Micro Granular Sludge Removal Effect Of Simultaneous Nitrogen And Phosphorus Removal In Low Dissolved Oxygen And Energy Saving Analysis

The water pollution problem has become very prominent in modern society,the traditional wastewater treatment methods have many shortcomings,such as high energy consumption and poor treatment efficiency.Many wastewater treatment workers at home and abroad try to find a wastewater treatment method through various channels,which is both energy saving and high effciency.SBR technology has been widely applied to wastewater treatment as an efficient,stable reaction process.In recent years,granular sludge has been widely studied by waste water treatment workers for its special structure and highly treatment efficiency.Therefore,this experiment studied the waste water treatment effect of granular sludge under low dissolved oxygen conditions using SBR technology.The proportion of carbon,nitrogen,phosphorus(COD:N:P)was in influent controlled as 100:1 during the period of granular sludge.Concentration of dissolved oxygen in the reactor was reduced step by step(eventually DO<1 mg/L).Settling time,sludge age,stirring speed and other parameters were timely adjusted.Eventually form the granular sludge,of which the average particle size was 0.42 mm,belongs to the micro granular sludge.The values of DO and pH value in the reactor has been monitored by DO analyzer and pH meter monitor.Combined with the change of pollutants,the best reaction time was determined as running 4 cycles daily,each cycle for 6 h,incoming water for 30 min,anaerobic mixing for 30 min,aerobic aeration for 180 min,subsiding for 30 min,draining for 30 min and other idle time respectively.During the period of determining the hydraulic retention time,the SVI value of granular sludge in the reactor was between 64?72 mL/g,the appearance characteristics were not significant changed.Treatment efficiency of the reactor was studied under the condition of low dissolved oxygen and different organic loading,the result shows as below:The average concentrations of reactor effluent COD,NH4+-N and PO43--P were 34.8 mg/L,4.01 mg/L and 4.2 mg/L respectively,removal rates were 78.83%,79.68%and 35.18%respectively,under low organic loading.Among them,COD and NH4+-N effluent concentration achieves the national emission standard,PO43--P did not achieve the requirements of emission standard.At the end of reaction period,the SVI value of granular sludge in the reactor increased to 237 mL/g,the sludge in the reactor expanded,granular sludge breakage pyrolysis and reactor can't maintain stable operation.The average concentrations of reactor effluent COD,NH4+-N and PO43--P are 39.5 mg/L,3.9 mg/L and 0.39 mg/L respectively,their removal rates were 89.62%,80.06%and 94.29%,respectively,under normal organic loading.Effluent concentrations satisfy the national emission standard.During operation,the SVI value of granular sludge in the reactor kept around 69 mL/g,no granular sludge breakage pyrolysis happened,the reactor can operate normally and stably.The average concentration of reactor effluent COD,NH4+-N and PO43--P are 47.3mg/L,6.4 mg/L and 0.40 mg/L respectively,average removal rate are 94.09%,70.05%and 94.22%respectively,under high organic loading,effluent concentration achieves the national emission standard.NH4+-N did not achieve the emission standard.After the operation cycle,SVI value of sludge in the reactor was 275 mL/g,the sludge in the reactor suffered serious inflation and decomposed into flocculent sludge,which lead to a failure of the reactor maintain normal operation.Aeration quantity demand under different DO value is calculated used the design parameters of certain sewage plant by aeration quantity calculation software.Compared with the aeration quantity in demand under the condition of 1 mg/L dissolved oxygen,14 m3/min,16.1 m3/min,18.7 m3/min,22.2 m3/min,26.7 m3/min and 32.6 m3/min aeration quantity are saved respectively,saving ratio are 7.18%,15.43%,25.01%,15.43%,50.08%and 66.78%respectively.DO analyzer and rotary flow meter were also used to measure aeration quantity in demand under different DO value in the lab.Through the comparison,5 Lfh,11 L/h,17 L/h,25 L/h,32 L/h and 39 L/h aeration quantity were saved respectively.The saving effect of aeration quantity was considerable.