Toxicity potential of disinfection agent in tannery wastewater

Wastewater from a tannery was investigated using chemical-specific analyses and assessment of the acute toxicity of the whole effluent over a 2-year period. The wastewater samples were overloaded with organic and inorganic compounds, and measured concentrations of the chemical parameters as well as dilution factors estimating acute toxicity, frequently exceeded the permissible limits for the discharge of wastewater from a tannery into the receiving stream. In the later part of the monitoring programme, the toxicity of the samples was significantly increased in comparison to the previous samples. The agent for hide disinfection was assumed to be the reason for the increased toxicity of the wastewater samples, and the extremely high acute and chronic toxicity of the agent to bacteria, algae, daphnids, and fish confirmed this suspicion. The most sensitive species was Daphnia magna; the 48 h EC50 was 0.70×10−5 v/v% and the 21 d IC25 was 0.40×10−6 v/v% of the agent. After withdrawal of this highly toxic agent for hide disinfection from the technological process in the tannery, the toxicity of the wastewater declined to the previous level.