Removal Of Trace Tetracycline And Drug Resistance By Anoxic/Oxic-forward Osmosis System

Tetracycline (TC) is one of the common used antibiotics which had inverse effect onenvironment. The presence of low concentrations of TC in wastewater will generate tetracyclineresistant bacteria (TRB) and tetracycline resistance genes (TRGs), thus posing a great risk tohuman health and ecosystems. Most conventional biological treatment processes can only partiallyremove TC, TRB and TRGs from wastewater. It is very important and urgent to systematicallyinvestigate the distribution of TC, TRB and TRGs in the wastewater treatment plants. Forwardosmosis (FO), a new emerging membrane process, has become increasingly attractive for its lowor no hydraulic pressures, low energy cost and high fouling resistance property. The aim of thispaper was to study the removal of trace TC, TRB and TRGs in the secondary effluent of ananoxic-oxic (AO) system by FO process.Fate of TC and TRB during the bench-scale AO system was investigated under differenthydraulic retention time (HRT)(6,8,10,12h) and sludge retention time (SRT)(5,10,15,20d).Under optimum operating condition, metagenomic technology and fluorescence quantitive PCRwere applied to determine the bacterial community structure and TRGs, respectively. The resultsshowed that HRT had no significant impact on TC removal efficiency and the removal efficiencymaintained at90%, but TC removal efficiency increased from81.8%to90.9%with the extensionof SRT from5d to20d. With the extension of HRT and SRT appropriately, the number of TRBdecreased. The dominant bacteria in theAO process were Proteobacteria and Bacteroidetes. Thedominant bacteria in anoxic’s aqueous phase, anoxic’s sludge phase and oxic’s aqueous phasewere Proteobacteria, the proportion were53.55%,44.29%and54.42%, respectively. Thedominant bacteria of oxic’s sludge phase and secondary effluent were Bacteroidetes, theproportion were46.83%and45.23%, respectively. The AO process could partially remove TRGs.Compared with the TRGs concentration of anoxic’s aqueous phase, TRGs declined about0~1log concentration in the secondary effluent.The rejection of trace TC in the secondary effluent of AO process by FO membranes was alsoinvestigated. The effects of different operating conditions including membrane orientation, flowvelocity, and draw solution concentration and solute on TC rejection were explored. Then theremoval of TRB and TRGs were also evaluated under optimum FO process operating conditions.The results revealed that increasing water flux by increasing draw solution from0.5M to2Munder FO mode and PRO mode. For the CTA-ES membrane, TC rejection increased withincreasing water flux. For the CTA-NW membrane, an initial and gradual increase in TC rejectionwas observed at low draw solution concentrations, which then decreased at high draw solutionconcentrations. In addition, the rejection behaviour of the TFC-ES membrane was similar to thatof the CTA-NW membrane. No significant changes in TC rejection by the CTA-ES membranewere detected with an increase in flow velocity from8cm/s to32cm/s. For the TFC-ESmembrane, flow velocity substantially influenced the rejection of TC. For the CTA-NWmembrane, in the FO mode, the rejection of TC was slightly increased with increasing flowvelocity. In contrast, the rejection of TC decreased gradually in the PRO mode. When NaCl,MgSO4, glucose, and urea were used as draw solutions, the rejection of tetracycline in FO andPRO mode occurred in the following order: NaCl> urea> MgSO4> glucose and NaCl> urea>MgSO4> glucose. For the CTA-ES membrane, the optimum TC rejection values were87.19%(2M,16cm/s) and90.03%(2M,16cm/s) in the FO mode and PRO mode, respectively. For theCTA-NW membrane, the optimum TC rejection values were78.43%(1.5M,32cm/s) and84.78%(1M,8cm/s) in the FO mode and PRO mode, respectively. For the TFC-ES membrane, theoptimum TC rejection values were64.58%(1.5M,32cm/s) and79.54%(1.5M,32cm/s) in theFO mode and PRO mode, respectively. In the FO mode and PRO mode, the permeation of TRB inthe CTA-ES membrane and TFC-ES membrane were lowest and highest, respectively. And thepermeation of TRB in the PRO mode was higher than in the FO mode. In the FO mode, theremoval rate of tet (C), tet (A) and tet (C) were highly by CTA-ES, CTA-NW and TFC-ESmembranes, respectively. In the PRO mode, the removal rate of tet (C) were the highest byCTA-ES, CTA-NW and TFC-ES membranes.Finally, FO process was applied to treat real wastewater of AO system for removal TC, TRBand TRGs. Compared to the laboratory condition, the rejection of TC decreased, the permeation ofTRB and TRGs increased. The results showed that the removal rate of TC, TRB and TRGs wereimpacted by the microconstituents in reclaimed water. These findings potentially can be useful forcombination of activated sludge and FO process operation in wastewater reclamation.