Study On Parameter Optimization And Membrane Fouling Of Immobilized Algae-bacteria In The Treatment Of Livestock Wastewater

In the treatment of livestock and poultry breeding wastewater by algal-bacteria symbionts-membrane combination system,there are advantages such as good treatment effect,high effluent quality and resource utilization of microalgae,etc.However,when algal-bacteria symbionts are directly exposed to water,there are also disadvantages such as poor resistance to external interference,serious membrane pollution and difficulty in microalgae harvesting.Embedding immobilization is a technique for embedding microorganisms in a gel mesh.Immobilization can not only effectively protect microorganisms,but also intercept microorganisms and their secretions into the water.In addition,the immobilized algal-bacteria particles settle quickly,which is conducive to the harvesting of microalgae.Based on this,this study combined the encapsulation immobilization of algal bacteria with membrane system for the treatment of livestock and poultry breeding wastewater,optimized the immobilization parameters,and studied the influence of immobilization on the treatment effect of algal bacteria,microbial growth and membrane pollution.In order to provide some theoretical basis for the practical application of the immobilized algal bacteria-membrane combination process.Using sodium alginate（SA）and calcium chloride（CaCl2）as immobilized materials,the effects of immobilized parameters on the properties of the immobilized algal spheres were preliminarily analyzed.Through orthogonal experiment,the most suitable immobilization parameters of livestock and poultry wastewater were optimized.The effect of immobilization on the treatment effect and the growth of microorganisms was studied in the contrast experiment.The influence of immobilization on membrane fouling was analyzed by ultrafiltration test,particle size analysis,infrared characterization and other methods.The main conclusions are as follows:The optimization results of parameters for the treatment of livestock and poultry wastewater by immobilized algal bacteria showed that the concentration of SA was the key factor affecting the quality of immobilized algal bacteria pellets.The higher the concentration of SA,the higher the mechanical strength of immobilized algal bacteria pellets,but the worse the mass transfer and pellet formation efficiency.SA concentration has the greatest effect on the growth of microorganisms,because the higher the SA concentration is,the closer the immobilized matrix is,which is not conducive to the absorption and utilization of nutrients by microorganisms.However,too low SA concentration will cause the loss of microalgae in the immobilized algal spheres due to hydraulic scour.The higher the SA concentration,the better the TN removal effect.The higher the CaCl2 concentration has a positive promoting effect on the TP removal effect.The lower the SA concentration and the shorter the immobilization time,the higher the COD removal rate.Using the optimal parameters for immobilized algae bacteria actual wastewater treatment experiment,the results show that compared with the system of suspended algae bacteria,immobilized obviously improved when the wastewater treatment of p H,immobilized system remains at more than 8,the p H to a maximum of 8.56,1.3 or so higher than suspended system,the nitrogen and phosphorus removal has certain auxiliary effect;The increase of chlorophyll a of microalgae in the immobilized system was 23.48 mg/L,which was higher than that in the suspended system（16.37 mg/L）.The immobilized system had significantly higher biomass.The removal rates of COD,TN,ammonia nitrogen,TP and phosphate in the immobilized system were 92.63,53.04%,40.43%,91.58%and 93.30%,respectively.Except that the COD removal rate is slightly lower than that of the suspended system,other projects have obvious advantages over the suspended system.The results of ultrafiltration cup membrane filtration experiment showed that the mixed liquid membrane contamination of the suspended system was more serious than that of the immobilized group.The mixed liquid of the two groups were mainly standard blockage and filter cake layer blockage,and the fitting degree of standard blockage and filter cake layer blockage of the immobilized group was higher than that of the suspended group.The average particle size d₅₀ of the immobilized group（150.18μm）was significantly higher than that of the suspended group（25.05μm）.Corresponding,the membrane fouling of the immobilized group was lighter.The main component of membrane contamination in both groups is protein,and the content of protein,polysaccharide and humic acid in the mixture of the immobilized group is lower than that of the non-immobilized group,indicating that immobilization can effectively retain the organic matter secreted by microorganisms,so as to reduce membrane contamination.