Treatment of low-turbidity water by coagulation combining Moringa oleifera Lam and polyaluminium chloride (PAC)

A natural coagulant extracted from Moringa oleifera (MO) using saline solution (CaCl2) was associated with aluminium polychloride (PAC) for the treatment of spring water with low turbidity (10, 20 and 30 NTU) in a Dissolved Air Flotation (DAF) system. The objective was to reduce the dependence on chemical coagulants in water treatment for environmental and health reasons. Treatments at different conditions (100% MO, MO:PAC 90:10, MO:PAC 80:20, MO:PAC 70:30 and 100% PAC) were performed and analyses of turbidity, apparent colour, residual aluminium, electrical conductivity, absorbance at UV254nm and Molecular Luminescence Spectrometry (MLS) were used to determine the treatment efficiency. The use of MO alone (20, 30 and 40 mg L-1 for 10, 20 and 30 NTU waters, respectively) showed lower performance (mean removal of 66.5% for turbidity and 64.9% for colour) compared to both 100% PAC (88.3% turbidity removal and 93.1% colour removal) and MO:PAC 70:30 (79.2% turbidity removal and 90.3% colour removal). The associated coagulant did not affect the water pH. PAC dosages of 2 to 12 mg L-1 did not raise the residual aluminium concentration but increased the removal of compounds with absorbance at UV254nm by an average of 39.9%. Although the isolated MO exhibits poor performance in treating low-turbidity water (<30 NTU), its association with PAC is efficient, safe and sustainable, especially at a 70:30 ratio. The effect of the MO:PAC treatments in the removal of organic compounds (OC) was confirmed by MLS. The higher the proportion of PAC (30%), the lower the fluorescence intensity in the CO-predominant regions. MLS proved an excellent quality control tool to identify alterations in the configuration of organic matter in water, mainly regarding protein identification.