Simultaneous partial nitrification, anaerobic ammonium oxidation and denitrification (SNAD) in a full-scale landfill-leachate treatment plant

Strategy of rapid start-up and the mechanism of de-nitrogen in landfill bioreactor

Nitrogen removal from landfill leachate via anaerobic ammonium oxidation (Anammox) process has been considered as an innovative and sustainable approach to the traditional nitrification and denitrification process. However, the various technologies for rapid start-up of Anammox are still being explored. In this study, two strategies (inoculating anaerobic sludge and without inoculation) were applied to treat landfill leachate based on biological nitrogen removal processes. The start-up and mechanism of de-nitrogen process in landfill bioreactor was explored using ¹⁵N stable isotopic tracing, quantitative polymerase chain reaction (qPCR) and high-throughput sequencing methods. Results showed that inoculating anaerobic sludge was beneficial to enhance the nitrogen removal at the initial stage (from day 10 to day 25), but no significant increase was found during days 25-55 (p > 0.05). ¹⁵N stable isotopic tracing demonstrated that the inoculation of sludge accelerated by denitrification other than Anammox. Inoculation of sludge was conducive to increase of ammonia-oxidizing bacteria (AOB)- amoA and niK genes. Thauera was the dominant genus for nitrogen removal due to inoculation of sludge in landfill bioreactor, whereas the abundance of Candidatus Kuenenia did not increase by inoculating the sludge. Moreover, seeding anaerobic sludge could not provide Anammox's ecological niches. The results will provide a scientific basis for the selection of suitable operational condition for the rapid start-up in the landfill bioreactor.

Metagenomics Response of Anaerobic Ammonium Oxidation (anammox) Bacteria to Bio-Refractory Humic Substances in Wastewater

Anammox-based processes have been widely applied for the treatment of wastewater (e.g., wastewater irrigation systems and constructed wetland) which consists of bio-refractory humic substances. Nonetheless, the impacts of bio-refractory humic substances on anammox consortia are rarely reported. In the present study, three identical lab-scale anammox reactors (i.e., HS0, HS1 and HS10), two of which were dosed with humic substances at 1 and 10 mg·L−1, respectively, were operated for nearly one year. The long-term operation of the reactors showed that the presence of humic substances in influent had no significant influence on nitrogen removal rates. Despite this, comparative metagenomics showed changes in anammox microbiota structure during the exposure to humic substance; e.g., the relative abundance of Candidatus Kuenenia was lower in HS10 (18.5%) than that in HS0 (22.8%) and HS1 (21.7%). More specifically, a lower level of humic substances (1 mg·L−1) in influent led to an increase of genes responsible for signal transduction, likely due to the role of humic substances as electron shuttles. In contrast, a high level of humic substances (10 mg·L−1) resulted in a slight decrease of functional genes associated with anammox metabolism. This may partially be due to the biodegradation of the humic substances. In addition, the lower dosage of humic substances (1 mg·L−1) also stimulated the abundance of hzs and hdh, which encode two important enzymes in anammox reaction. Overall, this study indicated that the anammox system could work stably over a long period under humic substances, and that the process was feasible for leachate treatment.

Efficient step-feed partial nitrification, simultaneous Anammox and denitrification (SPNAD) equipped with real-time control parameters treating raw mature landfill leachate

An innovative step-feed partial nitrification, simultaneous Anammox and denitrification (SPNAD), equipped with real-time control parameters, achieved efficient nitrogen removal from raw mature landfill leachate. The variables pH and ORP served as real time on-line parameters to flexibly control the durations of aerobic and anoxic. A nitrogen removal efficiency (NRE) of 98.7% and nitrogen removal rate (NRR) of 0.23 kg m^-3d^-1 were obtained at the influent NH₄⁺ -N, SCOD and total nitrogen (TN) of 1000 ± 250 mg L^-1, 1100 ± 200 mg L^-1, and 1300 ± 75 mg L^-1, respectively. Mass balance research demonstrated that Anammox contributed 69.3% to nitrogen removal and denitrification contributed 15.7%. A significant change in the Anammox community structure occurred (ca. Brocadia from 0.26% to 2.13%, ca. Kuenenia from 0.29% to 0.02%). This change is mainly attributed to different kinetic strategies (R-strategist of ca. Brocadia and K-strategist of ca. Kuenenia). Further study revealed the co-existence of functional microorganisms Nitrosomonas (3.0%), Cadidatus-Brocadia (2.13%), and Thauera (25.3%).

Microbial characteristics of nitrifiers, denitrifiers and anammox bacteria on different support media to treat space mission wastewater

Biomass attachment and growth are important factors for the startup and stability of fixed-film biological reactors being proposed to recycle wastewater for potable water use in manned space activity. Eight different biofilm support media commonly used in wastewater treatment plants, aquaculture, and aquariums were compared for their relative ability to support attachment and growth of nitrifiers, denitrifiers, and anaerobic ammonia oxidizing (anammox) bacteria biomass. Accumulated total biomass was determined by comparing dry weight of each media before and after culturing of biomass. Fluorescence In-Situ Hybridization (FISH) analysis was used to quantify the proportion and relative activity of each organism group on each media. Measurements of dry biomass normalized to several media properties showed polyether polyurethane foam to have the highest extent of specific biomass attachment and colonization. Six of the eight media were able to sustain a population of anammox bacteria that was more abundant than the other cohorts.

Denitrification- and anammox-dominant simultaneous nitrification, anammox and denitrification (SNAD) process in subsurface flow constructed wetlands

Simultaneous nitrification, anammox and denitrification (SNAD) process was developed in subsurface flow constructed wetlands (SFCWs) to treat polluted surface water. The effects of vegetation, hydraulic retention time (HRT), C/N, and influent nitrogen forms on nitrogen removal and microbial communities were investigated. Results showed that denitrification- and anammox-dominant SNAD corresponded to nitrate- and ammonia-dominant influent, respectively, and both could achieve more efficient nitrogen removal in planted SFCWs than the unplated. These higher efficiencies were due to the microbial growth, organic carbon release, oxygen supply and plant uptake promoted by vegetation. The electron donors accelerated denitrification but inhibited ammonia oxidation with deficient oxygen. Anammox contributed to nitrogen removal of 27.34% under oxygen-limited conditions without vegetation. Anammox combined with denitrification and plant uptake were over 90% in planted SFCWs. For the investigated factors, the ammonia, nitrate and C/N were the most significant ones influencing the microbial communities, further nitrogen removal pathways and performances.

