Study On The Influence Of Organic Wastewater Treatment And CO₂ Fixation Based On Microalgae Culture

Greenhouse gas emissions and water environmental pollution are becoming increasingly serious problems to mankind in the 21st century.Finding a green,low-cost way to deal with high-concentration organic wastewater and reducing carbon dioxide emissions has become an urgent problem for human beings in environmental protection.As a kind of important photosynthetic microorganisms,microalgae has the advantages of high carbon sequestration rate,strong environmental adaptability,and fast growth rate.It plays a vital role in wastewater treatment and CO₂ emission reduction.Therefore,the coupling system of organic wastewater treatment,CO₂fixation in flue gas and biomass production is constructed,which combines microalgae culture with wastewater and flue gas treatment,realizes wastewater treatment and CO₂ emission reduction while obtaining microalgae biomass,and has good environmental and economic benefits.In this paper,two strains of Chlorella sp.L38 and Chlorella sp.L166 were used as the research object.Firstly,the growth and carbon sequestration abilities of Chlorella sp.L38 and Chlorella sp.L166 under different CO₂ concentrations were studied.It was found that the growth and carbon sequestration of Chlorella sp.were the best under 5%CO₂ concentration,the maximum biomass yield was approximately3290.00 mg/L and 2890.00 mg/L,respectively.And the highest carbon sequestration rates were 7.16%and 11.17%respectively.Then the growth characteristics of Chlorella sp.L38 and Chlorella sp.L166 in different concentrations of soybean wastewater and the ability to remove nutrients in wastewater were investigated.The results showed that the growth rate of Chlorella sp.L166 and the removal rates of TN,TP and COD in the wastewater were higher than those of Chlorella sp.L38 in different concentrations of wastewater.Chlorella sp.L166 had the highest chlorophyll a content of 48.23 mg/L in raw water.Chlorella sp.L166 cultured in 5 times diluted wastewater had the best removal effect on TN and COD.The removal rates of TN and COD were 88.32%and 82.46%,respectively.The highest removal rate of TP by Chlorella sp.L166 occurred in the wastewater diluted 10 times,and the removal rate reached 96.50%.Chlorella sp.L166,which has better ability of removing nutrients from wastewater and fixing CO₂,was selected as experimental algae to construct a coupling culture system of soybean wastewater and simulated flue gas.The effects of CO₂ concentration in simulated flue gas,inflow of CO₂,light intensity,photoperiod,temperature and nitrogen-phosphorus ratio of nutrients in wastewater on the growth rate of Clorella sp.L166,CO₂ fixation and nutrients removal capacity of wastewater were investigated.The results showed that Chlorella sp.L166 could be cultured in the coupling culture system of organic wastewater and simulated flue gas.When the nitrogen and phosphorus ratio of the wastewater was 5:1 and the dilution rate was 0.1vvm,5%CO₂ was introduced into the system.The growth of Chlorella sp.Product wastewater treatment is the best,and it can also maximize the fixed CO₂ in simulated flue gas.Under this condition,the highest concentration of chlorophyll a was 48.08mg/L.The removal rates of TN,TP,COD and CO₂ fixation were 96.07%,95.11%,78.20%and 28.60%respectively.Finally,through multiple linear regression analysis,the weight of different environmental factors on the growth of Chlorella sp.L166 was obtained as follows:CO₂ concentration>photoperiod>N/P>temperature>CO₂ flow>light intensity;Then a Verhulst kinetic growth model was established to simulate the change of chlorophyll a concentration of Chlorella sp.L166 in the coupled culture system.The results showed that the change of chlorophyll a concentration of Chlorella sp.L166 was very suitable for the Verhulst growth model and the coefficient of determination reached 0.996.Based on the Verhulst growth model,a kinetic model for nitrogen and phosphorus removal in soybean wastewater of Chlorella sp.L166 was established.According to the nutrient removal kinetics model,the experimental data were fitted to verify the kinetic parameters of the nutrient removal of Chlorella sp.L166.The model has a good fit for the removal of TN and TP in the wastewater of soybean products.The determination coefficients of R² are0.986 and 0.982,respectively,which is suitable for the removal of TN and TP in the wastewater of soybean products.