Research On Deep Nitrogen Removal Performance Of Partial Denitrification + Anaerobic Ammonia Oxidation(PD + Anammox)combined Process Under Saline Wastewater

This study mainly explored the feasibility of simultaneous removal of nitrogen and organics from low C/N?ratio of chemical oxygen demand to total nitrogen,COD/TN?municipal and nitrate?NO₃^--N?wastewaters by the partial denitrification?PD?and anaerobic ammonia oxidation?Anammox?combined process under the condition of high-salt wastewater?1.25 wt%?.Meanwhile,the start-up and optimized operation characteristics,the removal characteristics of carbon and nitrogen,the microbial structure of PD system and the mechanisms of nitrogen and carbon removal of PD+Anammox combined process were studied.The main contents and research results of the paper were as follows:?1?Comparative study on the start-up and partial denitrification characteristics of PD systemIn order to explore NO₂^--N accumulation characteristics during the operational period of partial denitrification in different sludge sources using sodium acetate as a carbon source,No.1 SBR?sequencing batch reactor?and No.2 SBR were used to inoculate with surplus sludge taken separately from secondary sedimentation tank of a sewage treatment plant and simultaneous nitrification and denitrifying phosphorus removal system.By reasonably controlling initial nitrate concentration and anoxic time,the partial denitrification was realized.The carbon and nitrogen removal characteristics under different initial COD and NO₃^--N concentrations were investigated.The results showed that using sodium acetate as the carbon source,partial denitrification process in No.1 SBR and No.2 SBR sludge could be successfully started-up in 21 and 20 days,respectively.The accumulation of NO₂^--N and nitrite accumulation rate?NAR?in the reactors were maintained at high levels,12.61 mg/L,79.76%and 13.85 mg/L,87.60%respectively.When the initial NO₃^--N concentration of No.2 SBR was 20 mg/L and the initial COD concentration increased from 60 mg/L to 140 mg/L,the operation time for achieving the highest NO₂^--N accumulation in the system was shortened from 160 min to6 min.The specific denitrification rate?in VSS?increased from 3.84 mg/?g·h?to 7.35mg/?g·h?.Increased initial COD concentration was beneficial to the accumulation of NO₂^--N during partial denitrification.When the initial COD concentration of No.2 SBR was 100 mg/L and the initial NO₃^--N concentration increased from 20 mg/L to 30 mg/L,NAR was maintained above 90%and up to 100%?the initial NO₃^--N concentration was25 mg/L?.When the initial NO₃^--N concentration was?35 mg/L,insufficient COD caused NO₃^--N to be completely reduced to NO₂^--N.Under the conditions of different initial COD concentrations?80,100,120 mg/L?and different initial NO₃^--N concentrations?20,25,30,40 mg/L?,the nitrogen and carbon removal and partial denitrification performance of the No.2 SBR was better than that of No.1 SBR.?2?Long term optimized operation characteristics of PD-SBRIn order to explore the effect of adding low C/N municipal wastewater and inorganic salt?NaCl?on the long-term operation characteristics of PD-SBR system.By adding municipal wastewater and inorganic salt of different concentrations to PD system,the NO₂^--N accumulation characteristics and the variations of effluent indexes during the long-term operation of PD-SBR under different COD/NO₃^--N and salinity conditions were studied.And the structural characteristics of microflora were also investigated.The results showed that PD-SBR maintained stable NO₂^--N accumulation characteristics under the condition of organic matters in municipal wastewater as carbon source after an adaptation period of 22 d.When the COD was 127.5 mg/L,the initial COD/NO₃^--N was2.5,and the concentration of influent NO₃^--N is 120 mg/L,the NAR of the system was87.1%,and the NO₂^--N accumulation concentration was 24.3 mg/L.When the concentration of inorganic salt increased,the salinity was less than 1.00 wt%,the PD-SBR recovered stable nitrogen and carbon removal characteristics in about 20 d.When the salinity increased to 1.25 wt%,79.3%of carbon removal efficiency and 81.6%of NAR were achieved after 38 days of adaptation period.Under different influent substrate and anoxia reaction time,the overall change trend of nitrogen and COD was basically similar during operation.With the decreased of NO₃^--N concentration,the effluent NO₂^--N and NAR increased linearly with the consumption of COD.The specific NO₃^--N reduction rate and specific NO₂^--N production rate changed significantly in 0-20min,then decreased significantly.In addition,with the salinity increased,the effluent NO₂^--N and NAR increased slightly after 20 min.Moreover,microbial community analysis showed that Thauera-DOHOs?44.6%-55.8%?was the dominant bacteria to ensure high nitrite accumulation in the long-term operation of PD-SBR,and its overall abundance was not significantly affected by the addition of municipal wastewater and inorganic salt in the long-term operation.?3?Study on the mechanisms of nitrogen and carbon removal by PD+Anammox combined processIn order to explore the nitrogen and carbon removal performance of PD+Anammox combined process under the condition of high saline?1.25 wt%?wastewater.The salinity adaptability of Anammox system was by the way of salinity gradient reduction,and the stable nitrogen removal was realized under the condition of salinity of 1.25 wt%.The mechanisms of nitrogen and carbon removal of PD+Anammox combined process when simultaneous treatmented low C/N municipal and saline nitrate wastewaters under the condition of salinity of 1.25 wt%was investigated.The results showed that the Anammox system with salinity of 2.00 wt%started in 33 d,TN removal rate was 89.2%,and the removed NO₂^--N:NH₄⁺-N was about 1.04?NH₄⁺-N average concentration was 50 mg/L?.When the salinity was 1.75 wt%,the nitrogen removal performance of Anammox system was almost unaffected.When the salinity was reduced to 1.5 wt%,betaine was added to maintain the osmotic pressure inside and outside the cell,then nitrogen removal performance recovered slowly,and the TN removal rate reached 84.8%.When the salinity was 1.25 wt%,the system nitrogen removal performance was enhanced,the efficiency was improved,and the operation time was shortened.At this time,the removed NO₂^--N:NH₄⁺-N was about 1.08.PD+Anammox combined process could be basically realized in 30d when simultaneous treatmented low C/N municipal and saline nitrate wastewaters,and achieved the ideal removal of carbon and nitrogen.The TN removal rate of the system could also be maintained above 90%,and the removed NO₂^--N:NH₄⁺-N was about 1.04.