Evaluation of Biogas Sanitation Systems in Nepalese Prisons

In 2007, with the help of the International Committee of the Red Cross (ICRC), biogas sanitation systems were installed in three Nepalese District Jails to improve the poor sanitary conditions, reduce the health risks of the detainees, and provide a smoke-free source of cooking fuel. After one year of operation the functionality of these new systems was assessed and their impact and acceptance evaluated. The study was conducted between April and June 2009. Based on findings of a first assessment, repairs and user trainings were conducted. Further monitoring results were obtained during a third visit, when the facilities were considered to be running under optimal conditions. All five fixed-dome digesters (sizes of 10m3, 20m3 and 35m3) revealed gastight domes and showed high process stability with no accumulation of inhibitory substances. Average gas production from human waste exclusively are 28NL/person/day, and with addition of kitchen waste feedstock 62NL/person/day. Methane fraction varied between 57 and 78 Vol-%, depending on the feedstock. Hydraulic retention time was between 13 and 32 days which was far below the planned 70 days. This was due to the use of 3L of water per flush rather than the 1L planned. Pathogen analyses of effluent in the storage pits revealed E. Coli concentration to be acceptable for restricted irrigation (<10∩5 CFU/100ml). The vast majority (98%) of detainees favors the digesters and reports a general improvement of living conditions. Given the use of biogas for cooking, 59% of the interviewed inmates appreciated less smoke in the kitchen (and thus less respiratory health problems) and 49% mentioned the improved sanitary and hygienic conditions. Up to 41% of the money previously spent for conventional cooking fuel could be saved thanks to the use of biogas. Suggested improvements include a better design and slope of the inlet pipes, a buffer wall to increase the retention time, and an improved maintenance strategy.