Shortcut biological nitrogen removal in hybrid biofilm/suspended growth reactors

Regulation mechanism of hydrazine and hydroxylamine in nitrogen removal processes: A Comprehensive review

As the new fashioned nitrogen removal process, short-cut nitrification and denitrification (SHARON) process, anaerobic ammonium oxidation (anammox) process, completely autotrophic nitrogen removal over nitrite (CANON) process, partial nitrification and anammox (PN/A) process and partial denitrification and anammox (PD/A) process entered into the public eye due to its advantages of high nitrogen removal efficiency (NRE) and low energy consumption. However, the above process also be limited by long-term start-up time, unstable operation, complicated process regulation and so on. As intermediates or by-metabolites of functional microorganisms in above processes, hydroxylamine (NH2OH) and hydrazine (N2H4) improved NRE of the above processes by promoting functional enzyme activity, accelerating electron transport efficiency and regulating distribution of microbial communities. Therefore, this review discussed effects of NH2OH and N2H4 on stability and NRE of above processes, analyzed regulatory mechanism from functional enzyme activity, electron transport efficiency and microbial community distribution. Finally, the challenges and limitations for nitric oxide (NO) and nitrous oxide (N2O) produced from regulation of NH2OH and N2H4 are discussed. In additional, perspectives on future trends in technology development are proposed.

Efficient partial nitrification with hybrid nitrifying granular sludge based on a simultaneous fill/draw SBR mode

In this study, a simultaneous fill/draw SBR was applied to investigate the feasibility of partial nitrification process with inoculation of matured aerobic granular sludge. The system operated stably over 120 days with the relatively high ammonium removal efficiency (≥ 98.83%) and nitrite accumulation rate (≥ 89.60%). Moreover, a hybrid flocs/granules system was formed stably after long-term operation. The nitrite-oxidizing bacteria (NOB) was suppressed effectively because of the combined effect of simultaneous fill/draw mode and intermittent aeration conditions. Furthermore, batch tests were separately tested with isolated granules (> 200 μm) and flocs (< 200 μm), showing that the specific ammonia oxidation rate of granules and flocs were 15.94 ± 2.85 and 66.77 ± 0.83 mg N/(g MLSS·h), respectively. Correspondingly, the abundance of Nitrosomonas as a typical AOB in granules (6.24%) and flocs (11.94%) was obtained via the microbial diversity analysis, while NOB was almost hardly detected in granules and flocs.

Removal of nutrients and veterinary antibiotics from manure-free piggery wastewater in a packed-bed A/O process at normal atmospheric temperature

A packed-bed anaerobic-aerobic reactor (PBAOR) with two anaerobic and two aerobic compartments was constructed to treat manure-free piggery wastewater which was characterized by high ammonium (NH4⁺-N) and low ratio of chemical oxygen demand (COD) to total nitrogen (TN). Performed for 60 days at the normal atmospheric temperature of 25 °C with a constant hydraulic retention time of 32 h and reflux ratio of 2.0, a stable state in pollutants removal was obtained in the PBAOR. Within the next routine operation process, the removal of COD, NH4⁺-N and TN was above 85.7%, 98.2% and 85.8%, with a residual less than 81.7, 7.2 and 39.9 mg L^-1 in effluent, respectively. Twelve veterinary antibiotics classified into tetracyclines (TCs), sulphonamides (SAs) and fluoroquinolones (FQs) were detected from the piggery wastewater. The PBAOR was effective in removing TCs and SAs with an average removal of 74.8% and 93.3%, respectively, but presented a negative removal for FQs. Most COD in the piggery wastewater was mainly removed in the first two anaerobic compartments along with an obvious removal of TCs and SAs, while the TN were mainly removed in the last two aerobic compartments with the negative removal of FQs.

Nitrification kinetics, N2O emission, and energy use in intermittently aerated hybrid reactor under different organic loading rates

This study investigated the impact of intermittent aeration strategies and reduction in the reactor's organic and nitrogen loading rates on the course of particular stages of the nitrification process, as well as energy consumption and N2O emissions in a hybrid reactor with nitrification/denitrification. Each of the analysed series revealed the greatest ammonia oxidation activity in activated sludge flocs. The highest activity of nitrite nitrogen oxidation was demonstrated in the case of biofilm. A reduction in the reactor's organic and nitrogen loading rate value had a greater effect on changes in the activity of ammonia-oxidizing bacteria than nitrite-oxidizing bacteria. In a system where the operation of air pumps was controlled through switching them and off according to the adopted ratio between non-aerated and aerated sub-phase times and the assumed oxygen concentration, a reduction in the duration of aerated sub-phases caused no decrease in energy use for aeration. Lower N2O emission was recorded when the reactor operated with a longer duration of aerated sub-phases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13762-022-04715-6.

Investigating the long and short-term effect of free ammonia and free nitrous acid levels on nitritation biomass of a sequencing batch reactor treating thermally pre-treated sludge reject water

This work examined the short and long-term effects of different free ammonia (FA) and free nitrous acid (FNA) levels on (i) acclimatized biomass treating sludge reject water via nitrite in a sequencing batch reactor (SBR) and (ii) non-aclimatized biomass treating municipal wastewater via nitrate in the activated sludge process. In the acclimatized biomass, the threshold for the transition from nitrification to nitritation was the FA increase to 10-20 mgNH₃-N/L while the SBR unit showed no inhibition on the ammonia uptake rate (AUR) at FA levels up to 65 mgNH₃-N/L. Short-term exposure of the acclimatized biomass on FNA showed that AUR inhibition could be more than 50 % for FNA concentration >10 μgHNO₂-N/L. The FNA inhibition results were simulated using non-competitive inhibition kinetics that showed that the inhibition constant corresponding to the FNA concentration that inhibits the process by 50 % (i.e. K_iFNA) was much higher in the acclimatized biomass.

