Use of a filtering process to remove solid waste and antibiotic resistance genes from effluent of a flow-through fish farm.

The objective of this study was to investigate reduction in antibiotic resistance genes (ARGs) via targeting solid waste in effluent from a flow-through aquaculture in South Korea. The level of suspended solids in the filtrates was approximately 12.5±2.3mg/L, corresponding to a removal efficiency of 68.8±5.7% irrespective of variations in the size of the filter pores. The total number of particles in the effluent was reduced to the lowest numbers of particles using a filter pore size of 25µm, corresponding to a removal efficiency of 40.3%. Among the 23 ARGs conferring resistance to tetracyclines, beta-lactam antibiotics, sulfonamides, quinolones, macrolides, florfenicol and multidrug, tetracycline resistance genes were the most prevalent with a relative abundance of 67.5%. Of eleven tetracycline resistance genes (tetA, tetB, tetD, tetE, tetG, tetH, tetM, tetQ, tetX, tetZ, tetB/P) analyzed, the relative abundance of tetG was the highest in the effluent. The removal efficiency of the total number of particles showed similar patterns to the removal efficiency of ARGs depending on the size of the filter pores. Levels of ARGs in the filtrates were reduced to approximately 60.5% of those of the ARGs in the effluents. With a filter pore size of 25µm, a maximum removal efficiency of 66.0% was achieved. In particular, the relative abundance of detected tetracycline resistance genes decreased only after passing through the filters, perhaps reflecting the presence of high quantities of tetracycline resistance genes in particles from the fish farm. Using Illumina sequencing based on a 16S rRNA gene, the dominant phyla were found to be Bacteroidetes, Proteobacteria, Planctomycetes and Verrucomicrobia in the effluent. Although the overall composition of the bacterial communities was not significantly changed via filtering tests, only the relative abundance of Bacteroidetes and Proteobacteria was changed. These results demonstrate that a filtering process in aquaculture facilities can be used to reduce solid waste as well as ARGs from aquaculture farms.

Fate of antibiotic resistance genes and metal resistance genes during thermophilic aerobic digestion of sewage sludge.

This study examines the fate of twenty-three representative antibiotic resistance genes (ARGs) encoding tetracyclines, sulfonamides, quinolones, ß-lactam antibiotics, macrolides, florfenicol and multidrug resistance during thermophilic aerobic digestion (TAD) of sewage sludge. The bacterial community, class 1 integrons (intI1) and four metal resistance genes (MRGs) were also quantified to determine the key drivers of changes in ARGs during TAD. At the end of digestion, significant decreases in the quantities of ARGs, MRGs and intI1 as well as 16S rRNA genes were observed. Partial redundancy analysis (RDA) showed that shifts in temperature were the key factors affecting a decrease in ARGs. Shifts in temperature led to decreased amounts of ARGs by reducing resistome and bacterial diversity, rather than by lowering horizontal transfer potential via intI1 or co-resistance via MRGs.

Quantitative and qualitative changes in antibiotic resistance genes after passing through treatment processes in municipal wastewater treatment plants.

In this study, quantitative and qualitative changes in antibiotics resistance genes (ARGs) were investigated in two municipal wastewater treatment plants (WWTPs) treating pretreated livestock or industrial wastewater as well as municipal sewage. Total eight ARGs (tetX, tetM, tetA, sul1, sul2, ermB, qnrD, and blaTEM) were quantified, and their relative abundance was assessed by ARGs copies/16S rRNA gene copies. The fate of ARGs was observed to be different between two WWTPs: sul, qnrD, and blaTEM were proliferated during the treatment processes only in the WWTP1 which received pretreated livestock wastewater. Furthermore, dynamic shifts in patterns of ARGs occurrence were observed during biological, secondary sedimentation and coagulation processes. During biological treatment in both WWTPs, relative abundance of tet and ermB changed: tet increased significantly by 211.6-357.6%, while ermB decreased by 70.4-92.0%. Little variation was observed in sul, qnrD and blaTEM. Subsequently, the relative abundance of tet decreased during the secondary sedimentation and coagulation in both WWTPs: tet decreased by 56.0-86.3% during sedimentation and by 48.2-75.7% during coagulation, respectively. During the final treatment, different responses of antibiotic resistance bacteria (ARB) and ARGs to ultraviolet (UV) disinfection were found: removal efficiencies of ARB were observed in the range of 34-75%, while obvious reduction in ARGs was not observed at the UV dose of 27mJ/cm2. Although ARGs underwent various treatment processes, considerable levels of ARGs remained at discharge amounting to 4.2×1018 copies/day from WWTP1 and 5.4×1016 copies/day from WWTP2, respectively.

Biomethanation of Sewage Sludge with Food Waste Leachate Via Co-Digestion.

Anaerobic mono- and co-digestion of sewage sludge and food waste leachate (FWL) were performed by assessing methane production and characterizing microbial communities. Anaerobic digestion (AD) of waste activated sludge (WAS) alone produced the lowest methane (281 ml CH4), but an approximately 80% increase in methane production was achieved via co-digestion of WAS and FWL (506 ml CH4). There were less differences in the diversity of bacterial communities in anaerobic digesters, while archaeal (ARC) and bacterial (BAC) amounts reflected AD performance. Compared with the total ARC and BAC amounts in the mono-digestion of WAS, the ARC and BAC amounts increased two and three times, respectively, during co-digestion of FWL and WAS. In characterized archaeal communities, the dominant ratio of hydrogenotrophic methanogens in the mono-digestion of WAS approached nearly a 1:1 ratio of the two acetoclastic and hydrogenotrophic methanogens in the co-digestion of FWL and WAS. The ARC/BAC ratio in the digesters varied in the range of 5.9% to 9.1%, indicating a positive correlation with the methane production of AD.