The Impact of Process Sequences on Pollutant Removal Efficiencies in Tannery Wastewater Treatment

A laboratory-scale study was conducted to determine the removal efficiencies of nine contaminants from a tannery wastewater using a number of physicochemical processes. Coagulation-flocculation using bittern as coagulant, oxidation-utilizing ozone, and adsorption using activated carbon were applied separately and in different sequences. Jar tests were utilized to conduct the experimental work. Except for arsenic, the highest removal efficiencies were recorded when coagulation/flocculation was conducted on the alkalized samples using a bittern dose of 5 mL/L. Activated carbon adsorption improved removal efficiencies of several contaminants. The coagulation/flocculation-adsorption sequence using the optimum dose of 5 mL/L of bittern resulted in high removal efficiencies for total suspended solids (TSS) (97 %+/- 1), apparent color (100 %+/- 0), turbidity (97 %+/- 1), total nitrogen (86 %+/- 1), and chromium (100 %+/- 0). On the other hand, the same sequence resulted in moderate removal efficiencies for chemical oxygen demand (COD) (72 %+/- 7) and total phosphorus (74 %+/- 5) and relatively low removals for biochemical oxygen demand (BOD) (55 %+/- 10) and arsenic (42 % +/- 14). The removal efficiencies for the different tested sequences demonstrated that each sequence did improve the removal efficiencies for most of the parameters tested and consequently, the quality of tannery effluent. However, no single optimum sequence was capable of attaining high removal efficiencies for all nine parameters.