Chapter 10 - Coagulation–Flocculation Method for the Treatment of Pulp and Paper Mill Wastewater

Abstract

The coagulation-flocculation method has been used to treat pulp and paper mill wastewater. Single-coagulant, single-flocculant, and coagulant–flocculant processes have been investigated. Treatment efficiency was studied taking into consideration various effects such as pH, type and dosage of coagulant and flocculant, settling characteristics, and water recovery. Alum and polyaluminum chloride (PACl) were used as coagulants. Nine cationic and anionic polyacrylamides (PAMs) of various molecular weights and charge densities were chosen as flocculants. For the single coagulant, both alum of dosage 1000 mg/l and PACl of dosage 500 mg/l achieved higher than 90% treatment efficiency in turbidity reduction, TSS removal, and COD reduction. From the nine PAM flocculants studied, 5 mg/l of the cationic polyacrylamide, Organopol 5415, with high molecular weight and low-charge density produced the best flocculation efficiency: 95% turbidity reduction, 98% TSS removal, and 93% COD reduction. The sludge volume index (SVI) was 14 ml/g. For the coagulation–flocculation process, alum showed better treatment efficiency than PACl when combined with Organopol 5415. The results showed 99.7% turbidity reduction, 99.5% TSS removal, and 95.6% COD reduction, with an SVI of 37 ml/g and a settling time of 12 seconds. A pilot scale study gave very similar results. The water recovery from the process was 96.3%.