Photoassisted biodegradation of halogenated breakdown products from nuclear fuel recovery process water

• Main Author: Makgato, Seshibe Stanford
• Other Authors: Supervisor: Evans M.N. Chirwa.
• Format: Others
• Language: en
• Published: 2009
• Online Access: http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1000183

Thesis (MTech. degree in Engineering: Chemical)--Tshwane University of Technology === Due to the impact of the rapidly growing demand for energy worldwide, as well as concerns over global warming, there has been a resurgence of interest in nuclear energy in the developed world. However, further deployment of this otherwise cleaner source of energy in other lesser developed regions is hindered by concerns over accumulation of radioactive waste from nuclear reactor operation and fuel processing. In fuel processing, the problem is the volume of effluent waste generated which mainly consists of toxic organic compounds. The use of decontamination reagents such as CCl4 together with phenolic tar results in wastewater with a high content of chlorophenols. Chlorophenols are compounds of serious environmental concern due to their toxic and carcinogenic impacts. In this study, the extent of dehalogenation of toxic aromatic compounds was evaluated using a photolytic advanced oxidation process (AOP) followed by biodegradation in the second stage. A hard-to-degrade toxic pollutant, 4-chlorophenol (4-CP) was used as a model compound representing recalcitrant aromatic pollutants in wastewater streams from the nuclear industry. A two stage photo assisted AOP/bioreactor system demonstrated great potential in the removal of toxic 4-CP simulated nuclear process water wastewater. Adding hydrogen peroxide (H2O2) as a catalyst further improved the dehalogenation rate but the effect was limited by the scavenging of (OH•) radicals under high concentrations of H2O2. High degradation rate was achieved in the UV/H2O2 advanced oxidation system as opposed to direct UV photolysis. A Monod-like model was used to evaluate the biodegradation kinetics over a wide range of initial concentrations. The model revealed that 4-CP degradation process followed quasi-second order kinetics. This study demonstrates the potential of enhanced biological treatment of nuclear wastewater using a cleaner and energy effective technology.