Partial nitrification in a SHARON reactor in the presence of salts and organic carbon compounds

Assessment of nitrification process in a sequencing batch reactor: Modelling and genomic approach

Nitrification of ammoniacal nitrogen (N-NH4+) to nitrate (N-NO3-) was investigated in a lab-scale sequencing batch reactor (SBR) to evaluate its efficiency. During the nitrification process the removal of N-NH4+ reached 96%, resulting in 73% formation of N-NO3-. A lineal correlation (r2 = 0.9978) was obtained between the concentration of volatile suspended solids (VSS) and the maximal N-NO3- concentration at the end of each batch cycle under stationary state. The bacterial taxons in the initial inoculum were identified, revealing a complex diverse community mainly in the two major bacterial phyla Proteobacteria and Actinobacteria. The FAPROTAX algorithm predicted the presence in the inoculum of taxa involved in relevant processes of the nitrogen metabolism, highlighting the bacterial genera Nitrospira and Nitrosomonas that are both involved in the nitrification process. A kinetic model was formulated for predicting and validating the transformation of N-NH4+, N-NO2- and N-NO3- and the removal of organic and inorganic carbon (TOC and IC, respectively). The results showed how the increase in biomass concentration slowed down the transformation to oxidised forms of nitrogen and increased denitrification in the settling and filling stages under free aeration conditions.

Simultaneous aerobic nitrogen and phosphate removal capability of novel salt-tolerant strain, Pseudomonas mendocina A4: Characterization, mechanism and application potential

A salt-tolerant strain, Pseudomonas mendocina A4, was isolated from brackish-water ponds showing simultaneous heterotrophic nitrification-aerobic denitrification and phosphorus removal capability. The optimal conditions for nitrogen and phosphate removal of strain A4 were pH 7-8, carbon/nitrogen ratio 10, phosphorus/nitrogen ratio 0.2, temperature 30 °C, and salinity range of 0-5 % using sodium succinate as the carbon source. The nitrogen and phosphate removal efficiencies were 96-100 % and 88-96 % within 24 h, respectively. The nitrogen and phosphate removal processes were matched with the modified Gompertz model, and the underlying mechanisms were confirmed by the activities of key metabolic enzymes. Under 10 % salinity, the immobilization technology was employed to enhance the nitrogen and phosphate removal efficiencies of strain A4, achieving 87 % and 76 %, respectively. These findings highlight the potential application of strain A4 in both freshwater and marine culture wastewater treatment.

Applying response surface methodology to optimize partial nitrification in sequence batch reactor treating salinity wastewater

In this study, the operation parameters of a partial nitrification process (PN) treating saline wastewater were optimized using the Box-Behnken design via the response surface methodology (BBD-RSM). A novel strategy based on the control of the carbon/nitrogen ratio (C/N), alkalinity/ammonia ratio (K/A), and salinity in three stages was used to achieve PN in a sequence batch reactor. The results demonstrated that a high and stable PN was completed after 50 d with an ammonia removal efficiency (ARE) of 98.37 % and nitrite accumulation rate (NAR) of 85.93 %. Next, BBD-RSM was applied, where ARE and NAR were the responses. The highest responses from the confirmation experiment were 99.9 % ± 0.04 and 95.25 % ± 0.32 when the optimum C/N, K/A, and salinity were identified as 0.84, 2, and 5.5 (g/L), respectively. The results were higher than those for the nonoptimized reactor. The developed regression model adequately forecasts the PN performance under optimal conditions. Therefore, this study provides a promising strategy for controlling the PN process and shows how the BBD-RSM model can improve the PN performance.

Low C/N promotes stable partial nitrification by enhancing the cooperation of functional microorganisms in treating high-strength ammonium landfill leachate

Partial nitrification is an effective process for treating high-strength ammonium landfill leachate with low C/N ratio, for the cooperation with denitrification can save almost 40% carbon addition in biological nitrogen removal. However, high ammonia loading often causes the instability of partial nitrification process. Less carbon addition can promote the stability of partial nitrification and increase the nitrite accumulation ratio (NAR). Nevertheless, the microbial mechanisms within remain further elusive. In this study, two laboratory-scale sequencing batch reactors were constructed and operated for 125 days, which were fed with ammonia synthetic wastewater with C/N of 0.6 (CN system) and C/N of 0.0 as the control (N system). CN system performed more stably and had the highest NAR of 100%. Extracellular polymeric substances (EPS) generated from carbon source provided spatial and nutrient niches to tighten the cooperation of functional microorganisms, thus, enhanced the stability and efficiency of partial nitrification. Thauera was the dominant denitrifier in CN system. Nitrosomonas was one of the most important autotrophic ammonia oxidizing bacteria, while Paracoccus and Flavobacterium were the main heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria in CN system. The enrichment of HN-AD bacteria outcompeted nitrite oxidizing bacteria (NOB), therefore leaded to higher nitrite accumulation in CN system. The findings of this study may be conducive to increasing the understanding of the microbial collaboration mechanisms of partial nitrification, thereby provides theoretical support for the improvement of biological nitrogen removal technology.

Feeding strategy for single-stage deammonification to treat moderate-strength ammonium under low free ammonia conditions

Single-stage deammonification (SSD) processes have been successfully operated using the step-feeding strategy to treat high-strength NH₄⁺ (>300 mg/L), but often failed to treat moderate-strength NH₄⁺ (100-300 mg/L). Because it is hard to maintain the free ammonia (FA) above 1 mg/L, which is a concentration in which the activity of NO₂^- oxidizing bacteria (NOB) can be selectively suppressed. In this study, to evaluate the effectiveness of the step-feeding strategy on the long-term stability of treating moderate-strength NH₄⁺, two SSD sequential-batch reactors (SBRs) were operated under one-step feeding and multi-step feeding strategies. The one-step feeding SBR achieved a higher nitrogen removal efficiency (86 %), nitrogen removal rate (0.61 kg/m³/d), and COD removal efficiency (95 %) than the multi-step feeding SBR (73 %, 0.39 kg/m³/d, and 95 %, respectively). This means the appropriate FA to selectively suppress NOB activity was successfully maintained in the one-step feeding SBR (FA > 1 mg/L). Therefore, it the necessary to apply a step feed strategy that can be maintained above FA (1 mg/L) from the start-up of operation to treat moderate-strength NH₄⁺.