Efficiency and mechanism of nitrogen removal from piggery wastewater in an improved microaerobic process

Characterized by high ammonium (NH₄⁺ - N) and low ratio of chemical oxygen demand (COD) to total nitrogen (COD/TN), discharge of piggery wastewater has been identified as a primary pollution source resulting in water eutrophication. An improved microaerobic reactor, internal aerating microaerobic reactor (IAMR), was constructed to treat manure-free piggery wastewater without effluent recycle at dissolved oxygen of 0.3 mg/L and 32 °C. A removal rate of COD, NH₄⁺ - N and TN averaged 77.9%, 94.6% and 82.6% was obtained in the reactor, with the concentration of 258.5, 235.5 and 335.2 mg/L in influent, respectively. 16S rDNA amplicon sequencing, carbon and nitrogen mass balance and stoichiometry indicated that heterotrophic nitrification-anammox was the dominant approach to nitrogen removal. Microbiome phenotypes showed that aerobic bacteria were the dominant microorganisms, and the microbiome oxidative stress tolerance was intensified along with the continuous operation of the IAMR, resulting in the survival of various facultative and anaerobic bacteria for nutrients removal. With the good nutrients removal, less energy consumption, and high tolerance to influent fluctuation, the improved IAMR was confirmed as a promising process for treating wastewater with high NH₄⁺ - N and low COD/TN.

Comparing three mathematical models using different substrates for prediction of partial nitrification

Modelling of partial nitrification process is affected by several factors such as selection of true substrates, FA and FNA inhibition, and pH effect on growth rate. Among these factors, the selection of true substrates is very critical as it affects the structure of the model. In the present work, a new model adopting free ammonia (FA) and free nitrous acids (FNA) as the true substrate for ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) was proposed. Then the proposed model was compared with two reported models which adopted ammonium and nitrite, and FA and nitrite as the true substrate for AOB and NOB, respectively. The three mathematical models were compared in terms of predicted minimum dissolved oxygen (DO) in response to varied solids retention time (SRT) (10-30 d), pH (7-8.5), and temperature (10-35 °C). The input kinetic values were justified and updated based on statistical analysis of literature data. Adopting FA as the true substrate increased the minimum DO for AOB. Further, experimental data from different literature studies were taken for model simulation and comparison. Inconsistency was observed between the model prediction and literature data for all three models. The model that adopted ammonium and nitrite as the true substrate for AOB and NOB had better consistency with literature data than other two models. The affecting factors for the model prediction was classified into three levels and discussed in detail. Future work was proposed. The results of this study provide valuable information for the design and modelling of partial nitrification process.

Metagenomic and network analyses decipher profiles and co-occurrence patterns of antibiotic resistome and bacterial taxa in the reclaimed wastewater distribution system

Metagenomic and network analyses were applied to decipher the profiles and co-occurrence of resistome and microbial taxa in the reclaimed wastewater distribution system, including reclaimed wastewater and two types of biofilms, i.e., surface layer biofilms and inner layer biofilms. The effects of chlorination, UV irradiation and no disinfection treatment on ARG relative abundance and composition were systemically investigated. The reclaimed wastewater possesses more diverse and abundant ARGs than biofilms and total ARG relative abundance followed the order of reclaimed wastewater samples > surface layer biofilms > inner layer biofilms. Multidrug, bacitracin, sulfonamide, aminoglycoside, beta-lactam, and macrolide-lincosamide-streptogramin resistance genes were the six most dominant ARG types and their sum accounted for 90.1 %-96.0 % of the total ARG relative abundance in different samples. Beta-lactam resistance gene was the discriminative ARG type for reclaimed wastewater. Bacitracin resistance gene and bacA were the discriminative ARG type and subtype for biofilms. Chlorination significantly reduced ARG relative abundance in the reclaimed wastewater. Nevertheless, it could not reduce ARG relative abundance in biofilms. Regarding to the total ARG profiles, there were no obvious increasing or decreasing trends over time during one year period. Co-occurrence results revealed twenty-six genera were deduced as the potential hosts of twenty-two ARG subtypes.

Autotrophic Fixed-Film Systems Treating High Strength Ammonia Wastewater

The aim of the study was enrichment of nitrifying bacteria and to investigate the potential of autotrophic fixed-film and hybrid bioreactors to treat high strength ammonia wastewater (up to 1,000 mg N/L). Two types of fixed-film systems [moving bed biofilm reactor (MBBR) and BioCord^TM] in two different configurations [sequencing batch reactor (SBR) and a continuous stirred tank reactor (CSTR)] were operated for 306 days. The laboratory-scale bioreactors were seeded with activated sludge from a municipal wastewater treatment plant and fed synthetic wastewater with no organics. Strategies for acclimation included biomass reseeding (during bioreactor start-up), and gradual increase in the influent ammonia concentration [from 130 to 1,000 mg N/L (10% every 5 days)]. Stable ammonia removal was observed up to 750 mg N/L from 45 to 145 days in the MBBR SBR (94-100%) and CSTR (72-100%), and BioCord^TM SBR (96-100%) and CSTR (92-100%). Ammonia removal declined to 87% ± 6, in all bioreactors treating 1,000 mg N/L (on day 185). Following long-term operation at 1,000 mg N/L (on day 306), ammonia removal was 93-94% in both the MBBR SBR and BioCord^TM CSTR; whereas, ammonia removal was relatively lower in MBBR CSTR (20-35%) and BioCord^TM SBR (45-54%). Acclimation to increasing concentrations of ammonia led to the enrichment of nitrifying (Nitrosomonas, Nitrospira, and Nitrobacter) and denitrifying (Comamonas, OLB8, and Rhodanobacter) bacteria [16S rRNA gene sequencing (Illumina)] in all bioreactors. In the hybrid bioreactor, the nitrifying and denitrifying bacteria were relatively more abundant in flocs and biofilms, respectively. The presence of dead cells (in biofilms) suggests that in the absence of an organic substrate, endogenous decay is a likely contributor of nutrients for denitrifying bacteria. The nitrite accumulation and abundance of denitrifying bacteria indicate partial denitrification in fixed-film bioreactors operated under limited carbon conditions. Further studies are required to assess the contribution of organic material produced in autotrophic biofilms (by endogenous decay and soluble microbial products) to the overall treatment process. Furthermore, the possibility of sustaining autotrophic nitrogen in high strength waste-streams in the presence of organic substrates warrants further investigation.

