Variation of Al species during water treatment: correlation with treatment efficiency under varied hydraulic conditions

The concentration of hydrolyzed coagulant ion species is a key factor in determining drinking water treatment efficiency. Direct correlation of water treatment efficiency with changes in species during coagulation has not been addressed. We investigated the correlation under different hydraulic conditions and water treatment efficiencies including changes in removal of turbidity, ultraviolet adsorption at 254 nm (UV₂₅₄) and dissolved organic carbon (DOC). Results highlighted that Al species (monomeric species as Al_a, medium polymeric species as Al_b and colloidal species as Al_c) behaved differently during coagulation and treatment efficiencies were affected. When varying the mixing speed, the removal of Al_c species had a strong negative correlation with water treatment efficiency but under other hydraulic conditions positive correlations were found. The removal of Al_a species was positively correlated with water treatment efficiency, but under other hydraulic conditions the low abundance of Al_a species meant the correlation was difficult to observe. The Al_b species were significantly and positively correlated with water treatment efficiency with the highest correlation coefficient (R²) of 0.87. The correlation of metallic species with removal efficiencies of the DOC and the UV₂₅₄ produced higher R² values. Correlation of the rate of removal of Al_b species with the removal efficiencies of the DOC or the UV₂₅₄ was better than for Al_c.