Bioaugmentation performances with a powerful strain for nitrogen removal without N2O accumulation

N₂O is regarded as an inevitable intermediate during nitrogen removal, especially for wastewater treatment plants where good operating conditions would be required to mitigate N₂O releasing, which generally causes a high treatment cost. In this study, a novel bacterium capable of removing nitrogen without N₂O accumulation was isolated and identified as Citrobacter freundii XY-1. The nitrogen removal characteristics, nitrogen removal pathway, bioaugmentation in different reactors as well as microbial diversity were investigated. Results showed that 99.42% of NH+ 4-N and 95% of total organic carbon could be removed within 48 h with the corresponding removal rates being 4.03 mg/(L·h) and 39.42 mg/(L·h), respectively. It was inferred that traditional denitrification and N₂O generation do not exist in the pathway of removing nitrogen by XY-1 based on isotope analysis and functional genes detection. Bioaugmentations of XY-1 in both sequencing batch reactor and biological aerated filter significantly promoted the performances of nitrogen removal. The microbial diversity indicated that the relative abundance of strain XY-1 ranged from 45% to 66%, predominating throughout the running period. Overall, XY-1 could become an incredibly important candidate for the upgrading of wastewater treatment plants.

Wastewater Primary Treatment Using Forward Osmosis Introduces Inhibition to Achieve Stable Mainstream Partial Nitrification

Achieving stable long-term mainstream nitrite oxidizing bacteria (NOB) suppression is the bottleneck for the novel partial nitrification (PN) process toward energy- and carbon-efficient wastewater treatment. However, long-term PN stability remains a challenge due to NOB adaptation. This study proposed and demonstrated a novel strategy for achieving NOB suppression by the primary treatment of mainstream wastewater with a forward osmosis (FO) membrane process, which facilitated two external NOB inhibition factors (salinity and free nitrous acid, FNA). To evaluate the proposed strategy, a lab-scale sequencing batch reactor was operated for 200 days. A stable PN operation was achieved with a nitrite accumulation ratio of 97.7 ± 2.8%. NOB were suppressed under the combined inhibition effect of NaCl (7.9 ± 0.2 g/L, as introduced by the FO direct filtration) and FNA (0.11 ± 0.02 mg of HNO₂-N/L, formed as a result of the increased NH₄⁺-N concentration after the FO process). The two inhibition factors worked in synergy to achieve a more stable PN operation. The microbial analysis showed that the elevated salinity and accumulation of FNA reshaped the microbial community and selectively eliminated NOB. Finally, an economic and feasibility analysis was conducted, which suggests that the integration of an FO unit into PN/A is a feasible and economically viable wastewater treatment process.

Partition of Anammox and Nitrifiers Through Bio-Carriers for Full-Scale Sidestream Partial Nitrification-Anammox Plant

This study assessed the activity and community structure in different types of sludge to reveal the partition mechanism of anammox and nitrifiers in a full-scale partial nitrification-anammox plant. Batch experiments confirmed that suspended sludge had higher partial nitrification capacity, and biofilm sludge had higher anammox activity, 16.9 times higher than suspended sludge. qPCR analysis confirmed that the amoA gene was mainly present in suspended sludge, and the highest abundance of the Amx gene was observed in biofilm sludge, reaching 1.01 × 107 copies/ng DNA. High-throughput results revealed that Nitrosomonas was the main ammonia-oxidizing bacteria with high activity in suspended sludge, and Candidatus Brocadia had the highest abundance of 13.4% in biofilm sludge. This is the exploration of the microbial community of three different sludge types in the full-scale sidestream PN/A system for the first time, which can guide the construction and replication of full-scale PN/A plants.

Comparison between two anammox fiber fillers under load impact and the effect of HCO3 - concentration

Based on the establishment of a stable anaerobic ammonia oxidation treatment system in 100 days, the impact resistances of two different anammox fiber fillers (the curtain filler: R1 and the bundle filler: BR) were compared. Furthermore, the effect of HCO₃⁻ concentration on the bundle filler system was also investigated, the results have shown that the activity of the two anammox fiber fillers was not inhibited when the NO₂⁻–N concentration was lower than 750 mg L⁻¹ (FNA = 0.085 mg L⁻¹), while it was significantly suppressed at 900 mg L⁻¹ (FNA = 0.118 mg L⁻¹). However, the two fiber fillers could be recovered and exhibit a good impact resistance reduction of the substrate concentration. On day 95, the structure of the bundle filler was more conducive to the stable attachment, proliferation, and aggregation of anammox bacteria. Dominant anammox bacteria in both the curtain and bundle fillers were Candidatus Kuenenia, which accounted for 25.9% and 35.9% of the total population, respectively. When the influent HCO₃⁻ concentration was 900 mg L⁻¹, the bundled fiber filler had the highest total nitrogen (TN) removal efficiency, which reached 89.0%. Even though it was inhibited under 2000 mg L⁻¹ of HCO₃⁻ concentration, the reactor was able to recover within one week by reducing the substrate concentration. In addition, the HCO₃⁻ inhibition mechanism was independent of pH, which resulted in high FA content.

Based on the establishment of a stable anaerobic ammonia oxidation treatment system in 100 days, the impact resistances of two different anammox fiber fillers (the curtain filler: R1 and the bundle filler: BR) were compared.

Adaptation and evolution of freshwater Anammox communities treating saline/brackish wastewater

The most common way to apply Anammox for saline wastewater treatment is via salt adaptation of freshwater Anammox bacteria (FAB). To better apply this process in practice, it's essential to understand the salt adaptation process of FBA, as well as the underlying mechanisms. This study investigated the long-term salt adaptation process of a fixed-film FAB culture in three reactors (namely R1-R3), under salinities of 2, 8, and 12 NaCl g/L, correspondingly. All three reactors were under stable operation and achieved 80-90% total inorganic nitrogen removal efficiency throughout the 425-day operation period. R1 servers as a blank control, based on the clear microbial community shifts in R2 and R3, the operation period was divided into 2 phases. During Phase 1, all FAB in the three reactors belonged to Ca. Brocadia sp.. The Anammox activity (AA) and the ratio of nitrite/ammonium (NO₂^--N/NH₄⁺-N) consumption in R2 and R3 decreased with the increase of salinity and did not recover to the initial levels. During Phase 2, the relative abundance of Ca. Kuenenia sp. in R2 and R3 increased from nearly 0 to about 60 and 77%, respectively. With the growth of Ca. Kuenenia sp., the AA and stoichiometry of R2 and R3 gradually recovered. AA of R2 and R3 both reached 1.0 g NH₄⁺-N/L/day at the end of this phase, which was about 80% of that in R1. These results indicated that the salt adaptation of FAB culture was achieved by species shift from a low salt-tolerance one to a high salt-tolerance one.

