Experimental Study On Anaerobic/Anoxic Parallel AAO Process

The AAO process has both biological nitrogen removal and biological phosphorus removal functions.It is widely used in wastewater treatment projects such as urban sewage,which need to reduce nitrogen and phosphorus.Due to the differences on requirements of metabolic rate between denitrifying bacteria and polyphosphate bacteria.There are also differences between environmental and substrate conditions.Traditional AAO processes often use a wide range of control conditions to meet the requirements of different flora,which may have problems such as matrix competition and sludge age conflict.AAO is a traditional process for the removal of nitrogen and phosphorus from wastewater,however,the nitrogen and phosphorus removal efficiency of this technology is insufficient because of the biological environment conflicts and carbon source competition.Herein,a new anaerobic/anoxia parallel AAO process?P-AAO?,the anaerobic stage is arranged in parallel with the anoxic stage and followed by the aerobic stage,was proposed for improving the removal efficiency of the nitrogen and phosphorus.The effect of anaerobic tank sludge reflux ratio,anoxic tank sludge reflux ratio,and mixture reflux ratio on the treatment efficiency was investigated using artificial and actual sewage as raw water,and the results showed that:?1?Considering the energy consumption of recirculation and the effect of denitrification and dephosphorization,the optimal operating conditions of AAO process in parallel are:anaerobic tank sludge reflux ratio 60%,anoxic tank sludge reflux ratio60%,anoxic When the pool mixture reflux ratio is 250%.At this time,the average removal rates of effluent NH₄⁺-N,TN and TP were 97.10%,94.57%and 96.61%,respectively.The average effluent concentrations of NH₄⁺-N,TN and TP were 0.85-0.95,1.68-2.03 and 0.16-,respectively.0.18 mg/L.?2?When the actual water is used for the influent,the AAO process in parallel is at the optimum working condition,and the mass concentrations of TP,NH₄⁺-N and TN in the sedimentation tank reach 0.27,0.93 and 2.44 mg/L,respectively;They reached96.16%,96.42%,and 94.10%,respectively.?3?The influent COD is in the range of 120-300mg/L,and the AAO process in parallel is good for nitrogen and phosphorus removal.The concentration of influent organic matter has little effect on the removal of nitrogen and phosphorus.?4?When the two processes are operated at their respective optimal operating conditions until the effluent index is stable,the AAO process in parallel is better than the AAO process.?5?Under the optimal operating conditions.High-throughout sequencing analysis revealed that the proportion of denitrifying and phosphorus-removing microbial communities was signifycantly increased both in the anaerobic and anoxic stage,compared with that in a traditional AAO process.In addition,the competition between the denitrifying and phosphorus-removing bacteria would be alleviated in the P-AAO process,which is beneficial to the accumulation of functional flora and the improvement of nitrogen and phosphorus removal efficiency.