剩余污泥有机质资源回收利用原位驱动晚期垃圾渗滤液深度脱氮——一种具有显著能源优势的创新生物技术

The sustainable recovery and utilization of sludge bioenergy within a circular economy context has drawn increasing attention,but there is currently a shortage of reliable technology.This study presents an innovative biotechnology based on free nitrous acid(FNA)to realize sustainable organics recovery from waste activated sludge(WAS)in-situ,driving efficient nitrogen removal from ammonia rich mature landfill leachate by integrating partial nitrification,fermentation,and denitrification process(PN/DN-F/DN).First,ammonia((1708.5±142.9)mg·L^(-1))in mature landfill leachate is oxidized to nitrite in the aerobic stage of a partial nitrification coupling denitrification(PN/DN)sequencing batch reactor(SBR),with nitrite accumulation ratio of 95.4%±2.5%.Then,intermediate effluent(NO_(2)^(-)-N=(1196.9±184.2)mg·L^(-1))of the PN/DN-SBR,along with concentrated WAS(volatile solids(VSs)=(15119.8±2484.2)mg·L^(-1)),is fed into an anoxic reactor for fermentation coupling denitrification process(F/DN).FNA,the protonated form of nitrite,degrades organics in the WAS to the soluble fraction by the biocidal effect,and the released organics are utilized by denitrifiers to drive NOx-reduction.An ultra-fast sludge reduction rate of 4.89 kg·m^(-3)·d^(-1) and nitrogen removal rate of 0.46 kg·m^(-3)·d^(-1) were realized in the process.Finally,F/DN-SBR effluent containing organics is refluxed to PN/DN-SBR for secondary denitrification in the post anoxic stage.After 175 d operation,an average of 19350.6 mg chemical oxygen demand organics were recovered per operational cycle,with 95.2%nitrogen removal and 53.4%sludge reduction.PN/DN-F/DN is of great significance for promoting a paradigm transformation from energy consumption to energy neutral,specifically,the total benefit in equivalent terms of energy was 291.8 kW·h·t^(-1) total solid.

Enrichment of anammox biomass during mainstream wastewater treatment driven by achievement of partial denitrification through the addition of bio-carriers

Anammox is widely considered as the most cost-effective and sustainable process for nitrogen removal.However,how to achieve the enrichment of anammox biomass remains a challenge for its large-scale application,especially in mainstream wastewater treatment.In this study,the feasibility of enrichment of anammox biomass was explored through the realization of partial denitrification and the addition of bio-carriers.By using ordinary activated sludge,a sequencing batch reactor(SBR)followed by an up-fow anaerobic sludge bed(UASB)was operated at 25±2℃ for 214 days.The long-term operation was divided into five phases,in which SBR and UASB were started-up in Phases I and II,respectively.By eliminating oxygen and adjusting the infow ratios in Phases III-V,advanced nitrogen removal was achieved with the effuent total nitrogen being 4.7 mg/L and the nitrogen removal efficiency being 90.5%in Phase V.Both in-situ and ex-situ activity tests demonstrated the occurrence of partial denitrification and anammox.Moreover,16S rRNA high-throughput sequencing analysis revealed that Candidatus Brocadia was enriched from below the detection limit to in biofilms(0.4%in SBR,2.2%in UASB)and the foc sludge(0.2%in SBR,1.3%in UASB),while Thauera was mainly detected in the foc sludge(8.1%in SBR,8.8%in UASB),which might play a key role in partial denitrification.Overall,this study provides a novel strategy to enrich anammox biomass driven by rapid achievement of partial denitrification through the addition of bio-carriers,which will improve large-scale application of anammox processes in mainstream wastewater treatment.

Brain-inspired multimodal approach for effluent quality prediction using wastewater surface images and water quality data

Efficiently predicting effluent quality through data-driven analysis presents a significant advancement for consistent wastewater treatment operations.In this study,we aimed to develop an integrated method for predicting effluent COD and NH3 levels.We employed a 200 L pilot-scale sequencing batch reactor(SBR)to gather multimodal data from urban sewage over 40 d.Then we collected data on critical parameters like COD,DO,pH,NH_(3),EC,ORP,SS,and water temperature,alongside wastewater surface images,resulting in a data set of approximately 40246 points.Then we proposed a brain-inspired image and temporal fusion model integrated with a CNN-LSTM network(BITF-CL)using this data.This innovative model synergized sewage imagery with water quality data,enhancing prediction accuracy.As a result,the BITF-CL model reduced prediction error by over 23%compared to traditional methods and still performed comparably to conventional techniques even without using DO and SS sensor data.Consequently,this research presents a cost-effective and precise prediction system for sewage treatment,demonstrating the potential of brain-inspired models.