Mechanistic understanding of the pollutant removal and transformation processes in the constructed wetland system

Constructed wetland systems (CWs) are biologically and physically engineered systems to mimic the natural wetlands which can potentially treat the wastewater from the various point and nonpoint sources of pollution. The present study aims to review the various mechanisms involved in the different types of CWs for wastewater treatment and to elucidate their role in the effective functioning of the CWs. Several physical, chemical, and biological processes substantially influence the pollutant removal efficiency of CWs. Plants species Phragmites australis, Typha latifolia, and Typha angustifolia are most widely used in CWs. The rate of nitrogen (N) removal is significantly affected by emergent vegetation cover and type of CWs. Hybrid CWs (HCWS) removal efficiency for nutrients, metals, pesticides, and other pollutants is higher than a single constructed wetland. The contaminant removal efficiency of the vertical subsurface flow constructed wetlands (VSSFCW) commonly used for the treatment of domestic and municipal wastewater ranges between 31% and 99%. Biochar/zeolite addition as substrate material further enhances the wastewater treatment of CWs. Innovative components (substrate materials, plant species) and factors (design parameters, climatic conditions) sustaining the long-term sink of the pollutants, such as nutrients and heavy metals in the CWs should be further investigated in the future. PRACTITIONER POINTS: Constructed wetland systems (CWs) are efficient natural treatment system for on-site contaminants removal from wastewater. Denitrification, nitrification, microbial and plant uptake, sedimentation and adsorption are crucial pollutant removal mechanisms. Phragmites australis, Typha latifolia, and Typha angustifolia are widely used emergent plants in constructed wetlands. Hydraulic retention time (HRT), water flow regimes, substrate, plant, and microbial biomass substantially affect CWs treatment performance.

Recent advances in partial denitrification-anaerobic ammonium oxidation process for mainstream municipal wastewater treatment

To solve the bottleneck of the unstable accumulation of nitrite in the partial nitrification (PN)-anammox (AMX) in municipal wastewater treatment, a novel process called partial denitrification (PD)-AMX has been developed. PD-AMX, which is known for cost-efficiency and environmental friendliness, has currently exhibited a promising potential for the removal of biological nitrogen from municipal wastewater and has attracted much research interest regarding its process mechanisms, as well as its practical applications. Here, we review the recent advances in the PD process and its coupling to the anammox process, including the development, basic principles, main characteristics, and critical process parameters of the stable operation of the PD-AMX process. We also explore the microbial community and its characteristics in the system and summarize the knowledge of the dominant bacteria to clarify the key factors affecting PD-AMX. Then, we introduce the engineering feasibility and economic feasibility as well as the potential challenges of the process. The induction and implementation of partial denitrification and maintenance of mainstream anammox are critical issues to be urgently solved. Meanwhile, the implementation of a full mainstream anammox application remains burdensome, while the mechanism of partial denitrification coupled to anammox needs to be further studied. Additionally, stable operation performance and process control¹ methods need to be optimized or developed for the PD-AMX system for better engineering practice. This review can help to accelerate the research and application of the PD-AMX process for municipal wastewater treatment.

Secondary treatment phase of tertiary wastewater treatment works significantly reduces estrogenic load

Estrogenic compounds enter waterways via effluents from wastewater treatment works (WWTW), thereby indicating a potential risk to organisms inhabiting adjacent receiving waters. However, little is known about the loads or concentrations of estrogenic compounds that enter Australian WWTWs, the efficiency of removing estrogenic compounds throughout the various stages of tertiary WWTW processes (which are common in Australia), nor the concentrations released into estuarine or marine receiving waters, and the associated risk for aquatic taxa residing in these environments. Therefore, seven estrogenic compounds, comprising the natural estrogens estrone (E1), 17β-estradiol (E2) and estriol (E3), the synthetic estrogen (EE2), and the industrial chemicals bisphenol A (BPA), 4-t-octyl phenol (4-t-OP) and 4-nonyl phenol (4-NP), in wastewater samples were quantified via liquid chromatographic-mass spectrometry (LC-MS) after solid-phase extraction at different stages of wastewater treatment and associated receiving waters. The concentrations of the target compounds in wastewater ranged from < LOQ (limit of quantification) to 158 ng/L for Tanilba Bay WWTW and < LOQ to 162 ng/L for Belmont WWTW. Most target compounds significantly declined after the secondary treatment phase. Appreciable removal efficiency throughout the treatment process was observed with removal from 39.21 to 99.98% of influent values at both WWTWs. The reduction of the natural estrogens (E1, E2 and E3) and 4-t-OP were significantly greater than EE2, BPA, and 4-NP in both WWTWs. Risk quotients (RQs) were calculated to assess potential ecological risks from individual estrogenic compounds. In predicted diluted effluents, no targeted compounds showed any ecological risk (RQ ≤1.65 × 10^-2) at both WWTWs. Similarly, all RQs for shore samples at both WWTWs were below 1. Finally, the hazard index (HI), which represents combined estrogenic contaminants' ecological risk, indicated no mentionable risk for predicted diluted effluents (HI = 0.0097 to 0.0218) as well as shoreline samples (HI = 0.393 to 0.522) in the receiving estuarine or marine waters.

The Kinetics of Pollutant Removal through Biofiltration from Stormwater Containing Airport De-Icing Agents

The present study aimed to determine the kinetics of pollutant removal in biofilters with LECA filling (used as a buffer to prevent de-icing agents from being released into the environment with stormwater runoff). It demonstrated a significant effect of temperature and a C/N ratio on the rate of nitrification, denitrification, and organic compound removal. The nitrification rate was the highest (0.32 mg N/L·h) at 25 °C and C/N = 0.5, whereas the lowest (0.18 mg N/L·h) at 0 °C and C/N = 2.5 and 5.0. Though denitrification rate is mainly affected by the available quantity of organic substrate, it actually decreased as the C/N increased and was positively correlated with the temperature levels. Its value was found to be the highest (0.31 mg N/L·h) at 25 °C and C/N = 0.5, and the lowest (0.18 mg N/L·h) at 0 °C and C/N = 5.0. As the C/N increased, so did the content of organic compounds in the treated effluent. The lowest organic removal rates were noted for C/N = 0.5, ranging between 11.20 and 18.42 mg COD/L·h at 0 and 25 °C, respectively. The highest rates, ranging between 27.83 and 59.43 mg COD/L·h, were recorded for C/N = 0.5 at 0 and 25 °C, respectively.

