Session: Aquatic Photochemistry:

The use of advanced oxidation processes (AOPs) is a modern solution for the reduction of emerging contaminants in wastewater treatment plant effluent. UV-driven AOPs work on the principle of UV activation, to form highly reactive radical species that can be used to oxidize organic pollutants. Here, a light-emitting diode (LED) with an emission centered at 305 nm is employed to effect hypochlorite photolysis as an advanced oxidation process (AOP). The performance of this method was measured for the oxidation of four pharmaceutical compounds: carbamazepine, acetaminophen, tertbutryn, and sulfamethoxazole. The photolysis of free chlorine is accomplished by UV LEDs to form reactive oxygen species (ROS) and reactive chlorine species (RCS). This approach is advantageous in the presence of effluent organic matter (EfOM) compared to the UV/peroxide system, because the RCS (i.e. Cl. and ClO.) are more selective than ROS (primarily OH.) produced by H₂O₂ photolysis. UV LEDs provide further advantage over traditional Hg-fluorescence approaches given the ability to achieve higher molar absorptivities at the newly available UV wavelengths (e.g. 278 and 305 nm) at relevant pH values. The performance of this UV/Chlorine system on the degradation of five PPCPs is evaluated in the presence of carefully characterized EfOM from a municipal membrane bioreactor and compared to the cost effectiveness of using UV254/H₂O₂, on an energy basis. One possible pitfall of applying UV/Chlorine as an AOP is the potential to form disinfection byproducts (DBPs) due to the reaction of RCS with dissolved organics. As a preliminary examination of DBP formation, a microtoxicity test was conducted to observe changes in DOM toxicity based on the effects of the UV/chlorine AOP on the DOM.

$3DEEM images of <b>A</b>) EfOM and <b>B</b>) the HPO fraction$

3DEEM images of A) EfOM and B) the HPO fraction

Samuel Snow

Appearances