Influence of the dimensional characteristics of polyurethane foam on high rate anaerobic digestion of piggery manure

Summay

Completely mixed anaerobic reactors containing ca 10 % of their working volume as polyurethane (PUR) foam, can digest heterogenous slurries such as pig manure in a stable way at short hydraulic retention times of the order of 6.0 to 7.5 day. The influence of pore size and pad size of the PUR foam on the process was investigated. The PUR foam with the smallest pore size investigated (i.e. 45 pores per inch) gave the best biogas yield and biogas production rate. Pad size seemed to be of minor importance, having no effect on the performance of the digesters within the range examined (1 to 3.6 cm rib length). Apparently, diffusion of fatty acids into the PUR pads appeared not to be rate limiting under the lab scale reactor conditions examined.