Reduction of chlorination disinfection byproduct precursors by the synergy of advanced oxidation and biofiltration processes.

Chlorination of treated effluent water is the significant step in any drinking as well as wastewater treatment plant. The reaction of chlorine with the natural organic matter (NOM) present in the influent water as well as effluent organic matter (EfOM), for that matter, contributed by anthropogenic activities around the catchment, may prompt production of unwanted byproducts called disinfection byproducts (DBPs) or chlorination DBPs (CDBPs). Major CDBP compounds belongs to the class of trihalomethanes (THMs); group of most regulated and predominant CDBPs. Many studies have already reported their carcinogenic nature.NOM is known to act as a precursor to CDBPs. NOM/EfOM can be treated through oxidative breakdown by advanced oxidation processes (AOPs) followed by removal of simpler biodegradable compounds by biofilm/biofiltration (biological activated carbon (BAC)). NOM/EfOM is usually quantified in terms of dissolved organic carbon (DOC).AOPs alone have been shown to reduce DOC by 30-60 percent and increase the hydrophilicity of the sample matrix i.e. breakdown of complex organic matter to simpler organic molecules; which makes its removal easier and complete by BAC process. Thus, the objective of this work is to investigate first, the occurrence of THMs in the actual on-field samples. For that, two drinking water treatment plants have been selected and sampling and analysis was conducted over a period of 12 months for identification of THMs. Secondly, screening has been conducted among various AOPs viz., UV/H₂O₂, O₃ and O₃/H₂O₂. Selected AOPs were evaluated using kinetic studies based on their ability to mineralize DOC and decrease UV₂₅₄ at various pH, UV intensities, and ozone and hydrogen peroxide concentrations. Biofilm was allowed to establish on a raw GAC (granular activated carbon) column and the actual influent (surface water) was kept running through the set-up for a duration of 180-200 days. Pseudo steady state was established and the set-up was then optimised for final DOC reduction. BAC columns were then fed with AOP treated water and overall reduction in DOC, UV₂₅₄, hydrophobicity and THMFP was observed. This study provides insight into fate of a contaminant of emerging concern (THM) especially in drinking water treatment plant and provides an economically viable solution for their effective removal.