Photocatalytic oxidation of natural organic matter surrogates and the impact on trihalomethane formation potential.

Natural organic matter (NOM) consists of a complex mixture of organics and acts as precursors for a range of disinfection by-products (DBPs) including trihalomethanes (THMs). The characteristics of these precursors are still not well identified and here we have used a range of NOM surrogates that allows us to investigate how the characteristics of NOM relate to treatability with photocatalytical oxidation. Nine surrogates of NOM (five amino acids, two carbohydrates, two phenolic compounds) were evaluated and the impact of retention time on dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP) measured. Adsorption of the compounds onto TiO(2) was evaluated and electrostatic forces played a significant role in their removal although photocatalytic oxidation was found to be unselective. DOC and THMFP decreased significantly with retention time except for l-leucine where the by-products formed during photocatalytic oxidation were significantly more reactive with chlorine than the parent compound.

Photocatalytic oxidation, GAC and biotreatment combinations: an alternative to the coagulation of hydrophilic rich waters?

This study investigated the photocatalytic oxidation of a raw water rich in hydrophilic natural organic matter (NOM) and the impact on the removal of: dissolved organic carbon (DOC), UV absorbance at 254 nm (UV254) and trihalomethanes formation potential (THMFP). Dissolved organic carbon and UV254 removals were 40% and 55%, respectively, after 1 min irradiation time and 1 g L(-1) dose of TiO2. The THMFP content was reduced from 305 microg L(-1) in raw water to 144 microg L(-1) after 10 min treatment, whereas chlorine reactivity was stable with treatment. The results showed that larger molecular weight species were preferentially degraded during the process. Dissolved organic carbon and THMFP removals reached 60% and 70%, respectively, after photocatalytic oxidation and granular activated carbon (GAC) columns.