NATURAL AND EFFLUENT DERIVED ORGANIC MATTER REMOVAL USING SYNERGY OF ADVANCED OXIDATION AND BIOFILTRATION PROCESSES

Abstract

Disinfection of treated effluent water is a critical final step in any drinking water treatment plant. The reaction of the widely used disinfectant, chlorine, with the natural organic matter (NOM) and effluent organic matter (NefOM), from anthropogenic activities around the catchment, leads to formation of unwanted disinfection byproducts (DBPs). Major fraction of the DBPs are trihalomethanes (THMs), which are regulated in drinking water. Many studies have reported their carcinogenicity. NefOM, which are precursors to DBP formation, can be partially oxidised by advanced oxidation processes (AOPs), followed by degradation of the simpler and more biodegradable compounds by biological activated carbon (BAC) treatment, allowing for economical treatment. Two drinking water treatment plants, one conventional and one moving bed biofilm reactor, along river Yamuna were monitored over a period of 12 months for quatification of THMs. The total THM concentration was significantly above the Unites States Environmental Protection Agency (USEPA) limits, while lower than the Bureau of Indian Standards (BIS) limits. XAD resin fractionation indicated a preponderance of hydrophobic organic carbon and the inefficiency of both the plants in removing the hydrophobic fraction of NefOM. Kinetic screening experiments were conducted to identify the AOP (UV/H2O2, O3 and O3/H2O2) most effective in mineralizing dissolved organic carbon (DOC) and decreasing UV254 at various pH, UV intensities, and ozone and hydrogen peroxide concentrations. These experiments identified UV/H2O2 as most effective AOP in decreasing the THM formation potential. UV-L/H2O2 at an intensity of 47 mJ/cm2/min, pH=7, and hydrogen peroxide concentration of 0.5mM provided an optimum reduction of DOC (64%) and UV254 (66 %). Fractionation studies indicated that treatment by UV-L/H2O2 leads to the significant decrease in the hydrophobic fraction of the water along with maximum THM formation potential (THMFP) attenuation. Biofilm was allowed to establish on a raw granular activated carbon column with river Yamuna water as influent. Pseudo steady state was established after 90 days of operating the column. BAC columns were fed with AOP treated water and overall decrease in DOC, UV254, hydrophobicity and THMFP was observed. The AOP-BAC treatment was optimised for each AOP. Maximum increase in biodegradability was observed in case

of O3/H2O2 with biodegradable DOC (BDOC) of 3.43 mg/L at an ozone dose of 5.44 mg/L and 0.5mM H2O2.O3/H2O2-BAC showed the maximum decrease in DOC (80%) and UV254 (95%) along with the hydrophobicity (~98%) and THM formation potential (~80%) reduction.