Energy recovery from dairy waste-waters: impacts of biofilm support systems on anaerobic CST reactors

Anaerobic digestion is one of the major steps involved in the treatment of dairy industry waste-waters and many CSTRs (continuously-stirred tank reactors) are functioning for this purpose all over the world. In this paper, the authors describe their attempts to upgrade a CSTR's performance by incorporating a biofilm support system (BSS) within the existing reactor. The focus of the work was to find an inexpensive and easy to install BSS which could significantly enhance the rates of waste treatment and methane recovery. Rolls of nylon mesh (with 1 mm openings), of 5 cm height and 2 cm dia, when incorporated in the CSTR at the biofilm surface (with a digester volume ratio 0.3 cm²/cm³), enabled the CSTR to perform better with > 20% improvement in the methane yield. Such simple BSS devices can significantly improve the performance of a CSTR anaerobic digester treating dairy wastes. The enhancement is due to the development of active biofilms which not only enhance the microorganism-waste contact but also reduce the microbial washout. Such devices are inexpensive and very easy to incorporate — the gains are thus achieved with very little cost and effort.