Stenotrophomonas maltophilia T3-c, isolated from a biofilter for the removal of benzene, toluene, ethylbenzene, and xylene (BTEX), could grow in a mineral salt medium containing toluene, benzene, or ethylbenzene as the sole source of carbon. The effect of environmental factors such as initial toluene mass, medium pH, and temperature on the degradation rate of toluene was investigated. The cosubstrate interactions in the BTEX mixture by the isolate were also studied. Within the range of initial toluene mass (from 23 to 70 μmol), an increased substrate concentration increased the specific degradation of toluene by S. maltophilia T3-c. The toluene degradation activity of S. maltophilia T3-c could be maintained at a broad pH range from 5 to 8. The rates at 20 and 40°C were 43 and 83%, respectively, of the rate at 30°C. The specific degradation rates of toluene, benzene, and ethylbenzene by strain T3-c were 2.38, 4.25, and 2.06 μmol/g-DCW/hr. While xylene could not be utilized as a growth substrate by S. maltophilia T3-c, the presence of toluene resulted in the cometabolic degradation of xylene. The specific degradation rate of toluene was increased by the presence of benzene, ethylbenzene, or xylene in binary mixtures. The presence of toluene or xylene in binary mixtures with benzene increased the specific degradation rate of benzene. The presence of ethylbenzene in binary mixtures with benzene inhibited benzene degradation. The presence of more than three kinds of substrates inhibited the specific degradation rate of benzene. All BTEX mixtures, except tri-mixtures of benzene, ethylbenzene, and xylene or mixtures of all four substrates, had little effect on the degradation of ethylbenzene by S. maltophilia T3-c. The utilization preference of the substrates by S. maltophilia T3-c was as follows: ethylbenzene was degraded fastest, followed by toluene and benzene. However, the specific degradation rates of substrates, in order, were benzene, toluene, and ethylbenzene.

The effects of operational parameters such as carbon source, C/N ratio, initial nitrate concentration, temperature, and pH value on heterotrophic denitrification and functional denitrifying genes were evaluated. When methanol was used as the sole carbon source, complete denitrification was performed in a short time without nitrous oxide (N₂O) emission. Complete denitrification was performed at high C/N ratios (5.14 and 12.85) and low initial nitrate concentrations (75.9 and 151.6 mg N L⁻¹). The denitrification rate was not temperature-sensitive in the range of 25–35 °C, but tended to decrease at a low pH of 5–6. The relationships between N₂O emission and functional genes under various operational conditions were investigated by Pearson correlation and association network analyses. The C/N ratio was a key factor for N₂O emission during the heterotrophic denitrification process. This information on the denitrification performance and its association with functional gene dynamics under various operational conditions is useful for N₂O mitigation strategies for wastewater treatment processes.