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

Granular Activated Carbon (GAC) is commonly used in water treatment for the removal of Dissolved 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 prechlorination prior 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 analysed by fluorescence Excitation-Emission Matrices coupled to Parallel Factor Analysis (EEM + PARAFAC). Four different waters (three synthetic solutions containing structurally diverse model and identifiable fluorescent DOM -tyrosine, tryptophan, and humic substances- and real groundwater) were treated and compared. The solutions were sequentially subjected to prechlorination (at three different NaClO doses: 0, 4, and 8 mg/L), GAC adsorption, and posthclorination. The results showed that applying prechlorination prior to GAC adsorption resulted in lower concentrations of THM in postchlorinated water in comparison to the traditional practice of applying chlorination only after the GAC stage. The dose of 4 mg/L NaClO minimised the levels of THM in the finished water. The results also revealed that the fulvic-like EEM + PARAFAC component C1G (with λ exc = 240 and 325 nm, and λ em = 405 nm) showed a high correlation with THM levels and therefore appeared to be a very good predictor for THM formation. While promising with groundwater, this new approach to control THM in chlorinated finished water should be tested with water sources containing DOM with different properties before raising the technology readiness levels to pilot and real full-scale treatment trains. • Prechlorination prior to GAC adsorption reduced THM formation during final disinfection. • Chlorinated DOM showed higher adsorbability on GAC than nonchlorinated DOM. • NaClO dose of 4 mg/L yielded a minimum level of THM in postchlorinated water. • Fulvic-like EEM + PARAFAC component C1 was a very good predictor for THM production.