Post treatment of tannery wastewater using lime/bittern coagulation and activated carbon adsorption

The use of lime, bittern and activated carbon were evaluated in the post treatment of tannery wastewater effluent, collected from an existing tannery, after being subjected to medium sized screening and micro-screening. Effluent from an existing tannery was used as the test medium. Jar tests were conducted after raising the pH of the medium to 11.3 ± 0.1 by injecting 5% w/v lime slurry followed by the addition of different doses of bittern as a coagulant. The characteristics of the influent and effluent after the chemical treatment were determined. The clarified effluent was then passed through an activated carbon adsorption column and the various constituents of the effluent were re-measured. The results indicate very good removals of total suspended solids (TSS) (97%), apparent color and turbidity (99%), total phosphorus (87%), and chromium (99.7%). Good removals were also attained for chemical oxygen demand (COD) (71%) and biochemical oxygen demand (BOD) (57%). The addition of lime and bittern increased concentrations of total dissolved solids (TDS) and conductivity by 30% and 36%, respectively. Low arsenic removal was recorded in the range of 56% as a result of combined coagulation with lime, bittern, and activated carbon adsorption. Comparison of coagulation process using bittern, aluminum sulfate and ferric chloride indicated that the three coagulants operate equally well when applied at their optimal pH values.

Research Highlights
► Tannery wastewater is considered as one of the toxically most polluting effluents.
► The research analyzes the impact of each of the chemicals used in the treatment.
► Use of bittern as a coagulant was compared to use of the traditional coagulants.
► Aluminum sulfate, ferric chloride and bittern work equally good at respective pH.