Reduction in the toxicity of boiler blowdown effluent by addition of calcium or humic acid

Abstract

AbstractBoiler blowdown effluent from both nuclear and thermal electric generating stations was frequently toxic to both rainbow trout and Daphnia magna in monitoring tests. The toxicity could be caused either by the low ionic content of the effluent, or through interactions of the low ionic content and elevated metal concentrations. Followup studies were conducted to characterize the toxicity of the effluent and develop methods to reduce its toxicity. Addition of calcium, either by adding calcium chloride (CaCl2) or recirculating the effluent over a limestone filter for ∼ 12 h, largely eliminated the toxicity of boiler blowdown effluent to trout; however, the treated effluent remained toxic to D. magna. Adding humic acid (∼ 20 mg L−1 as dissolved organic carbon) significantly reduced the toxicity of boiler blowdown effluent to both D. magna and rainbow trout. The toxicity of boiler blowdown effluent appears to result from the interactions of its low ionic content and elevated metal concentrations, but ad...