Degradation of digestion residues by lignolytic fungi

Abstract

In different European countries new legislative regulations and laws demand the reduction of the amount of wastes. In nature, the reduction steps of organic compounds in waste material are managed by symbiotic organisms, where a combination of aerobic and anaerobic degradation sequences leads to a near mineralization of organic material. Modeled on this principle, the process presented here combines a two-stage digestion with a following aerobic mineralization step. To gain a maximum amount of methane which is a regenerative energy carrier, the process reducing organic waste—in this case kitchen refuse— was begun by a run through a digestion cascade. The residues from the anaerobic step, containing mainly lignocellulosic substances that are recalcitrant to anaerobic degradation, were concentrated and then treated aerobically by white-rot and soft-rot fungi. In this article, it is demonstrated that many fungi species can use digestion residues as a substrate. The soft-rot fungus Chaetomium cellulolyticum could aerobically degrade the digestion residues, measured as volatile solid reduction of 39%. Within the process, lignin was reduced by almost 45%. Exposed again to the digestion, these residues of the aerobic treatment were degraded anaerobically with a rate of 42%. Therefore, a three-stage process combining anaerobic, aerobic and anaerobic degradation leads to organic matter reduction of more than 96% of the original amount. It can be concluded at least that organic waste material can almost completely be mineralized by biotechnological treatment.