Treatment of Sewage Sludge and Phosphorus Removal Using Polyacrylamide and Calcium Chloride

The enhancement of the treatment of municipal wastewater treatment plants is limited by poor sludge settling qualities, and the excessive discharge of nitrogen and phosphorus exacerbate water eutrophication. The goal of the current work was to remove phosphorus from fresh sewage-activated sludge by developing a new conditioning and flocculation mechanism that included a coagulant and cationic polyelectrolytes in a dual conditioning system. The coagulant (CaCl2) and the high molecular weight polyacrylamide (CPAM-10) were chosen to be utilized singly or in pairs as cationic–coagulant combinations. The collected results showed that, in comparison to utilizing the coagulant (CaCl2), conditioning with the high molecular weight polymer (CPAM-10) produced improved settling and less turbidity. Only sludge with a lower solid content (TSS) exhibited better settling when pure CaCl2 was used for conditioning. CaCl2 conditioning enhanced settling by just 3%, while CPAM-10 improved the sludge setting by 60% for higher sludge TSSs. According to the results, conditioning settings using a dual mixture including 20 mL CPAM-10 and 50 mL CaCl2 improved settling by 80%. The amount of phosphorus in the supernatant was decreased by 15% and 9%, respectively, by using the coagulant (CaCl2) and 50 mL/L polyacrylamide (CPAM-10). As a result, there was a significant amount of phosphorus in the resultant supernatant. This suggested that the polymer had a significant impact on sludge settling because of its high positive charge, but had less of an impact on attracting phosphorus metal. Despite the lower positive charge of CaCl2, it has a dual action of settling and removing phosphorus. A considerable amount of phosphorus was removed from the sludge and leached to the supernatant during treatment. This treatment was coupled with less sludge settling. However, 90% phosphorus removal was achieved when mixed conditioning agents (20 mL CPAM-10 and 50 mL CaCl2) were used. Furthermore, phosphorus was reduced by 33 and 39%, respectively, by adding 20 milliliters of CaCl2 to 100 milliliters of the pre-conditioned supernatant with pure CPAM-10 and CaCl2. Using the CPAM-10 agent for sludge conditioning has a major impact on settling, because of the high positive charge, and because when a small amount of Ca++ is added to the polymer solution for conditioning to attract fine sludge particles and accelerate their combination, this results in flocculation and rapid dewatering. This mechanism allows for more phosphorus to be released to the supernatant, which has not been reported previously to the best of our knowledge.