Performance Of MBR For Treating High Sulfate Wastewater And Enhancement With High Efficiency Strains

Nutritional food processing plants will produce a large number of organic wastewater with high sulfate salt in the production process.In order to effectively degrade the nutrients（organic matter,nitrogen and phosphorus）in wastewater,aerobic Membrane Bioreactor（MBR）combined with bio-enhanced technology is adopted for treatment..In this paper,the high sulfate organic wastewater produced by a nutritious food factory was taken as the experimental object.The operation effect of MBR process was studied under the concentration of SO₄^2-in the influent of 1.6%and 2.6%respectively.At the same time,by using the mature sludge in MBR system as the strain source,several strains with high efficiency and salt tolerance were screened out,and then they were combined and put into the system to further study the treatment capacity of MBR system under different sulfate concentrations after strain strengthening.The main results are as follows:Therefore,this paper had taken the high sulfate organic wastewater produced by nutritious food process plant as the experimental object,and studied the operation performance of MBR process under the condition of the influent SO₄^2-concentration with 1.6%and 2.6%SO₄^2-respectively.Furthermore,by using the mature sludge in MBR system as the strain source,several strains with high efficiency and salt tolerance were screened out.And then they were combined and put into the system,and the performance of MBR system under different sulfate concentrations after strain strengthening was further investagated.The main results are as follows:（1）After 110 days of operation,it was found that the system with 1.6%SO₄^2-concentration in influent could obtain higher volumetric load rate（VLR）and better pollutant removal efficiency,with maximum VLR of 1.0 kg COD·（m³·d）^-1 and COD removal efficiency of 97.7%.However,the maximum VLR was only 0.5 kg COD·（m³·d）^-1 and the COD removal efficiency was 96.4%in the system with 2.6%SO₄^2-.At the concentration of 2.6%SO₄^2-,as the microorganisms were inhibited,the degradation efficiency of organic matter was lower than that of the system with 1.6%SO₄^2-.In addition,the ammonia nitrogen removal efficiency of1.6%SO₄^2-system could reach above 91%,while that of 2.6%SO₄^2-system was about 82%.After long-term operation,both MBR units have established simultaneous nitrification and denitrification nitrogen removal systems.The removal efficiency of total nitrogen in 1.6%SO₄^2-system was 89.5%,while that in 2.6%SO₄^2-system was 80.7%.Both reactor devices can achieve 100%removal fficiency of total phosphorus.In addition,the membrane fouling rate of the reactor with 1.6%SO₄^2-concentration was slower than that of the system with 2.6%SO₄^2-.Further analysis of the sludge properties showed that the mixed liquor suspended solids（MLSS）and mixed liquid volatile suspended solids（MLVSS）in the system with 1.6%SO₄^2-concentration were stable at about 7.1 g L^-1 and 5.9 g L^-1,and the MLVSS/MLSS ratio was increased from 80.2%in the the initial stage to 83%.In the system with 2.6%SO₄^2-concentration,MLSS and MLVSS were stable at about 6 g L^-1 and 4.5 g L^-1,and MLVSS/MLSS was lower than that in the initial stage,and finally stabilized at about 75%.After long-term acclimation in high-salt environment,the Soluble Microbial Products（SMP）and the Boud Extracellular Polymeric Substances（BEPS）of mature sludge in the 1.6%SO₄^2-and 2.6%SO₄^2-systems increased,with SMP rising from 13.5 mg·g VSS^-1 to 20.4 mg·g VSS^-1 and 65.3mg·g VSS^-1,and BEPS rising from 36.9 mg·g VSS^-1 to 181.8 mg·g VSS^-1.The values of SMP and BEPS of 2.6%SO₄^2-system were both higher than that of 1.6%SO₄^2-system,which made the trans-membrane pressure（TMP）rise faster and the membrane fouling worse.The particle size of sludge in MBR of 1.6%system increased from 82.3μm to 125.84μm,while that in 2.6%SO₄^2-system decreased to 78.23μm.Compared with the 1.6%SO₄^2-system,the sludge in the2.6%SO₄^2-system had smaller particle size and was easier to accumulate on the membrane surface,which made the filter cake layer more compact and accelerated the formation of membrane fouling.The membrane resistance of both devices mainly composed of external resistance,and the internal resistance of 2.6%SO₄^2-system was higher than that of 1.6%SO₄^2-system.The high salinity environment presented a certain influence on the microbial community composition,and the dominant species in both systems had changed from Candidatus＿Saccharibacteria to Proteobacteria.At the generic level,Saccharibactria＿Genera＿incertae＿Sedis and unclassified＿Bacteria were the dominant genera in the original inoculated sludge.Then it shift to Stappia in 1.6%system,but remained unchange in 2.6%system.At the same time,Pseudomonas with the function of simultaneous nitrification and denitrification appeared in certain abundance in the two systems.