Degradation of Trichloroethylene Using Advanced Reduction Processes

This research investigates degradation of trichloroethylene (TCE) using a new treatment method called advanced reduction processes (ARPs). This new set of water treatment processes employ a source of activation energy to activate reducing agents and produce reducing radicals that can effectively degrade oxidized contaminants. Screening experiments were conducted to evaluate three different reducing reagents (sulfite, sulfide, and dithionite) and three UV light sources (low-pressure mercury UV lamp (UV-L), medium-pressure mercury UV lamp (UV-M), and narrow band mercury UV lamp (UV-N)) for TCE dechlorination in water. Both removal efficiency of TCE and chloride ion recovery were examined together to identify the best ARP. Results of screening experiments showed that ARP that combines UV-L with sulfite achieved the highest TCE removal efficiency and maximum chloride ion recovery.

Effects of experimental parameters on the kinetics and behavior of TCE dechlorination using sulfite/UV-L were investigated in order to obtain optimum operating conditions for TCE degradation. The experimental parameters that were evaluated are: TCE initial concentration, sulfite dose, solution pH, and light intensity. TCE photodegradation followed a first-order decay rate. Increasing pH value and increasing sulfite dose resulted in increasing TCE removal efficiency and almost complete degradation was achieved at pH 11 using 50:1 molar ratio of sulfite dose to initial TCE concentration with chloride ion being the major reaction product. TCE dechlorination rate constant (kobs) was independent of its initial concentration, whereas kobs increased with increasing sulfite dose, pH, and light intensity.