Production of biogas from cattle waste at low temperature

Production of Bio gas from cattle waste and other biomass is now considered as one of the majorroutes to obtain gaseous fuel for sustainable development. In tropical countries like Indiathousands of rural families in villages are using 3 to 5 M3 biogas plants to suffice their dailycooking fuel need. All these plants are run on cattle waste. Since these plants are operated atambient temperatures, effect of temperature variation affects daily gas yield. The effect becomesvery prominent during winter season. In general about 50-60% reduction in daily biogas yield isobserved when ambient temperature is around l 5°C as compared to that produced at around 30-350C. A low cost and simple to operate technique to enhance biogas yield from the biogas plantduring winter season shall help to get optimum biogas yield from these plants during the winterseason. We thought of a simple technique of filtering the digested effluent slurry of biogas plantthrough a triple layer muslin cloth to obtain a filtrate, hence-forth called as clarified digestedslurry (CDS), rich in cell mass and then adding it back to the biogas plant along with the influentslurry. Experiments were carried out on 25 L capacity cattle dung biogas plant operated at 15°Cto see effect of recirculation of CDS. Addition of 25 and 40% v/v CDS in daily influent resultedin 15% and 37% increase in daily biogas yield. Recirculation of 40% v/v CDS supplementedwith Diammonium phosphate(DAP) increased the biogas yield by 75% v/v. In anotherexperiment use of clarified rumen fluid (CRF) to prepare influent slurry and added exclusivelyfor one day enhanced the daily biogas yield by 70% v/v for a period of two months. Popular dailywears in India called cotton dhoti or cotton sari can be used for the filtration of the slurry.