Propagation of antibiotic resistance genes during anaerobic digestion of thermally hydrolyzed sludge and their correlation with extracellular polymeric substances

Abstract

The positive impact of the thermal hydrolysis process (THP) of sewage sludge on antibiotic resistance genes (ARGs) removal during anaerobic digestion (AD) has been reported in the literature. However, little information is available on how changes in different extracellular polymeric substances (EPS) due to THP can influence ARG propagation during AD. This study focused on systematically correlating EPS components and ARG abundance in AD of sewage sludge pretreated with THP (80 °C, 110 °C, 140 °C, 170 °C). THP under different conditions improved sludge solubilization followed by improved methane yields in the biochemical methane potential (BMP) test. The highest methane yield of 275 ± 11.5 ml CH4/g COD was observed for THP-140 °C, which was 40.5 ± 2.5% higher than the control. Increasing THP operating temperatures showed a non-linear response of ARG propagation in AD due to the rebound effect. The highest ARGs removal in AD was achieved with THP at 140 °C. The multivariate analysis showed that EPS polysaccharides positively correlated with most ARGs and integrons, except for macrolides resistance genes. In contrast, EPS protein was only strongly correlated with β-lactam resistance genes. These results suggest that manipulating THP operating conditions targeting specific EPS components will be critical to effectively mitigating the dissemination of particular ARG types in AD.

Sludge Thermal Hydrolysis for Mitigating Oxidative Stress of Polystyrene Nanoplastics in Anaerobic Digestion: Significance of the Solids Content

“…Compared to the controls, exposure to PsNPs decreased the protein content in PsNPs-4%TS and PsNPs-8%TS by 14.28 and 10.10%, whereas a 6.16% increase was achieved in PsNPs-12%TS. Increasing the EPS protein content can facilitate methane production since protein can serve as an electron shuttle and enhance the number of exoenzymes participating in extracellular electron transfer (EET). , The improvement of EET can outweigh the negative effect of the mass transfer limitation at a higher TS%, thereby stimulating methane production . Notably, EPS polysaccharides demonstrated an opposite trend to protein, and a dramatic shift was observed after exposure to PsNPs.…”

“…This increased secretion may be due to the microbial selfdefense mechanism, as suggested in the literature. 13,36 In contrast, samples with 4 and 8%TS (i.e., PsNPs-8%TS, THP-PsNPs-8%TS, PsNPs-4%TS, and THP-PsNPs-4%TS) were grouped together in the top and bottom-right quadrants. The ROS, VFA, and VS removal loading vectors were shifted toward the top-right quadrant, suggesting increased hydrolysis, VS destruction, and ROS generation in PsNPs-8%TS and THP-PsNPs-8%TS.…”

“…21 Spearman's rank correlation was used, and the correlation coefficient values ranged from −1 to +1. 13 The alpha value of 0.05 was selected for the correlation confidence intervals.…”

“…13 A THP before AD can decrease the proliferation of most ARGs throughout the digestion process. 13 Most recently, Azizi et al 1 found that the THP can provide dual benefits of mitigating the adverse impact of PsNPs in AD and reducing ARGs proliferation encouraged by PsNPs. However, knowledge of the effect of different operational features of the THP, particularly the total solids (TS) content of sludge, on MP/NP-induced stress during AD is still limited.…”

Pharmaceuticals and Personal Care Products in the Environment with Emphasis on Horizontal Transfer of Antibiotic Resistance Genes

“…Recent research is focused on improving the process and optimising the conditions to increase methane production. Researchers have used extracellular polymeric complexes and thermal treatment of wastewater sludges to remove antibiotics associated ARG in the bacteria before Anaerobic digestion [45]. However, several pre-treatment processes such as microwave, alkaline and several additives are done before the anaerobic oxidation to enhance the reactions [46].…”