Aqueous photocatalysis, natural organic matter characterization and removal: A case study of the photacatalytic oxidation of fulvic acid

Natural organic matter (NOM) is a complex mixture of organic compounds that occurs ubiquitously in both surface and ground waters. Its presence in water supplies not only contributes to aesthetic problems such as taste, odor and color, but also to operational and regulatory issues which include increased chemical usage, increased sludge production and membrane fouling. The variability in the amount and nature of natural organic matter is a significant factor in controlling the reactivity of aquatic humic substances with chlorine during water treatment processes. Hence, the potential for the formation of carcinogenic disinfection byproducts necessitates the removal of organics prior to chlorination stage in search for alternative advanced oxidation technologies to ensure compliance with drinking water quality standards. Humic substances (HS) represent the major fraction of naturally occurring organic substances comprised of carbon rich polydisperse polyelectrolytes. During recent years a significant interest has been devoted to the photocatalytic treatment of HS as model compounds of NOM. This paper addresses some basic issues related to the photocatalytic treatment of a model fulvic acid in relation to the relevant UV-vis and fluorescence spectroscopic properties. The oxidative removal of fulvic, acid is evaluated by pseudo first order as well as Langmuir Hinshelwood kinetic models.