Assessment of toxicity of raw textile wastewater and after its reuse

Abstract

Five consecutive dyeings were made using the treated effluent in every step. All photochemical treatments obtained decolourization efficiency (DE) above 90%, allowing the effluent to be reused in dyeings with fluorescent brighteners, from the first until the last treated effluent. In this proposed process, the rate of total organic carbon (TOC) presented after five consecutive dyeings achieved with treated effluent was 34 mg L-1 compared with 435 mg L-1 of the final effluent that was obtained after five conventional processes. The salinity of the final effluent obtained by this proposed process was 2.34 g L-1 of NaCl compared with 25.00 g L-1 presented in the effluent obtained by the conventional process. The values of the colour fastness to water showed no significant differences between the colours that were made by two processes. The average water consumption for a one-kilogram cotton dyeing after fifteen dyeings achieved by this proposed process was approximately 24 litres compared with the 70 litres that were consumed by the conventional process. However, the final treated effluent presented values of toxicity < 6.25% (EC50, with 95% confidence interval) against 10.25% of the raw effluent. It means that in the sample concentration of the treated effluent presented 100% of Daphina similis mortality, indicating that this sample was more toxic than the raw effluent.