Removal of toxicity and some nonconventional pollutants by a dual power multicellular lagoon system

Abstract

ABSTRACT: Aerated stabilization basins (ASBs) are a common unit process for treating pulp and paper mill wastewaters in North America but are often unable to meet current requirements. One possible solution is the conversion of the existing system to a dual power level multicellular aerated lagoon. The dual power level lagoon process is a higher rate modified ASB system allowing effluent improvement, energy optimization, and total detention time reduction. To evaluate the suitability of such a system for the treatment of unbleached kraft mill effluent mixed with a municipal wastewater, industrial scale pilot plant tests were conducted over a period of 9 months. The BOD removal kinetics and the ability of the system to reduce effluent toxicity were evaluated for several operating conditions. The dual power level multicellular lagoon process was able to produce effluent nontoxic to rainbow trout, Daphnia magna, and photoluminescent bacteria, despite a median lethal concentration of the untreated effluent in the range of 18 to 24% (96 h LC 50). This effluent also met the requirements for BOD and suspended solids. The treated effluent was analyzed for several nonconventional pollutants (including toluene, styrene, phenolic compounds, and surfactants) and some extractable organic compounds. In general, few contaminants showed concentrations above analytical detection limit levels. Those that did have positive values were generally present in concentrations less than 1 μg/L. The observed concentrations were consistent with a joint U.S. EPA and Ontario Forest Industry Association screening study of pulp and paper mill effluents. The concentrations were close to analytical detection limits.