Degradation properties of fulvic acid and its microbially driven mechanism from a partial nitritation bioreactor through multi-spectral and bioinformatic analysis

This study employed multispectral techniques to evaluate fulvic acid(FA)compositional characteristic and elucidate its biodegradation mechanisms during partial nitritation(PN)process.Results showed that FA removal efficiency(FRE)decreased from 90.22 to 23.11%when FA concentrations in the reactor were increased from 0 to 162.30 mg/L,and that molecular size,degree of aromatization and humification of the effluent FA macromolecules all increased after treatment.Microbial population analysis indicated that the proliferation of the Comamonas,OLB12 and Thauera exhibit high FA utilization capacity in lower concentrations(<50.59 mg/L),promoting the degradation and removal of macromolecular FA.In addition,the sustained increase in external FA may decrease the abundance of above functional microorganisms,resulting in a rapid drop in FRE.Furthermore,from the genetic perspective,the elevated FA levels restricted carbohydrate(ko00620,ko00010 and ko00020)and nitrogen(HAO,AMO,NIR and NOR)metabolism-related pathways,thereby impeding FA removal and total nitrogen loss associated with N_(2)O emissions.

New perspectives in free nitrous acid (FNA) uses for sustainable wastewater management

The biocidal effects of free nitrous acid (FNA) have found applications in multiple units in an urban wastewater system, including sewer networks, wastewater treatment processes, and sludge treatment processes. However, these applications are associated with chemical costs as both nitrite and acid are needed to produce FNA at the required levels. The recent discovery of novel acid-tolerant ammonia oxidizers offers the possibility to produce FNA from domestic wastewater, enabling the development of next-generation FNA-based technologies capable of achieving self-sustaining FNA production. In this study, we focus on the concept of in situ FNA generation facilitated by acid-tolerant ammonia oxidizers and highlight the multiple benefits it creates, after a brief review of the historical development of FNA-based technologies. We will discuss how wastewater systems can be made more energy-efficient and sustainable by leveraging the potential of acid-tolerant ammonia oxidizers.

Sludge fermentation liquid addition attained advanced nitrogen removal in low C/N ratio municipal wastewater through short-cut nitrification-denitrification and partial anammox

Biological nitrogen removal of wastewater with low COD/N ratio could be enhanced by the addition of wasted sludge fermentation liquid(SFL),but the performance is usually limited by the introducing ammonium.In this study,the process of using SFL was successfully improved by involving anammox process.Real municipal wastewater with a low C/N ratio of 2.8–3.4 was treated in a sequencing batch reactor(SBR).The SBR was operated under anaerobic-aerobic-anoxic(AOA)mode and excess SFL was added into the anoxic phase.Stable short-cut nitrification was achieved after 46d and then anammox sludge was inoculated.In the stable period,effluent total inorganic nitrogen(TIN)was less than 4.3 mg/L with removal efficiency of 92.3%.Further analysis suggests that anammox bacteria,mainly affiliated with Candidatus_Kuenenia,successfully reduced the external ammonia from the SFL and contributed approximately 28%–43%to TIN removal.Overall,this study suggests anammox could be combined with SFL addition,resulting in a stable enhanced nitrogen biological removal.

Advanced nitrogen and phosphorus removal in A^(2)O-BAF system treating low carbon-to-nitrogen ratio domestic wastewater

A laboratory-scale anaerobic-anoxic-aerobic process(A^(2)O)with a small aerobic zone and a bigger anoxic zone and biologic aerated filter(A^(2)O-BAF)system was operated to treat low carbon-to-nitrogen ratio domestic wastewater.The A^(2)O process was employed mainly for organic matter and phosphorus removal,and for denitrification.The BAF was only used for nitrification which coupled with a settling tank Compared with a conventional A^(2)O process,the suspended activated sludge in this A^(2)OBAF process contained small quantities of nitrifier,but nitrification overwhelmingly conducted in BAF.So the system successfully avoided the contradiction in sludge retention time(SRT)between nitrifying bacteria and phosphorus accumulating organisms(PAOs).Denitrifying phosphorus accumulating organisms(DPAOs)played an important role in removing up to 91%of phosphorus along with nitrogen,which indicated that the suspended activated sludge process presented a good denitrifying phosphorus removal performance.The average removal efficiency of chemical oxygen demand(COD),total nitrogen(TN),total phosphorus(TP),and NH_(4)^(+)-N were 85.56%,92.07%,81.24%and 98.7%respectively.The effluent quality consistently satisfied the national first level A effluent discharge standard of China.The average sludge volume index(SVI)was 85.4 mL·g^(-1)additionally,the volume ratio of anaerobic,anoxic and aerobic zone in A^(2)O process was also investigated,and the results demonstrated that the optimum value was 1:6:2.

