| In order to comprehensively promote the resource utilization of livestock and poultry breeding waste,the traditional livestock and poultry breeding wastewater treatment methods can no longer meet the needs of the modern era.It is of great significance to study the green sustainable and resource recycling process for wastewater treatment.The treatment of wastewater by microalgae is considered to be an efficient,sustainable and environmentally friendly wastewater treatment method,which has attracted more and more attention.The introduction of activated sludge into microalgae treatment wastewater to form microalgae-bacteria symbionts can enhance the stability and reliability of the wastewater treatment process.The introduction of micro-electric field into microalgae-bacteria symbionts to treat livestock and poultry wastewater can promote the growth and metabolic activity of microorganisms through electrical stimulation,thereby improving pollutants treatment efficiency.The combination of microalgae-bacteria symbionts and membrane to form microalgae-bacteria symbiotic membrane bioreactor can further improve the treatment effect of pollutants.The presence of micro-electric field would affect the composition and content of EPS(extracellular polymeric substance),which would futher affect the membrane fouling conditions.In this study,the effects of micro-electric field on the wastewater treatment effect and biomass growth of pure microalgae system,pure activated sludge system and microalgae-sludge system in livestock and poultry breeding wastewater treatment were studied first.Secondly,according to the optimized microbial system,the electrolysis parameter optimization experiment of micro-electric field enhanced microbial system for wastewater treatment was carried out to explore the influence mechanism of micro-electric field on membrane fouling of microalgae-bacteria symbionts-membrane combined process.The results were as follows :In the treatment of livestock and poultry breeding wastewater by pure microalgae system,pure sludge system and microalgae-sludge system,the COD removal rates achieved up to over 87 %.The removal rates of microalgae-sludge system on carbon,nitrogen and phosphorus were better than that of pure microalgae system and pure sludge system.The microbial system under the action of microelectric field showed better and more stable pollutants removal effect,and the COD removal rates could be higher than 92 %.The total nitrogen removal rates of pure microalgae system,pure sludge system and microalgae-slugde system increased by12.55 %,6.29 % and 18.92 % respectively,and the removal rates of phosphorus were also improved.The contents of chlorophyll a,chlorophyll b and carotenoids in microalgae-sludge system were higher than those in pure microalgae system at the same conditions.In the three microbial systems,the biomass growth of the closed group was the largest,and the chlorophyll a content of the pure microalgae closed group R5 and the microalgae-slugde closed group R11 was 12.11 times and 10.83 times of the initial inoculation,respectively.The electrolysis time,electrode spacing and voltage were selected to carry out orthogonal experiments on the microalgae-bacteria symbiosis system.The multiindex comprehensive weighted scoring method was used to comprehensively consider the removal effect of carbon,nitrogen and phosphorus and the growth of biomass.The primary and secondary order of the three factors was: electrode voltage > electrolysis time > electrode spacing.The best operating parameters were electrolysis time at 24 h,electrode spacing at 0.5 cm,voltage at 0.5 V.From the perspective of membrane flux decline,Group B at the optimized electric field condition has the slowest membrane flux decline and the most minor membrane fouling conditions.From the content of proteins,polysaccharides and humic acids,for the total organic matterconcentration of each EPS components among the three groups,Group B showed a much lower amount than that of the other two groups.Results from a variety of characterization methods proved that,polysaccharides and proteins were the main contributors to membrane fouling.The above results demonstrated that micro-electric field could affect the secretion of microbial EPS,change the contents and concentration of EPS,and then mitigate the membrane fouling conditions. |