Treatment of municipal sewage with low carbon-to-nitrogen ratio via simultaneous partial nitrification, anaerobic ammonia oxidation, and denitrification (SNAD) in a non-woven rotating biological contactor

In this study, a non-woven rotating biological contactor was evaluated for the treatment of municipal sewage via simultaneous partial nitrification, anaerobic ammonia oxidation (anammox), and denitrification (SNAD). Fluorescence in situ hybridization analysis showed that the dominant bacterial group in the aerobic outer layer of the biofilm was ammonia-oxidizing bacteria (65.13%), whereas anammox (47.17%) and denitrifying (38.91%) bacteria were present in the anaerobic inner layer. Response surface methodology was applied to develop mathematical models for the interaction between C/N and dissolved oxygen (DO) for chemical oxygen demand (COD) and total nitrogen (TN) removal. Results showed that the optimum region for SNAD was at C/N = 1.4-2.3 and DO = 0.2-0.8 mg/L. The most optimal operating condition was determined at C/N = 2.3 and DO = 0.2 mg/L, with actual removal rates of COD and TN were 83.12% and 79.13%, respectively, which are in close model consistency with model prediction (84% and 80%).

A novel partial-denitrification strategy for post-anammox to effectively remove nitrogen from landfill leachate

Anaerobic ammonia oxidation (anammox) has shown great promise for nitrogen removal in low C/N wastewater such as landfill leachate. However, 11% of NO₃^--N is stoichiometrically produced, which decreases the total nitrogen (TN) removal efficiency. In this study, a strategy for post anammox was developed to effectively remove TN from leachate. A tandem conversion of NO₃^--N to NO₂^--N (partial denitrification) was accomplished by supplying substrate for subsequent anammox, by supplementing the electron donor deficient condition. This process greatly improved NH₄⁺-N and TN removal from leachate, reaching a 95% efficiency. Quantitative real-time polymerase chain reaction results showed that a high abundance of anammox bacteria, with a titer of 10⁹ copy numbers/L, was enriched, accounting for 9.66% of the total bacterial community, and indicating the success of this novel strategy for the TN removal in leachate.

Full nitration-denitration versus partial nitration-denitration-anammox for treating high-strength ammonium-rich organic wastewater

This study investigated the performance of full nitration-denitration (FND) and partial nitration-denitration-anammox (PNDA) in treating a synthetic wastewater with 300 mg/L NH₄⁺-N and 600 mg/L COD. It was found that approximately 40% higher total nitrogen removal was achieved via PNDA than via FND. Meanwhile, high-throughput sequencing also revealed that aerobic heterotrophic bacteria were predominant in the FND process, while facultative and even anaerobic bacteria including anammox bacteria were dominant in PNDA process. Furthermore, the mass balance on nitrogen showed that 44% of nitrogen was removed by partial nitration-denitration, while 36% via nitritation-anammox pathway in the PNDA process, with the significant saving in aeration and demand of organic carbon source. Compared to the FND process, it is obvious that the PNDA process will offer a more cost-effective alternative with easy operation for treating ammonium-rich organic wastewater.

Influence of temperature fluctuations on one-stage deammonification systems in northern cold region

Cold and fluctuant temperatures are still a bottleneck for the application of one-stage deammonification in mainstream anammox (anaerobic ammonium oxidation). In this study, to simulate the practical but critical operational condition under rapidly fluctuant temperatures between April and May in cold northern area, two deammonification reactors with anammox granular sludge and nitritation flocculent sludge were tested under the cold shock with temperature fluctuations (11-18 °C). Under the controlled temperature (32 °C), good performances were obtained in both reactors. However, after the cold shock (ca. 13 °C), both reactors deteriorated similarly. The ammonia removal efficiencies decreased by half, while total nitrogen (TN) removal efficiencies decreased by two thirds. Nitrite accumulated in both reactors, while nitrate production was not disturbed although its contributions from nitrite oxidizing bacteria (NOB) increased. In the stage with increasing wastewater temperatures (17.5 ± 2.2 °C), several operational conditions were tested to recover the performances, including limited dissolved oxygen, long hydraulic retention time (HRT), high nitrogen loading with elevated pH, and low NH₄⁺-N (60 mg/L), which did not significantly improve the performances, while the phenomena of heterotrophic nitrate reduction dramatically improved the nitrogen removal performances under limited aeration. During the cold temperature shock, insufficient anammox activity, and nitrate overproduction were the main problems.

A novel single-stage process integrating simultaneous COD oxidation, partial nitritation-denitritation and anammox (SCONDA) for treating ammonia-rich organic wastewater

In this study, simultaneous carbon oxidation, partial nitritation, denitritation and anammox (SCONDA) was successfully integrated into a one-stage sequencing biofilm batch reactor for treating ammonia-rich organic wastewater with carbon to nitrogen (C/N) ratio of 3. The results showed that 94.3% of COD removal together with 92.6% NH₄⁺-N and 88% TN removal were achieved via SCONDA. High-throughout sequencing analysis further revealed that the microbial community developed in the proposed system was primarily dominated by heterotrophic bacteria (e.g. Thauera, Azovibrio, Ohtaekwangia, Azospira), autotrophic bacteria (e.g. Nitrosomona) and unclassified genus of anammox bacterium, which were all essential for COD and N removal via SCONDA. The observed spatial distributions of the functional species in stratified biofilms were found to be crucial for successful SCONDA at the low dissolved oxygen of 1.3 mg/L. The integrated SCONDA system is expected to offer a promising alternative for advanced nitrogen and organic removal from high-ammonia organic wastewater.

