Title

Destruction of organic pollutants in water by oxidation with hydrogen peroxide and ultraviolet light

Date of Completion

January 1990

Keywords

Engineering, Chemical|Environmental Sciences

Degree

Ph.D.

Abstract

Advanced oxidation processes provide a completely destructive, economical alternative to conventional treatment methods for the removal of hazardous organic pollutants from groundwaters and industrial wastewaters. One such process which employs UV light-catalyzed hydrogen peroxide as the oxidant has been explored for the destruction of nine aromatic pollutants (benzene, phenol, toluene, chlorobenzene, three chlorophenols, and two phthalate esters), as well as trichloroethylene (TCE).^ Aromatic pollutants were treated in an annular batch-recycle photoreactor operated at 25$\sp\circ$C, pH 6.8, and an applied UV power of 1.6 watts/liter. Rates of reaction were determined for UV light alone and for the combination of UV light plus 1.5 mM hydrogen peroxide. The UV/peroxide combination yielded higher reaction rates than UV light alone. All the aromatics were oxidized at similar rates. A study of the formation and destruction of reaction intermediates for two pollutants showed that all detectable intermediates could be eliminated, given sufficient treatment time.^ The kinetics of TCE oxidation were studied in plate type batch photoreactors of two different depths. The reaction rate of TCE was first order in UV light intensity and pseudo first order in TCE concentration. The rate was first order in hydrogen peroxide concentration at low peroxide levels, but independent of peroxide concentration at high peroxide levels. The maximum rate attainable depended on the reactor depth, with the shallower reactor yielding the larger maximum rate. The effect of temperature on the rate was minimal. The rate was a factor of two slower at acidic and basic pH than at neutral pH.^ A mechanism for TCE oxidation was proposed which yielded a rate expression consistent with the experimental observations. The rate expression was semi-empirical in that it employed the concept of "effective" path lengths to account for the attenuation of UV light intensity with increasing reactor depth.^ Formic acid was identified as an intermediate of TCE oxidation. Chloride ion measurements during one experiment showed that complete conversion of organic chlorine to chloride ion was obtained, proving that complete dechlorination of TCE and its intermediates had been achieved. ^

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