ANAMMOX process start up and stabilization with an anaerobic seed in Anaerobic Membrane Bioreactor (AnMBR)

Variations of N concentrations and microbial community in the start-up of anammox using anaerobic heterotrophic sludge: Influence of a long reaction-phase time and comparison of the efficiencies of attached-versus suspended-growth cultures

Anaerobic sludge was capable of producing anaerobic ammonium oxidation (anammox) cultures. However, the low activity of anammox bacteria in the seed sludge often led to a long time for stable anammox to initiate. The objective of this study was to investigate the influence of an extended reaction-phase time in the sequencing batch reactor (SBR) on the rapid startup of anaerobic ammonium oxidation (anammox) using anaerobic heterotrophic bacteria as the seed sludge. After the startup, suspended and attached bacteria in anammox were separately analyzed for comparison. The variations of nitrogen concentrations and shifts of the microbial community structures were studied. The results showed that anammox occurred after a long reaction-phase time in the SBR with the efficient removals of NH₄⁺ (96.4%) and NO₂^- (99.8%). The effective NO₂^- treatment before anammox startup was attributable to inevitable denitrification or dissimilatory nitrate reduction (e.g., Denitratisoma). The occurrence of anammox was supported by the anammox stoichiometry, bacteria diversity variation, and principal component analysis. The overall nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) was 0.07 kg/m³-d and 92.8%, respectively. The relative molar quantities of NH₄⁺ and NO₂^- removed as well as N₂ and NO₃^- formed were 1(1):1.29(1.32):1.45(1.02):0.15(0.26), as the numbers in the parentheses represent the theoretical values. Denitratisoma and Desulfatiglans dominated in the seed sludge, whereas Candidatus_Jettenia abundances were significantly higher in anammox attached- (26.0%) and suspended-growth cultures (14.5%). Fifty-three genera were simultaneously identified in all samples, suggesting their importance in the startup of anammox from anaerobic sludge. Candidatus_Jettenia was observed to be more associated with the growth of anammox biofilm (the abundances were 26.0% and 14.5% in attached- and suspended-growth cultures, respectively) and supported the fine nitrogen removal performance in the attached-growth cultures.

Recent Advances in the Rejection of Endocrine-Disrupting Compounds from Water Using Membrane and Membrane Bioreactor Technologies: A Review

Water is a critical resource necessary for life to be sustained, and its availability should be secured, appropriated, and easily obtainable. The continual detection of endocrine-disrupting chemicals (EDCs) (ng/L or µg/L) in water and wastewater has attracted critical concerns among the regulatory authorities and general public, due to its associated public health, ecological risks, and a threat to global water quality. Presently, there is a lack of stringent discharge standards regulating the emerging multiclass contaminants to obviate its possible undesirable impacts. The conventional treatment processes have reportedly ineffectual in eliminating the persistent EDCs pollutants, necessitating the researchers to develop alternative treatment methods. Occurrences of the EDCs and the attributed effects on humans and the environment are adequately reviewed. It indicated that comprehensive information on the recent advances in the rejection of EDCs via a novel membrane and membrane bioreactor (MBR) treatment techniques are still lacking. This paper critically studies and reports on recent advances in the membrane and MBR treatment methods for removing EDCs, fouling challenges, and its mitigation strategies. The removal mechanisms and the operating factors influencing the EDCs remediation were also examined. Membranes and MBR approaches have proven successful and viable to eliminate various EDCs contaminants.

