Lab-scale testing of green coagulant activity for metals and As removal from municipal wastewater treatment plant effluent

Natural coagulant isolated from the common bean seeds was tested for the removal of metals (Cr, Cu and Zn) and As from the municipal wastewater treatment plant effluent (WWTP) spiked with target analytes dose of 100 µg/L. Optimal coagulant dose of 37.5 µL/L was initially obtained based on organic matter removal efficiency since this parameter is regulated by legislation. Subsequently, it was assessed how this particular dose affects metals and As content. A moderate coagulation activity at pH 6.0 was observed for the removal of As (32–39%) and Zn (23–52%). The results were compared with the kaolinite efficiency (dose 100 mg/L at pH 6.0) which significantly removed only As (36–48%), while for Cr and Cu removal was at the level of analytical method bias (near 20%). The combination of the two processes was tested by application of different dosing sequences (simultaneous dosing of coagulant and kaolinite and successive dosing of first coagulant and then kaolinite) and showed less removal than separate coagulation or adsorption process. Combined procedures were efficient only for As removal (above the analytical method bias range), and the observed efficiency was 18–25% by simultaneous dosing, while successive dosing achieved up to 31%.