Effects of Organic Matter Removal from a Wastewater Secondary Effluent by Aluminum Sulfate Coagulation on Haloacetic Acids Formation

Removal of effluent organic matter (EfOM) from a wastewater secondary effluent by aluminum sulfate (alum) coagulation and its effects on haloacetic acid (HAA) formation were studied in the range of alum dose 0-120 mg/L and the pH range 4.0-9.0. Surrogate parameters, such as dissolved organic carbon (DOC), UV254, specific UV absorbance (SUVA), and fluorescence regional integration method were employed to evaluate organic removal efficiency. Results indicated that incomplete coagulation noticeably increased HAA formation in treated effluent and that enhanced coagulation significantly reduced disinfection byproducts (DBPs) precursors. pH control was more important for reducing DBP formation than coagulant dosage in terms of precursor removal from the EfOM. Under the same coagulation conditions, removal efficiencies of DOC, UV254, and SUVA were very different, but all reached their maximum values at pH 6. Removal efficiency of EfOM by coagulation was not as high as that reported for natural organic matter removal in water treatment. This is likely due to the unique nature of the EfOM characterized by the inclusion of soluble recalcitrant microbial products in the effluent. In contrast to what was observed in water treatment, UV254 was found to be a better indicator for the precursor of HAA formation for the wastewater effluent. Dichloroacetic acid and trichloroacetic acid were the major species generated following chlorination of both the raw and treated effluent. Presence of bromide and iodide ions in solution increased formation of fractions of bromo-or iodoacetic acids and also total haloacetic acids (THAA) following chlorination after alum coagulation at all pH values. Minimum THAA formation was observed at the optimum coagulation pH of 6 regardless of addition of bromide ions and iodide ions.