Insights into fouling behavior in a novel anammox self-forming dynamic membrane bioreactor by the fluorescence EEM-PARAFAC analysis

Fouling behavior of the novel anaerobic ammonium oxidation (anammox) self-forming dynamic membrane bioreactor (SFDMBR) was elucidated, which is using nylon mesh as the filter with controlled fouling and successful anammox process. Properties of anammox sludge and foulants in the anammox SFDMBR and MBR (using PVDF microfiltration membrane) were compared to analyze the alleviated fouling in the SFDMBR, of which transmembrane pressure could be kept below 10 kPa for 50 days in one filtration cycle of 82 days with flux of 12 L m^-2 h^-1. Colorimetrical determination and excitation emission matrices-parallel factor (EEM-PARAFAC) analysis of the foulants showed that humic acid content in foulants on nylon mesh was obviously lower than that on PVDF membrane. Considering that the small-sized and flexible humic acids prefer to plug into membrane pores, the alleviated irreversible fouling in the SFDMBR could be attributed to the less microbial humic acid content of foulants (8.8 ± 1.0%) compared with the MBR (20.7 ± 2.9%). The adequate efflux of humic-like substances in the operation with nylon mesh was speculated to be the main mechanism of fouling control in the SFDMBR. These findings highlighted the potential of anammox SFDMBR in practical applications, because of the high humic acid contents in real ammonium-laden wastewater. Our study highlights the important role of humic acids in fouling behavior of the novel anammox SFDMBR to provide guidance for fouling control strategies. Graphical abstract.

Granule-based immobilization and activity enhancement of anammox biomass via PVA/CS and PVA/CS/Fe gel beads

Granule-based immobilization of anammox biomass assisted by polyvinyl alcohol/chitosan (PVA/CS) and PVA/CS/Fe gel beads was studied, via the operation of three identical up-flow reactors (R1 without gel beads, R2 with PVA/CS, R3 with PVA/CS/Fe) for 203 days. In the end, the nitrogen removal rates (NRR) were 5.3 ± 0.4, 10.0 ± 0.3 and 13.9 ± 0.5 kg-N m^-3 d^-1 for R1, R2 and R3, respectively. The porous PVA/CS and PVA/CS/Fe created a suitable eco-niche for anammox bacteria to grow and attach, thus being retained in the reactor. The EPS entangles newly grown cells within the gel beads, resulting in compact aggregation. The interaction between Fe ions added to PVA/CS/Fe gel beads and negatively charged EPS groups strongly promoted granule strength and compactness. The immobilization method proposed by this study was found to effectively improve biomass retention in the reactors, which is promising for advanced anammox process applications.

Extractive membrane bioreactor (EMBR): Recent advances and applications

Combining bioreactor and membrane, known as a membrane bioreactor (MBR), has been considered as an attractive strategy to solve the limitations of conventional activated sludge process, such as biological instability, poor sludge quality, and low concentration of mixed liquor suspended solid. Unlike the other MBRs, extractive membrane bioreactor (EMBR) focuses on enhancing the efficiency of wastewater treatment through toxic compounds extraction by using a selective membrane. Even though EMBR has been successfully demonstrated in wastewater and waste gas treatment by several studies, it still faces some obstacles such as biofilm formation and low selectivity of the membrane towards a specific component. Appropriate biofilm formation control strategies and membrane with high selectivity are needed to solve those problems. This paper reviews EMBR including its potential applications in wastewater treatment, denitrification process, and waste gas treatment. In addition, challenges and outlook of EMBR are discussed.

Characteristics of a Self-Forming Dynamic Membrane Coupled with a Bioreactor in Application of Anammox Processes

A novel anammox self-forming dynamic membrane bioreactor (SFDMBR) was proposed to achieve an efficient anammox process with high biomass retention and cost-effective operation. The cake layer formed on nylon mesh (pore size, 20-25 μm) was referred to as a dynamic membrane (DM). The high permeability of the DM layer contributed to low transmembrane pressure (TMP), which kept below 10 kPa for 50 days in one filtration cycle of 82 days. Compared to the high TMP (mainly > 20 kPa) in the MBR using polyvinylidene fluoride (PVDF) microfiltration membrane, energy can be significantly conserved in the SFDMBR. Besides, the mature DM layer achieved efficient biomass retention comparable to that of PVDF membrane, which favored anammox bacteria enrichment. Concomitantly, an appropriate microenvironment for autotrophic anammox bacterial growth with well-controlled extracellular polymeric substances (EPS) concentration (33.22 mg·g^-1 VSS) was achieved in SFDMBR. According to specific filtration resistance (SFR) analysis, reducing the EPS concentration in the bulk sludge improves sludge filterability and alleviate fouling, which was achieved in the SFDMBR system with a low SFR of 1.47 × 10¹² m^-1·kg^-1. Our results show that the cost-effective operations and technical merits make anammox SFDMBRs promising for practical applications.

