Pretreatment of instant coffee wastewater by coagulation and flocculation

Abstract

This study investigated the performance and effectiveness of coagulation and flocculation by using aluminum sulfate, ferric chloride and chitosan as a pretreatment for instant coffee wastewater. The removal of total suspended solids (TSS), turbidity, chemical oxygen demand (COD) and color by jar tests were used to determine the optimum dosage and pH. Optimum conditions for aluminum sulfate and ferric chloride was 1000 mg/L at pH 7, while for chitosan was 100 mg/L at pH 6. The dosage of chitosan was 10 times much lesser as it had the higher charge density. Chitosan exhibited the best result for turbidity and TSS removal by 96.95% and 91.43%, respectively. This was followed by ferric chloride that removed 95.38% turbidity and 91.43% TSS; and aluminum sulfate with 87.65% turbidity and 88.57% TSS removal. At the same time, ferric chloride was the best coagulant for color and COD removal, with 95% and 66.45%, respectively. This was followed by the aluminum sulfate with 90% color and 56% COD removal; and chitosan that removed 88.55% color and 46.46% COD. Chitosan produced the faster aggregation of colloids, with the lowest volume of sludge of 60 mL. This was followed by aluminum sulfate with 87 mL and ferric chloride with 103 mL. The cost of ferric chloride using per day, RM20,340 was the lowest, which was 16.8% lower than aluminum sulfate and 119.8% lower than chitosan. Overall, all coagulants can be used for pretreatment of coffee wastewater, with ferric chloride was preferable.