Purification capacity of a low-loaded sequencing batch activated sludge process pilot-plant, operated in a way to simulate the flow profile in small point sources, was studied. Oxidation capacity of organic matter and ammonium nitrogen, capacity to denitrify the oxidised nitrogen by alternating aerobic and anoxic operation, suspended solids removal and sludge settling characteristics were determined. Best results were obtained in a 24 h total cycle with three anoxic hours in addition to a three hours settling period. BOD7 removal was 94 %, residual concentration being less than 20 mg/l. Suspended solids were removed with equal efficiency. Hydrolysis of solid organic waste in a low loaded plant was efficient, and no excess sludge had to be removed. Almost complete nitrification could be maintained at 13°C, and 60 % of the oxidised nitrogen was denitrified without supplementary carbon source.

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