Benefits and drawbacks of food and dairy waste co-digestion at a high organic loading rate: A Moosburg WWTP case study

Anaerobic co-digestion (AcoD) is a key technology in reframing organic waste as a viable energy source. A lack of documented experience on full-scale AcoD at wastewater treatment plants (WWTPs) has created a bottleneck in AcoD implementation, which is further tightened by the focus of existing AcoD studies being on low co-substrate loading (<50%) and the obtainable benefits. This study aims to fill this gap by investigating the drawbacks and benefits of high-ratio co-substrate dosing of food and dairy wastes at the Moosburg WWTP (Germany) from 2014 to 2017. The Moosburg WWTP co-digests sewage sludge, food waste, and dairy wastes at a 35:47:18 ratio by volatile solids (organic loading rate (OLR) of 3.0 kg_VS/(m³·day)). During the study period, this high co-substrate dosing increased the methane potential by 300 ± 50%. The corresponding high methane yield significantly increased the on-site electricity production, resulting in energy neutrality in 2014-2015. The corresponding economic gain from gate fees was 48,000 ± 5,000 € per year. The observed drawbacks included solids accumulation inside the digester (5 m³/month), high nitrogen backload (65% increase from co-substrate addition), reduced retention time (loss of 1.18 days/year from solids accumulation), and reduced dewaterability. The high nitrogen content in the centrate is treated by sequential batch reactors (SBRs), using lactose as the carbon source for denitrification. This study presents an alternative approach for determining gate fees based on the economic gains from inherent methane content, which identified waste milk, lactose and grease trap sludge as the most profitable co-substrates.

Effect of external hydrazine addition on anammox reactor start-up time

Hydrazine is an intermediate product of the anaerobic ammonium oxidation (Anammox) process where both ammonium and nitrite in wastewater are converted to nitrogen gas by bacteria. In this study the effect of external hydrazine addition (5, 10, 15, and 20 mg/L) on the start-up period of the Anammox process was studied using sequencing batch reactors (SBRs). The SBR with an addition of 10 mg/L hydrazine took only 7 weeks to stabilize and achieve the maximum removal of ammonium and nitrite, whereas the SBR without the addition of hydrazine took 12 weeks. The amount of Heme C extracted from the biomass indicated that externally added hydrazine accelerated the growth of Anammox bacteria and reduced the release of nitrous oxide gas from the reactors.

Applications of membrane bioreactors for water reclamation: Micropollutant removal, mechanisms and perspectives

Membrane bioreactors (MBRs) have attracted attention in water reclamation as a result of the recent technical advances and cost reduction in membranes. However, the increasing occurrence of micropollutants in wastewaters has posed new challenges. Therefore, we reviewed the current state of research to identify the outstanding needs in this field. In general, the fate of micropollutants in MBRs relates to sorption, biodegradation and membrane separation processes. Hydrophobic, nonionized micropollutants are favorable in sorption, and the biological degradation shows higher efficiency at relatively long SRTs (30-40 days) and HRTs (20-30 h), as a result of co-metabolism, metabolism and/or ion trapping. Although the membrane rejection rates for micropollutants are generally minor, final water quality can be improved via combination with other technologies. This review highlights the challenges and perspectives that should be addressed to facilitate the extended use of MBRs for the removal of micropollutants in water reclamation.

