Abstract: A sewage treatment process is especially applicable to sewage that has been supplied with methanol to undergo anoxic denitrification. During anoxic denitrification bacteria use the methanol for food while reducing nitrates and nitrites to nitrogen gas and other products. From such denitrification step the sewage is subjected to stabilization by aeration for a time, e.g. 50 minutes, during which some contained protozoans, e.g. ciliates and rotifers, multiply. From the stabilization by aeration step the material is subjected to a mildly aerated, physical conditioning step and then clarification step. Resulting sludge is recycled to the denitrification step and separated, relatively clear effluent is removed from the process.