The use of polyurethane foam for microbial retention in methanogenic fermentation of propionate

Summary The use of polyurethane foam (PUF) as a microbial support carrier was evaluated with a mesophilic propionate-acclimatized sludge. The acclimatized sludge could be immobilized rapidly and stably in PUF of smaller pore size under shaking conditions. The sludge retained in PUF could maintain a high propionate metabolic activity for a long period. High conversion rates of propionate to methane of 23–65 g chemical oxygen demand (COD)·1^–1 · day^–1 could be achieved in reactors packed with PUF-retained sludge. A dense sludge of 0.08–0.25 g mixed-liquor volatile suspended solids (MLVSS)·cm^–3 was retained in PUF. Microscopic analysis suggested that filamentous microorganisms, e.g., Methanothrix spp. could play an important role in the efficient retention of acclimatized sludge in PUF. Offprint requests to: Shiro Nagai