Application of anaerobic dynamic membrane bioreactor (AnDMBR) for the successful enrichment of Anammox bacteria using mixed anaerobic and aerobic seed sludge

This study investigated a novel bioreactor configuration coupled with a side-stream dynamic membrane (DM) for Anammox enrichment as an alternative for conventional membrane. Bioreactor was fed with synthetic feed and seeded with a mix of anaerobic and aerobic sludge. In situ mechanical cleaning was employed for DM cleaning. DM development and performance was analysed over two polyamide-nylon meshes (200 and 52 µm). Solid-liquid separation of 52 µm mesh outperformed 200 µm with an average effluent turbidity of 2.4 ± 0.1 NTU. The system was operated at a maximum nitrogen loading rate of 696 mg-N L^-1 d^-1 and achieved a maximum nitrogen removal rate of 611.6 mg-N L^-1 d^-1. At steady state, the average ammonium, nitrite and total nitrogen removal efficiencies were 87 ± 0.6%, 98.5 ± 0.15% and 87.5 ± 0.56% respectively. Digital realtime PCRSequence analysis showed that Planctomycetales belonging to ascertained Anammox-specific genera progressively increased their presence in the reactor consistently with its nitrogen removal performance.

Performance and microbial community of simultaneous anammox and denitrification (SAD) process in a sequencing batch reactor

A sequencing batch reactor (SBR) was used to test the simultaneous anammox and denitrification process. Optimal nitrogen removal was achieved with chemical oxygen demand (COD) of 150mg/L, during which almost all of ammonia, nitrite and nitrate could be removed. Organic matter was a key factor to regulate the synergy of anammox and denitrification. Both experimental ΔNO2(-)-N/ΔNH4(+)-N and ΔNO3(-)-N/ΔNH4(+)-N values deviated from their theoretical values with increasing COD. Denitrifying bacteria exhibited good diversity and abundance, but the diversity of anammox bacteria was less abundant. Brocadia sinica was able to grow in the presence of organic matter and tolerate high nitrite concentration. Anammox bacteria were predominant at low COD contents, while denitrifying bacteria dominated the microbial community at high COD contents. Anammox and denitrifying bacteria could coexist in one reactor to achieve the simultaneous carbon and nitrogen removal through the synergy of anammox and denitrification.

Simultaneous nitrification, denitrification and phosphorus removal (SNDPR) in a full-scale water reclamation plant located in warm climate

The combination of simultaneous nitrification-denitrification (SND) with enhanced biological phosphorus removal (EBPR) provides a more efficient and economically viable option for nutrient removal from municipal wastewater compared to conventional two-step nitrification-denitrification. This study analyzed the nutrients (N and P) profiles in a full-scale municipal wastewater reclamation plant (WRP) located in the tropical region, in which more than 90% of nitrogen was removed. Interestingly, average SND efficiency in aerobic zones was found to be up to 50%, whereas phosphorus profile displayed a clear cyclic release and uptake pattern with a phosphorus removal efficiency of up to 76%. The capability of sludge to perform SND and EBPR was further confirmed through a series of batch experiments. Microbial analysis revealed the presence of Accumulibacter and Tetrasphaera phosphate accumulating organisms in the plant, while few glycogen accumulating organisms (GAO) was observed. This study showed the significant occurrence of combined SND and EBPR, known as simultaneous nitrification, denitrification and phosphorus removal (SNDPR), in the studied WRP under warm climate. The possible causes behind the observed SNDPR were also discussed.

A novel strategy for simultaneous removal of nitrogen and organic matter using anaerobic granular sludge in anammox hybrid reactor

The coexistence of organic matter (OM) and nitrogen in industrial effluent is the major bottleneck in field-scale application of anammox process. The present study emphasized on investigating the role of seeding anaerobic granular sludge towards simultaneous removal of ammonium and OM in anammox hybrid reactor (AHR). The study delineated simultaneous reduction of both OM (94.8%) and nitrogen (96.8%) at optimal COD/N ratio (0.54). Pearson correlation matrix showed positive and strong correlation of ARE (ammonium removal efficiency) and CRE (COD removal efficiency) with NRE (nitrogen removal efficiency). The negative correlation of OLR and COD/TN ratio with NRE indicated that increase in organic loadings may suppress anammox activity. The process inhibition was evaluated using Haldane model considering free ammonia, OM and nitrite as inhibitors. The strategy of using anaerobic granular sludge not only augmented endurance of bacterial communities against OM inhibition but also facilitated simultaneous removal of OM and nitrogen.

