Biotechnological processes can be established economically and ecologically advantageous for the substance recycling along with waste treatment. The center of interest hereby is the use of anaerobic or substance producing aerobic microorganisms. The best known substance recycling process of organic materials such as bio-waste or sewage sludge (as a kind of residual biomass) is the recovery of biogas as a renewable energy source.
By integrating further appropriate process steps, additional value substances such as fertilizer salts (from nitrogen and phosphate ingredients of sludge, sludge water and waste) can be recovered.