The effect of pre-ozone oxidation on acute toxicity and inert soluble COD fractions of a textile finishing industry wastewater

Abstract The present work evaluates pre-ozonation for removal of acute toxicity, color and COD as well as reduction of inert soluble COD fractions in two wastewater samples (S1 and S2) taken from a textile finishing industry, located in Istanbul (Turkey). The wastewater samples were oxidized at original pH of 8.6–8.8 under 18.5–24 mg/L of applied ozone doses. Acute toxicity was monitored using Daphnia magna . The results showed that pre-ozonation improved the biodegradability and reduced the acute toxicity. Acute toxicity in raw wastewaters was reduced by 80–90% using 129–200 mg/L transfered ozone (TrO 3 ) concentrations. At this point, 86–96% of color, 33–39% of soluble COD and 57–64% of total COD were removed from wastewaters. Both color and COD parameters were found related to the acute toxicity of the wastewater. Pre-ozonation decreased the inert soluble COD fraction ( S I ) of raw wastewater while soluble product formation ( S P ) increased slightly (5–10 mg/L). However, residual COD (the sum of S I and S P ) remained below discharge limit.