Experimental Study About Digestate And Biogas Upgrading Combined With Chlorella Culture

Due to the non renewable nature of conventional fossil energy and environmental problems caused by energy consumption,more and more attention has been paid to renewable energy research in the world.Biomass is recognized as an effective alternative energy to meet the global energy demand.Biogas is one of the energy forms suitable for the development of China.However,after fermentation,the methane content of crude biogas is low,the carbon dioxide content is too high,resulting in the low grade of biogas and the limited use of biogas.Moreover,if the fermented biogas liquid is discharged directly without treatment,it will cause serious environmental problems.Chlorella has strong adaptability,short growth cycle and rich chlorophyll.It has the highest chlorophyll content in nature.It can not only use CO2 to autotroph under light conditions,but also use inorganic carbon source for heterotrophic,with high tolerance of carbon dioxide concentration.In this paper,the biogas fluid was used as the culture medium of Chlorella,and the CO2 in biogas was used as the carbon source of Chlorella culture.The experiment of Chlorella culture and purification of biogas fluid to improve the quality of biogas was carried out(1)In the range of 20001ux-80001ux,Chlorella is the most suitable for growth under the condition of 60001ux and 24h continuous light.On the 12th day,od680 reaches the maximum value of 0.439;(2)The results showed that the dry weight of Chlorella cells reached the maximum value of 3.58g/l on the 10th day after adding 1mg/L Fe3+ to 60%biogas slurry,which was 10.84%higher than that without adding iron ions,and the removal rate of components in biogas slurry was the best,the absorption rates of COD,ammonium nitrogen,total nitrogen and total phosphorus were 84.70%,95.18%,88.39%and 98.46%respectively;(3)The experimental results of Chlorella culture with pretreated biogas slurry showed that the high concentration biogas slurry sterilized by high pressure steam for one hour greatly shortened the lag period of Chlorella entering the logarithmic growth compared with the original biogas slurry,and had a longer logarithmic growth period,and the absorption rates of COD,ammonium nitrogen,total nitrogen and total phosphorus reached 54.18%,90.81%,50.93%and 88.8g%,respectively;(4)The results showed that when the aeration rate was 1.01/min,the gas-liquid ratio was 8:1,the maximum cell dry weight of Chlorella was 3.24g/l;the methane content of biogas with different aeration rate and gas-liquid ratio was above 97%,the methane content reached the maximum value of 98.8%,and the oxygen concentration was lower than the maximum oxygen content of 4%(V/V);when the aeration rate was 1L/min,the oxygen concentration was lower than that of 4%(V/V)The removal efficiency of COD,ammonia nitrogen,total nitrogen and total phosphorus were 91.35%,99.87%,83.94%and 99.43%,respectively.