above 2500 m a.s.l. belong to the most precarious in the world. Inhabitants struggle for the minimum in terms of safe drinking water, food and sanitation. Reliable, affordable and clean energy for cooking, room heating and warm water for personal hygiene is often lacking and dependency on firewood very high. The remoteness and unlikeliness of electric grid connection in the coming decades make a diversified energy supply from renewable local resources crucial. Small-scale anaerobic digestion (AD) of organic substrates has been used for long in rural areas of developing countries to produce biogas as energy source and recover residue as organic fertilizer. AD is challenging at high elevations due to year around lower ambient temperatures and lower annual biomass production per area compared to lowlands. Nevertheless, examples of operational household AD exist even above 3000 m a.s.l. in the Andes. Here we compare firewood consumption with biogas potential from organic substrates in a community with 39 households at 3150 m a.s.l. in Jumla District, Nepal. In five households with varying numbers of members and animals kept, mean firewood use and its energy content per capita (cap) and day (d) were 2.1 kg or ca. 25 MJ in spring and 2.3 kg or ca. 28 MJ in winter. Easily available substrates include cow, sheep and horse dung from overnight shelters and human excrements from pit latrines, amounting on average to 1.7 kg wet weight (kg ww ) cap À1 d À1 in spring and 2.2 kg ww cap À1 d À1 in winter. Adjusted to normal conditions (Nm 3 at 0°C, 1013.15 hPa), these substrates yielded on average 0.08 Nm 3 cap À1 d À1 biogas in spring and 0.12 Nm 3 cap À1 d À1 in winter (35-60% methane content) in biochemical methane potential (BMPs) tests at 36°C. This could provide up to 60% of basic cooking needs on average and up to 75% in a "typical" household in terms of members and animals kept. Of the overall thermal energy needs including also room heating ca. 10-20% could be covered, substituting 0.1-0.4 (mean: 0.2) kg firewood cap À1 d À1 . If only animal dung and human excrements are considered, no competition for resources arises as residues can still be used as organic fertilizer. This study supports the design and introduction of planned pilot digesters integrated into on-going community development including pit latrines for substrate availability, greenhouses as possible way of thermal insulation, and planned pico-hydropower plants to use excess electricity during the night for digester heating.

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“…31.3% of the population in rural areas still use firewood as the main cooking fuel. This contributes to environmental and health issues such as forest degradation, carbon emission, breathing disorders and mortality (Abdullah, 2002;Gross, 2017). Meanwhile, LPG is utilized by 63% of the population in rural areas and this starts to be a new source of greenhouse gas emissions in the countryside (Andadari, 2014;Thoday, 2018).…”

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