TOXICITY SCREENING, ASSESSMENT, AND REDUCTION IN AN INDUSTRIAL WASTE-WATER TREATMENT-PLANT

The toxicity reduction capacity of a central wastewater treatment plan t (CWTP) receiving 21 000 metric ton/d of industrial wastewater was th oroughly investigated using a whole-effluent approach with a Microtox( TM) Toxicity Analyzer System. It was found that the highly toxic waste water introduced into the CWTP was almost completely detoxified during secondary treatment with a recycled activated-sludge system. The remo val mechanism was shown to be a combination of adsorption, volatilizat ion, and biodegradation, the first two being more clear than the other . Fractionation of toxic streams within the treatment plant provided v aluable information about the general characteristics of the toxicity- causing agents in the wastewater, namely that they were primarily comp osed of filterable and dissolved solids, volatile organics, and nitrog enous compounds. A toxicity reduction evaluation survey within the pla nt revealed that the observed Microtox(TM) toxicity could be readily r emoved by treatment with powdered activated carbon (PAC) and mechanica l aeration at properly selected operating conditions. The correlation between toxicity removal and the applied PAC dose was found to be expo nential and asymptotic to the ultimate effective toxicant concentratio n of the effluent. Reductions in chemical oxygen demand and dissolved organic carbon during PAC treatment were also related to the applied P AC dose and the initial concentrations of the parameter. Removal of vo latile components of-toxicity by aeration was correlated with detentio n time by a power function.