Biogas production from black water, kitchen refuse and farm waste : lab assessment and practical application at MCF Yatta, Kenya

Abstract

The possibilities for biogas production from black water, kitchen waste and farm waste are examined in this thesis. Theory on the subject of anaerobic digestion and biogas production is presented. Mulli’s Children Family (MCF) farm at Yatta, Kenya is used as a real life example. In addition to this, a biogas lab experiment is included.

The available resources for biogas production at MCF Yatta include animal waste, vegetable waste and human waste. The estimated biogas potential of the available resources is 7877 m3 /year or 21.58 m3 /day, assuming 60% methane content. The maximum energy equivalent of the estimated biogas potential is 184.3 GJ. A system for biogas production using a fixed dome bioreactor is proposed. Fecal sludge from pit latrines and vegetable waste from the kitchen is proposed as the main feedstock. Biogas utilization in cooking and lighting is recommended and reuse of the slurry and the effluent in the agriculture. Post treatment is recommended in drying beds for the slurry and a polishing bed with reeds for the effluent.

The samples used in the biogas lab experiment were black water (7.95 gr TS/l and 6.47 gr VS/l), kitchen waste (initially 168.52 gr TS/l and 150.33gr VS/l, later 49.97 gr TS/l and 44.39 gr VS/l after dilution) and a mixture of both (52.86 gr TS/l and 45.61 gr/VS/l). The incubation period was 30 days. The presented results represent the biogas production of the mixed sample and inoculum substrates. The reason is that the inoculum used was not fully degraded and consequently a substantial fraction of the produced biogas is attributed to it. The black water sample produced 371.64 ml biogas/gr VS added with 79.46% methane content. The kitchen waste and the mixture samples were inhibited because of high organic loading and pH drop.