Denitrification and phosphorus uptake by DPAOs using nitrite as an electron acceptor by step-feed strategies

Denitrifying phosphorus accumulating organ- isms （DPAOs） using nitrite as an electron acceptor can reduce more energy. However, nitrite has been reported to have an inhibition on denitrifying phosphorus removal. In this study, the step-feed strategy was proposed to achieve low nitrite concentration, which can avoid or relieve nitrite inhibition. The results showed that denitrification rate, phosphorus uptake rate and the ratio of the phosphorus uptaken to nitrite denitrified （anoxic P/N ratio） increased when the nitrite concentration was 15 rag. L-1 after step- feeding nitrite. The maximum denitrification rate and phosphorus uptake rate was 12.73 mg NO2-N.g MLSS- 1· h- 1 and 18.75 mg PO34--P- g MLSS- 1. h- 1, respec- tively. These rates were higher than that using nitrate （15 mg. L-l） as an electron acceptor. The maximum anoxic P/N ratio was 1.55 mg PO43- -Pmg NO2-N-1. When the nitrite concentration increased from 15 to 20 mg NO2 -N ~ L-I after addition of nitrite, the anoxic phosphorus uptake was inhibited by 64.85%, and the denitrification by DPAOs was inhibited by 61.25%. Denitrification rate by DPAOs decreased gradually when nitrite （about 20 mg · L-1） was added in the step-feed SBR. These results indicated that the step-feed strategy can be used to achieve denitrifying phosphorus removal using nitrite as an electron acceptor, and nitrite concentration should be maintained at low level （ 〈 15 mg. L-1 in this study）.

Simultaneous removal of hydrogen sulfide and volatile organic sulfur compounds in off-gas mixture from a wastewater treatment plant using a two-stage bio-trickling filter system

Simultaneous removal of hydrogen sulfide (H2S) and volatile organic sulfur compounds (VOSCs) in off-gas mixture from a wastewater treatment plant (WWTP) is difficult due to the occasional inhibitory effects of H2S on VOSC degradation. In this study, a two-stage bio-trickling filter (BTF) system was developed to treat off-gas mixture from a real WWTP facility. At an empty bed retention time of 40 s, removal efficiencies of H2S, methanethiol, dimethyl sulfide, and dimethyl disulfide were 90.1, 88.4, 85.8 and 61.8%, respectively. Furthermore, the effect of lifting load shock on system performance was investigated and results indicated that removal of both H2S and VOSCs was slightly affected. Illumina Miseq sequencing revealed that the microbial community of first-stage BTF contained high abundance of H2S-affinity genera including Acidithiobacillus (51.43%), Metallibacterium (25.35%), and Thionomas (8.08%). Analysis of mechanism demonstrated that first stage of BTF removed 86.1% of H2S, mitigating the suppression on VOSC degradation in second stage of BTF. Overall, the twostage BTF system, an innovative bioprocess, can simultaneously remove H2S and VOSC.

Community structures and population dynamics of “Candidatus Accumulibacter” in activated sludges of wastewater treatment plants using ppk1 as phylogenetic marker

Candidatus Accumulibacter has been identified as dominant polyphosphate-accumulating organisms（PAOs） in enhanced biological phosphorus（P） removal（EBPR） from wastewater.This study revealed the relevance of community structure, abundance and seasonal population dynamics of Candidatus Accumulibacter to process operation of wastewater treatment plants（WWTPs） in China using ppk1 gene as phylogenetic marker. All sludge samples had properties of denitrifying P removal using nitrate as an electron acceptor.Accumulibacter abundance in the anaerobic-anoxic-oxic（A^2O） process was the highest（26%of total bacteria）, and higher in winter than in summer with a better EBPR performance.Type-II was the dominant Accumulibacter in all processes, and type-I accounted for a small proportion of total Accumulibacter. The abundance of Clade-IIC as the most dominant clade reached 2.59 × 10~9 cells/g MLSS and accounted for 87.3% of total Accumulibacter. Clade IIC mainly contributed to denitrifying P removal. Clades IIA, IIC and IID were found in all processes, while clade-IIF was only found in oxidation ditch process through phylogenetic analysis. High proportion of clade IID to total Accumulibacter led to poor performance of aerobic P-uptake in inverted A^2O process. Therefore, Accumulibacter clades in WWTPs were diverse, and EBPR performance was closely related to the clade-level community structures and abundances of Accumulibacter.

