Study On The Deep Nitrogen Removal Of PN/A For Anaerobic Digestion Effluent Of Municipal Wastewater

The traditional municipal wastewater treatment with activated sludge process as the core has high energy consumption,large greenhouse gas emission and large sludge output,which has been difficult to meet the technical development needs of energy-saving,low-carbon and resource recover.In recent years,integration of anaerobic digestion?anaerobic digestion,AD?with partial nitrification-anaerobic ammonia oxidation?PN and Anammox,PN/A?has been widely concerned,due to the significant advantages of energy recovery,low carbon emissions and sludge reduction.In the process of AD,the effluent with low ammonia and low COD/TN?C/N?ratio is formed.The PN/A processes are all chemical autotrophic reactions,which can effectively deal with sewage treatment with low C/N ratio.However,the application of PN/A for AD effluent of municipal wastewater still faces many challenges.Among them,the low ammonia of AD effluent is the key factor affecting the stability of PN/A.This study in order to enhance the performance of PN/A in the AD effluent of municipal wastewater during continuous operation of 274 d,the SBR and USB reactor were used respectively as the PN and Anammox unit for PN?PN-SBR and Anammox-USB?.It explores the different hydraulic retention time?HRT?on PN/A processing efficiency,puts forward the system run efficiently in the best condition,and examines the related functional microbial activity and the sludge particle size.Meanwhile,the spatial distribution,community structure and functional characteristics of functional flora are illustrated by fluorescent hybridization?FISH?and MiSeq high-throughput sequencing technologies.The main results and conclusions are as follows:?1?HRT had a significant effect on the nitrogen removal efficiency of PN/A.Too long HRT conditions could not meet the nitrogen load?NLR?required by functional microorganisms,and too short HRT conditions resulted in high NLR and large hydraulic load,and both conditions achieved efficient nitrogen removal.HRT=6 h(HRT_PN=2h and HRT_Anammox=4h)was proved to be the best working condition of PN/A,with TN removal rate reaching 81.3%on average and 86.7%at the highest.The effluent TN concentration was stable below 13.0 mg/L.In addition,the low concentration of COD in water promoted the denitrification in the system,and the COD in the effluent was stable below 20.0 mg/L.?2?Sludge in PN-SBR was flocculent,and the control key of this unit was the enrichment of AOB and the inhibition of NOB.The regulation of intermittent aeration and sludge residence time?SRT?could effectively inhibit the growth of NOB.When the HRT_PN was 2 h,the ratio of AOB activity?SAOA?to NOB activity?SNOA?reaches the maximum of 12,and SAOA reaches the maximum of 2.22 g-N/g VSS/d in the whole experiment.?3?Sludge in Anammox-USB was mainly granular,and the nitrogen removal process mainly occurred at the bottom of the reactor.When the HRT_Anammox was 4 h,the activity of Anammox bacteria?SAA?reached the maximum value of 0.452 g-N/g VSS/d in the whole experiment.Partial nitrification and partial denitrification?NO₃^--N?NO₂^--N?were formed in the reactor in collaboration with Anammox.The former two provided a secondary NO₂^--N source for Anammox reaction and enhanced the system's nitrogen removal efficiency.?4?FISH results showed that AOB was the absolute dominant bacteria in PN-SBR,and the proportion of AOB in the total bacteria was 83.9±6.7%in the optimal working condition.Anammox was the absolute dominant bacteria in Anammox-USB,with a proportion as high as 95.2±2.1%in the interior and 52.9±5.3%at the edge of the particle under optimum conditions.?5?The high-throughput results showed that the AOB in PN-SBR was mainly Nitrosomonas,with a maximum abundance of 7.09%,and the NOB was mainly Nitrospira,with a maximum abundance of only 0.16%.In the Anammox-USB,the Anammox bacteria were mainly Candidatus Brocadia,with the highest abundance at the bottom of the reactor reaching 21.01%.Among them,the denitrifying Thauera bacteria had the characteristic of controlling the denitrification process at the NO₂^--N stage,which verified the synergistic effect of partial denitrification and Anammox bacteria.