Date of Award

Spring 1989

Document Type

Dissertation

Degree Name

Doctor of Engineering Science in Environmental Engineering

Department

Civil and Environmental Engineering

First Advisor

Yeun C. Wu

Second Advisor

Michael Bruno

Third Advisor

Paul N. Cheremisinoff

Fourth Advisor

Hsin Neng Hsieh

Fifth Advisor

George Y. Lei

Abstract

Anaerobic biodegradation of trichloroethylene (TCE) was carried out in a two-stage granular activated carbon fluidized bed bioreactor. The intermediate products were identified as: dichloroethylene (DCE), vinyl chloride (VC), 1,2-dichloroethane (DCA) and chloroethane (CA). Of the three geometric isomers of DCE, the trans-1,2 dichloroethylene (TDCE) was found to be the most predominant species, The production of DCA suggested a diverted reaction sequence from the conventional sequential reductive dechlorination pathway postulated in the past literature. CA was believed to be a product of VC and/or DCA. The co-substrate glucose was implicated for this reaction specificity. Based on our data and on other's work, a modified degradation pathway for TCE in anaerobic environment is postulated. The quantitative production of CA strongly implied a potential for complete mineralization of TCE under reductive conditions.

The rate constant, k, of TCE biodegradation in this process was found to be 8.7 min-1. The reaction kinetics resembled that of Michaelis-Menten model with the maximum rate, Vm and Michaelis-Menten constant, Km, determined as 1.63 mg/L-min and 0.11 mg/L, respectively. The kinetic constants for TDCE conversion were: k = 0.3 min-1, Vm = 0.06 mg/L-min and Km = 0.10 mg/L.

The material balance performed on one stage of the system revealed that, in the range of influent TCE concen-tration of 0.02 - 4.64 mg/L, about 1% of the TCE introduced into the system volatilized to the reactor headspace, a maximum of 2% remained unaltered on the granular activated carbon (GAC) particles, and a maximum of 35% escaped biotransformation and eluted with the effluent of the first stage. Over 62% of the TCE was biotransformed to the DCEs, about 75% of which was further transformed to CA. The percent reduction of TCE from the aqueous phase ranged from 81 to 98% for the first stage and 98 to 100% for the entire system.

The optimum recycle rate was found to range from 750 to 850 ml/min. With a target effluent TCE concentration of below 20 ug/L and allowing a contact time of one minute, the nutrient feed rate must be < 4 ml/min. A glucose/TCE ratio of greater than 4 seemed to result in the early cleavage of double bond in TDCE and thus lead to the production of CA via DCA rather than VC.

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