Adapting biodigesters to impoverished high altitudes in the Peruvian Andes

Biodigester

Building biodigesters. Source: Ferrer, I. et al. (2008)

Biodigesters are nowadays a common feature across millions of family plots in tropical China and India. Yet, as we abandon warmer areas, and ascend to higher altitudes, they soon become a rarity. The orthodox explanation goes that low temperatures of 8-10 ºC pose an insurmountable challenge. We sustain, however, that such conventional thinking is misleading, and that the technological barriers that prevent the adoption of biodigesters in high altitudes can be overcome. Therefore, our work on biodigesters – led by Ivet Ferrer and with the participation of Enric Velo – aims to generate economically viable fuels for cooking and heating that are comparable in their performance to commercial alternatives – e.g. propane.

Safe cooking and heating pose a challenge for the communities spread over high altitudes in Jabón Mayo (Cusco Region) and Cajamarca, Peru. Both areas host populations living above 3,000 metres. Jabón Mayo, for instance, stretches over 3,800 to 4,500 metres above sea level and is home to 1,800 families strewn over eleven communities. An effect of altitude, persistent low temperatures along both the dry and the rainy season co-exist with intense solar radiation averaging 5.5 kWh/m2 per day. Under such extreme conditions, EScGD, in partnership with Instituto por una Alternativa Agraria and ITDG-Soluciones Prácticas is analyzing how to raise the efficiency of high-altitude manure-fed low-temperature gasification by means of the installation of 20 pilot biodigesters.

Our results so far are encouraging, suggesting that improved technical performance will in a not so distant future lead to further dissemination. Thus, even under very low temperatures, a 5-m3 biodigester fed with cow manure allows 3-4 hours of cooking. To achieve design temperatures between 20 and 25 ºC the biodigester is placed inside a greenhouse. Under such conditions, the biogas generated can replace half of the previous consumption of conventional fuels – commonly firewood or dried manure. Moneywise, upfront investments are recovered over an average of 2 years and 8 months if replacing commercial fuels – and also when biogas is also used to elaborate foodstuff such as cheese, marmalade or yoghourt. Costing about 40 euros each, biodigesters are affordable for significant sections of the population. Furthermore, biodigesters can be made even more affordable if fed from a domestic pit latrine and adapted to produce fertilizer – i.e. biol – for nearby fields.

Biodigester

Schematic diagram of a low-cost plastic tubular digester. Source: Ferrer, I. et al. (2011)

Auspiciously, the performance observed in the laboratory is remarkable, too. The tests that we have carried out in two pilot digesters –subsequently contrasted in two representative rural digesters – indicate optimal volumes of 2.4 to 7.5 m3, as well as a hydraulic residence time (HRT) between 60 and 90 days. Thus, our laboratory biodigesters are able to generate 0.35 m3·kgVS-1 of biogas containing 65% CH4 – still too low probably, at least when contrasted with rates of 1 m3·kgVS-1 in tropical areas.

In view of such preliminary results, and in order to produce the biogas required for cooking and lighting every day, our present efforts are addressed toward increasing production in an affordable manner. We have therefore strategically opted to investigate the design of bigger digesters that ought to keep HRTs below 60 days whilst increasing organic loading rates. In parallel, we also pursue another promising line of research to adapt conventional gas burners to better suit the specific requirements of biogas production.

Interestingly enough, our work with biogas digesters also offers relevant insights for warmer areas across Southern Europe. In such case, solutions premised upon District Cooling fed by Combined Heat, Cooling and Power (CHCP) become a sound option. Our calculations attest to the fact that even if payback periods still exceed ten years, they are substantially lower for biogas-fed CHCP systems when compared to alternatives exclusively based upon Combined Heat and Power. Biogas constitutes a reliable and economic solution not only for China, India or the Peruvian Andes, but also for our industrialized and polluting Europe.


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