Experimental Study On The Effect Of Micro Levofloxacin On UASB Treatment Of Domestic Sewage

The chemical energy contained in organic pollutants in domestic sewage is a potential energy source.If this energy is employed recycled,the blueprint of"energy self-sufficiency"or even"energy output"of future municipal wastewater treatment plants can be realized.As the primary and core stage of carbon capture and energy recovery,the efficiency of anaerobic process can be easily affected by the composition of domestic sewage.Levofloxacin,as a typical organic pollutant of pharmaceutical and personal care products?PPCPs?in domestic sewage,might its influence the performance of anaerobic process,which has not gained much attention.In this study,upflow anaerobic sludge bed?UASB?reactors were used for energy recovery or carbon source recovery from the domestic sewage containing levofloxacin.The effects of trace levofloxacin on COD removal rate,VFAs production,microbial activity and resistance gene production in mesophilic anaerobic process and thermophilic anaerobic process were investigated.UASB reactor was successfully started with mesophilic mode,with COD removal rate reaching 87%and SMA value stable at 0.3 LCH₄/gVSS·d.Under mesophilic condionanaerobic,10 ug/L and 1 mg/L levofloxacin have effects on COD removal rate,pH,VFAs content and system gas yield of anaerobic process reactor.In contrast,the inhibitory effect of levofloxacin at 1 mg/L was more significant,with more fluctuated indicators.However,after a period of operation,the inhibitory effect of levofloxacin was eliminated and the system were recovered.Under these two concentrations,the mesophilic anaerobic process reached a stable state after 20 and 26 days respectively.The removal rate of COD was about 87%,the pH was6.8-7.2,the concentration of VFAs was about 200 mg/L,the system gas production was about3010 mL/d,and the SMA value gradually recovered to about 0.3012 LCH₄/gVSS·d.The removal rates of levofloxacin in reactor 2 and 3 were about 16%and 26%respectively.The existence of gyrA and gyrB resistance genes can be detected in reactor 2 and 3,and the content of gyrA and gyrB resistance genes in reactor 2 and 3 decreased with operation time.The greater the concentration of levofloxacin,the greater the anti-genes content of gyrA and gyrB.When turning to thermophilic mode,COD removal rate,pH,gas production and SMA value of the three UASB reactors increasedinitially and then stabilized at 89%,7.32,100 mg/L,3512 mL/d and 0.331 LCH₄/gVSS·d after 7 days,respectively.The removal rates of levofloxacin in reactor 2 and 3 were 54%and 44%respectively.The content of gyrA and gyrB resistance genes in reactor 2 and 3 decreased with the increase of operation time.The content of gyrA and gyrB resistance genes in reactor 3 was higher than that in reactor 2.Compared with mesophilic anaerobic process,COD removal rate and pH value were higher in mesophilic anaerobic process,but VFAs content,gyrA and gyrB resistance gene content were lower,system gas production and SMA value were higher,but system gas production and SMA in mesophilic anaerobic process are more stable.The thermophilic anaerobic process was more conducive to the degradation of levofloxacin and the contamination of gyrA and gyrB resistance genes.Thermophilic anaerobic process can capture carbon source of domestic sewage,remove trace levofloxacin and reduce resistance genes significantly.This study was of high academic significance and engineering value,providing a technical reference for stable operation of wastewater recycling process and anaerobic biological treatment of levofloxacin wastewater.