Characterization of the dissolved organic matter in sewage effluent of sequence batch reactor： the impact of carbon source

Dissolved organic matter （DOM） transforma- tion in sequence batch reactor （SBR） fed with carbon sources of different biodegradability was investigated. During the biologic degradation process, the low mole- cular weight （MW） fraction （〈 1 kDa） gradually decreased, while the refractory compounds with higher aromaticity were aggregated. Size exclusion chromatogra- phy （SEC） and fluorescence of excitation emission matrices （EEM） demonstrated that more biopolymers （polysaccharides or proteins） and humic-like substances were presented in the extracellular polymeric substance （EPS） extracted from the SBR fed with sodium acetate or glucose, while the EPS from SBR fed with slowly biodegradable dissolved organic carbon （DOC） substrate- starch had relatively less biopolymers. Comparing the EfOM in sewage effluent of three SBRs, the effluent from SBR fed with starch is more aromatic. Organic carbon with MW 〉 1 kDa as well as the hydrophobic fraction in DOM gradually increased with the carbon sources changing from sodium acetate to glucose and starch. The DOC fractiona- tion and the EEM all demonstrated that EfOM from the effluent of the SBR fed with starch contained more fulvic acid-like substances comparing with the SBR fed with sodium acetate and glucose.

Robustness of anammox granular sludge treating low-strength sewage under various shock loadings:Microbial mechanism and little N2O emission

With the increasing application of anammox for the treatment of high-strength industrial wastewater,application of anammox in municipal sewage has been gaining more attention.Sludge granulation in particular enhances the enrichment and retention of anammox bacteria in municipal sewage treatment systems.However,the performance of granular sludge under continuous and varying hydraulic loading shock remains little understood.In this study,the robustness of anammox granular sludge in treating lowstrength municipal sewage under various shock loadings was investigated.Results showed that an upflow anaerobic sludge blanket(UASB)reactor with anammox granules performed well,with anammox specific activity up to 0.28 kg N/kg VSS/day and anti-loading shock capability up to 187.2 L/day during the 8-month testing period.The accumulation rate of N2O(<0.01 kg N/kg VSS/day)in the liquid phase was seven times higher than that of the gas phase,which could be mainly attributed to the incomplete denitrification and insufficient carbon source.However,only a small part of the produced N2O escaped into the atmosphere.High-throughput sequencing and molecular ecological network analyses also identified the bacterial diversity and community structure,indicating the potential resistance against loading shock.The composition and structural analyses showed that polysaccharides were an important functional component in the tightly bound extracellular polymeric substances(TB-EPS),which was the major EPS layer of anammox granules.Scanning electron microscopy(SEM)also showed that the gaps in between the anammoxclusters in the granules inhibit the flotation of the sludge and ensure efficient settling and retention of anammox granules.

Partial anammox achieved in full scale biofilm process for typical domestic wastewater treatment

The slow initiation of anammox for treating typical domestic wastewater and the relatively high footprint of wastewater treatment infrastructures are major concerns for practical wastewater treatment systems.Herein,a 300 m^(3)/d hybrid biofilm reactor(HBR)process was developed and operated with a short hydraulic retention time(HRT)of 8 h.The analysis of the bacterial community demonstrated that anammox were enriched in the anoxic zone of the HBR process.The percentage abundance of Candidatus Brocadia in the total bacterial community of the anoxic zone increased from 0 at Day 1 to 0.33%at Day 130 and then to 2.89%at Day 213.Based upon the activity of anammox bacteria,the removal of ammonia nitrogen(NH_(4)^(+)-N)in the anoxic zone was approximately 15%.This showed that the nitrogen transformation pathway was enhanced in the HBR system through partial anammox process in the anoxic zone.The final effluent contained 12 mg/L chemical oxygen demand(COD),0.662 mg/L NH_(4)^(+)-N,7.2 mg/L total nitrogen(TN),and 6 mg/L SS,indicating the effectiveness of the HBR process for treating real domestic wastewater.