Treatment of high-strength sewage by textile fibers-based sequencing batch biofilm reactor for simultaneous removal of organics and nutrients

This study investigates the effectiveness of SBBR with low-cost textile fibers-based bio-carrier namely polypropylene fibers for the treatment of real sewage. The influent loading rates of COD, TN, and TP were averaged at 0.2780, 0.0170, and 0.0077 kg/m³.d, respectively. The removal efficiencies of BOD, COD, TN, and TP recorded in SBBR were 98%, 93%, 82%, and 44%, respectively at an aeration time of 4 h. The TN and TP removal achieved in SBBR were 2.05 and 2.75 times, respectively higher than SBR. The COD removal efficiency was more than 90% under all SRT conditions (10, 14, 18, 22, and 26 d) in SBBR, and the highest efficiency of 93% was obtained at an SRT of 22 days. As the SRT increased, the nitrogen and phosphorus removal decreased, because the denitrification rate and phosphorus release and uptake rate decreased at longer SRT. Simultaneous nitrification and denitrification (SND) efficiency was 85% in SBBR and 44% in SBR, indicating the co-existence of aerobic nitrifiers and anoxic denitrifiers in the biofilm reactor. In SBBR, the nitrogen mass balance showed 74% of nitrogen removed by denitrification, 9% was removed through sludge wasting process, and 13% was removed in effluent at an SRT of 22 days and DO concentration of 3 mg/L. The t-test results suggest that the performance of SBBR was better than SBR in nitrogen and phosphorus removal at a 95% confidence interval.

Quantification and Phylogenetic Analysis of Ammonia Oxidizers on Biofilm Carriers in a Full-Scale Wastewater Treatment Plant

Biofilm carriers have been used to remove ammonia in several wastewater treatment plants (WWTPs) in Japan. However, the abundance and species of ammonia oxidizers in the biofilms formed on the surface of carriers in full-scale operational WWTP tanks remain unclear. In the present study, we conducted quantitative PCR and PCR cloning of the amoA genes of ammonia-oxidizing bacteria and archaea (AOB and AOA) and a complete ammonia oxidizer (comammox) in the biofilm formed on the carriers in a full-scale WWTP. The quantification of amoA genes showed that the abundance of AOB and comammox was markedly greater in the biofilm than in the activated sludge suspended in a tank solution of the WWTP, while AOA was not detected in the biofilm or the activated sludge. A phylogenetic analysis of amoA genes revealed that as-yet-uncultivated comammox Nitrospira and uncultured AOB Nitrosomonas were predominant in the biofilm. The present results suggest that the biofilm formed on the surface of carriers enable comammox Nitrospira and AOB Nitrosomonas to co-exist and remain in the full-scale WWTP tank surveyed in this study.

Effects of different light conditions on ammonium removal in a consortium of microalgae and partial nitrifying granules

Ammonium removal by a coupling process of microalgae (Chlorella sorokiniana) with partial nitrifying granules was evaluated in batch reactors illuminated in a wide range of light intensities (0, 100, 450, and 1600 μmol photons m^-2 s^-1). Ammonium oxidation performance for different light exposure time showed that the granules had a light stress tolerance at 1600 μmol photons m^-2 s^-1 for up to 12 h, but continuous illumination induced severe inhibition on nitrifying bacteria thereafter. Ammonium removal efficiencies at the end of tests were 66%, 62%, 5%, and -10% (due to ammonification) for 0, 100, 450, and 1600 μmol photons m^-2 s^-1, respectively. The nitrogen mass balance shows co-occurrence of microalgal growth taking up 24% of fed ammonium and nitrifying bacteria oxidizing 38% of fed ammonium at 100 μmol photons m^-2 s^-1, while both nitrification and microalgal growth are inhibited at light intensity above 450 μmol photons m^-2 s^-1. In comparing results from this study with previous results, it was found that the ammonium removal pathway, i.e., nitrification or microalgal uptake, is regulated more strongly by daily average light intensity than by instantaneous light intensity. Empirical model equations to estimate the oxygen balance in consortium reactors categorized the effect of daily average light intensities on process performance as follows: (i) below 27 μmol photons m^-2 s^-1: insufficient oxygen for nitrification; (ii) 27 to 35: sufficient oxygen for nitrification via nitrite; (iii) 35 to 180: sufficient oxygen for nitrification via nitrate; (iv) above approximately 200-300: oversaturated dissolved oxygen, excess free ammonia and/or intensive light inhibitions.

Practicing anammox in a novel hybrid anaerobic-aerobic baffled reactor for treating high-strength ammonium piggery wastewater with low COD/TN ratio

A novel hybrid anaerobic-aerobic baffled reactor (HAOBR) with four compartments was constructed to treat manure-free piggery wastewater with an average COD/TN ratio as low as 0.98, without any supplement of external carbon source. Inoculated with aerobic activated sludge and operated at hydraulic retention time 36 h, 32 °C and reflux ratio 2.0, the reactor could perform steadily within 24 days. The removal of COD, NH₄⁺-N and TN within the 21-days steady phase averaged 87.0%, 100% and 91.3%, respectively. Analysis of stoichiometry and results of high-throughput pyrosequencing revealed that the excellent nitrogen removal in the HAOBR was achieved by the cooperation of heterotrophic and autotrophic denitrification with anammox as the dominant approach. Compared with the previously developed microaerobic treatment processes and the recently reported modified A/O process, the HAOBR was more cost-efficient in treating manure-free piggery wastewater because of the less energy consumption, rapid startup process and efficient nutrients removal.

