Study On The Effect Of Electric Field On The Treatment Of Swine Wastewater By Microalgae-bacteria Symbionts And The Mechanism Of Membrane Contamination

The swine wastewater produced in the process of live pig breeding is one of the main sources of agricultural non-point source pollution,and the environmental pollution issue has also become a bottleneck restricting the development of large-scale pig breeding.The microalgae-bacteria symbionts formed by co-cultivation of microalgae and bacteria are were combined with membrane bioreactors to treat swine wastewater,which could effectively remove excess carbon,nitrogen,phosphorus and other pollutants in swine wastewater.Meanwhile,the microalgae-bacteria symbionts can form considerable biomass resources through the growth and metabolism of pollutants,which is a green and sustainable wastewater treatment process.However,the characteristics of high color and turbidity in swine wastewater restrict the growth of microalgae-bacteria symbionts and the improvement of pollutant removal efficiency.The electric field treatment can rapidly reduce the color and turbidity of wastewater,and the combination of electric field and microalgae-bacteria symbionts treatment could improve the growth of microalgae-bacteria symbionts,regulate the secretion of extracellular polymers,and slow down and regulate the membrane fouling.The main objective of this thesis is to investigate the effect of electric field treatment on the microalgae-bacteria symbionts membrane bioreactor,study the effect of electric field treatment and the coupling mode of microalgae-bacteria symbiosis,the effect of different electrode materials on the growth of microalgae-bacteria symbionts and membrane fouling,and investigate its purification effect on swine wastewater,providing a theoretical basis and technical support for the application of the process in the field of wastewater treatment.The main results are as follows:1.The influence of electric field treatment and microalgae-bacteria symbionts combinations on the treatment efficiency and biomass yield were investigated.The results showed that the "electric field-microalgae-bacteria symbionts"(EF-MB)combination and "microalgae-bacteria symbionts-electric field"(MB-EF)combination showed different characteristics in pollutants removal.The EF-MB coupled system presented excellent nitrogen removal efficiency with 66.46% TN removal and 77.29% ammonia nitrogen removal;the MB-EF coupled system showed better COD and phosphorus removal rates at 81.53% and 97.32% for COD and TP,respectively..In terms of biomass yield,the chlorophyll content of the EF-MB coupled system was 1.78 times that of the MB-EF coupled system,indicating that microalgae grew better in wastewater treated by electric field.2.In the EF-MB coupled system,iron and aluminium anodes showed different results.Iron electrode exhibited higher COD removal rate at 41.41%,while aluminium electrode showed higher phosphorus emoval rate at 91.35% of TP.Besides,similar results were observed for nitrogen and color removal.In terms of microbial growth,the aluminium group showed higher chlorophyll growth,which was 4.13 times higher than when inoculated,indicating a better growth condition for microalgae.3.The electric field treatment influenced EPS secretion by microalgae-bacteria symbionts.EPS from iron electrode group(group 1),aluminium electrode(group 2)and no electric field group(group 3)were split and filtered through ultrafiltration tests.Results from all groups proved that SMP contributed the most to membrane fouling.Group 3 had the highest EPS content,the most rapid membrane flux decay and the most severe membrane fouling condition,while Group 1 had relatively mild membrane fouling condition.The major membrane foulants were hydrophilic proteins and polysaccharides based on results from multiple characteristic analysis methods.