Anoxic phosphorus removal in a pilot scale anaerobic-anoxic oxidation ditch process

The anaerobic-anoxic oxidation ditch(A^(2)/O OD)process is popularly used to eliminate nutrients from domestic wastewater.In order to identify the existence of denitrifying phosphorus removing bacteria(DPB),evaluate the contribution of DPB to biological nutrient removal,and enhance the denitrifying phosphorus removal in the A^(2)/O OD process,a pilot-scale A^(2)/O OD plant(375 L)was conducted.At the same time batch tests using sequence batch reactors(12 L and 4 L)were operated to reveal the significance of anoxic phosphorus removal.The results indicated that:The average removal efficiency of COD,NH^(+)_(4),PO^(3–)_(4),and TN were 88.2%,92.6%,87.8%,and 73.1%,respectively,when the steady state of the pilotscale A^(2)/O OD plant was reached during 31–73 d,demonstrating a good denitrifying phosphorus removal performance.Phosphorus uptake took place in the anoxic zone by poly-phosphorus accumulating organisms NO^(-)_(2) could be used as electron receptors in denitrifying phosphorus removal,and the phosphorus uptake rate with NO^(-)_(2) as the electron receptor was higher than that with NO^(–)_(3) when the initial concentration of either NO^(-)_(2) or NO^(–)_(3) was 40 mg/L.

Optimization of denitrifying phosphorus removal in a predenitrification anaerobic/anoxic/post-aeration+nitrification sequence batch reactor(pre-A_(2)NSBR)system:Nitrate recycling,carbon/nitrogen ratio and carbon source type

Because the efficiency of biological nutrient removal is always limited by the deficient carbon source for the low carbon/nitrogen(C/N)ratio in real domestic sewage,the denitrifying phosphorus removal(DNPR)was developed as a simple and efficient method to remove nitrogen and phosphorous.In addition,this method has the advantage of saving aeration energy while reducing the sludge production.In this context,a pre-denitrification anaerobic/anoxic/post-aeration+nitrification sequence batch reactor(pre-A_(2)NSBR)system,which could also reduce high ammonia effluent concentration in the traditional two-sludge DNPR process,is proposed in this work.The pre-A_(2)NSBR process was mainly composed of a DNPR SBR and a nitrifying SBR,operating as alternating anaerobic/anoxic/post-aeration+nitrification sequence.Herein,the long-term performance of different nitrate recycling ratios(0-300%)and C/N ratios(2.5-8.8),carbon source type,and functional microbial community were studied.The results showed that the removal efficiency of total inorganic nitrogen(TIN,including NH4^(+)-N,NO_(2)^(-)-N,and NO_(3)^(-)-N)gradually increased with the nitrate recycling ratios,and the system reached the highest DNPR efficiency of 94.45% at the nitrate recycling ratio of 300%.The optimum C/N ratio was around 3.9-7.3 with a nitrogen and phosphorus removal efficiency of 80.15%and 93.57%,respectively.The acetate was proved to be a high-quality carbon source for DNPR process.The results of fluorescence in situ hybridization(FISH)analysis indicated that nitrifiers and phosphorus accumulating organisms(PAOs)were accumulated with a proportion of 19.41%and 26.48%,respectively.

Research progress and prospects of complete ammonia oxidizing bacteria in wastewater treatment

Complete ammonia oxidizing bacteria,or comammox bacteria(CAOB),can oxidize ammonium to nitrate on its own.Its discovery revolutionized our understanding of biological nitrification,and its distribution in both natural and artificial systems has enabled a reevaluation of the relative contribution of microorganisms to the nitrogen cycle.Its wide distribution,adaptation to oligotrophic medium,and diverse metabolic pathways,means extensive research on CAOB and its application in water treatment can be promoted.Furthermore,the energy-saving characteristics of high oxygen affinity and low sludge production may also become frontier directions for wastewater treatment.This paper provides an overview of the discovery and environmental distribution of CAOB,as well as the physiological characteristics of the microorganisms,such as nutrient medium,environmental factors,enzymes,and metabolism,focusing on future research and the application of CAOB in wastewater treatment.Further research should be carried out on the physiological characteristics of CAOB,to analyze its ecological niche and impact factors,and explore its application potential in wastewater treatment nitrogen cycle improvement.