Effect of leachate circulation with ex situ nitrification on waste decomposition and nitrogen removal for early stabilization of fresh refuse landfill

We determined the effects of ex situ biological wastewater treatment on landfill stabilization under continuous circulation of leachate. Specifically, the waste composition and nitrogen in the leachate during leachate circulation (LC) alone was compared with that in a nitrified leachate circulation (NLC) system. An ex situ sequencing batch reactor (SBR) was applied in the NLC system to oxidize the ammonium to nitrite or nitrate, which was then circulated to landfill for denitrification to nitrogen gas. The chemical oxygen demand (COD) concentration in the leachate was low by NLC versus LC, because in the NLC system, ammonium was oxidized to nitrite/nitrate in the ex situ SBR, and aerobic decomposition and denitrification occurred simultaneously in the landfill, suggesting that the NLC system significantly improves the waste decomposition rate and accelerates landfill stabilization. Because denitrification in the landfill was activated in the NLC system and nitrite/nitrate was reduced to nitrogen gas, the proportion of nitrogen in the gas was higher compared with LC. LC, combined with an SBR, might have value in removing the nitrogen that is discharged from the leachate and in accelerating landfill stabilization, because landfill waste was used as the carbon source for denitrification.

Taxonomic relatedness and environmental pressure synergistically drive the primary succession of biofilm microbial communities in reclaimed wastewater distribution systems

Compared to drinking water, the higher bacterial abundance, diversity, and organic matter concentration in reclaimed wastewater suggest that it is more likely to form biofilms. Nevertheless, little is known regarding many important aspects of the biofilm ecology in reclaimed wastewater distribution systems (RWDS), such as the long-term microbial community succession and the underlying driving factors. In the present study, by sampling and analysing microbial compositions of pipe wall biofilms from six frequently used pipe materials under NaClO_disinfection (sodium hypochlorite-treated), NON_disinfection (without disinfection), and UV_disinfection (UV-treated) treatments over one year, it was found that the succession of microbial community structure followed a primary succession pattern. This primary succession pattern was reflected as increases in live cell number and α-diversity, along with metagenic succession in taxonomic composition. Proteobacteria, Nitrospirae, Bacteroidetes, Acidobacteria, Planctomycetes, Actinobacteria, and Verrucomicrobia comprised the dominant phyla in biofilm samples. Compared to biofilms in the NaClO_disinfection reactor, the bacterial communities of biofilms in NON_disinfection and UV_disinfection reactors were distributed more evenly among different bacterial phyla. Principal component analysis revealed a clear temporal pattern of microbial community structures in six kinds of pipe wall biofilms albeit a difference in microbial community structures among the three reactors. Adonis testing indicated that the microbial community composition variation caused by disinfection methods (R² = 0.283, P < 0.01) was more pronounced than that from the time variable (R² = 0.070, P < 0.01) and pipe material (R² = 0.057, P < 0.01). Significantly positive correlation between average local abundance and occupancy was observed in biofilm communities of the three reactors, suggesting that the 'core-satellite' model could be applied to identify biofilm-preferential species under specific disinfection conditions in RWDS. The prevalence of family Sphingomonadaceae, known to show chlorine tolerance and powerful biofilm-forming ability in NaClO_disinfection reactors, evidenced the habitat filtering consequent to environment pressure. Correlation-based network analysis revealed that taxonomic relatedness such as similar niches, cooperation, taxa overdispersion, and competition all functioned toward driving the bacterial assembly succession in RWDS.

Evaluating the process performance and potential of a high-rate single airlift bioreactor for simultaneous carbon and nitrogen removal through coupling different pathways from a nitrogen-rich wastewater

The feasibility of a continuous feed and intermittent discharge airlift bioreactor for simultaneous carbon and nitrogen removal from a low COD/N wastewater was evaluated. The effect of two independent variables, HRT (10-20 h) and NH₄⁺/(NH₄⁺+NO₃^-) ratio (0.25-0.75), on the bioreactor performance was studied. The relatively high anaerobic to aerobic time ratio made an effective contribution to NH₄⁺, NO₃^-, and TN removal. TN removal was enhanced with increase in HRT and decrease in NH₄⁺/NH₄⁺+NO₃^- and at the optimum condition, 616 mg/L (88%) and 213 mg/L (76%) of sCOD and TN were removed, respectively. The results suggested that the nitrogen removal process was based on a combination of anaerobic ammonium oxidation (Anammox), simultaneous nitrification-denitrification (SND), and presumable dissimilatory nitrate reduction to ammonium (DNRA) mechanisms.

Intermittent Aeration Suppresses Nitrite-Oxidizing Bacteria in Membrane-Aerated Biofilms: A Model-Based Explanation

Autotrophic ammonium oxidation in membrane-aerated biofilm reactors (MABRs) can make treatment of ammonium-rich wastewaters more energy-efficient, especially within the context of short-cut ammonium removal. The challenge is to exclusively enrich ammonium-oxidizing bacteria (AOB). To achieve nitritation, strategies to suppress nitrite-oxidizing bacteria (NOB) are needed, which are ideally grounded on an understanding of underlying mechanisms. In this study, a nitrifying MABR was operated under intermittent aeration. During eight months of operation, AOB dominated, while NOB were suppressed. On the basis of dissolved oxygen (DO), ammonium, nitrite, and nitrate profiles within the biofilm and in the bulk, a 1-dimensional nitrifying biofilm model was developed and calibrated. The model was utilized to explore the potential mechanisms of NOB suppression associated with intermittent aeration, considering DO limitation, direct pH effects on enzymatic activities, and indirect pH effects on activity via substrate speciation. The model predicted strong periodic shifts in the spatial gradients of DO, pH, free ammonia, and free nitrous acid, associated with aerated and nonaerated phases. NOB suppression during intermittent aeration was mostly explained by periodic inhibition caused by free ammonia due to periodic transient pH upshifts. Dissolved oxygen limitation did not govern NOB suppression. Different intermittent aeration strategies were then evaluated for nitritation success in intermittently aerated MABRs: both aeration intermittency and duration were effective control parameters.

