Use of new local plant-based coagulants for turbid water treatment

This study was conducted to identify low-cost plant materials as coagulants for water treatment. Four abundantly grown and protein-enriched plant materials (normally used as forage for livestock) were selected as bio coagulants: Medicago sativa, Dolichos lablab, Pennisteum glucum and Opuntia microdasys. Their efficiencies for turbidity removal from laboratory-prepared water were analyzed and compared with the chemical coagulant (alum). The optimum doses for alum, Medicago sativa, Dolichos lablab, Pennisteum glucum and Opuntia microdasys were found out to be 20 mg/L, 50 mg/L, 10 mg/L, 50 mg/L and 40 mg/L, respectively. Optimum pH was 6.5, 5, 6.5, 8.5 and 7, respectively. The maximum coagulation activity observed was 96% for alum and 96%, 99%, 98% and 69% for Medicago sativa, Dolichos lablab, Pennisteum glucum and Opuntia microdasys, respectively. Single-factor analysis of variance showed that pH had more dominant effect on turbidity removal as compared to coagulant dosage. Fourier transform infrared analyses confirmed the presence of protein-specific functional groups including strong and broad 1° and 2° amines, medium aliphatic amines group and Amide I in all bio coagulants responsible for coagulation activity. Through micro-photographic analysis, floc sizes observed for alum, Medicago sativa, Dolichos lablab, Pennisteum glucum and Opuntia microdasys were up to 15 µm, 22 µm, 20–50 µm, 20–40 µm and ≤ 10 µm. The common coagulation mechanism for all coagulants observed was charge neutralization. Among all coagulants, the most economically feasible coagulant was found out to be Pennisteum glucum.