Research On Technology And Equipment Of Anaerobic Digested Dairy Manure Based Microalgae Bioenergy Utilization

The use of fossil energy has economic and environmental consequences including increased energy prices from growing shortages, and detrimental emissions to the environment. Yet, fuels derived from algae can be used to displace fossil fuels without competing with food and crop production, which is a major drawback of first-generation biofuels. However, because of its high cost, algal biodiesel production at a commercial scale is not yet feasible. Algae production requires the input of macronutrients, and this can be a major operational expense when synthetic fertilizers are used. Agricultural wastes and other wastewaters containing sufficient nitrogen and phosphorus concentrations may be used in their place to offset these costs, while preventing these nutrients from entering the environment.In this study, Chlorella was grown using anaerobic digested dairy manure, and later separated, purified, and enriched. Using this growth culture, we then investigated the collection, pre-treatment, and oil extraction from the algae biomass. During cultivation of Chlorella sp, the growth rate and maximum biomass yield reached0.307/d and1.30g/L, and entered the stable phase within6days, which suggested this wastewater was a suitable substrate for Chlorella cultivation. After14days, the amount of available nutrients and organic carbon in the growth medium significantly decreased. With the enriched culture, the removal rate of TN, TP, NH4-N, NO3-N, POP and COD was53.95%,99.67%,78.81%,98.22%and85.88%, respectively. These results demonstrated that Chlorella can be used to effectively assimilate wastewater nutrients and reduce COD, while simultaneously generating commercially valuable microalgae products.Also, magnesium chloride (PAC) was used to test flocculation efficiency and kinetics. An economic evaluation was then performed using these data. Different dosages of PAC were added into microalgae suspensions. After stirring at200rpm for lmin, the contents of Chlorophyll were recorded at different times. The results showed that5different dosages of PAC exhibited flocculation efficiencies as high as over86%after8min. The flocculation efficiency was98.6%when the dosage of PAC was123.5mg/L. The flocculation efficiency increased significantly along with the dosage of PAC. And the cost was300-460Yuan when flocculating microalgae biomass was1ton. The results indicated that the flocculation of PAC obeyed second-order kinetics.We tested the fat content, ash, protein, fatty acid composition, and identification of volatile components in different temperatures of microalgae cultured in anaerobic digested dairy manure. The results show that the lipid content of dry Chlorella was10.14%and fatty acid content accounted for84.76%, mainly as polyunsaturated fatty-acids. The volatile components included hydrocarbons, aldehydes, ketones, alcohols, acids, amines, heterocyclic compounds and similar compounds. The gas compositions of Chlorella at different temperatures were identified by electronic nose, and the results indicated minimal changes over temperatures of60℃to90℃. At higher temperatures, composition changed significantly.Compared to other oil extraction methods, the results show that ultra high pressure achieves the highest cell breakage rate and oil extraction rate, which were10.02%and86.80%respectively. Oil extraction and cell disruption rate increased with increasing pressure. Regarding the cell disruption rates with four extraction methods, ultra high pressure was greatest, followed by high pressure homogenizer, ultrasonic and microwave. For oil extraction, the order was ultra high pressure, ultrasound, high pressure homogenization and microwave processing.Finally, we explored the possibility of combining the pre-treatment and extraction process into synchronous step. Experimental results show that at an optimum high pressure, cell disruption and oil extraction rates reached11.24%and92.75%respectively. Compared to separated pre-treatment and extraction, the cell disruption rates using the one-step approach were significantly higher. Thus, synchronous step can effectively improve the crushing ratio and oil extraction rate, reduce processing steps, particularly when ultra-high pressure is used. After analysis response surface, we received an optimum condition:pressure580MPa, time699s and solvent rate1:2.25.