Anaerobic biodegradation of trichloroethylene with the addition of sugar using activated carbon-fluidized beds

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Huang, Suxan
Biodegradation.; Trichloroethylene--Biodegradation.; Environmental Engineering
thesis / dissertation description
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.