Research On Enhance Nitrogen And Phosphorus Removal Performance Of UniTank Process Under Low-carbon Source Condition

UniTank process integrates space flow of traditional activated sludge process and time flow of the SBR process and can remove nitrogen and phosphorus simultaneously.Now due to low-strength wastewater as influent,some wastewater treatment processes in the south of Jiangxi province need to be improved,even rebuilt,urgently.This paper built a lab-scale UniTank device to treat low-strength wastewater from a wastewater treatment plant（WWTP）in Ganzhou.UniTank rapid start-up method was deteted.Low-strength wastewater and sludge characteristics and their effect on UniTank process were analysed.Effect of internal recycle and side tank anaerobic time on nitrogen and phosphorus removal in the UniTank were studied.Conclusions were as follows:（1）For UniTank treating low-strength wastewater,we combined actual wastewater and artificial wastewater as influent.And sludge adaptability to actual wastewater was inproved graduadlly with decreased artificial wastewater proportion in influent.NH₃-N removal rate reached 98.3%,when time ratio of side tank and middle tank was 2:1.（2）Sludge in side tank flowed into middle tank of UniTank.Within a Half cycle,sludge concentration in side tank declined from 2510 mg/L to 2110 mg/L and that in middle tank increased from 2100 mg/L to 2190 mg/L.Results of sludge characteristic analysis showed that sludge Y_H in side tank and middle tank were 0.68 d^-1and 0.69^-1,and b_H were 0.44^-1 and 0.52^-1relatively.Sludge activity in middle tank was higher than that in side tank.（3）Results of influent characteristic analysis showed that proportions in COD of X_S、S_S、S_I、X_I were 31.28%、24.11%、11.39%、32.22%correspondingly and proportion in TN of NH₃-N、TKN、NO₂-N、NO₃-N were 85.48%、91.93%、5.33%、1.54%、6.45%relatively.Ratio of biodegradable COD was 55.39%,illustrating only part of organic pollutant in wastewater was participating in nitrogen and phosphorus removal process.Relative lower portion of organic nitrogen in TN showed that water slightly polluted by organic nitrogen.（4）Internal recycle has minor effect on COD and NH₃-N removal.During this experiment,effluent COD and NH₃-N concentration were lower than 30 mg/L and 2 mg/L relatively,which met the discharge standard’s demand（GB18918-2002）of the first-A level for WWTPs.However,removal of TN and TP was effected by internal recycle significantly.With improved internal recycle,TN removal rates were increased firstly then decreased and TP removal rates were decreased.When internal recycle was 100%,effluent average TN and TP concentration were 8.19 mg/L and 0.69 mg/L correspondingly.（5）Anaerobic time of side tank in UniTank has negligible effect on COD and NH₃-N removal.During this experiment,effluent average COD and NH₃-N concentration were 17.31mg/L and 1.01 mg/L relatively,which were lower than the discharge standard’s demand（GB18918-2002）of the first-A level for WWTPs.However,removal of TN and TP was effected by side tank anaerobic time significantly.With improved side tank anaerobic time,TN removal rates were increased firstly then reduced and TP removal rates were enhanced gradually.When side tank anaerobic time was 60 min,average TN removal rate reached 48.74%and effluent average TN concentration was 11.78 mg/L.While side tank anaerobic time was 100 min,average TP removal rate reached 65.33%and effluent average TP concentration was 0.65 mg/L.（6）For competition of carbon resource between denitrification and phosphorus removal with low-strength wastewater in WWPTs of the south of Jiangxi province,internal recycle of100%and side tank anaerobic time of 60-80 min were suggested.