Restoration of real sewage partial nitritation-anammox process from nitrate accumulation using free nitrous acid treatment

This study presented a strategy for recovering partial nitritation-anammox (PN/A) of real sewage from nitrate accumulation using free nitrous acid (FNA) treatment. Sewage PN/A was successfully achieved in an integrated fixed-film activated sludge (IFAS) reactor but effluent nitrate gradually increased. For recovering the system performance, flocculent sludge of the reactor was collected and treated with FNA of 1.35 mg/L for 24 h. After FNA treatment, effluent nitrate decreased from 17.6 to 6.1 mg/L with an increase of total nitrogen removal efficiency from 29.1% to 63.1% within 32 days. The improvement of nitrogen removal was mainly due to the selective suppression of FNA on nitrite-oxidizing bacteria. Its relative abundance decreased from 0.32% to 0.08% and the activity declined from 9.05 to 2.42 mg N/(g MLSS·h). Meanwhile, ammonium-oxidizing bacteria and anammox bacteria were barely affected. Overall, IFAS reactor combined with FNA treatment potentially provided a promising technology for stable operation of one-stage sewage PN/A.

Influence of biomass acclimation on the performance of a partial nitritation-anammox reactor treating industrial saline effluents

The performance of the partial nitritation/anammox processes was evaluated for the treatment of fish canning effluents. A sequencing batch reactor (SBR) was fed with industrial wastewater, with variable salt and total ammonium nitrogen (TAN) concentrations in the range of 1.75-18.00 g-NaCl L^-1 and 112 - 267 mg-TAN L^-1. The SBR operation was divided into two experiments: (A) progressive increase of salt concentrations from 1.75 to 18.33 g-NaCl L^-1; (B) direct application of high salt concentration (18 g-NaCl L^-1). The progressive increase of NaCl concentration provoked the inhibition of the anammox biomass by up to 94% when 18 g-NaCl L^-1 were added. The stable operation of the processes was achieved after 154 days when the nitrogen removal rate was 0.021 ± 0.007 g N/L·d (corresponding to 30% of removal efficiency). To avoid the development of NOB activity at low salt concentrations and to stabilize the performance of the processes dissolved oxygen was supplied by intermittent aeration. A greater removal rate of 0.029 ± 0.017 g-N L^-1 d^-1 was obtained with direct exposure of the inoculum to 18 g-NaCl L^-1 in less than 40 days. Also, higher specific activities than those from the inoculum were achieved for salt concentrations of 15 and 20 g-NaCl L^-1 after 39 days of operation. This first study of the performance of the partial nitritation/anammox processes, to treat saline wastewaters, indicates that the acclimation period can be avoided to shorten the start-up period for industrial application purposes. Nevertheless, further experiments are needed in order to improve the efficiency of the processes.

Impact of different schemes for treating landfill leachate

Different technological schemes for treating the leachate generated by an existing landfill were compared in a life cycle perspective. On-site advanced processes based on reverse osmosis and evaporation were compared to conventional off-site co-treatment with civil sewage in wastewater treatment plant (WWTP). The inventories of the different scenarios were built by both direct observation of existing facilities and by retrieving data from the literature and similar equipment. Particular care was given for evaluating the energetic and chemical needs for operating the on-site advanced treatments. The evaporation system required 40 kW h/m3 of electricity and 18.5 kW h/m3 of heat, whereas reverse osmosis needed only 8.5 kW h/m3 of electricity. On the other hand the amount of liquid concentrate returned by the evaporation system was only about 0.03 m3/m3 instead of about 0.30 m3/m3 returned by reverse osmosis. The evaporation system also consumed the highest amount of chemicals. Life cycle analysis showed that the impact categories most affected by the different options were human toxicity, both non-cancer and cancer, together with freshwater ecotoxicity. The uncertainty analysis highlighted the major contribution associated with direct emissions from the processes. On the basis of mean values, the qualitative trends were substantially confirmed.

Anaerobic ammonium oxidation-denitrification synergistic interaction of mature landfill leachate in aged refuse bioreactor: Variations and effects of microbial community structures

In this work, anammox-denitrification process was verified by ¹⁵N stable isotopic tracing methods and variations and effects of microbial community structures were studied using Illumina MiSeq sequencing and Quantitative Polymerase Chain Reaction (qPCR). The results showed that higher nitrogen removal efficiency and richer microbial consortia was observed at hydraulic loading rate (HLR) of 15L/m³·d, BOD₅/TN ratio of 0.4:1, respectively. Proteobacteria, Chloroflexi, Acidobacteria and Firmicutes were the dominant phyla in the anamox-denitrification biomass. The number of amx gene changed significantly during the HLR downshift and BOD₅/TN ratio upshift period. The obtained results enhance understanding regarding the microbial community structures of anammox-denitrification bacteria in aged refuse, leading to a more effective controlling of anammox-denitrification process.

Effect of low COD/N ratios on stability of single-stage partial nitritation/anammox (SPN/A) process in a long-term operation

This study investigates the effects of varying COD/N ratios on single-stage partial nitritation/anammox (SPN/A) process in a SBR. The operational period was divided into three phases with different influent COD/N ratios (0.4, 0 and 0.5). Stable nitrogen removal was achieved in phase I with a COD/N of 0.4. In phase II COD was absent, effluent nitrite and nitrate increased and nitrogen removal performance gradually deteriorated. In phase III SPN/A failed to recover from nitrate accumulation when COD/N was increased. Microbial activity was measured and microbial community was analyzed by high-throughput sequencing. These results revealed that ordinary heterotrophic organisms (OHO) was suppressed when influent COD was absent, leading to the promotion of nitrification even at a low DO (0.2mgL^-1). Therefore, nitrite oxidizing bacteria (NOB) was gradually enriched and anammox bacteria was suppressed. Besides, it was observed that flocs were sensitive to influent COD variations than granules, which requires further investigation.

