Biosorption of chromium from tannery effluent using carbon-activated algae granules of Chlorella vulgaris and Scenedesmus obliquus

The discharge of chromium into the environment has become a problem of great concern all over the world including Pakistan for a few decades. The present research was conducted to study the bioremediation effect of carbon-activated granules (CAAGs) of two algal strains as a novel biosorbent for chromium from tannery effluent in addition to improvement of different water quality indicators. Effect of sorbent dose (5, 7 and 9 g L-1) and contact time (0-140 h with interval of 20 h) on chromium removal was evaluated. Maximum chromium removal (9.33 mg L-1 and 7.60 mg L-1) from raw tannery wastewater (WW) was reached after 120 h using 9 gL(-1) of Chlorella vulgaris and Scenedesmus obliquus biomass, respectively. Rate of Cr removal was found directly proportional with dose of granulated algae and incubation period. Carbon-activated granules of Chlorella vulgaris as a biosorbent (9 g L-1) exhibited 19.47% more chromium removal in 10 times diluted WW compared to raw WW. The CAAG of both isolates reduced COD (38.08% and 34.72%), BOD (37.04% and 13.60%) and TSS (34.01% and 36.30%) for Chlorella vulgaris and Scenedesmus obliquus, respectively. Meanwhile, both CAAG types decreased TSS by around 85% while resulting in a slide increase in pH compared to initials. The CAAG of both isolates proved to be promising candidates for environmental bioremediation by reducing chemical and biological oxygen demand and total suspended solids of tannery WW by developing cost-effective and ecofriendly process in the prevalence of sunlight.