Squeezing more energy from feedstocks: enzyme addition and enzymatic activity monitoring
Williams, H.G., Kumi, P., Devlin, D., Williams, J., Dinsdale, R., Esteves, S. and Guwy, A., University of Glamorgan, UK
(free)
Abstract:
The organic fraction of municipal solid waste (OFMSW) can be treated by percolation with hot water (35Oc) to produce a chemical oxygen demand (COD) rich liquor prior to anaerobic digestion. In this study we investigate the effect of addition of exogenous enzymes on the percolation process. Addition of commercial cellulase preparations resulted in greater solublisation of organic matter and increased volume of percolate liquor. The yield of COD released increased with enzyme dose. Other commercial enzyme preparations such as proteases were also seen to enhance release of soluble organic material. The effect of enzymatic activity on the subsequent anaerobic digestion processes was also monitored. We conclude that enzymatic treatment has significant potential to improve industrial percolation and anaerobic digestion processes.
Key words:
Municipal Waste, Enzymes, COD, percolation, anaerobic digestion
Introduction:
Municipal wastes contain a variety of valuable materials which rather than being disposed of to landfill could be recovered and used. For example, the organic fraction of municipal solid waste (OFMSW) is an excellent source of biodegradable organic material that could be used as a feedstock for the production of renewable energy through anaerobic digestion. The physically heterogeneous composition of municipal wastes however, can make them difficult to handle in a traditional AD process. Commercial processes such as the UR-3R process (Urban Resource – Reduce, Recover, Recycle) have been developed that use percolation with warm water to extract biodegradable material from the OFMSW in a liquid form (figure 1). Various pre-treatment’s such as thermochemical, precomposting and alkali treatment have also been suggested to enhance the hydrolysis and solublisation of OFMSW prior to methane production (Fdez-Gallego et al., 2010; Torres & Llorens, 2008). The objective of this study was to determine whether pretreatment with enzymes would enhance the solublisation of organic material during percolation of OFMSW and hence improve the yield of biogas produced. Enzymatic hydrolysis has been shown to be an effective pre-treatment to solubilise complex organic matter in a variety of other applications. For example, pretreatment with cellulase enzymes has been shown to increase the yield of hydrogen biogas from sewage (Massanet-Nicolau et al., 2008).
