Influence of the size reduction of organic waste on their anaerobic digestion

The rate-limiting step in anaerobic digestion of organic solid waste is gen erally their hydrolysis. A size reduction of the particles and the resultin g enlargement of the available specific surface can support the biological process in two ways. Firstly, in case of substrates with a high content of fibres and a low degradability, their comminution yields to an improved dig ester gas production. This leads to a decreased amount of residues to be di sposed of and to an increased quantity of useful digester gas. The second e ffect of the particle size reduction observed with all the substrates but p articularly with those of low degradability is a reduction of the technical digestion time. Furthermore, the particle size of organic waste has an inf luence on the dewaterability after codigestion with sewage sludge. The pres ence of organic waste residues improves the dewaterability measured as spec ific resistance to filtration but this positive effect is attenuated ii the particle size of the solids is reduced.