Application of amine-modified tannins gels as coagulants in wastewater treatment

Abstract

Tannin (T) is an organic substance that may potentially be used as an inexpensive, environmentally friendly, and effective bio-coagulant to remove impurities from residential and commercial wastewater. In this study, bio-coagulants were prepared using tannins obtained from the wattle tree (Acacia mearnsii). The bio-coagulants were modified using formalin and optionally, ethanolamine (ETA) and ammonium chloride (NH₄Cl) as amine sources through the Mannich Reaction scheme. Three coagulants were prepared, T-ETA modified tannin, T-NH₄Cl modified tannin and a mixture of T-ETA: T-NH₄Cl in molar ratio 1:1. Aluminium sulphate [Al₂(SO₄)₃], a metal-coagulant was also used as the standard for comparison. The three coagulants were tested at varied concentrations (500–1250 mg/L) using jar tests on laundry wastewater to see their effect on remediation of wastewater. A mixture of bio-coagulant T-NH₄Cl and T-ETA was most effective with highest removal efficiencies for turbidity (94%), COD (85%), Total solids (87%) and nitrates (99%). For colour removal T-NH₄Cl modified tannin showed the highest removal efficiency of 92%. The results support the use of cheaper and environmentally friendly amine modified tannin-based flocculants in laundry wastewater treatment as they showed less toxicity on the treated water.