The ANAMET and BIOMET systems for biomethanation of organic materials

Abstract

The ANAMET system was originally developed to handle wastes from the Swedish sugar industry. It is a combined anaerobic-aerobic waste water treatment process (ANAMET — ANaerobic-Aerobic-METhane) where the waste water is firstly processed in an anaerobic contact reactor and secondly in an activated sludge plant. In the anaerobic stage, 60–95 percent of incoming biodegradable material is converted to biogas which is recovered as a fuel. In the subsequent aerobic stage, most of the remaining biodegradable material is removed resulting in overall BOD5 reductions of 95–99 percent. The excess biomass produced in the aerobic stage is digested in the anaerobic stage further increasing yield of biogas. The ANAMET process has found wide-spread application in the food industry. In treatment of food industry waste waters, it has been possible to achieve 98–99.9 percent BOD5 reduction in the ANAMET system. Gas recoveries amount to 0.18–0.33 m3 methane per kg added COD.Recently, the ANAMET process was introduced in the pulp and paper industry. The treatment of these waste waters often is somewhat problematic due to the presence of toxic or inhibitory materials and sulphate. This results in a somewhat lower anaerobic efficiency and also in lowered gas yields. In the ANAMET system, anaerobic BOD5 reductions of 60–85 percent have been demonstrated. Totally, 90–95 percent BOD5 reduction can relatively easily be obtained.The BIOMET system has been developed to treat solid organic wastes and energy crops. In this process, a thermophilic methanogenic stage is used up-stream the ANAMET process. Promising results were demonstrated in a 50 m3 pilot plant treating beet pulp.The paper reviews AC Biotechnics' pilot and full scale experience in treating waste waters and solid wastes by methane fermentation. Special attention is paid to the influence of different substrates in the biomethanation process, and on the possible biogas yield.