Assessment of molecular detection of anaerobic ammonium-oxidizing (anammox) bacteria in different environmental samples using PCR primers based on 16S rRNA and functional genes

Eleven published PCR primer sets for detecting genes encoding 16S ribosomal RNA (rRNA), hydrazine oxidoreductase (HZO), cytochrome cd ₁-containing nitrite reductase (NirS), and hydrazine synthase subunit A (HzsA) of anaerobic ammonium-oxidizing (anammox) bacteria were assessed for the diversity and abundance of anammox bacteria in samples of three environments: wastewater treatment plant (WWTP), wetland of Mai Po Nature Reserve (MP), and the South China Sea (SCS). Consistent phylogenetic results of three biomarkers (16S rRNA, hzo, and hzsA) of anammox bacteria were obtained from all samples. WWTP had the lowest diversity with Candidatus Kuenenia dominating while the SCS was dominated by Candidatus Scalindua. MP showed the highest diversity of anammox bacteria including C. Scalindua, C. Kuenenia, and Candidatus Brocadia. Comparing different primer sets, no significant differences in specificity for 16S rRNA gene could be distinguished. Primer set CL1 showed relatively high efficiency in detecting the anammox bacterium hzo gene from all samples, while CL2 showed greater selectivity for WWTP samples. The recently reported primer sets of the hzsA gene resulted in high efficiencies in detecting anammox bacteria while nirS primer sets were more selective for specific samples. Results collectively indicate that the distribution of anammox bacteria is niche-specific within different ecosystems and primer specificity may cause biases on the diversity detected.

Achievement, performance and characteristics of microbial products in a partial nitrification sequencing batch reactor as a pretreatment for anaerobic ammonium oxidation

This study was carried out to evaluate achievement, performance and characteristics of microbial products in a partial nitrification sequencing batch reactor as a pretreatment for anaerobic ammonium oxidation (anammox). After 100 days long-term operation, the effluent NO₂^--N/NH₄⁺N ratio of the reactor was average at 1.3 and NO₃^--N concentration was low by controlling low dissolved oxygen (DO) concentration, which was considered as the ideal influent for anammox. Specific oxygen uptake rate (SOUR) implied that (SOUR)_NH4 and (SOUR)_NO2 of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in sludge changed from 21.73 ± 0.52 and 27.39 ± 0.50 O₂/g SS/h to 36.37 ± 0.85 and 12.04 ± 0.17 O₂/g SS/h, respectively. The main compositions of extracellular polymeric substances (EPS) and soluble microbial products (SMP), including proteins (PN) and polysaccharides (PS), were both reduced during the achievement of partial nitrification. Three-dimensional excitation-emission matrix (3D-EEM) and synchronous fluorescence spectra revealed that PN-like, fulvic acid-like and humic acid-like substances were identified in both EPS and SMP, and their fluorescence intensities changed significantly after partial nitrification achievement. It was found from typical cycle that free ammonia (FA) may play a significant role on inhibiting the activity of NOB. The obtained results could provide more information on the performance of partial nitrification through the characteristics of microbial products when treating high ammonium wastewater.

Interaction of short-chain fatty acids carbon source on denitrification

Short-chain fatty acids (SCFAs) could be obtained from organic waste anaerobic digestion. The ability and interaction of different SCFAs on denitrification were investigated in this study. Two kinds of SCFAs (acetate and propionate with 5 different ratios) and 4 kinds of SCFAs (acetate, propionate, butyrate and valerate with 10 different ratios) were evaluated. Using acetate (Ac) and propionate (Pr) as carbon sources, the highest nitrate removal efficiency of 97.5% was obtained. When using the mixture of acetate (Ac), propionate (Pr), butyrate (Bu) and valerate (Va) as the carbon source, the highest nitrate removal efficiency obtained was 92.0%. The denitrification performance was affected significantly by different kinds and proportions of SCFAs. In addition, nitrite accumulation and chemical oxygen demand consumption for different contents of SCFAs were also analyzed.

High rate nitrogen removal by ANAMMOX internal circulation reactor (IC) for old landfill leachate treatment

This study aimed to evaluate the performance of a high rate nitrogen removal lab-scale ANAMMOX reactor, namely Internal Circulation (IC) reactor, for old landfill leachate treatment. The reactor was operated with pre-treated leachate from a pilot Partial Nitritation Reactor (PNR) using a high nitrogen loading rate ranging from 2 to 10kgNm^-3d^-1. High rate removal of nitrogen (9.52±1.11kgNm^-3d^-1) was observed at an influent nitrogen concentration of 1500mgNL^-1. The specific ANAMMOX activity was found to be 0.598±0.026gN₂-NgVSS^-1d^-1. Analysis of ANAMMOX granules suggested that 0.5-1.0mm size granular sludge was the dominant group. The results of DNA analysis revealed that Candidatus Kueneniastuttgartiensis was the dominant species (37.45%) in the IC reactor, whereas other species like uncultured Bacteroidetes bacterium only constituted 5.37% in the system, but they were still responsible for removing recalcitrant organic matter.

Whole-Community Metagenomics in Two Different Anammox Configurations: Process Performance and Community Structure

Anaerobic ammonia oxidation (anammox) combined with partial nitritation (PN) is an innovative treatment process for energy-efficient nitrogen removal from wastewater. In this study, we used genome-based metagenomics to investigate the overall community structure and anammox species enriched in suspended growth (SGR) and attached growth packed-bed (AGR) anammox reactors after 220 days of operation. Both reactors removed more than 85% of the total inorganic nitrogen. Metagenomic binning and phylogenetic analysis revealed that two anammox population genomes, affiliated with the genus Candidatus Brocadia, were differentially abundant between the SGR and AGR. Both of the genomes shared an average nucleotide identify of 83%, suggesting the presence of two different species enriched in both of the reactors. Metabolic reconstruction of both population genomes revealed key aspects of their metabolism in comparison to known anammox species. The community composition of both the reactors was also investigated to identify the presence of flanking community members. Metagenomics and 16S rRNA gene amplicon sequencing revealed the dominant flanking community members in both reactors were affiliated with the phyla Anaerolinea, Ignavibacteria, and Proteobacteria. Findings from this research adds two new species, Ca. Brocadia sp. 1 and Ca. Brocadia sp. 2, to the genus Ca. Brocadia and sheds light on their metabolism in engineered ecosystems.

