REMOVAL OF CHLOROPHENOLS IN A MUNICIPAL SEWAGE-TREATMENT PLANT USING ACTIVATED-SLUDGE

The study was carried out in southern Finland in a municipal sewage treatment plant using activated sludge and dimensioned for a population equivalent of 2600. The study period was 407 days. Polluted groundwater led to the plant caused a chlorophenol (CP) concentration in the influent of 4-120-mu-g/l. CP removal averaged 71%. The proportion of the fed CP stored in the activated sludge was 0.2% and the dewatered sludge contained 1.8%, while 1% of the CP vaporized. Therefore, 68% of the CP led to the process was degraded. Percent removal of BOD, COD and phosphorus stayed high in spite of the CP feeding. However, occurrence of nitrification decreased the pH value in the aeration basin and the percent CP removal. Satisfactory CP removal was achieved when the solids retention time (SRT) exceeded 10 days. The concentrations of chloroanisoles, -guaiacols and -catechols in the influent, effluent and sludges were below detectable limits.