Control of disinfection by products formation potential by enhanced coagulation

Abstract

Jar-test experiments were conducted to study enhanced coagulation effectiveness in removal of disinfection by products (DBPs) from Zayandehrud River at Isfahan Province-the center part of Iran-in 2004. In this study, the removal of suspended and colloidal particles and natural organic matter (NOM) at various coagulant doses and coagulation pHs was assessed through raw and treated water measurements of turbidity, UV 254 absorbance, TOC, and dissolved organic carbon (DOC). The trihalomethane formation potential (THMFP) was also determined by a mathematical relationship with TOC. Results indicated that NOM removal was a function of coagulant type, coagulant dose, and pH of coagulation. In general, TOC, DOC, and UV 254 absorbance removal enhanced with increasing coagulant dose. However, further increases in coagulant dosage had little effect on disinfection by-products precursors removal. Ferric chloride was consistently more effective than alum in removing NOM. Coagulation pH was appeared to be a determining factor for maximum NOM removal and the removal of DBPs precursors by enhanced coagulation was significantly enhanced at pH 5.5 in comparison with initial pH of water. Furthermore, it is specified that preadjustment of pH with sulfuric acid reduced the coagulant dosage and thus, production of sludge. The reduction in THMFP was consistent with the trends observed for DBPs precursors removal data (i.e. UV 254 and TOC data).

Decomposition of two haloacetic acids in water using UV radiation, ozone and advanced oxidation processes

“…The rate constants for the decomposition of DCAA and TCAA decreased by 41.1% and 23.8%, respectively, when humic acids were added at a concentration of 1.2 mg TOC/L. The rate constants decreased by 43.5% and 25.9%, respectively, at an HCO 3 − concentration of 1.0 mmol/L.…”

“…In the semi-continuous experiments, the HAAs decomposition in HAAs mixture system was compared using O 3 TCAA within 30 min, although the reaction rates were much lower than those for DCAA. TCAA was of relatively lower decomposition rates than DCAA, because the three chlorine atoms on its ␣-carbon provide greater space block, protecting carbon atom against attack from the radicals [18,24], and there is no hydrogen atom on ␣-carbon of TCAA, posing a higher oxidation state, thus more difficult to be oxidized than DACC.…”

“…Owing to their carcinogenic risks, people show great concerns about drinking water hygiene. In the past, the main efforts focused on the mechanisms and the effective control of HAAs formation by reducing precursors [2,3] or using alternative disinfectants [4,5]. Recently, some treatment techniques, such as microbial degradation [6][7][8], activated carbon adsorption [9], etc., have been tried for the elimination of HAAs formed in drinking water.…”

“…Among the many AOPs studied, the combinations of ozone and ultraviolet (O 3 /UV), O 3 and hydrogen peroxide (O 3 /H 2 O 2 ), and H 2 O 2 and UV (H 2 O 2 /UV), etc., have been considered as the most potential processes, and some commercial plants using these processes have been established for drinking water and wastewater treatments [13][14][15]. The AOPs involving UV irradiation demonstrate to be effective for the dehalogenation of chlorinated organics [16][17][18][19][20], in which alkylic-oxidation, dealkylation, and dechlorination-hydroxylation (minor in catalytic oxidation process without UV-light) are the leading pathways with steric hindrance effect.…”

“…The objective of this study is to determine the feasibility of adopting single oxidants: ozone, UV radiation; and the advanced oxidation processes constituted by combinations of O 3 on the decomposition process by effective AOPs. HAAs include nine compounds, among which, dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) are generally of higher concentration level in chlorinated drinking water [21] and higher carcinogenic risks, and are chosen as the target pollutants.…”