Study On The Removal Effect Of Immobilized Chlorella On Nitrogen And Phosphorus In Sludge Anaerobic Digestion Solution

The residual digestatc formed after the remaining sludge after anaerobic digestion treatment has a low carbon-to-nitrogen ratio(C/N)due to the high nitrogen and phosphorus content,and the general biological treatment effect is not good.Algae has good nitrogen and phosphorus absorption capacity and low cost,and it is feasible to use algae to reduce the residual digestion solution.In this study,the removal effect of suspended microalgae(chlorella and four-tailed Chlorella)on nitrogen and phosphorus in the residual digestive solution was compared and analyzed.Immobilized chlorella was prepared by immobilized embedding technology,and its purification effect on residual digestive juice was clarified.On this basis,the main influencing factors of immobilized chlorella on nitrogen and phosphorus removal in residual digestion solution were discussed.The main research results of the paper are as follows:(1)Microalgae species with good nitrogen and phosphorus removal effect in the residual digestate were screened,and the optimal dosage of microalgae and the concentration range of the residual digestate suitable for growth were obtained.The test results showed that the proportion of ammonia nitrogen in the residual digestate was as high as 82.2%,and when the dosages of chlorella and four-tailed Chlorella were 60mg/L and 80mg/L,respectively,the growth state of the two algae in the residual digestive juice was better,and the removal rate of total nitrogen could reach 83.52%and 67.44%,respectively,and chlorella was better than that of Tetracera tetraceraridae.However,the removal effect of phosphorus and CODCr was average,only 34.4%and 24.76%respectively.The high residual digestate eoncentration had a significant inhibitory effect on the growth of chlorella,and when the residual digestate concentration was diluted 5 times(CODCr and TP concenrations decreased to 245.8mg/L and 10.3mg/L,respectively),the removal effect of chlorella on CODCr was increased by 20.5%compared with the undiluted stock solution,and the removal efficiency of total nitrogen and total phosphorus was increased by 60.3%and 11.8%,respectively.The nitrogen and phosphorus concentrations suitable for the growth of chlorella in the residual digestate ranges:16.44～43.8mg/L and 6.41～10.26mg/L,respectively.(2)Immobilized chlorella was prepared,and the optimal ratio of additives in immobilized chlorella and its removal effect on nitrogen and phosphorus in the residual digest were determined.By comparing and analyzing the effects of sodium alginate(SA),CaCl2 and activated carbon(AC)on the specific growth rate,mass transfer and mechanical properties of chlorella,the optimal concentration ratios of the three additives were obtained:2.5%SA,4%CaCl2 and 0.2%AC.The removal rates of TN,TP and CODCr in the residual digestate after fixation could reach 94.56%,53.21%and 51.3%,respectively,which were 3.76%,17.1%and 7.34%higher than those in suspended chlorella,and the removal effect was the best on day 5.(3)N/P,Ca2+ and CODCr in the residual digestate had a certain effect on the removal of nitrogen and phosphorus by immobilized chlorella.When N/P=14:1,the growth of algal beads was the most vigorous,and the removal efficiency of total nitrogen and total phosphorus was the highest,reaching 91.2%and 86.5%,respectively.The calcium ion concentration had little effect on the growth of chlorella and the removal effect of total nitrogen,and the removal rate of total nitrogen reached the maximum when C(Ca2+)=20mg/L,which was 76.83%.The removal rate of total phosphorus was positively correlated with the concentration of calcium ions,and when C(Ca2+)=40mg/L,the removal rate of total phosphorus was 90%.When CODCr=600mg/L,the growth of immobilized algae beads is the best,and the removal effect of total nitrogen and total phosphorus is the highest,reaching 84.4%and 83.5%,respectively,when the CODcr concentration is increased to 900mg/L,the removal effect is reduced.