（2）Three high-efficient strains with salt tolerance were screened from the mature sludge of the MBR with SO₄^2-concentration of 2.6%by the method of repeated acclimation of salinity,among which Klebsiella michiganensis and Marinobacter alkaliphilus were both aerobic denitrifying strains.They had excellent salt tolerance and could survive at 6%salinity.The other strain was Pseudomonas stutzer,a strain with heterotrophic nitrification and aerobic denitrification function,which could survive at 4%salinity.Through the study on the combination of strains,it was found that the combination of mixed culture of three strains had the highest degradation efficiency for pollutants,and the degradation efficiency of COD,ammonia nitrogen and TN could reach above 70%.（3）After inoculation with mixed strains,the operation efficiency of MBR under two kinds of SO₄^2-concentration systems was improved.Under the condition that kept the effluent COD below 200 mg·L^-1,the VLR of the 1.6%SO₄^2-system was up to 1.8 kg COD·（m³·d）^-1,and the VLR of the 2.6%system was also improved compared with that before strengthening.Under the load of 1.0 kg COD·（m³·d）^-1,the effluent COD remained at 150 mg·L^-1.At the same time,the removal efficiency of ammonia nitrogen and TN were also enhanced.When the influent VLR reached 2.0 kg COD·（m³·d）^-1,the effluent ammonia nitrogen concentration remained below 1.0 mg·L^-1,and the removal efficiency was above 95.0%.However,the ammonia nitrogen concentration of effluent in the reactor with 2.6%SO₄^2-improved with the increase of VLR.When the VLR was 1.2 kg COD·（m³ d）^-1,the ammonia nitrogen removal efficiency decreased to about 77.4%.At the same time,the TN removal efficiency of the system with 1.6%SO₄^2-concentration was better than that of the system with 2.6%.By analyzing the sludge properties,it was found that the inoculation of strains could effectively improve the microbial biomass.The MLSS and MLVSS in the system with 1.6%SO₄^2-concentration were stable at about 7.1g·L^-1 and 5.7g·L^-1,and the MLVSS/MLSS ratio remained at about 80.2%.In the system with 2.6%SO₄^2-concentration,MLSS and MLVSS were stable at about 7.3 g·L^-1 and5.9 g·L^-1,and MLVSS/MLSS was finally stable at about 80.8%.It was found that the SMP content in the sludge could be significantly reduced by inoculation of the strains.The SMP of the 1.6%system was 20.5 mg·g VSS^-1 before strengthening,and it was reduced to 11.5mg·g VSS^-1 under the VLR of 1.2 kg COD·（m³ d）^-1 after inoculation of mixed strains.After strain strengthening,the SMP of the reactor with 2.6%SO₄^2-concentration decreased from 65.4mg·g VSS^-1 to 30.0 mg·g VSS^-1.However,with the increase of VLR,the SMP value of the two systems kept rising.It was found from the changes of BEPS that the VLR had a great influence on BEPS,and the protein content of BEPS gradually accumulated in the two systems.In the reactor with 1.6%SO₄^2-,the protein content of BEPS increased from 119.4 mg·g VSS^-1 to 197.4mg·g VSS^-1.However,the protein content of BEPS increased from 153.8 mg g VSS^-1 to 178.5mg g VSS^-1 in the reactor with 2.6%SO₄^2-concentration.At the same time,the particle size of sludge in the two systems was affected.The particle size of sludge in the reactor with 1.6%SO₄^2-increased from 125.8μm to 156.2μm,while that in the reactor with 2.6%SO₄^2-increased from 78.2μm to 128.4μm.From the change of microbial community composition,it was found that the absolute dominant bacteria in 1.6%and 2.6%systems was Proteobacteria after the VLR increase at the Phylum level.However,it was found through genus level that the inoculated mixed strains of Marinobacter and Pseudomonas survived well in the two systems and gradually became the dominant bacteria.