Cationic Organic Polymers for Flocculation of Municipal Wastewater - Experiments and Scenario Study

Abstract

Organic polymers can be favourable flocculants in comparison with inorganic (metal-)flocculants because chemical sludge production is absent and the increase in salt concentration of the effluent is low. Jar test experiments showed that a higher weight (8.10⁶ g/mol; (+) 24%) cationic polyacrylamide gave good flocculation results, with turbidity- and COD_particulate removal efficiencies of 65-90% and a TSS removal of > 90% at relatively low dosing concentrations. Rapid coagulation mixing conditions were optimal with a mixing time of 30 s (G = 800 s^-1). A decrease in low flocculation mixing time from 180 s to 30 s (G = 50 s^-1) resulted in a decrease in particle removal of 25%. A scenario study was conducted to estimate the costs involved and to quantify the environmental impacts. The scenario study showed that the total costs of a complete wastewater treatment system based on coagulation-flocculation with organic polymers are in the same range (-5%) as those of a system with FeCl_v Total sludge production is 15% lower. Salinisation is of the order of +0.2 mg Cl per litre effluent for dosing polymer and +29 mg Cl per litre effluent for dosing FeCl₃.