Toxicity Screening, Assessment, And ReductionOf Tannery Wastewater

Abstract

Many industrial plants are facing a requirement to conduct toxicity reduction evaluations (TREs). The TRE is an evaluation intended to determine those actions necessary to achieve compliance with water quality based effluent limits (reducing an effluent toxicity or chemical concentrations to acceptable levels). Wastewater from leather production is known to be heavily loaded with inorganic and organic components. We were faced with wastewater from the largest tannery in Slovenia, which has a system of physico chemical pretreatment (coagulation and flocculation with Al-sulphate and anionic polyelectrolyte). The wastewater is highly polluted with components, which are specific to the leather industry. Prior to initiation the TRE program chemical and toxicological analyses were conducted with tannery effluents ten times during the year. An acute toxicity test of whole effluent using an aquatic organism Daphnia magna was performed. We identified key toxic components in the pre-treated discharge with fractionation of samples through chemical and physical means (filtration, air stripping, adsorption on activated carbon and zeolite treatment). The goal of each fractionation step was to reduce toxicity due to specific group of chemicals and compare the results to the toxicity present in the unaltered sample. The inorganic parameters (ammonia and chromium) seem to play a minor role for toxic effects for marine bacteria Vibrio fischeri. Vibrio fischeri is tolerant against high salt contents and poorly susceptible to metals. Insoluble and suspended material is more toxic for Daphnia magna. Toxic effect of ammonia strongly depends on pH value due to concentrations of un-ionized form. Toxicity of ammonia does not have an important effect on toxicity of tannery wastewater when organic load is still present. Due to adsorption of organic load to activated carbon toxicity for Daphnia magna and Vibrio fischeri decreased. For more complex determination of toxicity in wastewater, containing many unknown compounds, finer fractionation steps are required for toxicity identification purposes.