Nitrogen removal via nitrite in a partial nitrification sequencing batch biofilm reactor treating high strength ammonia wastewater and its greenhouse gas emission

In present study, the feasibility of partial nitrification (PN) process achievement and its greenhouse gas emission were evaluated in a sequencing batch biofilm reactor (SBBR). After 90days' operation, the average effluent NH₄⁺-N removal efficiency and nitrite accumulation rate of PN-SBBR were high of 98.2% and 87.6%, respectively. Both polysaccharide and protein contents were reduced in loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) during the achievement of PN-biofilm. Excitation-emission matrix spectra implied that aromatic protein-like, tryptophan protein-like and humic acid-like substances were the main compositions of both kinds of EPS in seed sludge and PN-biofilm. According to typical cycle, the emission rate of CO₂ had a much higher value than that of N₂O, and their total amounts per cycle were 67.7 and 16.5mg, respectively. Free ammonia (FA) played a significant role on the inhibition activity of nitrite-oxidizing bacteria and the occurrence of nitrite accumulation.

Effects of carbon sources, COD/NO2--N ratios and temperature on the nitrogen removal performance of the simultaneous partial nitrification, anammox and denitrification (SNAD) biofilm

The aim of the present work was to evaluate the effects of carbon sources and chemical oxygen demand (COD)/NO₂^--N ratios on the anammox-denitrification coupling process of the simultaneous partial nitrification, anammox and denitrification (SNAD) biofilm. Also, the anammox activities of the SNAD biofilm were investigated under different temperature. Kaldnes rings taken from the SNAD biofilm reactor were operated in batch tests to determine the nitrogen removal rates. As a result, with the carbon source of sodium acetate, the appropriate COD/NO₂^--N ratios for the anammox-denitrification coupling process were 1 and 2. With the COD/NO₂^--N ratios of 1, 2, 3, 4 and 5, the corresponding NO₂^--N consumption via anammox was 87.1%, 52.2%, 29.3%, 23.7% and 16.3%, respectively. However, with the carbon source of sodium propionate and glucose, the anammox bacteria was found to perform higher nitrite competitive ability than denitrifiers at the COD/NO₂^--N ratio of 5. Also, the SNAD biofilm could perform anammox activity at 15 °C with the nitrogen removal rate of 0.071 kg total inorganic nitrogen per kg volatile suspended solids per day. These results indicated that the SNAD biofilm process might be feasible for the treatment of municipal wastewater at normal temperature.

The role of inoculum and reactor configuration for microbial community composition and dynamics in mainstream partial nitritation anammox reactors

Implementation of partial nitritation anammox (PNA) in the mainstream (municipal wastewater treatment) is still under investigation. Microbial community structure and reactor type can influence the performance of PNA reactor; yet, little is known about the role of the community composition of the inoculum and the reactor configuration under mainstream conditions. Therefore, this study investigated the community structure of inocula of different origin and their consecutive community dynamics in four different lab‐scale PNA reactors with 16S rRNA gene amplicon sequencing. These reactors were operated for almost 1 year and subjected to realistic seasonal temperature fluctuations as in moderate climate regions, that is, from 20°C in summer to 10°C in winter. The sequencing analysis revealed that the bacterial community in the reactors comprised: (1) a nitrifying community (consisting of anaerobic ammonium‐oxidizing bacteria (AnAOB), ammonia‐oxidizing bacteria (AOB), and nitrite‐oxidizing bacteria (NOB)); (2) different heterotrophic denitrifying bacteria and other putative heterotrophic bacteria (HB). The nitrifying community was the same in all four reactors at the genus level, although the biomasses were of different origin. Community dynamics revealed a stable community in the moving bed biofilm reactors (MBBR) in contrast to the sequencing batch reactors (SBR) at the genus level. Moreover, the reactor design seemed to influence the community dynamics, and reactor operation significantly influenced the overall community composition. The MBBR seems to be the reactor type of choice for mainstream wastewater treatment.

Inhibition factors and Kinetic model for ammonium inhibition on the anammox process of the SNAD biofilm

The aim of the present work was to evaluate the anaerobic ammonium oxidation (anammox) activity of simultaneous partial nitrification, anammox and denitrification (SNAD) biofilm with different substrate concentrations and pH values. Kaldnes rings taken from the SNAD biofilm reactor were incubated in batch tests to determine the anammox activity. Haldane model was applied to investigate the ammonium inhibition on anammox process. As for nitrite inhibition, the NH₄⁺-N removal rate of anammox process remained 87.4% of the maximum rate with the NO₂^--N concentration of 100mg/L. Based on the results of Haldane model, no obvious difference in kinetic coefficients was observed under high or low free ammonia (FA) conditions, indicating that ammonium rather than FA was the true inhibitor for anammox process of SNAD biofilm. With the pH value of 7.0, the r_max, Ks and K_I of ammonium were 0.209kg NO₂^--N/kg VSS/day, 9.5mg/L and 422mg/L, respectively. The suitable pH ranges for anammox process were 5.0 to 9.0. These results indicate that the SNAD biofilm performs excellent tolerance to adverse conditions.

Complete Nitrogen Removal from Synthetic Anaerobic Sludge Digestion Liquor through Integrating Anammox and Denitrifying Anaerobic Methane Oxidation in a Membrane Biofilm Reactor

Partial nitritation and Anammox processes are increasingly used for nitrogen removal from anaerobic sludge digestion liquor. However, their nitrogen removal efficiency is often limited due to the production of nitrate by the Anammox reaction and the sensitivity to the nitrite to ammonium ratio. This work develops and demonstrates an innovative process that achieves complete nitrogen removal from partially nitrified anaerobic sludge digestion liquor through the use of a membrane biofilm reactor (MBfR), with methane supplied through hollow fiber membranes. When steady state with a hydraulic retention time (HRT) of 1 day was reached, the process achieved complete nitrite and ammonium removal at rates of 560 mg N/L/d and 470 mg N/L/d, respectively, without any nitrate accumulation. The process is relatively insensitive to the nitrite to ammonium ratio, achieving complete nitrogen removal when their ratio in influent varied in the range of 1.125-1.32. Pyrosequencing and fluorescence in situ hybridization analysis revealed that denitrifying anaerobic methane oxidation (DAMO) archaea, Anammox bacteria and DAMO bacteria jointly dominated the microbial community. Mass balance analysis showed that nitrate produced by Anammox (122.2 mg N/L/d) was entirely converted to nitrite by DAMO archaea, while nitrite in the feed and produced by DAMO archaea was jointly removed by Anammox (90%) and DAMO bacteria (10%). The nitrogen removal rate of over 1 kg N/m³/d is comparable to the practical rates reported for side-stream nitrogen removal processes.