Performance evaluation of the anammox hybrid reactor seeded with mixed inoculum sludge

Long startup and poor granulation are the major bottlenecks in field-scale application of the anammox (ANaerobic AMMonium OXidation) process. In the present study, the anammox process was investigated in a modified anammox hybrid reactor (AHR) inoculated with mixed seed culture (anoxic and activated sludge). The startup study delineated four distinct phases, i.e. cell lysis, lag phase, activity elevation and stationary phase. Use of mixed seed culture at influent [Formula: see text] ratio (1:1) and hydraulic retention time (HRT) of 1 d led to early startup of the anammox process. The removal efficiencies of [Formula: see text] and [Formula: see text] during acclimation were found to be 94.3% and 96.4%, respectively, at nitrogen loading rate (NLR) of 0.35 kg N/m(3) d. Pearson correlation analysis dictated strong and positive correlation of HRT and sludge retention time (SRT) with nitrogen removal efficiency (NRE) while NLR and sludge loading rate (SLR) were negatively correlated. Attached growth system (AGS) in AHR contributed an additional 11% ammonium removal and reduced the sludge washout rate by 29%. Mass balance of nitrogen revealed that the major fraction (74.1%) of input nitrogen was converted into N2 gas indicating higher substrate conversion efficiency of anammox biomass. Scanning electron microscope (SEM) study of biomass indicated the presence of heterogeneous population of cocci and rod-shaped bacteria of average diameter varying from 1.2 to 1.5 mm. Owing to the features of early start-up, ability to retain high biomass and consistently higher NRE, hybrid reactor configuration seeded with mixed culture offers noble strategy for cultivation of well-compacted anammox granules for field-scale installation.

Current state of sewage treatment in China

The study reported and analyzed the current state of wastewater treatment plants (WWTPs) in urban China from the aspects of scale, treatment processes, sludge handling, geographical distribution, and discharge standards. By 2012, there were 3340 WWTPs in operation in China with a capacity of 1.42 × 10(8) m(3)/d. The number of medium-scale WWTPs (1-10 × 10(4) m(3)/d) counted for 75% of total WWTPs. On average, the chemical oxygen demand (COD) removal efficiencies of small-scale, medium-scale, large-scale and super-large-scale WWTPs were 81, 85.5, 87.5 and 86.5%, respectively. Generally speaking, the nutrients removal instead of COD removal was of concern. As to the different processes, oxidation ditch, anaerobic-anoxic-oxic (A(2)/O) and sequencing batch reactor (SBR) were the mainstream technologies in China. These technologies had minor difference in terms of overall COD removal efficiency. The sludge treatment in WWTPs was basically "thickening-coagulation-mechanical dehydration" and the major disposal method was sanitary landfill in China. The distributions of WWTPs and their utilization showed significant regional characteristics. The sewage treatment capacity of China concentrated on the coastal areas and middle reaches of Yangtze River, which were the economically developed zones. Besides, most WWTPs enforced the Class 1 or Class 2 discharge standards, but few realized wastewater reuse. Finally, existing problems were discussed, including low removal efficiency of nitrogen and phosphorus, emerging contaminants, low reuse of reclaimed water, poor sludge treatment and disposal, low execution standard of effluent, and emissions of greenhouse gas from WWTPs. Suggestions regarding potential technical and administrative measures were given.

Start-up characteristics of a granule-based anammox UASB reactor seeded with anaerobic granular sludge

The granulation of anammox sludge plays an important role in the high nitrogen removal performance of the anammox reactor. In this study, anaerobic granular sludge was selected as the seeding sludge to start up anammox reactor in order to directly obtain anammox granules. Results showed that the anammox UASB reactor was successfully started up by inoculating anaerobic granular sludge, with substrate capacity of 4435.2 mg/(L·d) and average ammonium and nitrite removal efficiency of 90.36% and 93.29%, respectively. During the start-up course, the granular sludge initially disintegrated and then reaggregated and turned red, suggesting the high anammox performance. Zn-Fe precipitation was observed on the surface of granules during the operation by SEM-EDS, which would impose inhibition to the anammox activity of the granules. Accordingly, it is suggested to relatively reduce the trace metals concentrations, of Fe and Zn in the conventional medium. The findings of this study are expected to be used for a shorter start-up and more stable operation of anammox system.

