A novel fed-batch digestion system for biomethanation of plant biomasses

Plant biomasses, which in the absence of adequate pretreatment pose serious operational problems in biogas production using conventional domestic flow-through digesters, can be successfully digested in a novel fedbatch digestion system that produces a steady rate of biogas. Basically, the system is a batch digestion operated with a regular input of a calculated amount of feed based on first order decay kinetics in order to maintain a regular biogas production rate. For nearly three years the system was tested in a laboratory-scale fed-batch digester (10 l) using dried water hyacinth as feed providing the desired biogas production rate. A field-scale domestic digester of masonry construction with a working volume of 10 m 3 was designed and tested for about 9 months by feeding a mixture of dried water hyacinth or banana stem along with sugarcane press mud, yielding an average biogas production of 90–100% of the expected rate calculated on the basis of the feed rate.