Construction Of Vertical Microalgae Biofilm System And Its Application In Industrial Wastewater Treatment

As a new type of bio-energy material,microalgae have the advantages of fast growth rate and high photosynthetic efficiency.At the same time,it can produce abundant proteins,polysaccharides,lipids and other abundant biologically active substances.Compared with suspended cultivation,microalgae attached biofilm culture has high biomass density,convenient harvesting,and low energy consumption,so it has greater prospects.In order to effectively increase the yield of microalgae biomass per unit land area,this paper uses the hydrophilic cellulose acetate membrane material with high strength and good biocompatibility as the microalgae supporting matrix material to construct a vertical microalgae biofilm photobioreactor.The effects of membrane pore size and different initial inoculum concentration on the contents of microalgae biomass,oil,protein and carbohydrate were investigated in detail,and the application of vertical microalgae biofilm system in industrial wastewater treatment was studied.The specific research content is as follows:（1）The effects of membrane blocking on the adherence culture of microalgae were studied by inoculating microalgae biofilms with cellulose acetate membranes with different pore sizes of 0.45,1.2,2.0 and 3.0μm.The results show that under the inoculation filtration model,the algae growth rate of the vertical microalgae biofilm system has nothing to do with the roughness,hydrophilicity and surface free energy of the cellulose acetate membrane.In the vertical microalgae biofilm system,the maximum productivity of microalgae cultured for the first time was 5.02 g/（m²·d）on the membrane with 1.2μm pore size under the middle blocking model.Due to nitrogen deficiency and high light intensity,the maximum total lipid content was 23.74%.Logistic model and linear model were used to fit the growth and regeneration rate of microalgae biofilm.With the increased of membrane pore size to 3μm,the blocking model changed from the middle blocking model to the complete blocking model,which affected the light and nutrient transport,and the production decreased to 4.5 g/（m²·d）.（2）Different inoculated layers of algae cells were inoculated on 1.2μm cellulose acetate membrane,and the influence of different inoculated layers on the adherent culture of microalgae was studied.The results showed that the biomass and lipid production of microalgae biofilms increased with the increase of the number of inoculated layers.Under 3-layer algae cell inoculation,the algae biofilm has the highest biomass yield of 12.58 g/m² and lipid accumulation of 24.35%.When the number of inoculated layers increased to 4,the increase of biofilm thickness affected the transport of nutrients,light and CO₂,and the biomass yield decreased to 10.61 g/m².（3）In the treatment of heavy metal ion wastewater,the removal rates of Cd²⁺and Cr⁶⁺in single metal ion wastewater by microalgae biofilm were 93.85%and 56.94%respectively,and the algae biomass decreased by 6.6%and 14.6%respectively.In the mixed wastewater,the removal rates of Cd²⁺and Cr⁶⁺were 90.16%and 50.79%respectively,and the algae biomass decreased by 20.6%.In the removal of nitrogen and phosphorus,the removal rate of nitrate nitrogen（NO₃^-）by microalgae biofilm in mixed metal ion wastewater is 52.44g/（m²·d）,and the removal rate of total phosphorus（TP）by various metal ion wastewater can reach more than98%.In conclusion,in the vertical microalgae biofilm system,the biomass yield of microalgae biofilm can be effectively improved by using cellulose acetate membrane with pore size of 1.2μm and three inoculation layers.At the same time,in the application of industrial wastewater,the vertical microalgae biofilm system has a good removal effect on heavy metal ions and nitrogen and phosphorus in wastewater.This provides an effective technical support and theoretical basis for the future practical application of vertical microalgae biofilm system.