Feasibility and interest of the anammox process as treatment alternative for anaerobic digester supernatants in manure processing--an overview

Completely autotrophic nitrogen removal (ANR) is based on the combination of partial nitritation (PN) and anaerobic ammonium oxidation (anammox). It is a promising alternative for the subsequent treatment of biogas digester supernatants in livestock manure processing and nitrogen surplus scenarios. However, as no full-scale experiences in the treatment of manure digestates by ANR have been published to date, future field studies addressing treatment of this kind of effluent would be of great interest. Some topics to be considered in these studies would be coupling anaerobic digestion and ANR, analysis of the factors that affect the process, comparing reactor configurations, microbial ecology, gas emissions, and achieving robust performance. This paper provides an overview of published studies on ANR. Specific issues related to the applicability of the process for treating manure digestates are discussed. The energy requirements of ANR are compared with those of other technological alternatives aimed at recovering nitrogen from digester supernatants. The results of the assessment were shown to depend on the composition of the supernatant. In this regard, the PN-anammox process was shown to be more competitive than other alternatives particularly at concentrations of up to 2 kg NH4(+)-N m(-3).

Cultivation of planktonic anaerobic ammonium oxidation (anammox) bacteria using membrane bioreactor

Enrichment cultures of anaerobic ammonium oxidation (anammox) bacteria as planktonic cell suspensions are essential for studying their ecophysiology and biochemistry, while their cultivation is still laborious. The present study aimed to cultivate two phylogenetically distinct anammox bacteria, "Candidatus Brocadia sinica" and "Ca. Scalindua sp." in the form of planktonic cells using membrane bioreactors (MBRs). The MBRs were continuously operated for more than 250 d with nitrogen loading rates of 0.48-1.02 and 0.004-0.09 kgN m(-3) d(-1) for "Ca. Brocadia sinica" and "Ca. Scalindua sp.", respectively. Planktonic anammox bacterial cells were successfully enriched (>90%) in the MBRs, which was confirmed by fluorescence in-situ hybridization and 16S rRNA gene sequencing analysis. The decay rate and half-saturation constant for NO2(-) of "Ca. Brocadia sinica" were determined to be 0.0029-0.0081 d(-1) and 0.47 mgN L(-1), respectively, using enriched planktonic cells. The present study demonstrated that MBR enables the culture of planktonic anammox bacterial cells, which are suitable for studying their ecophysiology and biochemistry.

Application of membrane bioreactor for completely autotrophic nitrogen removal over nitrite (CANON) process

A membrane bioreactor (MBR) was adopted for completely autotrophic nitrogen removal over nitrite (CANON) process at ambient temperature. CANON was rapidly started-up within around 50d under oxygen-limited condition. The average nitrogen removal rate reached to 0.70kgNm(-3)d(-1) with a removal efficiency of 88%. The ratio of air flow rate to volumetric ammonium loading rate should be maintained below 0.28Lairmin(-1)kg(-1)Nm(3)d for stable CANON. The feasibility of MBR for CANON process was proved in batch experiments. FISH results showed that aerobic ammonium-oxidizing bacteria predominated in the reactor sludge, whereas anaerobic ammonium-oxidizing bacteria predominated in the membrane biofilm. This study demonstrated that MBR was a suitable experimental setup for the operation of CANON process.

