Revisiting Chemically Enhanced Primary Treatment of Wastewater: A Review

Abstract

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.

Optimization of Coagulation-flocculation Process for Pre-treatment of Artisanal Tannery Wastewater Using Response Surface Methodology

“…The percentage COD removal is quite low depicting that most of the COD exist in the soluble form. The removal efficiency obtained agrees with that reported by Shewa & Dagnew (2020).…”

“…Coagulation-flocculation process, a physicochemical treatment method which is robust against wastewater toxicity and highly efficient in removal of both organic and suspended contaminants from wastewater (Aboulhassan et al 2006) was, therefore, employed in this study. It is a commonly used wastewater pretreatment technology due to its efficiency and simplicity in its design and operation (Shewa & Dagnew 2020). The mechanism involved in the coagulation-flocculation treatment process is by the initial destabilization of colloidal particles in the wastewater during the coagulation phase and the subsequent aggregation of the destabilized colloids into floc particles during the flocculation phase.…”

“…Aluminium sulphate is one of the most widely used coagulants due to its availability, relatively low cost and high coagulation performance (Shewa & Dagnew 2020). Nevertheless, it suffers a major drawback of releasing toxic aluminium ions into the environment, particularly when applied in excess.…”

Efficacy Advanced Chemical Oxidation Process (AOP) for Sustainable Pretreatment of Mixed Dairy and Poultry Wastewaters in Nablus, Palestine

“…They underlined the role of AOP with coagulation and flocculation as a cost-competitive option for the pretreatment of industrial wastewaters. Advanced oxidation process is not a new technology, Peres et al [18] listed other advanced technologies including electrochemical [19], and membrane-based processes,…”

Development of emerging technologies for a low carbon footprint wastewater treatment

“…Chemicals used as coagulants are divided into two categories, i.e., aluminum-and ironbased coagulants. Most used aluminum-based coagulants are aluminum sulfate (alum), aluminum chloride, and sodium aluminate, while the most common iron-based coagulants include ferric sulfate, ferrous sulfate, and ferric chloride (Shewa and Dagnew, 2020). Apart from these traditional chemicals, some alternative coagulants are used, including pre-hydrolyzed forms of aluminum (e.g.…”