Abstract
Abstract
Use of landfill gas as a fuel often requires pretreatment for removal of contaminants that damage energy-recovery equipment. Because these contaminants are present in trace levels, biofiltration may be a suitable treatment option. However, the high carbon dioxide (CO2) concentrations in the gas could encourage autotrophic growth in place of consumption of the trace organics, or decrease the pH of the biofilter material. Xanthobacter autotrophicus GJ10 has broad ability to transform halogenated hydrocarbons, and is also known to grow on CO2 as a sole carbon source. Microcosms of this bacterium, grown on CO2, were spiked with 1,2-dichloroethane (1,2-DCA) to monitor the bacterium's ability to switch from autotrophic to heterotrophic transformation at moderate pH. Additional cultures of X. autotrophicus GJ10 were established over a range of pH from 4 to 8, values that might result from media exposure to landfill gas. Growth on a nonchlorinated organic carbon source was monitored under these conditions. Also, dechlorination of 1,2-DCA was correlated to high, moderate, or low pH microcosms. Results demonstrated no effect on transformation of 1,2-DCA under high CO2 concentrations when pH remained near 6. On the other hand, pH conditions lower than 5.5 impeded growth of the organism. No growth was observed when pH was less than 4.6. Within the range of good growth (pH between 5.5 and 8.1), low pH influenced transformation rates. Conditions of pH less than 6 reduced the transformation rate coefficient by 25%. Therefore, pH control in a biofilter unit for treatment of 1,2-DCA will be an important consideration.