Characterizing the performance of coagulation-flocculation using natural coagulants as pretreatment of tannery wastewater

Coagulation/flocculation followed by clarification is the most widely used process for treating wastewater from tannery industry. The coagulation step usually consists of the rapid dispersal of a coagulant into the wastewater followed by an intense agitation commonly defined as rapid mixing. The most widely used coagulants are aluminum (III) and iron (III) salts. However, there are two major drawbacks inherently associated with these such as the addition of chemicals and the increased ionic conductivity of the treated wastewater. In order to avoid such problems, the performance of different biopolymers (chitosan, alginate and starch) in the coagulation process for the pretreatment of two different tannery wastewater samples (liming and quenching washing water) was characterized. The various operating parameters optimized in this study were the duration and the stirring speed, the type and added coagulant dosage. The optimal stirring time and speed were 5 min and 200 r/min respectively and the optimal coagulant dosage was varied between 100 and 200 mg/L. The maximum removal efficiencies for turbidity and ionic conductivity observed were 87% and 55% respectively, in the case of treating wash water from liming process.