The Operating Characteristics of Partial Nitrification by Controlling pH and Alkalinity

In many experiments, a partial nitrification device is initiated with the use of highly active nitrating sludge because of the large number of nitrifying bacteria. Ammonia-oxidizing bacteria (AOB) are more adaptable to low-dissolved oxygen environments than nitrite-oxidizing bacteria (NOB). NOB activity was inhibited when the dissolved oxygen (DO) levels were decreased, causing the nitrate-nitrogen concentration to gradually decrease in the effluent and the nitrite-nitrogen concentration to gradually increase, achieving the accumulation of nitrous nitrogen. In this experiment, a sequencing batch reactor (SBR) was used to suppress NOB activity at a given pH while maintaining DO at a very low level so that the ammonia–water reaction mainly occurred in the device, and then the mud and water separated. Compared with other experiments, this approach can occur in 25 days, and it runs stably for more than two months until the device closes when the ammonia-nitrogen concentration is about 170 mg/L. This experiment also compared the difference between the pH change at the beginning of the device operation and after the device was stable. In order to increase the efficiency of bacterial appreciation, supplementing NaHCO3 increased the HCO3− concentration by 300 mg/L on the 25th day. It was found that some nitrification reactions still occurred, but they were not enough to destabilize the device. The nitrosate accumulation efficiency still gradually increased, and the average nitrite accumulation efficiency was 87.25% after NaHCO3 supplementation.

Removal of Nutrients From Anaerobically Digested Swine Wastewater Using an Intermittent Cycle Extended Aeration System

Swine wastewater contains high concentrations of organic compounds, nutrients (nitrogen and phosphorus), heavy metals, and residual antibiotics, amongst others, that have negative impacts on the water environment. The main aim of this work was to remove nutrients from anaerobically digested swine wastewater using an intermittent cycle extended aeration system (ICEAS). The effects of operational parameters such as cycle time, organic loading rate, C/N ratio, and aeration/mixing ratio on the pollutant removal efficiencies of ICEAS were studied and compared with the performance of a conventional sequencing batch reactor (SBR). The following optimal conditions were obtained: cycle time, 6 h; organic loading rate, 0.86 kg COD m-3 day-1; C/N ratio, 2.49-2.82; and aeration/mixing ratio, 1.57. The pH was maintained in the range of 6.0-8.0. The total organic carbon (TOC), total nitrogen (TN), ammonium (NH4 +), total phosphorus (TP), and color removal efficiencies of ICEAS were higher than those of the conventional SBR, with removal efficiencies of 95.22, 88.29, 97.69, 85.81, and 97.84%, respectively, compared to 94.34, 81.16, 94.15, 77.94, and 96.95%, respectively, observed in the SBR. TOC, TN, NH4 +, TP, and the color removal efficiencies of ICEAS were higher by 0.88, 7.13, 3.54, 7.87, and 0.95%, respectively, than the conventional SBR. The good results from this study show that ICEAS is a promising technology for the removal of organic contaminants and nutrients from anaerobically digested swine wastewater and that the effluent water quality meets the Vietnamese discharge standard (QCVN 62-MT:2016/BTNMT) for swine wastewater effluents.

Operation of pilot-scale nitrification-anammox reactors for the treatment of reject-water produced from the anaerobic digestion of thermal hydrolysis-treated sludge

Two-stage pilot-scale partial nitrification (PN)-anammox reactors were successfully operated for the treatment of reject-water (record as TRW) produced from the anaerobic digestion of thermal hydrolysis-treated sludge (THPAD). The PN reactor was operated stalely and Nitrosomonas was the major ammonia-oxidizing bacteria. In the anammox reactor, anammox activity doubled from day 3 to day 53 demonstrating that anammox adapted to the PN effluent. After acid shock at pH 4 for approximately 1 h, anammox was seriously inhibited and required approximately 60 days for recovery. This provided a reference for handling similar accidents. In the next 166 days, the load reached 0.40-0.51 kg N/(m³·d) in the presence of high concentration COD (798-1313 mg/L), suggesting anammox can be used in high concentration organic wastewater. Under the combined action of anammox and denitrification, 94.7% nitrogen was removed. These results demonstrated TRW can be treated using PN-anammox technology which was conducive to the popularization of THPAD.

Biogenic Fe(II-III) Hydroxycarbonate Green Rust Enhances Nitrate Removal and Decreases Ammonium Selectivity during Heterotrophic Denitrification

Nitrification-denitrification is the most widely used nitrogen removal process in wastewater treatment. However, this process can lead to undesirable nitrite accumulation and subsequent ammonium production. Biogenic Fe(II-III) hydroxycarbonate green rust has recently emerged as a candidate to reduce nitrite without ammonium production under abiotic conditions. The present study investigated whether biogenic iron(II-III) hydroxycarbonate green rust could also reduce nitrite to gaseous nitrogen during bacterial nitrate reduction. Our results showed that biogenic iron(II-III) hydroxycarbonate green rust could efficiently decrease the selectivity of the reaction towards ammonium during heterotrophic nitrate reduction by native wastewater-denitrifying bacteria and by three different species of Shewanella: S. putrefaciens ATCC 12099, S. putrefaciens ATCC 8071 and S. oneidensis MR-1. Indeed, in the absence of biogenic hydroxycarbonate green rust, bacterial reduction of nitrate converted 11–42% of the initial nitrate into ammonium, but this value dropped to 1–28% in the presence of biogenic hydroxycarbonate green rust. Additionally, nitrite accumulation did not exceed the 2–13% in the presence of biogenic hydroxycarbonate green rust, versus 0–28% in its absence. Based on those results that enhance the extent of denitrification of about 60%, the study proposes a water treatment process that couples the bacterial nitrite production with the abiotic nitrite reduction by biogenic green rust.

Technologies for biological removal and recovery of nitrogen from wastewater

Water contamination is a growing environmental issue. Several harmful effects on human health and the environment are attributed to nitrogen contamination of water sources. Consequently, many countries have strict regulations on nitrogen compound concentrations in wastewater effluents. Wastewater treatment is carried out using energy- and cost-intensive biological processes, which convert nitrogen compounds into innocuous dinitrogen gas. On the other hand, nitrogen is also an essential nutrient. Artificial fertilizers are produced by fixing dinitrogen gas from the atmosphere, in an energy-intensive chemical process. Ideally, we should be able to spend less energy and chemicals to remove nitrogen from wastewater and instead recover a fraction of it for use in fertilizers and similar applications. In this review, we present an overview of various technologies of biological nitrogen removal including nitrification, denitrification, anaerobic ammonium oxidation (anammox), as well as bioelectrochemical systems and microalgal growth for nitrogen recovery. We highlighted the nitrogen removal efficiency of these systems at different temperatures and operating conditions. The advantages, practical challenges, and potential for nitrogen recovery of different treatment methods are discussed.

Partial nitritation performance and microbial community in sequencing batch biofilm reactor filled with zeolite under organics oppression and its recovery strategy

Influences of organics on partial nitritation performance were investigated in a lab-scale sequencing batch biofilm reactor filled with zeolite. Significant differences in nitrite production rate (NPR) were observed between different dosages of glucose. With influent COD/N ratio from 0 to 1.5, NPR declined from 0.4 to 0.05 kg/(m3·d). Meanwhile, an appropriate NO2--N/NH4+-N ratio (1.4 ± 0.5) could be obtained for simultaneous anammox denitrification at COD/N ratio of 0.5. Increasing airflow rate was found as an effective recovery strategy. Other than competition of heterotrophs with nitrifiers for dissolved oxygen, it has been verified that addition of organics generated higher free ammonia, and then further inhibitedammonium oxidizing bacteria (AOB). Moreover, three-dimensional excitation-emission matrix (3D-EEM) results revealed that protein-like and humic acid-like substances were the main components in extracellularpolymericsubstances (EPS). And high-throughput sequencing analysis demonstrated that the relative abundance of AOB decreased.

