Joint toxic actions of organic flocculating polymers: impact on whole effluent toxicity testing-part 3

摘要

Most states and/or U.S. Environmental Protection Agency (EPA) regions have adopted narrative water quality criteria requiring various forms of Whole Effluent Toxicity (WET) testing as a component of the National Pollutant Discharge Elimination System (NPDES) discharge criteria. Toxicity control, which is often regulated through costly and time-consuming Toxicity Reduction Evaluation (TRE) programs, is one of the most difficult problems that must be addressed by NPDES permittees. WET may be the result of a myriad of different sources, including unidentified wastewater contaminants discharged to municipal wastewater treatment plants or the result of manufacturing processes used by direct industrial dischargers. Toxocity, however, may also be the result of the use of chemical additives, such as coagulant aids, that are either refractory materials not degraded in the treatment process or toxic degradation products of these additives. In previous reports by Fort et al. and Fort and Stover, toxicological comparisons were made between cationic polymers and commonly used inorganic coagulant aids, including ferric chloride (FeCl_3) and alum (Al_2(SO_4)_3) based on results obtained by other investigators. Differences in toxicity due to the type of treatment application were also evaluated. Results from these studies clearly demonstrated that the series of cationic polymers tested were dramatically more toxic to Ceriodaphnia dubia on an equimolar basis than either FeCl_3 or Al_2(SO_4)_3. The potential for toxicity problems with both types of flocculant/coagulant aids, particularly the cationic polymers, when used in final effluent polishing was found to more problematic than when used in secondary clarification. Because polymers and inorganic coagulant aids are commonly used in conjunction with one another for wasteater treatmet, an assessment of potential interactions between the two types of additives was warranted. Thus, joint-compound interaction studies with both the polymer and FeCl_3 or Al_2 (SO_4)_3 were conducted to determine the effect of co-treatment on WET. Results from these studies clearly demonstrated that the toxicity of co-treatment of WET. Rexults from these studies clearly demonstrated that the toxicity of these additives during combined treatment was musch more dramatic than for each compound undividually and that individual toxic assessment would not account for the total magnitude of toxicity induced during combined treatment.