Achieving partial nitrification by inhibiting the activity of Nitrospira-like bacteria under high-DO conditions in an intermittent aeration reactor

It is generally accepted that a low dissolved oxygen （DO） concentration is more beneficial for achieving partial nitrification than high-DO. In this study, partial nitrification was not established under low-DO conditions in an intermittent aeration reactor for treating domestic wastewater. During the operational period of low-DO conditions （DO： 0.3 ± 0.14 rag/L）, stable complete nitrification was observed. The abundance of Nitrospira-like bacteria, which were the major nitrite-oxidizing bacteria, increased from 1.03 x 10^6 to 2.64 x 10^5 cells/mL. At the end of the low-DO period, the batch tests showed that high-DO concentration （1.5, 2.0mg/L） could inhibit nitrite oxidation, and enhance ammonia oxidation. After switching to the high-DO period （1.8 ± 0.32 mg/L）, partial nitrification was gradually achieved. Nitrospira decreased from 2.64 x 10^6 to 8.85 x 10^5 cells/mL. It was found that suddenly switching to a high-DO condition could inhibit the activity and abundance of Nitrospira-like bacteria, resulting in partial nitrification.

Achieving nitritation at low temperatures using free ammonia inhibition on Nitrobacter and real-time control in an SBR treating landfill leachate

Free ammonia（FA） inhibition on nitrite-oxidized bacteria（NOB） and real-time control are used to achieve nitrogen removal from landfill leachate via nitrite pathway at low temperatures in sequencing batch reactor. The inhibition of FA on NOB activity during the aerobic period was prolonged using real-time control. The degree of nitrite accumulation was monitored along with variations of the ammonia-oxidizing bacteria and NOB population using fluorescence in situ hybridization techniques. It is demonstrated that the end-point of ammonia oxidization is detected from the on-line measured dissolved oxygen,oxidization–reduction potential, and p H signals, which could avoid the loss the FA inhibition on NOB caused by excess aeration. At low temperature（13.0–17.6°C）, the level of nitrite pathway rapidly increased from 19.8% to 90%, suggesting that nitritation was successfully started up at low temperature by applying syntrophic association of the FA inhibition and real-time control, and then this high level of nitrite pathway was stably maintained for as long as 233 days. Mechanism analysis shows that the establishment of nitritation was primarily the result of predominant ammonia-oxidizing bacteria developed in the nitrifying bacteria population compared to NOB. This was mainly due to a gradual reduction of nitrite amount that is available to provide energy for the growth of NOB,eventually leading to the elimination of NOB from the bacterial clusters in sequencing batch reactor sludge system.

On-line controlling system for nitrogen and phosphorus removal of municipal wastewater in a sequencing batch reactor (SBR)

The objectives of this study were to establish an on-line controlling system for nitrogen and phosphorus removal synchronously of municipal wastewater in a sequencing batch reactor(SBR).The SBR for municipal wastewater treatment was operated in sequences:filling,anaerobic,oxic,anoxic,oxic,settling and discharge.The reactor was equipped with on-line monitoring sensors for dissolved oxygen(DO),oxidation-reduction potential(ORP)and pH.The variation of DO,ORP and pH is relevant to each phase of biological process for nitrogen and phosphorus removal in this SBR.The characteristic points of DO,ORP and pH can be used to judge and control the stages of process that include:phosphate release by the turning points of ORP and pH;nitrification by the ammonia valley of pH and ammonia elbows of DO and ORP;denitrification by the nitrate knee of ORP and nitrate apex of pH;phosphate uptake by the turning point of pH;and residual organic carbon oxida-tion by the carbon elbows of DO and ORP.The controlling system can operate automatically for nitrogen and phosphorus efficiently removal.

Production of N2O in two biologic nitrogen removal processes： a comparison between conventional and short-cut Nitrogen removal processes

The N2O production in two nitrogen removal processes treating domestic wastewater was investigated in laboratory-scale aerobic-anoxic sequencing batch reactors （SBRs）. Results showed that N2O emission happened in the aerobic phase rather than in the anoxic phase. During the aerobic phase, the nitrogen conversion to N2O gas was 27.7% and 36.8% of NH＋-N loss for conventional biologic N-removal process and short-cut biologic N-removal process. The dissolved N2O was reduced to N2 in the anoxic denitrification phase. The N2O production rate increased with the increasing of nitrite concentration and ceased when NH＋-N oxidation was terminated. Higher nitrite accumulation resulted in higher NEO emission in the short-cut nitrogen removal process. Pulse-wise addition of 20 mg NO2 -N. L- 1 gave rise to 3-fold of N2O emission in the conventional N-removal process, while little change happened with 20 mg NOS-N L-1 was added to SBR1.