Treatment of wastewater from a gas station by tannin-based coagulant and the sludge characteristics

Present study reports the treatment of gas station wastewater (GSW) after oil/water separation. Coagulation-flocculation tests were performed by using inorganic coagulants such as aluminium sulfate (Al-2(SO4)(3)) and ferrous chloride (FeCl3). The natural tannin-based coagulant Tanfloc (R) was also studied as an organic and biodegradable alternative. The effectiveness of the coagulants have been investigated in jar test experiments evaluating total organic carbon (TOC), turbidity removals, and final pH as a function of coagulant dosage and initial pH. Optimum dosage and initial pH were found to be 500 mg L-1 and 9.5, respectively, for both Al-2(SO4)(3) and FeCl3. Optimum dosage for Tanfloc (R) was also found to be 500 mg L-1 at in natura pH. At optimum conditions for Tanfloc (R), TOC and turbidity was lowered by 49% and 97%, respectively (initial TOC and turbidity were 187 mg L-1 and 326 NTU, respectively). The sludge generated by Tanfloc (R) showed good settleability, sludge volume index of 98 mg L-1 and exothermic degradation profile.