Performance Of One-stage Partial Nititation/anammox Process Treating Municipal Wastewater

Eutrophication problem is still serious in China,therefore nutrient removal remain one of the main tasks of wastewater treatment.In traditional municipal wastewater treatment process,both biological nitrogen and phosphorus removal consume organic matter.The lack of carbon sources becomes the main bottleneck of the improvement of nutrient removal performance.Anammox process was a novel biological nitrogen removal technology.Autotrophic nitrogen removal from municipal wastewater could be achieved by applying anammox process.Therefore,the competition of organic matter between nitrogen and phosphorus removal could be avoided and the improvement of nutrient removal performance could be expected.Till now,the feasibility of municipal wastewater anammox treatment has been proved.However,the nitrogen removal performance and process stability remain to been improved.How to suppress and wash out nitrite-oxidizing bacteria while retaining anammox bacteria effectively was the key problem to be soloved.To solove this problem,a new idea was proposed in this study,that is using granular sludge or biofilm to retain anammox bacteria while using flocculent sludge to retain nitrifiers in one reactor.Based on this idea,two process was developed: one-stage partial nitritritation/anmmox(PN/A)process based on granule-flocs coexsitence system and one-stage PN/A process based on continuous-flow integraed fixed-biofilm activated sludge(IFAS)reactor.The nitrogen removal performance,microbial community evolution,the strategy of NOB suppression and process stability under low temperature were investigated.Finally a novel integrated process of enhanced biological phosphorus removal(EBPR)and one-stage PN/A was developed to achived the simultaneous phosphorus and nitrogen removal from municipal wastewater.When cultivating anammox bacteria using ammonium-rich wastewater in a pilot sequencing batch reactor(SBR),it was found that granular and flocculent sludge could coexist in one reactor.Anammox bacteria preferentially grow in the granular sludge while ammonium-oxidizing bacteria(AOB)is prone to grow in the flocculent sludge.Therefore the sludge retention time(SRT)of anammox bacteria and nitrifiers could be different in this hybrid system.Based on this observation,a novel one-stage PN/A process based on granule-flocs coexsitence system was developed.The lab-scale SBR reactor was inoculated with the sludge take from the pilot SBR and fed with real pretreated municipal wastewater.Efficient nitrogen removal was achieved with a TN removal efficiency of 79% and rate of 0.09 kg N/(m3·d).The distribution of anammox bacteria and AOB did not change under low ammonium conditions.However,a major shift in anammox community was observed.Brocadia was gradually washed out while Kuenenia became the dominant anammox bacteria from the reactor.NOB supression strategy in one-stage PN/A system was studied in the lab-scale SBR.After long-term operation under low DO concentrations,Nitrospira became the dominant NOB in the reactor and was mainly resided in the flocculent suldge.Different stategies was used for restore PN/A from nitrate accumulation,namely low DO,intemittent aeration and bio-augmentation.Controlling low DO failed to suppress NOB.Controlling low flocculent sludge SRT while bio-augmenting AOB with nitritation sludge successfully reduced nitrate produciton.Intemittent aeration(A 15 min/O 9 min)could suppress NOB activity,but the recovery process need a long term.The effects of low temperature on one-stage PN/A was investigated.When temperature was gradually reduced from 24 °C to 12 °C,nitrogen removal rate decreased by 3 times while nitrogen removal efficiency decreased from 85.0% to 30.5%.Low temperature had a higher impact on anammox bacteria than AOB.When temperature was reduced to 18 °C,nitrite accumulation was observed,indicating unbalanced activity of anammox bacteria and AOB.Besides,low temperature triggered the overgrowth of NOB,which further decreased the nitrogen removal performance of PN/A.It was found the dominat anammox bacteria belongs to Cadidatus Brocadia.Furthermore,a plug-flow integrated fixed-biofilm activated sluge(IFAS)reactor was developed for mainstream PN/A.In IFAS reactor,anammox bacteria was enriched and retained in biofilm while AOB grew in the activated sludge.The feasibility of IFAS reactor in applying mainstream PN/A was proved in this study.The ammonium and nitrogen removal efficiency was up to 91% and 82% when influnt concentration of COD and TN was 56.1 and 44.2 mg/L,respectively.Finally,a novel integrated process of EBPR and one-stage PN/A was proposed for simultaneous nutrient removal from municipal wastewater.The feasibility of the integrated process was proved in a SBR-SBBR system with high removal efficiency of COD,ammonium,TN and TP of 82%,90%,86% and 95%,respectively.Besides,sludge granulation was achieved in EBPR reactor by shortening the settling time.With the formation of granules,the efficiency of EBPR was improved significantly.The hydraulic retention time was shortened from 4.5 h to 1.3 h.Carbon-balance and energy consumption analysis of WWTPs based on anammox process was conducted.By applying integrated process of EBPR and one-stage PN/A,more organic matter was captured into activated sludge of EBPR,rather than oxidized to CO2.By reducing aeration energy and applying anaerobic digestion,the energy selfsufficiency of WWTPs is improved.