A model for determination of operational conditions for successful shortcut nitrification

Accumulation of nitrite in shortcut nitrification is influenced by several factors including dissolved oxygen concentration (DO), pH, temperature, free ammonia (FA), and free nitrous acid (FNA). In this study, a model based on minimum dissolved oxygen concentration (DO_min), minimum/maximum substrate concentration (S_min and S_max), was developed. The model evaluated the influence of pH (7-9), temperature (10-35 °C), and solids retention time (SRT) (5 days-infinity) on MSC values. The evaluation was conducted either by controlling total ammonium nitrogen (TAN) or total nitrite nitrogen (TNN), concentration at 50 mg N/L while allowing the other to vary from 0 to 1000 mg N/L. In addition, specific application for shortcut nitrification-anammox process at 10 °C was analyzed. At any given operational condition, the model was able to predict if shortcut nitrification can be achieved and provide the operational DO range which is higher than the DO_min of AOB and lower than that of NOB. Furthermore, experimental data from different literature studies were taken for model simulation and the model prediction fit well the experiment. For the Sharon process, model prediction with default kinetics did not work but the model could make good prediction after adjusting the kinetic values based on the Sharon-specific kinetics reported in the literature. The model provides a method to identify feasible combinations of pH, DO, TAN, TNN, and SRT for successful shortcut nitrification.

Microbial activity balance in size fractionated suspended growth biomass from full-scale sidestream combined nitritation-anammox reactors

The purpose of this study was to determine the abundance, distribution and activity of aerobic ammonia-oxidizing bacteria (AOB) and anammox in size fractionated aggregates from full-scale suspended growth combined nitritation-anammox sidestream reactors. Plants with or without a cyclone device were also studied to assess a purported enrichment of anammox granules. Specific aerobic ammonium oxidation rates (p=0.01) and specific oxygen uptake rates (p=0.02) were significantly greater in flocs than in granules. AOB abundance measured using quantitative FISH was significantly higher in flocs than in granules (p=0.01). Conversely, anammox abundance was significantly greater in granules (p=0.03). The average ratio of anammox/AOB in systems employing hydrocyclone separation devices was 2.4, significantly higher (p=0.02) than the average ratio (0.5) in a system without a hydrocyclone. Our results demonstrate substantial functional and population-level segregation between floccular and granular fractions, and provide a key corroboration that cyclone separation devices can increase anammox levels in such systems.

Novel nitrifiers and comammox in a full-scale hybrid biofilm and activated sludge reactor revealed by metagenomic approach

Biofilms are widely used in wastewater treatment for their particular enhancement of nitrogen removal and other significant advantages. In this study, the diversity and potential functions of nitrogen removal bacteria in suspended activated sludge (AS) and biofilm of a full-scale hybrid reactor were uncovered by metagenomes (∼34 Gb), coupled with PCR-based 454 reads (>33 K reads). The results indicated that the diversity and abundance of nitrifiers and denitrifiers in biofilm did not surpass that in AS, while more nitrification and denitrification genes were indeed found in biofilm than AS, suggesting that the increased nitrogen removal ability by applying biofilm might be attributed to the enhancement of removal efficiency, rather than the biomass accumulation of nitrogen removal bacteria. The gene annotation and phylogenetic analysis results revealed that AS and biofilm samples consisted of 6.0 % and 9.4 % of novel functional genes for nitrogen removal and 18 % and 30 % of new Nitrospira species for nitrite-oxidizing bacteria, respectively. Moreover, the identification of Nitrospira-like amoA genes provided metagenomic evidence for the presence of complete ammonia oxidizer (comammox) with the functional potential to perform the complete oxidation of ammonia to nitrate. These findings have significant implications in expanding our knowledge of the biological nitrogen transformations in wastewater treatment.

Production of nitrogen oxide gases from an oxic/anoxic process via nitrite: influence of liquid parameters and impact on mass balance

The produced nitrogen oxides from the biological treatment of swine and dairy anaerobic supernatant are evaluated. The quantification of the emissions has been conducted in a continuous way and coupled with batch tests to determine the mechanisms of formation. Using a continuous monitoring system, N2O and NO forms are present in higher quantities than NO2. The elevated emissions are linked with the increment of the influent nitrogen load both in the daily variations and in the long period. The NH4-N and NO2-N accumulations are recognized as the main parameters which determine the great nitrogen oxide emissions even at dissolved oxygen concentration of around 2 mgL(-1). The nitrogen oxides' impacts are between 0.0034 and 0.0044N% for the N2O and between 0.0020 and 0.0026N% for NO. A strict dependence between the N2O and the oxidation reduction potential is found.

Acceleration of aged-landfill stabilization by combining partial nitrification and leachate recirculation: a field-scale study

Leachate recirculation for rapid landfill stabilization can result in the accumulation of high-strength ammonium. An on-site sequencing batch reactor (SBR) was therefore, applied to oxidize the ammonium to nitrite, which was then recirculated to the landfill for denitrification to nitrogen gas. At relatively higher ammonium levels, nitrite accumulated well in the SBR; the nitrite was denitrified stably in the landfill, despite an insufficient biodegradable carbon source in the leachate. As the leachate was recirculated, the methane and carbon dioxide contents produced from the landfill fluctuated, implying that the organic acids and hydrogen produced in the acid production phase acted as the carbon source for denitrification in the landfill. Leachate recirculation combined with ex-situ partial nitrification of the leachate may enhance the biodegradation process by: (a) removing the nitrogen that is contained with the leachate, and (b) accelerating landfill stabilization, because the biodegradation efficiency of landfill waste is increased by supplying sufficient moisture and its byproducts are used as the carbon source for denitrification. In addition, partial nitrification using an SBR has advantages for complete denitrification in the landfill, since the available carbon source is in short supply in aged landfills.

