Abstract: The invention relates to a process for anaerobically degrading highly concentrated process waste waters as obtained particularly in the chemical industry, in paper mills and cellulose plants, fish-processing plants, and in the production and elimination of alcohol or the like, whereby the CSB-content may be up to 10.sup.6 mg/l or more. This process comprises a putrefactive process which is induced in at least one decomposition tank at about 34.degree. C. by circulating normal sewage sludge, whereby upon start-up of the putrefactive process, a change to chemical process waste waters is carried out without adding communal sewage sludge. Subsequently, the sludge is withdrawn from the decomposition tank, flocculated, and returned to the external circulation for circulating the putrefactive sludge in the decomposition tank.

Abstract: A process for the anaerobic digestion of sludge or for the anaerobic decomposition of organically contaminated waste waters while obtaining fermentation gas containing methane as the main component, wherein a sufficient quantity of air or oxygen is added to the digestion process together with the crude sludge or the waste water whereby a residual oxygen content of 0.01 to 3.0% by volume, preferably 0.1 to 1.5% by volume is obtained in the formed sewage gas.