Pollution reduction and biodegradability index improvement of tannery effluents

Al2 (SO4)3, 18H2O, FeCl3 and Ca (OH)2 were used for the treatment of tannery wastewaters. The influences of pH and coagulant dosages were studied. Conditions were optimised according to the pollutant removal efficiencies, the volume of decanted sludge and the biodegradability index improvement. The results indicate that 6771% of total COD, 76-92% of color and 79-97% of Cr can be removed using the optimum coagulant dosages at the optimum pH range. Al2 (SO4)3, 18H2O and Ca (OH)2 produced better results than FeCl3 in terms of COD, color and Cr removal as well as in terms of biodegradability improvement. Moreover, Al2 (SO4)3, 18H2O and FeCl3 produced the least amount of sludges for a given amounts of COD, color and Cr removed in comparison with Ca (OH)2. Al2 (SO4)3, 18H2O seems to be suitable for yielding high pollutant removals and corresponding low volumes of decanted sludges in addition to improving wastewaters biodegradability index.