Nitrite accumulation from simultaneous free-ammonia and free-nitrous-acid inhibition and oxygen limitation in a continuous-flow biofilm reactor

To achieve nitrite accumulation for shortcut biological nitrogen removal (SBNR) in a biofilm process, we explored the simultaneous effects of oxygen limitation and free ammonia (FA) and free nitrous acid (FNA) inhibition in the nitrifying biofilm. We used the multi-species nitrifying biofilm model (MSNBM) to identify conditions that should or should not lead to nitrite accumulation, and evaluated the effectiveness of those conditions with experiments in continuous flow biofilm reactors (CFBRs). CFBR experiments were organized into four sets with these expected outcomes based on the MSNBM as follows: (i) Control, giving full nitrification; (ii) oxygen limitation, giving modest long-term nitrite build up; (iii) FA inhibition, giving no long-term nitrite accumulation; and (iv) FA inhibition plus oxygen limitation, giving major long-term nitrite accumulation. Consistent with MSNBM predictions, the experimental results showed that nitrite accumulated in sets 2-4 in the short term, but long-term nitrite accumulation was maintained only in sets 2 and 4, which involved oxygen limitation. Furthermore, nitrite accumulation was substantially greater in set 4, which also included FA inhibition. However, FA inhibition (and accompanying FNA inhibition) alone in set 3 did not maintained long-term nitrite accumulation. Nitrite-oxidizing bacteria (NOB) activity batch tests confirmed that little NOB or only a small fraction of NOB were present in the biofilms for sets 4 and 2, respectively. The experimental data supported the previous modeling results that nitrite accumulation could be achieved with a lower ammonium concentration than had been required for a suspended-growth process. Additional findings were that the biofilm exposed to low dissolved oxygen (DO) limitation and FA inhibition was substantially denser and probably had a lower detachment rate.

Autotrophic denitrification of nitrate and nitrite using thiosulfate as an electron donor

This study was carried out to determine the possibility of autotrophic denitritation using thiosulfate as an electron donor, compare the kinetics of autotrophic denitrification and denitritation, and to study the effects of pH and sulfur/nitrogen (S/N) ratio on the denitrification rate of nitrite. Both nitrate and nitrite were removed by autotrophic denitrification using thiosulfate as an electron donor at concentrations up to 800 mg-N/L. Denitrification required a S/N ratio of 5.1 for complete denitrification, but denitritation was complete at a S/N ratio of 2.5, which indicated an electron donor cost savings of 50%. Also, pH during denitrification decreased but increased with nitrite, implying additional alkalinity savings. Finally, the highest specific substrate utilization rate of nitrite was slightly higher than that of nitrate reduction, and biomass yield for denitrification was relatively higher than that of denitritation, showing less sludge production and resulting in lower sludge handling costs.

Advanced treatment of biologically pretreated coal gasification wastewater using a novel anoxic moving bed biofilm reactor (ANMBBR)-biological aerated filter (BAF) system

A novel system integrating anoxic moving bed biofilm reactor (ANMBBR) and biological aerated filter (BAF) with short-cut biological nitrogen removal (SBNR) process was investigated as advanced treatment of real biologically pretreated coal gasification wastewater (CGW). The results showed the system had efficient capacity of degradation of pollutants especially nitrogen removal. The best performance was obtained at hydraulic residence times of 12h and nitrite recycling ratios of 200%. The removal efficiencies of COD, total organic carbon, NH4(+)-N, total phenols and total nitrogen (TN) were 74.6%, 70.0%, 85.0%, 92.7% and 72.3%, the corresponding effluent concentrations were 35.1, 18.0, 4.8, 2.2 and 13.6mg/L, respectively. Compared with traditional A(2)/O process, the system had high performance of NH4(+)-N and TN removal, especially under the high toxic loading. Moreover, ANMBBR played a key role in eliminating toxicity and degrading refractory compounds, which was beneficial to improve biodegradability of raw wastewater for SBNR process.

Microfauna communities as performance indicators for an A/O Shortcut Biological Nitrogen Removal moving-bed biofilm reactor

The microfauna communities present in the mixed liquor and biofilm of an Anoxic/Oxic Shortcut Biofilm Nitrogen Removal moving-bed biofilm process were characterised in order to optimise process control through the use of bioindicators. The system operated at high ammonium concentrations, with an average of 588 ± 220 mg N-NH4(+) L(-1) in the influent, 161 ± 80 mg L(-1) in the anoxic reactor and 74 ± 71.2 mg L(-1) in the aerobic reactor. Up to 20 different taxa were identified, including ciliates (4), flagellates (11), amoebae (4) and nematodes (1). Compared to conventional wastewater treatment processes (WWTPs), this process can be defined as a flagellates-predominant system with a low diversity of ciliates. Flagellates were mainly dominant in the mixed liquor, demonstrating high tolerance to ammonium and the capacity for survival over a long time under anoxic conditions. The data obtained provide interesting values of maximum and minimum tolerance ranges to ammonium, nitrates and nitrites for the ciliate species Cyclidium glaucoma, Colpoda ecaudata, Vorticella microstoma-complex and Epistylis cf. rotans. The last of these was the only ciliate species that presented a constant and abundant population, almost exclusively in the aerobic biofilm. Epistylis cf. rotans dynamics showed a high negative correlation with ammonium variations and a positive correlation with ammonium removal efficiency. Hence, the results indicate that Epistylis cf. rotans is a good bioindicator of the nitrification process in this system. The study of protozoan communities in unexplored WWTPs sheds light on species ecology and their role under conditions that have been little studied in WWTPs, and could offer new biological management tools.

