Chemically Assisted Primary Sedimentation as a tool to improve energy balance of a large wastewater treatment plant

Abstract

Chemicals addition at the mechanical part of wastewater treatment plant can improve overall treatment efficiency and help in solving some plant’s operational problems. Application of such process in the primary clarifiers, named as Chemically Assisted Primary Sedimentation, can also be a huge step towards energy balance improvement for the whole plant. Use of relatively cheap coagulants, such as ferric or alum salts can be an easy way to increase treatment efficiency significantly, as coagulation and flocculation intensifies followed by chemical precipitation. Additional removal of soluble pollutants and suspended solids increases their load in the primary sludge, avoiding their potential removal in the biological part of the plant. Additional organic matter in the primary sludge allows to produce more gas in the anaerobic digestion process and thus increase energy production by the CHP units. Efficiency of different coagulation agents (PIX 109 and PAX XL3) supported by polymer addition was investigated using real municipal wastewater collected from a large Polish wastewater treatment plant (over 500 000 p.e.) in a series of lab-scale tests. Proper selection of coagulant and potential polymer dosage has a serious impact on the overall costs of this additional treatment and energy balance. Based on obtained results, economic analysis was performed for the same plant to evaluate potential gains and losses of implementing such practice.