Improved Design of Low-Cost Anaerobic Digester

Presented in CHEMECA 2010 (Adelaide, 26-29 September 2010)


Wiratni1 and Largus T. Angenent2

1Chemical Engineering Department

Gadjah Mada University

Jl. Grafika 2 Kampus UGM Yogyakarta 55281 Indonesia

2Biological and Environmental Engineering Department

Cornell University

Riley-Robb Hall, Ithaca, NY 14853, USA



A low-cost anaerobic digester was developed with a 0.3-m diameter PVC pipe and was subsequently installed and tested in ~ 30 households in Indonesian rural areas. Diluted cow manure was fed to one end of the digester while effluent was collected from the other end for land application. For each digester, enough biogas was accumulated in a gasbag to cook for ~ 1 h/day. However, some of these plug-flow digesters clogged after a one-year operating period. Here, we have optimized the digester configuration to guarantee maximum methane yields while preventing clogging. We performed controlled experiments with four laboratory-scale digesters that were operated with a 21-day hydraulic retention time. All four digesters were fed with dairy manure (40 g/L volatile solids [VS]) and operated at 27±1°C. Two control reactors were operated as conventional plug-flow digesters, while either internal mixing or effluent recycle was tested for two treatment digesters. The performance of each digester was compared based on measured parameters, such as VS removal efficiencies and methane yields, for an operating period exceeding 200 days. During most of the operating period, solids accumulation was more pronounced in the control reactors compared to the treatment reactors. The internal mixing reduced solids accumulation compared to the control reactors, however, the methane yields were also lower for most of the operating period due to a shorter solids retention time. Recycling effluent produced more methane, but we observed more solids accumulation than the digester with internal mixing. At the end of the operating period of ~ 220 days, steady-state conditions were approached with methane yields for all reactors that were similar (~ 0.15 L CH4/VSin). Therefore, for optimized long-term performance, a simple internal mixing device prevented solids accumulation with similar steady-state methane yields.


Keywords: Anaerobic digestion; Biogas; Low-cost digester; Renewable energy; Cow manure

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