Study On Large-Scale Harvesting Of Microalgae Using Electro-flocculation

Microalgae is a kind of autotrophic single cell organisms which have high carbon sequestration efficiency,strong photosynthesis,short growth cycle,and its cell could synthesis accumulation of oil,protein and a variety of active substances.As the algae easy-scale farming,and not competing with people and arable land,use of microalgae carbon sequestered biofuel and other high value bio-based products,the industrialization process is maturing,which is formation of a new type of agriculture and green industry integration development of the pilot high-tech industry.However,the high cost and low efficiency of microalgae harvest is still a problem,in the industrial chain of microalgae large-scale breeding and high-value product processing,which need to be solved urgentlyIn order to establish an efficient and low cost microalgae large-scale harvesting technology system,we selected the Shanxi Province native Chlorella emersonii as the target algae.First,we analyzed the chemical flocculation efficiency of different chemical flocculants to Chlorella emersonii and selected the optimum flocculants and the flocculation conditions,Secondly the flocculation efficiency of different electrode materials was studied by using single factor test,and the flocculation condition of Chlorella emersonii by electric field flocculation method with graphite and aluminum as electrode material,and the flocculation efficiency of aluminum was used as the electrode material.Thirdly,a new type of microalgae flocculation system combining chemical flocculation and electric flocculation was established and the laboratory scale was tested.Finally,the efficient and low-cost microalgae scale harvesting equipment and process was designed and constructed.The main findings are as follows:(1)To compare the flocculation effect of different flocculants on Chlorella emersonii,Ten flocculants including metal salts(ferric chloride,ferric sulfate,aluminium chloride and aluminium potassium sulphate),alkaline(sodium hydroxide and calcium hydroxide),inorganic macromolecules(polyaluminum chloride,polyferric chloride)and organic polymer compounds(polyacrylamide and chitosan),were chosen to flocculate Chlorella emersonii in this study.we analyzed the chemical flocculation efficiency of different chemical flocculants to Chlorella emersonii,The results were as follows:0.3 g·L-1 ferric sulfate,0.7 g·L-1 potassium aluminum sulfate,0.5 g·L-1 calcium hydroxide,0.3 g·L-1 polyaluminium chloride,Flocculation efficiency of ? 95%,and choose 0.9 g·L-1 sodium hydroxide as a flocculant,the flocculation efficiency is 93%.The other flocculants failed to achieve efficient flocculation of Chlorella emersonii in the above five option flocculants,0.5 g·L-1 calcium hydroxide was selected as the best flocculant for Chlorella emersonii.The results showed that the pH value of the algae was 8,the concentration of alginate OD680nm was 1.2,the stirring rate was 150 r·min-1,and the stirring time was 2 min.After 80 min,0.5 g·L-1 calcium hydroxide the flocculation efficiency of Chlorella emersonii was 97%.(2)Comparative analysis of the flocculation efficiency of different electrode materials for electrocoagulation.The electrocoagulation of the algae was studied by electrocoagulation of the four electrode materials(copper,iron,graphite and aluminum).The results showed that aluminum was used as the electrode material,and the flocculation effect of Chlorella emersonii was the best,The electrocoagulation of aluminum was used as the electrode material,the conditions were as follows:the width of the aluminum plate was 2 cm,the distance between the plates was 2 cm,the voltage was 15 v,the pH of the algae was between 7-9,the algae OD680nm was between 2-2.5,the stirring time was 2 min,the stirring rate was 200 rpm,5min flocculation efficiency of 95%.(3)We establishment of graphite as the electrode material and add appropriate amount of calcium hydroxide efficient electrocoagulation system.Use of the above research results,graphite was selected as the electrode material,and the appropriate amount of calcium hydroxide was added to assist the flocculation,and the efficient microalgae flocculation recovery system was constructed.After the optimization of the harvesting system,the graphite electrode plate width was 2 cm,the plate spacing was 2 cm,the voltage was 15 v,the concentration of calcium hydroxide was 0.35 g·L-1,the alginate OD680nm.was 2.01,the stirring rate was 300 rpm,Time 2 min,electric flocculation 6 min,flocculation efficiency of 95%.(4)To establish a new type of high efficiency electrocoagulation system suitable for large-scale harvesting of microalgae.Based on the results of the above laboratory scale test,a highly efficient electrocoagulation system with a capacity of 1000 L algae was designed and constructed.The main technical parameters include voltage 15v,electrode thickness 1mm,electrode cross-sectional area 20cm × 30cm,electrode spacing 2cm,algae OD60nm.2.03,pH 8.51,calcium hydroxide concentration 0.35 g·L-1,The flocculation efficiency of Chlorella emersonii was more than 91%,and the cost was significantly lower than that of the existing microalgae harvesting technology.This study has laid a theoretical and technical foundation for the establishment of efficient and low-cost microalgae large-scale harvesting devices and processes,which can help improve the overall economic benefits of microalgae industry chain.