Sensitized photolysis as pretreatment to biological degradation of trichlorobenzenes.

The role of photolysis as a pretreatment process was examined for the biological degradation of trichlorobenzenes (TCBs), namely 1,2,3-, 1,2,4- and 1,3,5-trichlorobenzenes. Initially, direct and indirect photolysis experiments were conducted using aqueous solutions with 1% acetonitrile of the three isomers of trichlorobenzenes with and without sensitizers. The sensitizers used were Fenton's reagent, nitrite, triethylamine, humic acid and TiO$\sb2$. The photochemical experiments were performed using laboratory simulated sunlight and the kinetic rates for these processes were calculated. The results showed that the photolysis of 1,2,3-TCB was most significantly enhanced by the sensitizers with TiO$\sb2$ being the most efficient. Photooxidation reactions were indicated by Fenton's reagent, TiO$\sb2$, humic acid and nitrite, while reductive dechlorination was observed using triethylamine. The TCBs were exposed to both sunlamp and black lamp for the photoproduct study. The results indicated that Fenton's reagent, humic acid and TiO$\sb2$ promote hydroxylation of 1,2,3-TCB to a smaller degree than those of 1,2,4- and 1,3,5-TCB. Nitrite produced trichloronitrobenzenes and phenol derivatives as a result of nitration and hydroxylation. 1,2,3-, 1,2,4- and 1,3,5-TCB yielded significant amounts of pentachlorobiphenyl isomers, depending on the radiation source and intensity, period of exposure and type of sensitizers. The effect of photolysis on the biological degradation of the chlorobenzenes were examined using a chemical activation system (CAS) which consists of EDTA, ferrous sulfate, ascorbic acid, catalase and H$\sb2$O$\sb2$ in potassium phosphate buffer (monobasic) and a primary sewage effluent. Initially, kinetic rates by CAS biodegradation and primary sewage were obtained and compared. In general, the rates of biodegradation were greater in the test media with catalase. The rate of transformation in CAS was enhanced in the order: monoCB $<$ 1,2,3-TCB $<$ 1,2,4-TCB $<$ 1,3,5-TCB; whereas, when CAS was used as a control, the kinetic rates in the presence of catalase increased in the sequence: 1,2,3-TCB, 1,3,5-TCB $<$ 1,2,4-TCB $<$ MonoCB. Photolysis studied in concert with the biological systems showed significant enhancement of the degradation rate of trichlorobenzenes. The photolysis rates were higher for those with sensitized photolysis. This study shows that photolysis can be used as a pretreatment of enhancing biodegradation of trichlorobenzenes in aqueous systems.Ph.D.Environmental Health SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105551/1/9135621.pdfDescription of 9135621.pdf : Restricted to UM users only