Quantitative impact of influent characteristics on nitrogen removal via anammox and denitrification in a landfill bioreactor case

In this paper, Quantitative Polymerase Chain Reaction (qPCR), Illumina MiSeq sequencing and ¹⁵N stable isotopic tracing methods were applied to study the effects of influent organic loading, BOD₅/TN and NO₂-N/NH₄-N ratios on the combined nitrogen removal through denitrification and anammox. The results show that, the total nitrogen removal was above 90% at the optimum reaction condition: organic loading 0.04kg/m³·day, BOD₅/TN 0.2, and NO₂-N/NH₄-N 1.0. Approximately 9.43% of the nitrogen removal occurred through anammox process when BOD₅/TN was 0.1, and increased to 21.46% when BOD₅/TN was 0.2. The anammox accounted for 10% when NO₂-N/NH₄-N was 0.5, and that increased to 20.72% when NO₂-N/NH₄-N was 1.0-1.5. hzsA was directly proportional to the influent BOD₅/TN. A positive correlation between BOD₅/TN and anammox microorganisms existed. Similarly, there was a positive correlation between NO₂-N/NH₄-N and denitrification microorganisms. Therefore, it is feasible to regulate the influent to improve nitrogen removal efficiency.

Anammox biofilm in activated sludge swine wastewater treatment plants

We investigated anammox with a focus on biofilm in 10 wastewater treatment plants (WWTPs) that use activated sludge treatment of swine wastewater. In three plants, we found red biofilms in aeration tanks or final sedimentation tanks. The biofilm had higher anammox 16S rRNA gene copy numbers (up to 1.35 × 10¹² copies/g-VSS) and higher anammox activity (up to 295 μmoL/g-ignition loss/h) than suspended solids in the same tank. Pyrosequencing analysis revealed that Planctomycetes accounted for up to 17.7% of total reads in the biofilm. Most of them were related to Candidatus Brocadia or Ca. Jettenia. The highest copy number and the highest proportion of Planctomycetes were comparable to those of enriched anammox sludge. Thus, swine WWTPs that use activated sludge treatment can fortuitously acquire anammox biofilm. Thus, concentrated anammox can be detected by focusing on red biofilm.

Anammox Process

Application of anammox based processes is nowadays an efficient way to remove nitrogen from wastewaters, being good alternative to the conventional nitrification-denitrification process. This chapter reviews the possible configurations to apply the anammox process, being special attention to the previous partial nitritation, necessary to obtain the adequate substrates for anammox bacteria. Furthermore a description of the main technologies developed and patented by different companies was performed, with focus on the advantages and bottlenecks of them. These technologies are classified in the chapter based on the type of biomass: suspended, granular and biofilm. Also a review is presented for the industrial applications (food industry, agricultural wastes, landfill leachates, electronic industry, etc.), taking into account full scale experiences and laboratory results, as well as microbiology aspects respect to the anammox bacteria genera involved. Finally the possibility to couple nitrogen removal, by anammox, with phosphorus recovery, by struvite precipitation, is also evaluated.

Stoichiometric evaluation of partial nitritation, anammox and denitrification processes in a sequencing batch reactor and interpretation of online monitoring parameters

A laboratory-scale sequencing batch reactor (SBR) performing partial nitritation - anammox and denitrification was used to treat anaerobic digester effluents. The SBR cycle consisted of a short mixing filling phase followed by oxic and anoxic reaction phases. Working at 25 °C, an ammonium conversion efficiency of 96.5%, a total nitrogen removal efficiency of 88.6%, and an organic carbon removal efficiency of 63.5% were obtained at a nitrogen loading rate of 0.15 kg N m^-3 d^-1, and a biodegradable organic carbon to nitrogen ratio of 0.37. The potential contribution of each biological process was evaluated by using a stoichiometric model. The nitritation contribution decreased as the temperature decreased, while the contribution from anammox depended on the wastewater type and soluble carbon to nitrogen ratio. Denitrification improved the total nitrogen removal efficiency, and it was influenced by the biodegradable organic carbon to nitrogen ratio. The characteristic patterns of conductivity, oxidation-reduction potential (ORP) and pH in the SBR cycle were well related to biological processes. Conductivity profiles were found to be directly related to the decreasing profiles of ammonium. Positive ORP values at the end of the anoxic phases were detected for total nitrogen removal efficiency of lower than 85%, and the occurrence of bending points on the ORP curves during the anoxic phases was associated with nitrite depletion by the anammox process.

In-situ restoration of one-stage partial nitritation-anammox process deteriorated by nitrate build-up via elevated substrate levels

The one-stage partial nitritation and anammox process (PN/A) has been a promising microbial process to remove ammonia from wastewater especially with low carbon/nitrogen ratio. The main breakdown was the deterioration caused by overgrowth of nitrite oxidizing bacteria (NOB) resulting effluent nitrate build-up in the PN/A process. This study presented an in-situ restoring strategy for suppressing NOB activity in a one-stage granular PN/A system deteriorated over 2 months, using elevated concentrations of substrates (ammonia and nitrite) under limited dissolved oxygen level. The results showed that the NOB activity was successfully suppressed after 56 days of restoration, and finally the ratio of produced nitrate/consumed ammonium was reduced from 36.8% to 7%. On day 66 the nitrogen removal rate obtained as 1.2 kg N/(m³·d). The high FA level (5-40 mg/L) and low dissolved oxygen (<0.13 mg/L) were responsible for NOB suppression. From quantitative PCR (qPCR) analysis, after this restoration, anammox bacteria had a widely growth, and AOB stay stable, but Nitrospira increase and Nitrobacter declined. High amount of NOB was still persistent in the granules, which was not easy to wash-out and threaten the deammonification performance.

