AbstractA synthetic waste (with glucose as carbon source) devoid of a source of nitrogen was purified in a laboratory scale pilot plant by a new modification of the activated sludge process. The process makes use of a separate carbon assimilation (oxidative assimilation) phase and an endogenous phase in which ammonia is added to a portion of the settled sludge and non‐nitrogenous products stored in the cells in the assimilation phase are converted to protein. It was found that sludge so treated, when recycled to the assimilation tank, could carry out continuous oxidative assimilation of the waste. Various COD:N ratios were studied. At the highest, 70:1, 90% purificaton efficiency was achieve