Comparative toxicity assessment using plant and luminescent bacterial assays after anaerobic treatments of dyeing wastewater in a recirculating fixed bed bioreactor

The textile industry, at various stages of fabric dyeing, generates huge volumes of wastewaters which eventually overload the aquatic bodies with wide range of dyes as persistent pollutants. In the present study, a recirculating fixed-bed bioreactor (RFBB) was operated in anaerobic and, anaerobic-aerobic environments to treat the simulated textile wastewater containing Congo red dye. The performance of the RFBB was evaluated in terms of color, COD and TOC removal at varied organic loading rates in the range of 1.37-2.23 kg COD/m(3).d (equivalent to 200-800 ppm inlet dye concentrations). Although the anaerobic treatment was found to remove the color efficiently, the COD and TOC were not removed completely even after its integration with an aerobic step; hence the toxicity of the finally treated dyeing water remained a concern. The main objective of this study was to determine and compare the acute and chronic toxicities of treated dyeing water using phytotoxicity and bacterial toxicity (based on luminescent P. luminescens). While Vigna radiata seeds exhibited only 23.33% germination in the polluted water, the germination increased to similar to 87% and 90% in the anaerobically and anaerobically-aerobically treated dyeing water respectively. On the contrary, the acute bioluminescence inhibitions for anaerobically and anaerobically-aerobically treated dyeing water were found to be 40.11% and 4.51% respectively. It was observed that the treated-water samples could be well-distinguished, in terms of their toxicity levels, using bioluminescence assays even when the same samples were non-differentiable in the phytotoxicity assays.