| Compared with conventional water treatment process,the treatment of livestock wastewater by algal-bacteria symbiosis can enhance the removal efficiency of C,N,P and other nutrients in sewage water as well as reduce energy consumption,but there are also disadvantages such as the loss of biomass and the deterioration of water quality caused by algal-bacteria EPS secretion in the effluent.Ultrafiltration membrane can not only effectively retain biomass to achieve the separation of hydraulic retention time and sludge retention time,but also improve the quality of effluent.However,membrane fouling is one of the main factors restricting its large-scale application.Based on this,this paper investigated the mechanism of ultrafiltration membrane fouling in the treatment of livestock wastewater by algal-bacterial symbiosis,which provides a theoretical basis for the treatment of livestock wastewater by algal-symbiotic coupling with membrane process.Co-cultivation of different algal-bacteria symbiont(combined system with algae as the main component and combined system with activated sludge as the main constitute)and livestock wastewater,the dead-end filtration experiment was then carried out to investigate the UF membrane fouling of different co-culture systems.In addition,a variety of analysis methods(infrared characterization,molecular weight distribution,and three-dimensional fluorescence spectroscopy,etc.)were used to analyze the distribution and composition of pollutants on the membrane,and the formation mechanism of the membrane fouling was further elaborated.Extracellular polymer(EPS)was extracted from algae,activated sludge and activated sludge-algae systems respectively,and the characteristics of ultrafiltration membrane fouling caused by EPS were also studied.The main conclusions are as follows::Membrane pollution mechanism of algae as the main component showed that the membrane fouling of both the algae-fungus group and the algae-activated sludge group was less severe than that of the algae group.The membrane fouling of the algae group was dominated by standard blocking and cake filtration.However,the membrane fouling of the algae group had a high degree of fitting with standard blocking,intermediate blocking and cake filtration models,thus the membrane fouling mechanism was more complicated.The addition of fungi and activated sludge increased the particle size of the algae system,resulting in the blockage of the membrane pore,which made the cake layer in the membrane surface looser and alleviated the membrane fouling.The organic pollutants on the membrane surface were mainly proteins and polysaccharides.In addition,the symbiotic effect of algal and bacteria greatly reduces the production of EPS,especially tryptophan-like proteins,thereby reducing membrane pollution.The study of the membrane fouling mechanism of the algal bacteria symbiosis with activated sludge as the main constitute showed that the membrane fouling of the activated sludge-algae group was more serious than that of the activated sludge group.Activated sludge-algae group membrane fouling model is governed by standard blocking and cake filtration,while activated sludge group membrane fouling was composed of standard blocking,intermediate blocking and cake filtration models.The activated sludge-algae group has a lower Zeta potential and smaller particle size,leading to faster clogging of the membrane pores and tighter cake layer.The addition of algae increased the hydrophilic component of the pollutants on the membrane surface in activated sludge-algae group,which aggravated membrane fouling.The study of the membrane fouling characteristics of the algal bacteria EPS composition on the ultrafiltration membrane showed that:the tightest membrane fouling was caused by bound(TB-EPS)and the most serious membrane fouling was caused by soluble EPS(SMP)in three systems.The membrane fouling model of EPS component was dominated by complete blocking and intermediate blocking,while the membrane fouling of EPS component in activated sludge and activated sludge-algae group was mainly standard blocking and cake filtration model.The concentration of tyrosine proteins were the most,followed by tryptophan proteins,and humic-like substances were the least.The addition of algae reduced the production of polysaccharides tryptophan and humic-like substances in TB-EPS in the activated sludge-microalgae group,thus alleviate membrane fouling. |
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