DETERMINING TOXICITY TRENDS IN THE OZONATION OF SYNTHETIC DYE WASTEWATERS USING THE NEMATODE CAENORHABDITIS-ELEGANS

The nematode Caenorhabditis elegans was used in 72-h toxicity tests to evaluate the influence of ozonation on the toxicity of three syntheti c azo dye wastewaters (two reactive dyes and one acid-based dye). The two reactive dye wastewaters contained high concentrations of NaCl (89 -112 g/L) in addition to potentially toxic dye components. To determin e the contribution of NaCl to toxicity, simulated dye wastewater sampl es with and without NaCl were tested. Samples were collected at variou s times during ozonation (t = 0, 8, 32, 64 min); nematodes were expose d to the samples for 72 h. The influence of ozonation on toxicity vari ed between dye wastewater types. For the acid-based dye wastewater, to xicity increased as duration of ozonation increased. For the reactive dyes without NaCl, toxicity did not appear to be influenced by ozonati on. For the reactive dyes with NaCl, mortality was 100% with or withou t ozonation. Range-finding experiments with NaCl in water and NaCl in dye wastewaters suggested an additive toxic interaction between NaCl a nd the dyes in wastewater to the nematodes. The duration of ozonation for acid-based dyes and the relatively high NaCl concentrations for th e reactive dyes appear to influence effluent toxicity in the ozonated dye wastewaters.