Treatment of waste water of slaughter-house with activated sludge system was investigated and the following results were obtained. It was found necessary to average the amount of filth in waste water in the storage tank bofore the digestion in the aeration tank. Preaeration of waste water by mechanical stirring before treatment with activated sludge was not so effective. In the experiment of aeration tank and test plant, the digestion proceeded rapidly after three hours'aeration with activated sludge. When the first aeration could not give satisfactory effect, subsequent second aeration was performed for further three hours and afforded good result.
