Toxicity assessment of raw and ozonated benzothiazole synthetic wastewater

Abstract

Ozonation experiments were performed with model wastewater containing 100 g m−3 benzothiazole concentration. Ozonation was carried out in jet-loop reactor with external recirculation of the reaction mixture. Benzothiazole removal efficiency was 87%. Benzothiazole residual concentration and concentration of its degradation products after ozonation were expressed as COD and TOC values. In terms of biodegradability, respirometric measurements with activated sludge microorganisms were performed on samples of ozonated model wastewater. Increase in oxygen uptake rate compared to the endogenous phase was recorded in all measurements. Experimental data were fitted by Monod and Haldane equations. The best match of experimental and calculated data was achieved by Haldane kinetic model due to substrate and degradation products inhibition. The results of respirometric measurements indicate that ozonation improves the biodegradability of model wastewater and increases the oxygen uptake rate of activated sludge. However, substrate inhibition was observed with higher COD content. Toxicity test was performed on three organisms (Sinapis alba, Daphnia magna and Vibrio fischeri), and has shown that each studied organism responds differently on ozonated wastewater. Inhibition of S. alba decreases with ozonation time. Inhibition of V. fischeri reached maximum at 10 min of ozonation and inhibition of D. magna has minimum at the same ozonation time.