Mass fluxes of nitrogen and phosphorus through water reclamation facilities: Case study of biological nutrient removal, aerobic sludge digestion, and sidestream recycle

At water reclamation facilities, recycling of nutrients (nitrogen and phosphorus) from solids-handling processes to the mainstream treatment process can have detrimental effects on biological nutrient removal systems. In this study, mass fluxes of nitrogen and phosphorus were quantified through the treatment trains at the Northwest Regional Water Reclamation Facility (NWRWRF) and the adjoining Biosolids Management Facility (BMF), which receives sludge from several water reclamation facilities in Hillsborough County, Florida. The driving objectives were to determine (a) whether the return stream from BMF to NWRWRF (i.e., the "sidestream") represents a significant source of nitrogen and phosphorus to NWRWRF, and (b) whether the sidestream return from BMF is interfering with biological nutrient removal processes at NWRWRF. We determined that nearly half of the overall phosphorus flux into NWRWRF is recycled from the BMF sidestream. This leads to an increased cost of treatment, for example, for alum used in phosphorus removal at NWRWRF. In contrast to phosphorus, the flux of nitrogen from BMF to NWRWRF is small (~3%) compared with the flux of nitrogen entering NWRWRF in raw wastewater. However, nitrogen in the sidestream is mostly in the form of nitrate, which prevents anaerobic conditions from developing in the fermentation basin at NWRWRF, and thereby interferes with the enhanced biological phosphorus removal (EBPR) process. Some measurements suggest that fermentation and release of phosphorus may occur in the return activated sludge line (despite the relatively short residence time in that line), which supports EBPR and may partially compensate for anoxic (denitrifying) conditions in the fermentation basin. Therefore, overall, NWRWRF is able to meet its permit limits for phosphorus through a combination of EBPR and alum addition. Although the fluxes measured here are particular to the treatment systems under consideration, the general trends observed are likely to apply to many similar facilities that employ biological nutrient removal, aerobic digestion, and sidestream recycle, particularly those with regional biosolids management facilities. We recommend that such facilities consider (a) removal or recovery of phosphorus from their sidestreams and (b) returning sidestreams downstream of fermentation basins to avoid inhibition of EBPR processes. PRACTITIONER POINTS: Sidestreams from aerobic digestion can represent significant sources of phosphorus to mainstream wastewater treatment. Recycle of nitrate in aerobic digestion sidestreams can interfere with enhanced biological phosphorus removal (EBPR) during mainstream treatment. Fermentation of return activated sludge (RAS) can support EBPR, even under short average hydraulic residence times (minutes).

The effect of different denitrification and partial nitrification-Anammox coupling forms on nitrogen removal from mature landfill leachate at the pilot-scale

The effects on nitrogen removal from landfill leachate were compared between the denitrification (DN) direct coupling in Partial nitrification (PN)-Anammox (DN+(PN-Anammox)) and pre-DN followed by PN-Anammox (DN-PN-Anammox). Both processes can achieve coupling and high nitrogen removal. However, the DN+(PN-Anammox) process was not conducive to the treatment of high-COD wastewater. The total nitrogen removal rate (TNRR) and total nitrogen removal efficiency (TNRE) were stable at 0.31 kg/(m³·d) and 76.3%. When UASB was added to denitrification and transform the process into DN-PN-Anammox, the influent NH₄⁺-N and COD concentrations were increased to 2230 and 2612 mg/L, TNRR and TNRE reached 0.45 kg/(m³·d) and 96.7%, respectively. The DN-PN-Anammox process not only was able to make full use of degradable COD in wastewater to realize the NO₃^--N removal, but also benefited the growth of autotrophic bacteria. The DN-PN-Anammox reduced the oxygen supply and was more conducive to the treatment of highly-concentrated mature landfill leachate.

Effect of aquaculture salinity on nitrification and microbial community in moving bed bioreactors with immobilized microbial granules

The novel immobilized microbial granules (IMG) shows a significant effect of nitrification for freshwater aquaculture. However, there is lack of evaluation study on the performance of nitrification at high salinity due to the concentration of recycled water or seawater utilization. A laboratory scale moving bed bioreactor (MBBR) with IMG was tested on recycled synthetic aquaculture wastewater for the nitrification at 2.5 mg/L NH₃-N daily. The results indicated that IMG showed a high salinity tolerance and effectively converted ammonia to nitrate up to 92% at high salinity of 35.0 g/L NaCl. As salinity increased from near zero to 35.0 g/L, the microbial activity of nitrite oxidation bacteria (NOB) in the IMG decreased by 86.32%. The microbial community analysis indicated that salinity significantly influenced the community structure. It was found that Nitrosomonas sp. and Nitrospira sp. were the dominant genera for ammonia oxidation bacteria (AOB) and NOB respectively at different salinity levels.

Two-stage granular sludge partial nitritation/anammox process for the treatment of digestate from the anaerobic digestion of the organic fraction of municipal solid waste

The increasing amount of source separated organic fraction of municipal solid wastes (OFMSW) treated by anaerobic digestion for energy recovery requires the implementation of cost-efficient processes for the treatment of the produced digestate, especially in terms of nitrogen removal. The autotrophic nitrogen removal process, based on the coupling of two biological processes, partial nitritation (PN) and anammox (A), appears as a suitable solution due to important savings in operational costs compared to conventional treatment processes. However, its application could be hampered by the high salinity and inhibitory potential of this kind of digestate. In this contribution, two lab-scale granular sludge reactors performing the PN and anammox processes, respectively, were used to treat (opportunely diluted) real OFMSW digestate originating from full-scale biogas plants with the aim of assessing their treatment feasibility in a two-stage PN/A configuration. The PN process was implemented in an air-lift granular sludge reactor and was able to treat a nitrogen loading rate of about 1 g N L^-1 d^-1 at 30 ± 0.5 °C; moreover, its effluent was suitable for the subsequent anammox treatment, with an appropriate effluent NO₂^-/NH₄⁺ ratio and marginal inhibiting effects. In the anammox granular sludge reactor, the anammox activity was affected by high salinity levels, nonetheless a stable reactor performance at a nitrogen removing rate of 0.83 ± 0.20 and 0.31 ± 0.04 g N L^-1 d^-1 at 35 ± 0.5 °C, were achieved when treating 50% and 30% diluted real wastewaters at a conductivity in the reactor of 9.1 and 11.2 mS cm^-1, respectively.

