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CASE STUDIES IN EFFLUENT TOXICITY TREATABILITY

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Toxicity Reduction Evaluation (TRE) studies often incorporate bench- or pilot-scale assessments of full-scale Whole Effluent Toxicity (WET) control methods. However, traditional Toxicity Identification Evaluation (TIE) studies, typically preceding TREs, do not incorporate bench-scale evaluations of full-scale treatments. Such bench-scale data can be useful in the design of pilot-scale studies or provide data to identify key sources of WET. This paper briefly overviews conventional TIE approaches as compared to treatability-based methods, and summarizes the results of three treatability-based TIE/TRE studies with full-scale WET control measures in the steel products, latex products, and organic chemical sectors. Conventional chemical toxicants (salts, nitrite), and “test artifacts” (fish pathogens) were identified as causing WET or interfering with proper WET test data application. Key aspects of each of the case studies are summarized below.

In the steel production facility, an oily wastewater was found to induce acute and chronic WET to the fathead minnow. “Symptoms” included a general absence of WET to Ceriodaphnia, “fungus-like” growths on fish gills, a clear pattern of irregular dose/response, and high intra-replicate variability that indicated fish pathogens. The presence of pathogens was also confirmed by a veterinary pathologist, re-infection experiments, and successful treatment techniques at the TIE stage (i.e., ultrafiltration). Although ultraviolet light treatments, chlorine, and various biocides were of limited success in pathogen control, GAC, activated sludge, and attached growth biological treatment were successful bench-scale treatments. Through source testing, key areas were identified for intense housekeeping activities, and the problem has been controlled through improved housekeeping and increased frequency of clarifier cleaning and floc removal.

The latex production facility exhibited a history of acute and chronic WET to both Ceriodaphnia dubia and the fathead minnow. Conventional EPA “fractionation” methodologies (C18, sodium thiosulfate, air stripping, and pH adjustment) and unconventional TIE methods (0.45μm filtration, peroxide oxidation, zeolite, ferric chloride, GAC, and combinations of treatments) were used to identify the mixture of nitrite and ammonia in the effluent as the causative effluent toxicant. Implementation of upgrades in solids pretreatment and the biological nitrification system (in the form of an anoxic basin and additional nitrification) has resulted in a dramatic and consistent decrease in WET, and compliance with permit limits.

A high ionic strength wastewater from an organic chemicals plant exhibited intermittent WET to Ceriodaphnia. Although WET levels were not well above permit limits, their frequency triggered a TIE. A “weight of evidence” approach to toxicant identification was used. This included species sensitivity patterning, treatment evaluations that supported salts as the causative toxicant (e.g., paired cation and anion exchange treatment), literature searches and development of “toxic ratios” for component ions, correlation assessments of WET and chemical parameters, chemical analyses, mock effluent testing, and computer modeling of salt toxicity. The species sensitivity patterning approach was very useful due to the well-known sensitivity of various test organisms to salts. Mock effluents, given the additive nature of salt toxicity, were very useful to confirm the absence of non-salt toxicants and demonstrate similarity in actual and salt-only mock effluent toxicity. Calcium and chloride were identified as the causative toxicants, and the weight of evidence approach proved very useful. Source control measures were implemented to achieve WET compliance.
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Document Type: Research Article

Publication date: 2004-01-01

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