Solid–Liquid Separation of Dairy Barn by Electrocoagulation with Cationic Polymer Coagulant

High–molecular-weight polymer coagulants are widely used in wastewater treatment combined with traditional inorganic coagulants to improve the solid–liquid separation efficiency. However, it is desirable to keep chemicals used in treatments at minimum levels for economic and safety reasons. This study aimed to increase the efficiency of two-stage electro- and chemical-coagulation treatment with a minimum chemical dosage for the separation of solids and liquid in dairy manure slurry for the safe composting of solids and safe discharge of wastewater. Accordingly, dairy manure slurry was treated with aluminum (Al) coagulants, such as polyaluminum chloride (PAC), aluminum chloride (AlCl3), and aluminum sulfate (Al2(SO4)3), PAC combined with the cationic polyacrylamide (CPAM), and PAC and CPAM combined with electrocoagulation (EC). Results revealed that PAC was the best among the Al coagulants evaluated for the reduction in turbidity in the liquid fraction at a dosage of 100 mg/L. PAC dosage was reduced to 40 mg/L when the treatments were combined with CPAM at a dosage of 40 mg/L, which was further reduced to 30 mg/L when treatments were combined with 5 min EC and 20 mg/L of CPAM dosage.