Partial denitrification providing nitrite: Opportunities of extending application for anammox

Anaerobic ammonium oxidation (anammox) has been extensively investigated for cost-efficient nitrogen removal from wastewater. However, the major issues of nitrate (NO₃^--N) residue and instability in the current combination of nitritation and anammox process necessitates being addressed efficiently. The recently proposed partial-denitrification (PD), terminating NO₃^--N reduction to nitrite (NO₂^--N), has been regarded as a promising alternative of NO₂^--N supplying for anammox bacteria. Given the engineering practices, the steadily high NO₂^--N production, alleviating organic inhibition, and reducing greenhouse gas of PD process offers a viable and efficient approach for anammox implementation. Moreover, it allows for the extending applications of anammox process due to the NO₃^--N removal availability. Here we comprehensively review the important new outcomes and discuss the emerging applications of PD-based anammox including the process development, mechanism understanding, and future trends. Significant greater stability and enhanced nitrogen removal efficiency have been demonstrated in the novel integrations of PD and anammox process, indicating a broad perspective in dealing with the mainstream municipal sewage, ammonia-rich streams, and industrial NO₃^--N contained wastewater. Furthermore, researches are still needed for the predictable and controllable strategies, along with the detailed microbiological information in future study. Overall, the achievement of PD process provides unique opportunity catalyzing the engineering applications of energy-efficient and environmental-friendly wastewater treatment via anammox technology.

Effect of anaerobic/aerobic duration on nitrogen removal and microbial community in a simultaneous partial nitrification and denitrification system under low salinity

In this study, the simultaneous partial nitrification and denitrification (SPND) process was investigated in a hybrid sequencing batch biofilm reactor (HSBBR) fed with synthetic wastewater with 1.2% salinity. Different anaerobic/aerobic (An/Ae) durations were selected for evaluating the removal performance of contaminants and the succession of the microbial community in the reactor. The highest organic matter removal efficiency was obtained at An/Ae hour ratio of 0/6.5, with an average chemical oxygen demand (COD) removal of 89.6% at the steady state. Similarly high nitrogen removal efficiencies were achieved at An/Ae hour ratios of 1/5.5, 1.5/5 and 2/4.5,with over 92% of average total nitrogen removed. This represents an increase of more than 10% compared to the mode with An/Ae hour ratio of 0/6.5. High-throughput sequencing analysis revealed that the increase of the An/Ae hour ratio changed the characteristics of the community structures in the HSBBR. Azoarcus was the most dominant genus when the An/Ae hour ratio was 0/6.5 in both suspended sludge (S-sludge) and biofilm, while Candidatus_Competibacter was the most abundant genus at An/Ae hour ratios of 2/4.5 and 3/3.5. Nitrosomonas was the only ammonia oxidizing bacteria (AOB) detected in this study. Nitrospira, a kind of nitrite oxidizing bacteria (NOB), was sensitive to salinity and altering the An/Ae mode; this was detected only in S-sludge samples in a fully aerobic mode with a low percentage of 0.1%. S-sludge and biofilm samples shared a similar bacterial composition. This research demonstrated that efficient nitrogen and carbon removal could be achieved via the SPND process by the symbiotic functional groups in a hybrid S-sludge and biofilm reactor.

Isolation and Nitrogen Removal Characteristics of an Aerobic Heterotrophic Nitrifying-Denitrifying Bacterium, Klebsiella sp. TN-10

Nitrogen removal by microorganisms has attracted increasing attention in wastewater treatment. In the present study, a heterotrophic nitrification bacterium was isolated from tannery wastewater and identified as Klebsiella sp. TN-10 based on phenotypic and phylogenetic characteristics. The optimal conditions for cell growth and nitrogen removal were investigated, and the results showed that the greatest ammonium removal rate and maximum biomass were achieved by using sodium pyruvate (7 g/L) as carbon source, C/N 12, pH 7, and temperature 30 °C. Under optimal conditions, the removal rate of ammonia nitrogen reached 96%. Besides, the growth characteristic and the ability of utilizing nitrate and nitrite were investigated. The results demonstrated that strain TN-10 exhibited excellent characteristics to remove both nitrate and nitrite, with the removal rate of 95.44% and 99.87%, respectively. In addition, the nitrite reductase (NiR) and nitrate reductase (NR) involved in denitrification were both active, with the activities of 0.0815 and 0.0283 U/mg proteins, respectively. Furthermore, the aggregation ability, auto-aggregation kinetics, and the relationship between zeta potentials and flocculating efficiency were determined. These results indicated that the strain Klebsiella sp. TN-10, with efficient heterotrophic nitrification-aerobic denitrification ability, has potential application in wastewater treatment.

Bottom-up approach in the assessment of environmental impacts and costs of an innovative anammox-based process for nitrogen removal

In recent decades, the wastewater treatment sector has undergone a shift to adapt to increasing discharge limits. In addressing the evaluation of innovative technologies, it is necessary to determine the scale at which reliable and representative values of environmental impacts and costs can be obtained, ensuring that the system under assessment follows the direction of eco-efficiency. This study has evaluated the environmental and economic indicators of an autotrophic nitrogen removal technology (ELAN^®) from laboratory conception (1.5 L) to full scale (2 units of 115 m³) using the Life Cycle Assessment (LCA) methodology. Indirect emissions related to electricity consumption are the main contributor in all impact categories except eutrophication. Electricity consumption referred to the functional unit (1 m³ of treated wastewater) decreases as the scale increases. The rationale behind this can be explained, among other reasons, by the low energy efficiency of small-scale equipment (pumps and aerators). Accordingly, a value of approximately 25 kg CO_2eq per m³ of treated water is determined for laboratory scale, compared to only 5 kg CO_2eq per m³ at full-scale. When it comes to assessing the reliability of data, a pilot scale system of 0.2 m³ allowed to perform a trustworthy estimation of environmental indicators, which were validated at full-scale. In terms of operational costs, the scale of approximately 1 m³ provided a more accurate estimate of the costs associated with energy consumption.

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.

