Study On Pyrolysis Sludge As Additional Carbon Source For Two-stage A/O Process

The two-stage A/O process is one of the mainstream processes for removing high-nitrogen wastewater due to high total nitrogen removal rate,good reststance to shock-loading and convenient management et al.The supernatant produced by the thermal hydrolysis of the excess sludge can be used as a carbon source for improving the denitrification efficiency.If this method is applied to practical projects,the excess sludge can be used as the carbon resource.In this paper,the optimum conditions for thermal hydrolysis were determined by small tests and pilot tests of excess sludge thermal hydrolysis.The two-stage A/O process pilot system was used to simulate the actual operation of the Qing Ji wastewater treatment plant?WWTP?.The sludge thermal hydrolysis supernatant was used as the additional carbon source to conduct the pilot test of four influent TN concentration gradients.The feasibility of using a sludge thermal hydrolysis supernatant as the additional carbon source of two-stage A/O process was investigated.The ability of the designed two-stage A/O process to resist impact loading was explored.The nitrogen migration and transportation model of the two-stage A/O process was established,and the results of the pilot test were used to verify the model.The main results were as follows:?1?The orthogonal test of the thermal hydrolysis sludge was conducted according to the C/N ratio in the thermal hydrolysis supernatant as the evaluation index.The environmental protection and energy consumption et al.were taken into account to ensure the the most suitable conditions for the thermal hydrolysis of the sludge in the pilot test,which was:the moisture content of the sludge was 98%,the thermal hydrolysis temperature was 80?,the thermal hydrolysis time was 90minutes,and the alkali dosage was zero.The C/N ratio of the hydrolyzed supernatant was 15.It could be used as an additional carbon source for the two-stage A/O pilot system.?2?The mixed liquor suspended solids?MLSS?in the biological tank was approximately 5000 mg/L,and the internal recycle ratio were 150%to 200%,there was no need to add the carbon source in the secondary anoxic tank,the effluent could meet the standards when the influent COD was approximately 600 mg/L and the influent TN was approximately 70 mg/L.?3?The MLSS in the biological tank was approximately 5500 mg/L,and the internal recycle ratio was 250%,approximate 150 mg/L carbon source?COD?was added to the intake tank,or approximate 30 mg/L carbon source?COD?was added to the secondary anoxic tank,the effluent could meet the standards when the influent COD was approximately 600 mg/L and the influent TN was approximately 100mg/L.?4?The MLSS in the biological tank was approximately 6000 mg/L,and the internal recycle ratio was 300%,approximate 45 mg/L carbon source?COD?was added to the secondary anoxic tank,the effluent could meet the standards when the influent COD was approximately 600 mg/L and the influent TN was approximately120 mg/L.?5?The MLSS in the biological tank was approximately 6000 mg/L,and the internal recycle ratio was 300%,approximate 80 mg/L carbon source?COD?was added to the secondary anoxic tank,the effluent could meet the standards when the influent COD was approximately 600 mg/L and the influent TN was approximately140 mg/L.The N and P substances were carried by the thermal hydrolysis supernatant would not have adverse effects on the effluent quality even if the 80mgCOD/L of the sludge hydrolysis supernatant is added into the secondary anoxic tank.The supernatant of sludge thermal hydrolysis could be used as a high-quality carbon source for deepening nitrogen removal.?6?The nitrogen migration and transportation model of the two-stage A/O process?TN_i=?C+1.6?+?R₁C+R₂C₁?×r₁+?1+R₁?×C₁×r₂+0.059X/?_c?was established.Comparison between the results of the pilot experiment and prediction under different conditions showed that high prediction accuracy of the model when the influent TN?140 mg/L.The effect of water temperature on the denitrification rate of the secondary anoxic tank should be considered in the case of secondary denitrification,and the model should be modified.The constructed model could be applied to optimise the operating parameters of the two-stage A/O process and guide the economic operation of Qing Ji WWTP.