Nutrient removal from separated pig manure digestate liquid using hybrid biofilters

In this study, laboratory-scale hybrid biofilters were set up to treat the separated pig manure digestate liquid at two loading rates of 0.12 and 0.07 kg N m(-3) per day. The hybrid biofilters were operated with a sequencing batch reactor mode. Over the operation of 136 days, 84% and 88% of total nitrogen was removed on average in addition with complete nitrification at the high loading rate and low loading rate, respectively. In the anoxic phase, the nitrate reduction rates were 0.31 and 0.24 mg L(-1) min(-1); and in the aerobic phase, nitrification rates were 0.29 and 0.18 mg L(-1) min(-1) at the high loading rate and low loading rate, respectively. It was found that in the hybrid biofilters, biofilm biomass had much higher nitrification and denitrification activities than suspended growth biomass. Phosphorus removals achieved were up to 88%. The results show the hybrid biofilter technology is valid for high nutrient pig manure digestate liquid treatment.

Partial nitrification in a sequencing batch reactor treating acrylic fiber wastewater

A sequencing batch reactor was employed to treat the acrylic fiber wastewater. The dissolved oxygen and mixed liquor suspended solids were 2-3 and 3,500-4,000 mg/L, respectively. The results showed ammonium oxidizing bacteria (AOB) had superior growth rate at high temperature than nitrite oxidizing bacteria (NOB). Partial nitrification could be obtained with the temperature of 28 °C. When the pH value was 8.5, the nitrite-N accumulation efficiency was 82 %. The combined inhibitions of high pH and free ammonium to NOB devoted to the nitrite-N buildup. Hydraulic retention time (HRT) was a key factor in partial nitrification control, and the optimal HRT was 20 h for nitrite-N buildup in acrylic fiber wastewater treatment. The ammonium oxidation was almost complete and the transformation from nitrite to nitrate could be avoided. AOB and NOB accounted for 2.9 and 4.7 %, respectively, corresponding to the pH of 7.0. When the pH was 8.5, they were 6.7 and 0.9 %, respectively. AOB dominated nitrifying bacteria, and NOB was actually washed out from the system.

Using porous ceramic media in the upflow packed-bed reactor (UPBR) system for nitrogen removal via autotrophic nitrification and denitrification

In this study, the feasibility of an innovative upflow packed-bed reactor (UPBR) system using porous sulfur and lime ceramic media (CERAMED-L and CERAMED-SL) to remove nitrogen for wastewater treatment was evaluated. The specific lime dissolution rates for CERAMEDs in the UPBRs show an inverse proportion to pH and resulted in 2.32 g as CaCO(3) kg(-1) CERAMED-L d(-1) and 1.64 g as CaCO(3) kg(-1) CERAMED-SL d(-1) at a pH 6.7. The calculated specific nitrification rate resulted 1.73-2.29 kg NH(4)(+)-N m(-3) CERAMED-L d(-1), with a F/M ratio in the range 0.08-0.31 g NH(4)(+)-N g(-1) VS d(-1). The alkalinity shortage in the feed solution seemed to be overcome by supplying specific alkalinity of 3.88 kg as CaCO(3) m(-3) CERAMED-L d(-1) through the dissolution of lime from CERAMED-L. Autotrophic denitrification efficiencies were in the range of 83-96% during the test period, and the average specific denitrification rates of 0.97-1.92 kg NO(3)(-)N m(-3) CERAMED-SL d(-1) and 0.19-0.36 g NO(3)(-)-N g(-1) VS d(-1) were obtained.

Effect of sludge age on simultaneous nitrification and denitrification in membrane bioreactor

This study evaluated the effect of sludge age on simultaneous nitrification and denitrification in a membrane bioreactor treating black water. A membrane bioreactor with no separate anoxic volume was operated at a sludge age of 20 days under low dissolved oxygen concentration of 0.1-0.2mg/L. Its performance was compared with the period when the sludge age was adjusted to 60 days. Floc size distribution, apparent viscosity, and nitrogen removal differed significantly, together with different biomass concentrations: nitrification was reduced to 40% while denitrification was almost complete. Modelling indicated that both nitrification and denitrification kinetics varied as a function of the sludge age. Calibrated values of half saturation coefficients were reduced when the sludge age was lowered to 20 days. Model simulation confirmed the validity of variable process kinetics for nitrogen removal, specifically set by the selected sludge age.

Partial nitrification/denitrification can be attributed to the slow response of nitrite oxidizing bacteria to periodic anoxic disturbances

This work aims to assess and model the behavior of both ammonium (AOB) and nitrite (NOB) oxidizing bacteria during the transition from completely anoxic to aerobic conditions. An enhanced aerobically grown culture containing AOB and NOB was subjected to anoxic conditions of varying durations from 1.5 to 12 h before its exposure to aerobic conditions. Experiments were carried out in both continuously stirred tank reactor (CSTR) and batch type reactors. Although the AOB did not exhibit any impact in their performance following the anoxic disturbance, the NOB were seriously inhibited presenting a period of reduced growth rate, which was proportional to the duration of the disturbance. This finding proves the previously postulated mechanism (NOB inhibition under periodic aerobic/anoxic operation) for achieving nitrogen removal via the partial nitrification/denitrification (PND) process as demonstrated in lab- and pilot-scale operating conditions. A mathematical model was developed to describe with sufficient accuracy the performance of AOB and NOB under aerobic, anoxic, and transient conditions in both CSTR and batch type systems. The model is able to describe the inhibitory effect of anoxic exposure to NOB by assuming enzyme deactivation (under anoxic conditions) and reactivation (adjustment of the NOB enzymatic mechanism) under aerobic conditions. The presented kinetic model is quite simple and general and therefore may be used for predicting the performance of mixed growth biological systems operating via the PND process.

Kinetic model for biological nitrogen removal using shortcut nitrification-denitrification process in sequencing batch reactor

A kinetic model for shortcut nitrification-denitrification process with sequencing batch reactor (SBR) was developed. To test this model, the kinetic parameters of the model including maximum specific rates and half-maximum rate concentrations for shortcut nitrification and denitrification were estimated from the results obtained from a laboratory-scale SBR fed with a soybean curd processing wastewater (400-800 mg COD L(-1), 50-65 mg NH(4)(+)-N L(-1)) at 26 degrees C. In the nitrification step, two DO levels (0.5 and 3.5 mg L(-1)) were tested and the predicated nitrification rates under different NH(4)(+)-N concentrations using this model fit well with correlation coefficient R = 0.9902. In the denitrification step, the process of nitrite removal was close to a zero-order reaction if the concentration of electron donor was not so low (COD > 100 mg L(-1)), and concentrations of nitrite and organic matter (as COD) had limited effect on denitrification rate. The model can be used to predict nitrogen removal performance with different influent NH(4)(+)-N and COD concentrations and under various DO concentrations.