Nitrogen removal capacity and bacterial community dynamics of a Canon biofilter system at different organic matter concentrations

Three Canon bench-scale bioreactors with a volume of 2 L operating in parallel were configured as submerged biofilters. In the present study we investigated the effects of a high ammonium concentration (320 mgNH₄⁺· L^-1) and different concentrations of organic matter (0, 100 and 400 mgCOD·L^-1) on the nitrogen removal capacity and the bacterial community structure. After 60 days, the Canon biofilters operated properly under concentrations of 0 and 100 mgCOD·L^-1 of organic matter, with nitrogen removal efficiencies up to 85%. However, a higher concentration of organic matter (400 mgCOD·L^-1) produced a partial inhibition of nitrogen removal (68.1% efficiency). The addition of higher concentrations of organic matter a modified the bacterial community structure in the Canon biofilter, increasing the proliferation of heterotrophic bacteria related to the genera of Thauera, Longilinea, Ornatilinea, Thermomarinilinea, unclassified Chlorobiales and Denitratisoma. However, heterotrophic bacteria co-exist with Nitrosomonas and Candidatus Scalindua. Thus, our study confirms the co-existence of different microbial activities (AOB, Anammox and denitrification) and the adaptation of a fixed-biofilm system to different concentrations of organic matter.

Simultaneous domestic wastewater and nitrate sewage treatment by DEnitrifying AMmonium OXidation (DEAMOX) in sequencing batch reactor

A novel DEAMOX system was developed for nitrogen removal from domestic wastewater and nitrate (NO₃^--N) sewage in sequencing batch reactor (SBR). High nitrite (NO₂^--N) was produced from NO₃^--N reduction in partial-denitrification process, which served as electron acceptor for anammox and was removed with ammonia (NH₄⁺-N) in domestic wastewater simultaneously. A 500-days operation demonstrated that the efficient and stable nitrogen removal performance could be achieved by DEAMOX. The total nitrogen (TN) removal efficiency was as high as 95.8% with influent NH₄⁺-N of 63.58 mg L^-1 and NO₃^--N of 69.24 mg L^-1. The maximum NH₄⁺-N removal efficiency reached up to 94.7%, corresponding to the NO₃^--N removal efficiency of 97.8%. The biomass of partial-denitrification and anammox bacteria was observed to be wall-growth. The deteriorated nitrogen removal performance occurred due to excess denitrifying microbial growth in the outer layer of sludge consortium, which prevented the substrate transfer for anammox inside. However, an excellent nitrogen removal could be guaranteed by scrapping the superficial denitrifying biomass at regular intervals. Furthermore, the high-throughput sequencing analysis revealed that the Thauera genera (26.33%) was possibly responsible for the high NO₂^--N accumulation in partial-denitrification and Candidatus Brocadia (1.7%) was the major anammox species.

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.

Performance and microbial ecology of a nitritation sequencing batch reactor treating high-strength ammonia wastewater

The partial nitrification (PN) performance and the microbial community variations were evaluated in a sequencing batch reactor (SBR) for 172 days, with the stepwise elevation of ammonium concentration. Free ammonia (FA) and low dissolved oxygen inhibition of nitrite-oxidized bacteria (NOB) were used to achieve nitritation in the SBR. During the 172 days operation, the nitrogen loading rate of the SBR was finally raised to 3.6 kg N/m³/d corresponding the influent ammonium of 1500 mg/L, with the ammonium removal efficiency and nitrite accumulation rate were 94.12% and 83.54%, respectively, indicating that the syntrophic inhibition of FA and low dissolved oxygen contributed substantially to the stable nitrite accumulation. The results of the 16S rRNA high-throughput sequencing revealed that Nitrospira, the only nitrite-oxidizing bacteria in the system, were successively inhibited and eliminated, and the SBR reactor was dominated finally by Nitrosomonas, the ammonium-oxidizing bacteria, which had a relative abundance of 83%, indicating that the Nitrosomonas played the primary roles on the establishment and maintaining of nitritation. Followed by Nitrosomonas, Anaerolineae (7.02%) and Saprospira (1.86%) were the other mainly genera in the biomass.

Response of performance and ammonia oxidizing bacteria community to high salinity stress in membrane bioreactor with elevated ammonia loading

Effect of elevated ammonia loading rate (ALR) and increasing salinity on the operation of membrane bioreactor (MBR) and the response of microbial community were investigated. Results showed that MBR started up with 1% NaCl stress achieved amazing nitrification performance at high salinity up to 4% when treating wastewater containing 1000mg/L NH(+)4-N. Further increasing salinity to 7% led to failure of MBR unrecoverably. Steep decline of sludge activity contributed to the extremely worse performance. High-throughput sequencing analysis showed that both ALR and salinity had selective effects on the microbial community structure. In genus level, Methyloversatilis and Maribacter were enriched during the operation. Survival of salt-resistant microbes contributed to the rising of richness and diversity at 2% and 4% NaCl stress. Analysis of amoA-gene-based cloning revealed Nitrosomonas marina are chiefly responsible for catalyzing ammonia oxidation in high ALR at high salinity stress.

Cultivation and characteristics of partial nitrification granular sludge in a sequencing batch reactor inoculated with heterotrophic granules

The aim of this study was to develop a simple operation strategy for the cultivation of partial nitrification granules (PNGs) treating an autotrophic medium. For this strategy, aerobic granular sludge adapted to high concentration organics removal was seeded in a sequencing batch reactor (SBR) with a height/diameter ratio of 3.8, and the ratio of organics to the ammonia nitrogen-loading rate (C/N ratio) in the influent was employed as the main control parameter to start up the partial nitrification process. After 86 days of operation, the nitrite accumulation rate reached 1.44 kg/(m³ day) in the SBR, and the removal efficiency of ammonia nitrogen (NH₄⁺-N) was over 95 %. The PNGs showed a dense and compact structure, with an excellent settling ability, a typical extracellular polymeric substance (EPS) composition, and a high ammonia oxidation activity. The high-throughput pyrosequencing results indicated that the microbial community structure in the granules was significantly influenced by the C/N ratio, and ammonia-oxidizing bacteria (AOB), including the r-strategist Nitrosomonas and k-strategist Nitrosospira genre, which accounted for approximately 40 % of the total biomass at the end of operation. The effective suppression of nitrite-oxidizing bacteria (NOB) growth was attributed to oxygen competition on the granular surface among functional bacteria, as well as the high free ammonia or free nitrous acid concentrations during the aeration period.

Enhanced short-cut nitrification in an airlift reactor by CaCO3 attachment on biomass under high bicarbonate condition

The short-cut nitrification (SCN) performance of an airlift reactor (ALR) was investigated under increasing bicarbonate condition. The sequential increase of bicarbonate from 2.5 to 7.0 g/L accelerated the nitrite accumulation and improved the NAP to 99 %. With the increase of bicarbonate dose to 11 g/L, the ammonium removal efficiency and the ammonium removal rate (ARR) were improved to 95.1 % and 0.57 kg/m(3)/day, respectively. However, the elevation of bicarbonate concentration from 11.0 to 14.0 g/L gradually depreciated the nitrite accumulation percentage to 62.5 %. Then, the reactor was operated in increasing ammonium strategy to increase the nitrogen loading rate (NLR) to 1.1 kg/m(3)/day under 700 mg/L influent ammonium concentration. The ARR and nitrite production rate were elevated to 1.1 and 0.9 kg/m(3)/day, respectively. The SCN performance was improved to 1.8 kg/m(3)/day (NLR) by the subsequent progressive shortening of HRT to 4.8 h at ammonium concentration of 350 mg/L, which was 1.6 times higher than that of the increasing ammonium strategy. Chemical analysis with EDS, FTIR and XRD confirmed the presence of CaCO3 precipitates on biomass surface during the long-term operation under high bicarbonate conditions. The attachment of precipitates to the SCN sludge helped to improve the biomass settleability and finally enhanced the SCN performance of the ALR.

