The biodegradation and microbiological impacts of micropollutants in methanogenic communities

Abstract

Pervasive usage of chemicals generates micropollutants throughout the environment. Anaerobic environments in particular accumulate high levels of hydrophobic micropollutants, and it is estimated that over 200 metric tons of micropollutants are discharged with biosolids each year. It is important to understand how treatment processes impact the fate of micropollutants as well as understand how micropollutants impact microbiological communities so that environmental risks can be minimized. This research elucidated the impact of an emerging treatment process, thermal-hydrolysis coupled to mesophilic anaerobic digestion (TH-MAD), on the fate of nonylphenol ethoxylates as well as the impacts of triclosan and perfluorooctane sulfonate (PFOS) on methanogenic community structure and function. The TH-MAD process inhibited biodegradation of nonylphenol ethoxylates to nonylphenol relative to MAD with no pretreatment. Indeed, the ratio of nonylphenol to the sum of nonylphenol ethoxylates + nonylphenol only increased by 24.6±3.1% in TH-MAD reactors compared to a 56% increase following MAD treatment. While post-aerobic treatment did reduce the sum of nonylphenol ethoxylates + nonylphenol, and concomitantly reduced estrogenicity, this research implied that source control is likely the most efficient option for removing these micropollutants. Triclosan is another wide-spread micropollutant that is persistent under anaerobic conditions. Triclosan is an antimicrobial agent that could therefore impact environmental systems that rely on healthy functioning of microorganisms. Methanogenic communities with no previous exposure to triclosan were able to adapt to triclosan at environmentally relevant levels and maintain function. When previously-exposed communities were exposed to triclosan at 4x current detected environmental levels, community structure shifted and methane production was inhibited. These levels of triclosan also selected for mexB, a gene that confers multidrug resistance, in previously unexposed communities. Lastly, PFOS was found to directly impact methanogenic communities and augment the impacts of triclosan in long-term exposure studies (140 days), but not in short-term (14 day) exposure studies.