Effect of prechlorination prior to activated carbon adsorption on trihalomethanes formation during final disinfection

Abstract

Granular Activated Carbon (GAC) is commonly used in water treatment for the removal of Dis-solved Organic Matter (DOM) and diminution of the formation of Disinfection By-Products (DBP)during final disinfection. The aim of the present study was to evaluate whether prechlorinationprior to GAC affected the character of DOM and could result in a decrease of trihalomethanes(THM) levels in finished water when postchlorination was applied. DOM character was analysedby fluorescence Excitation-Emission Matrices coupled to Parallel Factor Analysis (EEM + PAR-AFAC). Four different waters (three synthetic solutions containing structurally diverse model andidentifiable fluorescent DOM -tyrosine, tryptophan, and humic substances- and real groundwater)were treated and compared. The solutions were sequentially subjected to prechlorination (atthree different NaClO doses: 0, 4, and 8 mg/L), GAC adsorption, and posthclorination. The resultsshowed that applying prechlorination prior to GAC adsorption resulted in lower concentrations ofTHM in postchlorinated water in comparison to the traditional practice of applying chlorinationonly after the GAC stage. The dose of 4 mg/L NaClO minimised the levels of THM in the finishedwater. The results also revealed that the fulvic-like EEM + PARAFAC component C1G (with λexc= 240 and 325 nm, and λem = 405 nm) showed a high correlation with THM levels and thereforeappeared to be a very good predictor for THM formation. While promising with groundwater, thisnew approach to control THM in chlorinated finished water should be tested with water sourcescontaining DOM with different properties before raising the technology readiness levels to pilotand real full-scale treatment trains.