Biodegradation of MCHM and PPH in River Microcosms and Activated Sludge

A mixture of coal processing agents, namely crude-MCHM (primarily 4-methylcyclohexanemethanol) and stripped-PPH (primarily dipropylene glycol phenyl ether and propylene glycol phenyl ether) spilled into the Elk River near Charleston, West Virginia in January 2014. The spill resulted in a do-not-use ban on drinking water for up to 10 days. Studies were undertaken to determine the potential for aerobic biodegradation of crude-MCHM and PPH in the riverine system and in the sewage treatment plant postflushing of affected water lines. Complete biotransformation of crude-MCHM occurred only when MCHM was initially $<6\mathrm{mg}{\mathrm{L}}^{-1}$. When both PPH and crude-MCHM were present, biotransformation of both compounds only occurred when MCHM was initially $<2.3\mathrm{mg}{\mathrm{L}}^{-1}$ and PPH was $<3\mathrm{mg}{\mathrm{L}}^{-1}$. Limited conversion of PPH was typically observed ($<40\%$). Estimated maximum specific biodegradation rates were 0.087 mg cis-MCHM ${(\mathrm{mg}\text{biomass}\mathrm{h})}^{-1}$ and 0.23 mg trans-MCHM ${(\mathrm{mg}\text{biomass}\mathrm{h})}^{-1}$. The estimated half saturation constants were 2.7 mg cis-MCHM ${\mathrm{L}}^{-1}$ and 10.5 mg trans-MCHM ${\mathrm{L}}^{-1}$. Toxicity studies with agar diffusion plates and ToxTrac indicate both MCHM and PPH exhibit toxicity to Elk River microcosm cultures and that microbiological degradation of MCHM and PPH may generate more toxic products. Phylogenetic analysis of sediments and biodegradation microcosm cultures identified methanotrophs, methylotrophs, and organisms associated with xenobiotic biodegradation, acid mine drainage, and sulfidic mine tailings. These studies can be used to understand the likelihood of biological degradation of MCHM and PPH in environmental and treatment systems.