Multi-species nitrifying biofilm model (MSNBM) including free ammonia and free nitrous acid inhibition and oxygen limitation

A multi-species nitrifying biofilm model (MSNBM) is developed to describe nitrite accumulation by simultaneous free ammonia (FA) and free nitrous acid (FNA) inhibition, direct pH inhibition, and oxygen limitation in a biofilm. The MSNBM addresses the spatial gradient of pH with biofilm depth and how it induces changes of FA and FNA speciation and inhibition. Simulations using the MSNBM in a completely mixed biofilm reactor show that influent total ammonia nitrogen (TAN) concentration, bulk dissolved oxygen (DO) concentration, and buffer concentration exert significant control on the suppression of nitrite-oxidizing bacteria (NOB) and shortcut biological nitrogen removal (SBNR), but the pH in the bulk liquid has a weaker influence. Ammonium oxidation increases the nitrite concentration and decreases the pH, which together can increase FNA inhibition of NOB in the biofilm. Thus, a low buffer concentration can accentuate SBNR. DO and influent TAN concentrations are efficient means to enhance DO limitation, which affects NOB more than ammonia-oxidizing bacteria (AOB) inside the biofilm. With high influent TAN concentration, FA inhibition is dominant at an early phase, but finally DO limitation becomes more important as TAN degradation and biofilm growth proceed. MSNBM results indicate that oxygen depletion and FNA inhibition throughout the biofilm continuously suppress the growth of NOB, which helps achieve SBNR with a lower TAN concentration than in systems without concentration gradients.

Treatment of municipal wastewater using a contact oxidation filtration separation integrated bioreactor

A new contact oxidation filtration separation integrated bioreactor (CFBR) was used to treat municipal wastewater. The CFBR was made up of a biofilm reactor (the upper part of the CFBR) and a gravitational filtration bed (the lower part of the CFBR). Polyacrylonitrile balls (50mm diameter, 237 m(2)/m(3) specific surface, 90% porosity, and 50.2% packing rate) were filled into the biofilm reactor as biofilm attaching materials and anthracite coal (particle size 1-2mm, packing density 0.947 g/cm(3), non-uniform coefficient (K(80)=d(80)/d(10))<2.0) was placed into the gravitational filtration bed as filter media. At an organic volumetric loading rate of 2.4 kg COD/(m(3)d) and an initial filtration velocity of 5m/h in the CFBR, the average removal efficiencies of COD, ammonia nitrogen, total nitrogen and turbidity were 90.6%, 81.4%, 64.6% and 96.7% respectively, but the treatment process seemed not to be effective in phosphorus removal. The average removal efficiency of total phosphorus was 60.1%. Additionally, the power consumption of the CFBR was less than 0.15 kWh/m(3) of wastewater treated, and less than 1.5 kWh/kg BOD(5) removal.

Contributions of biofilm and suspended sludge to nitrogen transformation and nitrous oxide emission in hybrid sequencing batch system

Hybrid system combines the nature of suspended growth and attached growth has been widely applied to wastewater treatment. In this research, the contributions to N transformation and N2O emission by biofilm and suspended sludge in the hybrid sequencing-batch reactor for a simultaneous nitrification, denitrification and phosphorus removal process were investigated. For the hybrid system, nitrification occurred mostly in the suspended sludge, while the biofilm played the major role in denitrification. The interaction of the biofilm and the suspended sludge in the same reactor resulted in a better overall nitrogen removal performance with simultaneous nitrification and denitrification. However, N2O emission was the main end product of nitrogen removal for the hybrid system; while it was N2 for the biofilm. The relative low N2O emissions from the pure biofilm and the pure suspended sludge corresponded to the relatively high nitrate at the end of the aeration period compared with the hybrid system.

Operational boundaries for nitrite accumulation in nitrification based on minimum/maximum substrate concentrations that include effects of oxygen limitation, pH, and free ammonia and free nitrous acid inhibition

Recent studies on shortcut biological nitrogen removal (SBNR), which use the concept of denitrification from nitrite, have reported the key factors affecting nitrite build-up, such as dissolved oxygen (DO) limitation, pH, and free ammonia (FA) and free nitrous acid (FNA) inhibition. This study extends the concept of the traditional minimum substrate concentration (S(min)) to explain the simultaneous effect of those factors. Thus, we introduce the minimum DO concentration (DO(min)) and the maximum substrate concentration (S(max)) that are needed to support a steady-state biological system. We define all three values as the MSC values. The model provides a method to identify good combinations of pH, DO, and total ammonium nitrogen (TAN) to support shortcut nitritation. We use MSC curves to show that the effect of DO-alone and the effect of DO plus direct pH inhibition cannot give strong enough selection against nitrite oxidizing bacteria to work in a practical setting. However, adding the FA and FNA effects gives a strong selection effect that is accentuated near pH 8. Thus, a generalized conclusion is that having pH approximately 8 is favorable in many situations. We defined a specific operational boundary to achieve shortcut nitritation coupled to anaerobic ammonium oxidation (ANAMMOX), in which the effluent concentrations of total nitrite and total ammonium should be approximately equal. Experimental results for alkaline and acidic nitrite-accumulating systems match the trends from the MSC approach. In particular, acidic systems had to maintain higher total ammonium, total nitrite, and DO concentrations. The MSC values are a practical tool to define the operational boundaries for selecting ammonium-oxidizing bacteria while suppressing nitrite-oxidizing bacteria.