Impact of methionine on a partial-nitritation biofilter

It has been demonstrated that an anaerobic digestion process cannot attain an efficient removal of several amino acids, with methionine being one of the most persistent of these. Thus, the effect that methionine amino acid has over the partial-nitritation process with fixed-biofilm configuration in terms of performance and bacterial community dynamics has been investigated. With respect to the performance with no addition, 100 mg/L methionine loading decreased ammonium oxidation efficiency in 60% and 100% at concentrations of 300 and 500 mg/L methionine, respectively. Bacterial biomass sharply increased by 30, 65, and 230% with the addition of 100, 300, and 500 mg/L methionine, respectively. Bacterial community analysis showed that methionine addition supported the proliferation of a diversity of heterotrophic genera, such as Lysobacter and Micavibrio, and reduced the relative abundance of ammonium oxidizing genus Nitrosomonas. This research shows that the addition of methionine affects the performance of the partial-nitritation process. In this sense, amino acids can pose a threat for the of partial-nitritation process treating anaerobic digester supernatant at full-scale implementation.

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.

Impact of quinoline on activity and microbial culture of partial nitrification process

In this study, the effect of quinoline on nitrification in an activated sludge system was evaluated in batch assays. Quinoline was evaluated to partial nitrification process or to partial nitrification-quinoline degrading process. In partial nitrification assays, 50-150mg/L quinoline presence promoted the ammonium oxidation efficiency (200-100%). Nonetheless, the consumption efficiencies for quinoline were less than 66.6%. On the other hand, in partial nitrification-quinoline degrading process, the promotion effect of quinoline (50-150mg/L) diminished significantly, ammonium oxidation were similarity to the control. However, the consumption efficiencies for quinoline were nearly 100%. DGGE results showed that the bacteria communities varied significantly. Acidovorax sp. JS42 and Acidovorax ebreus TPSY were responsible for ammonium oxidation in partial nitrification process, while Nitrosomonas in partial nitrification-quinoline degrading process. This information might be useful for treating wastewaters of ammonium/quinoline by partial nitrification technology.

Detection of nitrifiers and evaluation of partial nitrification for wastewater treatment: A review

Partial nitrification has gained broad interests in the biological nitrogen removal (BNR) from wastewater, since it alleviates carbon limitation issues and acts as a shortcut nitrogen removal system combined with anaerobic ammonium oxidation (Anammox) process. The occurrence and maintenance of partial nitrification relies on various conditions, which favor ammonium oxidizing bacteria (AOB) but inhibit or limit nitrite oxidizing bacteria (NOB). The studies of the AOB and NOB activities have been conducted by state-of-the-art molecular techniques, such as Polymerase Chain Reaction (PCR), Quantitative PCR, denaturing gradient gel electrophoresis (DGGE), Fluorescence in situ hybridization (FISH) technique, Terminal Restriction Fragment Length Polymorphism (T-RFLP), Live/Dead BacLight, and quinone profile. Furthermore, control strategies for obtaining partial nitrification are mainly focused on the pH, temperature, dissolved oxygen concentration, real-time aeration control, sludge retention time, substrate concentration, alternating anoxic and aerobic operation, inhibitor and ultrasonic treatment. Existing problems and further perspectives for the scale-up of partial nitrification are also proposed and suggested.

Rapid start-up and microbial characteristics of partial nitrification granular sludge treating domestic sewage at room temperature

The successful suppression of nitrite-oxidizing bacteria in the partial nitrification (PN) stage was the main challenge for the application of autotrophic nitrogen removal process treating mainstream sewage. In this study, two identical PN granular reactors (P1 and P2) were rapid started-up using the simultaneous PN and granulation strategy, for treating the domestic sewage. P1 was seeded with 30% PN granular sludge to induce nucleation, in which the granule size achieved to more than 400μm in 12d, with ammonia oxidation rate and nitrite accumulation rate of 80% and 95%, respectively, while P2 realized granulation in 42d. The presence of organic matters and specific structure of granules were profitable for the stability of PN for treating sewage with low ammonia. High-throughput pyrosequencing results indicated the biodiversity of both reactors decreased after start-up, and Nitrosomonas was the predominant specie of aerobic ammonia-oxidizing bacteria in PN granular sludge.

Partial nitrification in an air-lift reactor with long-term feeding of increasing ammonium concentrations

The partial nitrification (PN) performance under high ammonium concentrations was evaluated in an airlift reactor (ALR). The ALR was operated for 253days with stepwise elevation of ammonium concentration to 1400mg/L corresponding nitrogen loading rate of 2.1kg/m(3)/d. The ammonium removal rate was finally developed to 2.0kg/m(3)/d with average removal efficiency above 91% and nitrite accumulation percentage of 80%. Results showed that the combined effect of limited DO, high bicarbonate, pH and free ammonia (FA) contributed to the stable nitrite accumulation substantially. The biomass in the ALR was improved with the inception of granulation. Precipitates on biomass surface was unexpectedly experienced which might improve the settleability of PN biomass. Organic functional groups attached to the PN biomass suggested the possible absorbability to different types of pollutant. The results provided important evidence for the possibility of applying an ALR to treat high strength ammonium wastewater.

Algal biofuels from urban wastewaters: maximizing biomass yield using nutrients recycled from hydrothermal processing of biomass

Recent studies have proposed algal cultivation in urban wastewaters for the dual purpose of waste treatment and bioenergy production from the resulting biomass. This study proposes an enhancement to this approach that integrates cultivation of an acidophilic strain, Galdieria sulphuraria 5587.1, in a closed photobioreactor (PBR); hydrothermal liquefaction (HTL) of the wet algal biomass; and recirculation of the nutrient-rich aqueous product (AP) of HTL to the PBR to achieve higher biomass productivity than that could be achieved with raw wastewater. The premise is that recycling nutrients in the AP can maintain optimal C, N and P levels in the PBR to maximize biomass growth to increase energy returns. Growth studies on the test species validated growth on AP derived from HTL at temperatures from 180 to 300°C. Doubling N and P concentrations over normal levels in wastewater resulted in biomass productivity gains of 20-25% while N and P removal rates also doubled.