Reduction of biogas slurry and CO2 by Chlorella vulgaris in semi-continuous and continuous cultures.

Chlorella vulgaris was cultivated by semi-continuous and continuous mode to reduce the emissions of both biogas slurry and CO2.In semi-continuous cultivation mode,when the renewal rate was 30%,nitrogen and phosphorus contents in the biogas slurry were stable at 16 to 18 mg/L and 0.4 to 0.6 mg/L,respectively,which met the secondary sewage discharge regulations.While the renewal rate increased to higher than 40%,a dynamic equilibrium was obtained between the microalgae biomass and its absorption of nitrogen and phosphorus in the biogas slurry after three days,but the removal rates of nitrogen and phosphorus did not meet the direct sewage discharge standard.Effects of chlorella vulgaris on the removal of nitrogen and phosphorus in the biogas slurry were investigated in a columnar photobioreactor by selecting the daily renewal rates at 20% and 30% in continuous mode.The results exhibited that the total nitrogen amount in the biogas slurry remained at 55.64 mg/L after 12 days on the 7 L scale.Emission reduction of biogas slurry employing the microalgae method was primarily restricted by the light limitation during the large-scale cultivation.