The geochemical effects of benzene, toluene, and xylene (BTX) biodegradation

Walton R. Kelly, Janet S. Herman, Aaron L. Mills

Research output: Contribution to journalArticlepeer-review


The geochemical effects of microbially mediated degradation of aromatic hydrocarbons were observed as changes in solution composition of an artificial groundwater in packed-sand laboratory columns. Benzene, toluene, and xylene, both individually and in a combined fashion, were used as substrates in biodegradation experiments conducted under oxygenated and anoxic conditions in columns filled with quartz, calcite, or Fe3+-coated quartz sand. Typically, column effluent had increased concentrations of dissolved inorganic C, decreased pH, and decreased concentrations of NO3 and dissolved O2 relative to column influent. Efficiency of CO2 generation was similar for the three different substrates, ranging from 22.5 to 26.6% organic C converted to CO2. When all three substrates were combined, the percentage of CO2 produced fell within the range observed in the single substrate experiments. Nitrate disappearance was more varied as a function of substrate identity, with greatest amounts lost when toluene was the substrate. Calcite dissolved as a result of CO2 generated during the biodegradation reactions, and empirically calculated dissolution rates varied between 1.9 and 4.0 x 10-9 mmol cm-2 s-1. The calcite dissolution rate was slower than the biodegradation rate, as evidenced by excess generation of CO2 relative to Ca2+ production. The decrease in pH was less in experiments with calcite present than in those with quartz sand present due to buffering by calcite dissolution. Dissolution of Fe oxyhydroxides was not observed under any experimental conditions.

Original languageEnglish (US)
Pages (from-to)291-303
Number of pages13
JournalApplied Geochemistry
Issue number3
StatePublished - May 1997

ASJC Scopus subject areas

  • Environmental Chemistry
  • Pollution
  • Geochemistry and Petrology


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