Autotrophic ammonia removal from landfill leachate in anaerobic membrane bioreactor

Anaerobic ammonium oxidation (ANAMMOX) process, an advanced biological nitrogen removal, removes ammonia using nitrite as the electron acceptor without oxygen. In this paper, ANAMMOX process was adopted for removing NH4+-N from landfill leachate having low COD using anaerobic membrane bioreactor (AnMBR). The AnMBR was optimized for nitrogen loading rate (NLR) varying from 0.025 to 5 kg NH4+-N/m3/d with hydraulic retention time (HRT) ranging from 1 to 3d. NH4+-N removal efficacy of 85.13 +/- 9.67% with the mean nitrogen removal rate of 5.54 +/- 0.63 kg NH4+-N/m3/d was achieved with NLR of 6.51 +/- 0.20kg NH4+-N/m3/d at 1.5 d HRT. The nitrogen transformation intermediates in the form of hydrazine (N2H4) and hydroxylamine (NH2OH) were 0.008 +/- 0.005 and 0.006 +/- 0.001 mg/l, respectively, indicating co-existence of aerobic ammonia oxidizers and ANAMMOX. The free ammonia (NH3) and free nitrous acid (HNO2) concentrations were 26.61 +/- 16.54 mg/l and (1.66 +/- 0.95) x 10(-5) mg/l, preventing NO2(-)-N oxidation to NO3(-)-N enabling sustained NH4+-N removal.

Ecological characteristics of seeding sludge triggering a prompt start-up of anammox

Anammox start-up can be limited by the availability of seeding biomass in some areas. Previous studies have listed suitable alternative seeding sludge for anammox start-up such as anaerobic digestion sludge and conventional activated sludge (CAS), the ecological reasons behind has long been ignored. In this study, the inherent ecological factors that trigger a prompt start-up of anammox were identified, focusing on the initial relative abundance and concentration of anammox bacteria. An external membrane bioreactor was utilized as an enriching tool due to its suitability of retaining cells. Results revealed that a high initial concentration of anammox bacteria benefitted the start-up, meanwhile an even community seeding sludge (Gini coefficient<0.25) gained a more than three-time higher anammox activity compared to the uneven one (Gini coefficient>0.5). The discovery reminds to select the seeding sludge that is ecologically appropriate rather than to only care for the type of sludge in general.

Comparison between MBR and SBR on Anammox start-up process from the conventional activated sludge

Anammox start-up performances from the conventional activated sludge were compared between a MBR and SBR. Both the reactors successfully started up Anammox process. The start-up period in the MBR (59 days) was notably shorter than that in the SBR (101 days), and the max nitrogen (NH(4)(+)+NO(2)(-)) removal capacity of 345.2 mg N L(-1) d(-1) in the MBR was also higher than that of 292.0 mg N L(-1) d(-1) in the SBR. FISH analysis showed that Anammox bacteria predominated in both reactors. Phylogenetic analysis further disclosed that the MBR had the better biodiversity of Anammox bacteria and gained a higher ecological stability. Generally, the results showed that MBR exhibited a more excellent performance for Anammox start-up.

Biological catalyzed denitrification by a functional electropolymerization biocarrier modified by redox mediator

Electropolymerization biocarriers were prepared by the electropolymerization of polypyrrole (PPy) on an active carbon felt (ACF) electrode using doping anions anthraquinone-2-sulfonate (AQS) or Na(2)SO(4). The functional electropolymerization biocarrier (ACF/PPy/AQS) with AQS was used as an immobilized redox mediator for the denitrification process. The characteristics of the electropolymerization biocarriers were analyzed by scanning electron microscope, elemental analyses, Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The results suggested that the denitrification efficiency increased nearly 1.5-fold with ACF/PPy/AQS (0.04 mmol L(-1) AQS) compared to the control. A linear correlation was found for the k value and the AQS concentration (C(AQS)), which was k=624.71C(AQS)+83.87 (R(2)=0.9893). The ORP value stabilized around -200 mV for the denitrification process with ACF/PPy/AQS, which was -25 mV lower than that with ACF/PPy/Na(2)SO(4). Repeated-batch operations indicated that the denitrification efficiency with ACF/PPy/AQS maintained over 90% of the original value and exhibited better catalytic activity and durability.