Revisiting Chemically Enhanced Primary Treatment of Wastewater: A Review

Chemically enhanced primary treatment (CEPT) is a process that uses coagulant and/or flocculant chemicals to remove suspended solids, organic carbon, and nutrients from wastewater. Although it is not a new technology, it has received much attention in recent years due to its increased treatment capacity and related benefits compared to the conventional primary treatment process. CEPT involves both physical and chemical processes. Alum and iron salts are the commonly used coagulants in CEPT. Several types of anionic, cationic, and uncharged polymers are used as flocculants, where poly aluminum chloride (PACL) and polyacrylamide (PAM) are the widely used ones. Some of the coagulants and flocculants used may have inhibitory and/or toxicity effects on downstream treatment and recovery processes. There has been an increasing amount of work on the treatment of wastewaters from various sources using CEPT. These wastewaters can range from municipal/domestic wastewater, combined sewer overflow, landfill leachate, cattle manure digestate to wastewaters from textile industry, pulp and paper mill, slaughterhouse, milk processing plant, tannery and others. In recent cases, CEPT is employed to enhance carbon redirection for recovery and substantially reduce the organic load to secondary treatment processes. CEPTs can remove between 43.1-95.6% of COD, 70.0-99.5% suspended solids, and 40.0-99.3% of phosphate depending on the characteristics of wastewater treated and type of coagulants and/or flocculants used. This article reviews the application, chemicals used so far, removal efficiencies, challenges, and environmental impacts of CEPT.