Effect of short term external perturbations on bacterial ecology and activities in a partial nitritation and anammox reactor

This research investigated the short term effects of temperature changes (lasting 2-4weeks each) from 35±2°C to 21±2°C and 13±2°C and sulfide toxicity on partial nitrification-anammox (PN/A) system. Temperatures below 20°C and sulfide content as low as 5mgSL(-1) affected both aerobic and anaerobic catabolic activities of ammonia oxidation and the expression of related functional gene markers. The activity of AOB was inversely correlated with ammonium monooxygenase (amoA) gene expression. In contrast, the activity of AMX bacteria was positively correlated with the expression of their hydrazine synthase (hzsA) gene. Although the overall activities of AMX bacteria decreased at lower temperatures, the AMX bacteria were still active at the low temperatures. The inverse correlation between amoA gene expressions and the corresponding AOB activities was surprising. 16S rDNA based high throughput amplicon sequencing revealed the dominance of Chloroflexi, Planctomycetes and Proteobacteria phyla the distribution of which changed with temperature changes.

Integrating landfill bioreactors, partial nitritation and anammox process for methane recovery and nitrogen removal from leachate

A new process consisting of a landfill bioreactor, partial-nitritation (PN) and the anammox process has been developed for landfill leachate treatment. In this study, the landfill bioreactor exhibited excellent performance in methane-rich biogas recovery, with a specific biogas yield of 0.47 L gas g⁻¹ COD and methane percentages of 53–76%. PN was achieved in the aerobic reactor by high free ammonia (101 ± 83 mg NH₃ L⁻¹) inhibition for nitrite-oxidizing bacteria, and the desired PN effluent composition (effluent nitrite: ammonium ratio of 1.1 ± 0.3) was controlled by adjusting the alkalinity concentration per unit of ammonium oxidized to approximately 14.3 mg CaCO₃ mg⁻¹ N in the influent. The startup of anammox process was successfully achieved with a membrane bioreactor in 160 d, and a maximum nitrogen removal rate of 216 mg N L⁻¹ d⁻¹ was attained for real landfill leachate treatment. The quantitative polymerase chain reaction results confirmed that the cell-specific anammox activity was approximately 68–95 fmol N cell⁻¹ d⁻¹, which finally led to the stable operation of the system.

Combined autotrophic nitritation and bioelectrochemical-sulfur denitrification for treatment of ammonium rich wastewater with low C/N ratio

A novel combined autotrophic nitritation and bioelectrochemical-sulfur denitrification (CANBSD) process was developed for treatment of synthetic ammonium-rich wastewater with low carbon/nitrogen ratio. Total nitrogen removal of the CANBSD was higher than 95 %, the effluent SO4 (2-) was lower than 1280 mg L(-1), and the maximum nitrogen volumetric loading rate was 1.2 kg m(-3) day(-1) when (1) the influent NH4 (+)-N was lower than 1008 mg L(-1), (2) hydraulic retention time was between 3.7 and 32 h, (3) the DO was between 0.5 and 1.2 mg L(-1), (4) the pH was between 7.5 and 8.2, and (5) the temperature was between 28 and 30 °C. Both the NH4 (+)-N removal and conversion to NO2 (-)-N in the nitritation membrane reactor (NMBR) were maintained at about 50 %, and the residual NH4 (+)-N and accumulated NO2 (-)-N were subsequently treated in the bioelectrochemical-sulfur three-dimensional denitrification reactor. The CANBSD energy consumption was 0.13 and 3.4 kWh m(-3), respectively, for influent NH4 (+)-N of 100 and 1000 mg L(-1). The energy consumption of CANBSD was close to that of partial nitritation-ANNMMOX.

Influence of COD/N ratio and carbon source on nitrogen removal in a structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA)

This study aimed to evaluate the influence of COD/N ratio and carbon source on simultaneous nitrogen and carbon removal processes. A continuous up-flow structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) was operated with hydraulic retention time (HRT) of 11.2 ± 0.6 h. The carbon sources were meat peptone and sucrose. The COD/N ratio varied by maintaining the organic loading rate fixed at 1.07 kg COD m(-3) d(-1) and changing the total-N concentration. The COD/N ratios tested were 9.7 ± 1 (sucrose); 7.6 ± 1 (meat peptone); 2.9 ± 1 (meat peptone) and 2.9 ± 0.4 (sucrose). COD removal efficiencies remained above 90% in all experimental phases. At lower COD/N ratios, NH4(+)-N oxidation efficiencies were higher than 90%. An autotrophic metabolism by anammox process was observed in Phases III and IV, which was responsible for 35% and 27% of total-N loading removal rates, respectively. Therefore, the system achieved total nitrogen removal efficiencies of 84.6 ± 10.1 and 81.5 ± 5.3%, under low availability of organic electron donors.

A case study of coupling upflow anaerobic sludge blanket (UASB) and ANITA™ Mox process to treat high-strength landfill leachate

A pilot study was conducted to study the treatability of high-strength landfill leachate by a combined process including upflow anaerobic sludge blanket (UASB), carbon removal (C-stage) moving bed biofilm reactor (MBBR) and ANITA™ Mox process. The major innovation on this pilot study is the patent-pending process invented by Veolia that integrates the above three unit processes with an effluent recycle stream, which not only maintains the low hydraulic retention time to enhance the treatment performance but also reduces inhibiting effect from chemicals present in the high-strength leachate. This pilot study has demonstrated that the combined process was capable of treating high-strength leachate with efficient chemical oxygen demand (COD) and nitrogen removals. The COD removal efficiency by the UASB was 93% (from 45,000 to 3,000 mg/L) at a loading rate of 10 kg/(m(3)·d). The C-stage MBBR removed an additional 500 to 1,000 mg/L of COD at a surface removal rate (SRR) of 5 g/(m(2)·d) and precipitated 400 mg/L of calcium. The total inorganic nitrogen removal efficiency by the ANITA Mox reactor was about 70% at SRR of 1.0 g/(m(2)·d).

