Production of methane gas, e.g. from brewery waste streams, comprises two-step process which has improved conversion of organic materials and improved bacterial growth rates
The conversion of organic materials to methane comprises two-step process. The biological conversion of organic materials to methane gas. comprises a two-step process comprising, in the first step, hydrolysis and acidification of organic materials by facultatively anaerobic bacteria. In this step, complex organic materials are degraded to fatty acids, alcohols, carbon dioxide, hydrogen, ammonia and nitrate. The second step is carried out in an anaerobic reactor and uses acetogenic bacteria and methane bacteria. These bacteria further degrade the hydrolysis products to acetic acid, methane and carbon dioxide. The improvements to this process are: (a) retention of non-reacted substrates by a membrane filter; (b) retention of the biomass by a continuously operating filter; (c) splitting up the degradation of organic substances into several biological stages; (d) control of the first step by gassing the mixture; (e) removal of solids which can not be degraded, prior to entry into the methane reactor; (f) control of the second step by regulation of the throughflow of material; and (g) separation and recycling of dissolved organic substances, after leaving the methane reactor, by membrane filtration.
