Survey on LPS endotoxin in rejected water from sludge treatment facility

In this study, we applied the Limulus amebocyte lysate (LAL) test to rejected water samples from a sludge treatment facility in Sapporo, Japan. The endpoint LAL test was performed using a commercial kit and involved incubating a mixture of water samples and LAL reagent at 37 °C. We have observed that all of the rejected water showed endotoxic activity. Overflow from thickener and dewatering are the main contributor to this high concentration in the influent of treatment plants receiving return flow from sludge treatment facilities. The LAL test was also applied to sample batch tests, where sewage was mixed with rejected waters and aerated for 12 hours. It was found that the low biodegradability of endotoxic material in the mixture led to higher endotoxicity in comparison to the sewage and sludge aerated without rejected water. Several batch tests were also operated using sewage, sludge and different types of rejected water (overflow from thickener, dewatering, dehumidification, and desulfurization). The findings indicated that samples from reactors using water from thickener and dewatering had significant concentrations and these contributed to the high values of the effluent.