Sustainable operation of submerged Anammox membrane bioreactor with recycling biogas sparging for alleviating membrane fouling

A submerged anaerobic ammonium oxidizing (Anammox) membrane bioreactor with recycling biogas sparging for alleviating membrane fouling has been successfully operated for 100d. Based on the batch tests, a recycling biogas sparging rate at 0.2m(3)h(-1) was fixed as an ultimate value for the sustainable operation. The mixed liquor volatile suspended solid (VSS) of the inoculum for the long operation was around 3000mgL(-1). With recycling biogas sparging rate increasing stepwise from 0 to 0.2m(3)h(-1), the reactor reached an influent total nitrogen (TN) up to 1.7gL(-1), a stable TN removal efficiency of 83% and a maximum specific Anammox activity (SAA) of 0.56kg TNkg(-1) VSSd(-1). With recycling biogas sparging rate at 0.2 m(3) h(-1) (corresponding to an aeration intensity of 118m(3)m(-2)h(-1)), the membrane operation circle could prolong by around 20 times compared to that without gas sparging. Furthermore, mechanism of membrane fouling was proposed. And with recycling biogas sparging, the VSS and EPS content increasing rate in cake layer were far less than the ones without biogas sparging. The TN removal performance and sustainable membrane operation of this system showed the appealing potential of the submerged Anammox MBR with recycling biogas sparging in treating high-strength nitrogen-containing wastewaters.

Interaction of organic carbon, reduced sulphur and nitrate in anaerobic baffled reactor for fresh leachate treatment

Interaction of organic carbon, reduced sulphur and nitrate was examined using anaerobic baffled reactor for fresh leachate treatment by supplementing nitrate and/or sulphide to compartment 3. Nitrate was removed completely throughout the study mostly via denitrification (>80%) without nitrite accumulation. Besides carbon source, various reduced sulphur (e.g. sulphide, elemental sulphur and organic sulphur) could be involved in the nitrate reduction process via sulphur-based autotrophic denitrification when dissolved organic carbon/nitrate ratio decreased below 1.6. High sulphide concentration not only stimulated autotrophic denitrification, but it also inhibited heterotrophic denitrification, resulting in a shift (11-20%) from heterotrophic denitrification to dissimilatory nitrate reduction to ammonia. High-throughput 16S rRNA gene sequencing analysis further confirmed that sulphur-oxidizing nitrate-reducing bacteria were stimulated with increase in the proportion of bacterial population from 18.6% to 27.2% by high sulphide concentration, meanwhile, heterotrophic nitrate-reducing bacteria and fermentative bacteria were inhibited with 25.5% and 66.6% decrease in the bacterial population.

Nitrate removal by organotrophic anaerobic ammonium oxidizing bacteria with C2/C3 fatty acid in upflow anaerobic sludge blanket reactors

In anaerobic ammonium oxidation (Anammox) process, a harsh ratio of nitrite to ammonia in influent was demanded, and the max nitrogen removal efficiency could only achieve to 89%, both of which limited the development of Anammox. The aim of this work was to study the nitrate removal by organotrophic anaerobic ammonium oxidizing bacteria (AAOB) with C2/C3 fatty acid in upflow anaerobic sludge blanket (UASB) reactors. In this study, organotrophic AAOB was successfully enriched by adding acetate and propionate with the total organic carbon to nitrogen (TOC/N) ratio of 0.1. In the condition of low substrate, the TN removal efficiency reached 90%, with the effluent TN of around 11.8 mg L(-1). After the addition of acetate and propionate, the predominant species in Anammox granular sludge transformed to Candidatus Jettenia that belonging to organotrophic AAOB from the Candidatus Kuenenia relating to general AAOB.

Reactor performance and microbial characteristics of CANON process with step-wise increasing of C/N ratio

In this study, the nitrogen removal performance and microbial characteristics of completely autotrophic nitrogen removal over nitrite (CANON) process was investigated with a step-wise increasing of C/N ratio (0.5, 1, 2 and 4) in a membrane bioreactor. The microbial distribution of aerobic ammonia-oxidizing bacteria (AOB) and anaerobic AOB (AAOB) was analysed by fluorescence in situ hybridization (FISH). Results showed that the denitrification ratio rose up correspondingly with the increase of influent C/N, and nitrogen removal rate (NRR) reached the maximum when C/N was 1 due to the harmonious work of denitrification and CANON. However, NRR decreased when influent C/N was more than 2. The threshold C/N ratio of CANON process was 2.2; so the sewage with a high C/N ratio should be pretreated by combining with pre-oxidation of organics or anaerobic-energy-producing process. FISH results showed decreasing numbers of both AOB and AAOB with the addition of organics.

The performance of a combined nitritation-anammox reactor treating anaerobic digestion supernatant under various C/N ratios

A combined nitritation-anammox reactor was developed to treat the digestion supernatant under various C/N ratios. Due to the difficulties for heterotroph to utilize the refractory organics, the reactor presented relatively stable performance with increasing supernatant addition. Nevertheless, the adverse effects of supernatant would accumulate during the long-term operation and thus weakened the activity and shock resistance of microbes, which further led to the gradual decrease of reactor performance after 92 days' operation. Under this circumstance, supernatant with volatile fatty acids (VFAs) residuals was further introduced into the reactor to investigate the performance of combined nitritation-anammox process with VFA addition. With the appearance of VFAs, the nitrogen removal performance gradually restored and the reactor finally achieved stable and efficient performance with C/N ratio of 0.35. The VFA residuals within 150 mg/L in the supernatant served as the extra electron donors and stimulated the heterotrophic denitrification process, which was vital for the enhancement of reactor. The nitrogen removal rate and total nitrogen removal efficiency reached 0.49 kg N/(m3·day) and 88.8% after 140 days' operation, respectively. The combined nitritation-anammox reactor was proved suitable to treat digestion supernatant.