Study On Enhancing Hydrolytic Acidification Of Excess Activated Sludge By High Pressure Homogenization And Adding Sludge Liquor As Denitrification Carbon Source Denitrification Carbon Source

Along with the improvement of people’s living standard, nitrogen and phosphorus in domestic sewage are becoming higher and higher, which causes C/N ratio reduction and denitrification carbon source becomes more seriously insufficient in biological denitrification process. So, the effluent total nitrogen is very high in the wastewater treatment plants (WWTPs), which cannot meet the national wastewater discharge standards. Meantime, large amount of excess activated sludge (EAS) is produced in WWTPs and its treatment and disposal cost a lot. However, the EAS contains many organic matters, which can be applied to produce denitrification carbon source through sludge hydrolytic acidification. Using sludge liquor as denitrification carbon source not only solves the problem of denitrification carbon source lack, but also reduces the EAS treatment and disposal cost.In this study, the denitrification carbon source was prepared by combining high-pressure homogenization (HPH) technology and hydrolytic acidification; then the sludge liquor from disintegration and hydrolytic acidification (SLDHA) was added as carbon source; and low C/N ratio wastewater was treated without ammonia nitrogen removal from SLDHA by optimizing addition strategy. In order to improve the hydrolytic acidification effect of EAS, the HPH was adopted to disintegrate the EAS. The effectiveness of EAS hydrolysis and acidification was studied, and the SLDHA was prepared as denitrification carbon source under the optimal conditions. Then the SLDHA was added in a SBR wastewater denitrification system, and the effectiveness of SLDHA as denitrification carbon source was discussed.The EAS was disintegrated by HPH and the sludge disintegrated degree reached the highest of 22.88% under 40 MPa. Although the SOCD production under 40 MPa was a few less than that under 60 MPa when the EAS was disintegrated and hydrolytically acidified, the volatile fatty acids (VFAs) production reached 1936 mg/L under 40 MPa, which were higher than that under 60 MPa. Moreover, the NH4+-N production was lower about 10.23% than that under 60 MPa, and the energy consumption was smaller under 40 MPa. Thus,40 MPa was chosen as the optimum pressure for EAS disintegration and hydrolytic acidification.pH of 6.5-7.0 was suitable for the hydrolytic acidification process of disintegrated EAS. So, there was no need to adjust the pH when the EAS pH was within this range. When the system temperature was 35 ℃, the VFAs/SCOD ratio reached 73.7%, which was 11.6% higher than that with a temperature of 55 ℃. The NH4+-N production was also lower at 35℃. In a certain range of sludge total solid content (TS), more VFAs were obtained after hydrolytic acidification with a higher sludge TS. However, the sludge TS was limited by the HPH machine, so the sludge TS of 20-25 g/L was chosen for better hydrolytic acidification. There was no significant influence on the effectiveness of hydrolytic acidification of disintegrated EAS under a stirring intensity of 50-150 r/min. The SCOD and VFAs reached the peak value after 3-day hydrolytic acidification, and the VFA composition was basically stable. It is concluded that the SLDHA was prepared as denitrification carbon source to treat the low C/N ratio wastewater under the following conditions:disintegration pressure of 40 MPa, pH of 6.5-7.0, temperature of 35℃, EAS TS of 20-25 g/L, stirring intensity of 50-150 r/min and hydrolytic acidification time of 3 d.Denitrification was efficiently enhanced by adding SLDHA into the SBR wastewater denitrification system as carbon source for the treatment of low C/N ratio wastewater. When the raw water influent C/N ratio was 4:1, and different carbon sources prepared were added at anoxic stage, the TN removal rate enhanced by adding the SLDHA was the highest. The addition time was optimized and the SLDHA should be added at 30 min before the end of aeration. About 70% of NH4+-N in the SLDHA was removed, but the carbon source was still insufficient, leading to high effluent NO3--N and TN. The results manifested that the denitrification effectiveness was enhanced by adding the SLDHA to a system of C/N ratio of 6:1 when the raw water C/N ratio was 4:1. When the influent C/N ratio was 6:1, the SLDHA addition as carbon source showed better denitrification effectiveness. When the SLDHA was added at oxic stage, low NH4+-N and high TN of the effluent were observed, when the SLDHA was added at anoxic stage, the effluent showed high NH4+-N and low TN. When the SLDHA was added at the end of aeration, the effluent NH4+-N and TN was respectively 4.1 and 12.2 mg/L, which met the level A of national wastewater discharge standards. In conclusion, the SLDHA can be added as denitrification carbon source between the end of aeration and anoxic stage when the system C/N ratio reached to (7-8):1. Not only enough denitrification carbon source was satisfied, but also the NH4+-N of SLDHA was efficiently removed.