| The solvent in antibiotic wastewater is a typical refractory pollutant in the wastewater of pharmaceutical industries.It has been listed as a priority pollutant in China,the United States and Germany.Long-term residue of solvent in antibiotic wastewater will pose a serious threat to human health and ecosystem.Anaerobic membrane bioreactor?AnMBR?is a new type of wastewater treatment technology.It has the advantages of high sludge concentration,high impact loading capacity and good removal effect due to the interception of the membrane.It is especially suitable for the removal of toxic and harmful substances such as solvent in antibiotic wastewater.Therefore,in view of the complex influent quality of antibiotic wastewater containing solvents,the research method of stable operation and shock change is adopted for multiple boundary conditions.The effect of long-term operation and pollutant removal mechanism of the AnMBR process are investigated,the sludge characteristics are determined.This study reveals the mechanism of membrane fouling,and provides reference for practical engineering application of AnMBR.This paper studied the long-term performance and pollutant removal mechanism of AnMBR,the results showed that AnMBR had good removal effect on antibiotic wastewater containing solvents during the period of startup and stable operation,the total removal rate of chemical oxygen demand?COD?and solvents exceeded 90.0% and 92.0% respectively.The average values of permeate COD,N,N-Dimethylformamide?DMF?,tetrahydrofuran?THF?,m-Cresol?MC?and iso-Propyl alcohol?IPA?were 269.6,22.0,6.2,18.4,1.2mg/L,respectively.On the basis of this,the effects of hydraulic retention time?HRT?,influent COD concentration,temperature and membrane shear rate?MSV?on AnMBR were investigated.The results showed that HRT and influent COD concentration had a great impact on the total removal rate of COD,DMF,THF,MC and IPA.When the influent COD was 5000.0,8000.0,12000.0,18000.0mg/L,HRT should be controlled at 18.0,24.0,36.0 and 48.0h in order to achieve good removal effect.When the influent COD was over 21000.0mg/L,the effluent quality deteriorated and the performance of reactor decreased.The effects of temperature and MSV on the total removal rate of COD,DMF,THF,MC and IPA were not significant,but the effects on the biological removal rate and physical removal rate were significant.In this study,we proposed the removal mechanism of AnMBR to treat antibiotic wastewater containing solvents.The characteristics of sludge in AnMBR were studied under different operating conditions.The indexes included mixed liquid suspended solids?MLSS?,mixed liquor volatile suspended solids?MLVSS?,extracellular polymeric substances?EPS?,soluble microbial products?SMP?,specific methanogenic activity?SMA?,methanogens and sludge rheological properties.The results of stable operation showed that average values of MLSS,MLVSS and MLVSS/MLSS were 31.0g/L,24.7g/L and 0.8,respectively.The MLSS and MLVSS of attached sludge on membrane surface increased first and then decreased,the concentration ranges were 68.6-28.9g/m2 and 55.7-22.3g/m2,respectively.In both the suspended sludge and attached sludge,the EPS concentration decreased with running time.The range of protein and polysaccharide in suspended sludge was 67.7-30.8g/m2 and 14.5-7.6 g/m2,respectively.The range of protein and polysaccharide in attached sludge was 18.7-5.5g/m2 and 9.5-3.7g/m2,respectively.The protein/polysaccharide in the suspended sludge increased to 5.3 and then declined to 4.0,while the protein/polysaccharide in the attached sludge showed a decreasing trend from 1.9 to 1.4.The effect of MSV on SMP in suspended sludge was investigated.The results showed that SMP increased with the increase of MSV.The effect of temperature on SMA indicated that the SMA of suspended sludge increased with the increase of temperature,while SMA of attached sludge decreased gradually.SMA of the attached sludge was always below the SMA of suspended sludge.The changes of methanogens in different periods were studied.The results showed that during the start-up period and the stable run-time Methanosarcinaceae was the dominant flora,the average relative abundance were 22% and 15.5%-30.0%,respectively.When the temperature was 15.0±3.0 ?,the Methanosarcinaceae and Methanomicrobiales were the dominant populations,the average relative abundance were 28.7% and 27.7%,respectively.Finally,the relationship between the shear pressure and shear rate of anaerobic sludge was simulated by using the Carson model,the power law model and the Bingham model.The rheological parameters of anaerobic sludge under different MLSS concentration,temperature and MSV were calculated.The results showed that the non-Newtonian fluid characteristics and shear thinning of anaerobic sludge were more obvious under low temperature.At the same temperature,MSV exhibited a nonlinear relationship with shear stress.The formation mechanism of membrane fouling in AnMBR was analyzed.The changes of membrane flux,transmembrane pressure?TMP?,membrane contamination rate and membrane fouling rate under different MSV,MLSS and colloidal total organic carbon?TOC?conditions were investigated.The general mathematical model of membrane contamination rate was established.The results showed that the increase of MSV significantly affected the pseudo-state flux?J6h?after 6 h filtration,both at low and high MLSS.The highest J6 h and J6h/J0 were obtained when MLSS was 30.0g/L and MSV was 2.1m/s,the lowest J6 h and J6h/J0 were obtained when MLSS was 40.0g/L and MSV was 0.1m/s.The results of TMP showed that MLSS had a great effect on TMP when MSV = 0.1m/s and 0.7m/s,while colloidal TOC concentration did not play a major role.When MSV=1.5m/s and 2.1m/s,colloidal TOC had a greater effect on TMP,while MLSS concentration did not play a major role,too.At the MSV of 0.1-1.5m/s and the same MLSS,the membrane contamination rate increased with the increase of colloidal TOC.And the the rate of membrane fouling increased with the invrease of colloidal TOC at high concentration of MLSS.However,when MSV=2.1m/s,although the membrane fouling rate increased with the increase of colloidal TOC,but different MLSS no longer affect its increasing slope.The contribution rate of MLSS to membrane fouling decreased with the increase of MSV,and the contribution rate of colloidal TOC and soluble substances to membrane fouling increased gradually.The effect of the periodic MSV operation mode and the higher MSV mode on the AnMBR membrane fouling rate and the pollutant removal performance was compared at the same time.The results showed that both of them could achieve the same membrane fouling and pollutant removal performance.Therefore,the periodic MSV operation mode can be used to save energy consumption of AnMBR. |
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