Role of methanogenesis on the biotransformation of organic micropollutants during anaerobic digestion

Abstract

Several studies showed that some organic micropollutants (OMPs) are biotransformed during anaerobic digestion (AD). Yet, most of them aim at reporting removal efficiencies instead of understanding the biotransformation process. Indeed, how each of the main AD stages (i.e., hydrolysis, acidogenesis, and methanogenesis) contribute to OMP biotransformation remains unknown. This study focuses on investigating the role of methanogenesis, the most characteristic step of AD, to OMP removal. More specifically, the sorption and the biotransformation of 20 OMPs by methanogenic biomass were analyzed determining their concentrations in both liquid and solid phases. Sorption onto methanogenic biomass displayed a similar behavior as reported for digested sludge. Most of the OMPs were biotransformed to a medium extent (35-70%) and only sulfamethoxazole was completely removed. Comparing these results with those reported for the complete AD process, methanogenesis was proven to play a key role, accounting for more than 50% of the OMP biotransformation (except for roxithromycin) during AD. An increase in the organic loading rate from 1 to 2gCOD/Ld, typical loads employed in sewage sludge anaerobic digesters, did not exert a clear cometabolic effect on the OMPs biotransformation. It is hypothesized that biotransformation occurs in both liquid and solid phases because no link between the partition coefficient (Kd) and the overall biotransformation efficiency was found. These findings allow a better understanding of the OMPs fate under anaerobic conditions, which is necessary to design efficient biological mitigation strategies.

Reversibility of enzymatic reactions might limit biotransformation of organic micropollutants

“…However, during the second step of the assay (after the second pulse of ATP and HK), a recovery of the BPA concentration was not observed, probably because of the much lower reaction time (52 h) than that in the AK assays (215 h), which likely was not enough to have a significant decrease in the ATP concentration that shifted the equilibrium. Finally, it should be noticed that the maximum removal efficiencies achieved in the in vitro experiments with AK ( Figure 2) and HK ( Figure 3) are lower than the reported values in * * * * * some anaerobic reactors (40-80%) (Gonzalez-Gil et al, 2018b;Samaras et al, 2014;Wijekoon et al, 2015). This is an expected result, since many other enzymes are involved in anaerobic processes that could also participate in the biotransformation of BPA.…”

“…Biological systems can transform a wide variety of organic micropollutants (OMPs); actually, biotransformation is a key removal mechanism of OMPs in sewage treatment plants (STPs). However, most compounds are not fully biotransformed and concentration kinetic plateaus are reported in a wide variety of aerobic (Blair et al, 2015;Fernandez-Fontaina et al, 2014;Gulde et al, 2018;Xue et al, 2010) and anaerobic (Gonzalez-Gil et al, 2018b;Xue et al, 2010) reactors operating in batch or continuously. Since no substrate limitations are expected in steady-state continuous reactors, a decrease of the metabolic activity and thus of the cometabolic transformation of OMPs is excluded.…”

Integrating independent microbial studies to build predictive models of anaerobic digestion inhibition by ammonia and phenol

“…However, The European Biomass Association (AEBIOM) estimates that anaerobic digestion still has a considerable potential for expansion with a biogas potential at about 78 billion m 3 biomethane. To reach this goal, the optimization of biogas production is essential to improve high process stability and efficiency and lower susceptibility to disturbances.…”

Machine learning analysis of microbial flow cytometry data from nanoparticles, antibiotics and carbon sources perturbed anaerobic microbiomes

“…We also demonstrated for the first time, the use of unsupervised autoencoders for microbial flow cytometry data. Applications of the machine learning analysis of microbial flow cytometry data in potentially improving the performance of biodigesters, and to characterize the syntrophic resilience [ 31 ] of the microbial community structure when exposed to nanoparticles and antibiotics has also been demonstrated. Perhaps in the future such tools would enable futuristic endeavors such as waste treatment in long-term human spaceflight missions [ 32 – 34 ] or to transform human waste into food [ 35 ].…”