Self-sustainable Chlorella pyrenoidosa strain NCIM 2738 based photobioreactor for removal of Direct Red-31 dye along with other industrial pollutants to improve the water-quality.

The genotoxic and carcinogenic effects of diazo dyes from industrial effluents pose a serious environmental threat by contaminating aquatic ecosystem and consequently impact human health. The potential of a diazo dye resistant, self-sustainable photosynthetic green alga Chlorella pyrenoidosa NCIM 2738 provides a viable green technology for an efficient biodegradation of diazo dye Direct Red-31 (DR-31) and overall improvement of water quality. Herein, we for the first time report the degradation of DR-31 using C. pyrenoidosa. Batch experiments were performed to optimize the effect of initial pH, contact time and toxicity-range of DR-31 in order to achieve the optimal conditions for maximum decolourization in continuous cyclic photobioreactor. In batch culture, C. pyrenoidosa exhibited 96% decolourization with 40mgL(-1) dye at pH3. The equilibrium was attained within 30min and the maximum uptake of 30.53mgg(-1) algal biomass was observed during this period. This was found to be fitted well with Langmuir and Freundlich adsorption isotherm. The FT-IR spectra showed a change from -N=N- to N-H suggesting the possible involvement of the azoreductase enzyme. The application of C. pyrenoidosa not only degraded the DR-31 but also improved the quality of water by reducing COD (82.73%), BOD (56.44%), sulphate (54.54%), phosphate (19.88%), and TDS (84.18%) which was further enhanced in continuous cyclic bioreactor treatment. The results clearly showed that C. pyrenoidosa provides an efficient, self-sustainable green technology for decolourization of DR-31 and improved the water quality.