Mainstream Deammonification Research Articles

Optimization of the carbon to nitrogen ratio for mainstream deammonification and the resulting shift in nitrification from biofilm to suspension

Mainstream deammonification performance in an integrated fixed film activated sludge (IFAS) reactor improved from 46% to 73% TIN removal after routing 10% of the primary effluent around the A-stage reactor.

Towards mainstream deammonification of municipal wastewater: Partial nitrification-anammox versus partial denitrification-anammox.

The mainstream deammonification has been believed as a viable technology for the energy-neutral municipal wastewater treatment, which can be realized through two approaches known as partial nitrification-anammox (PN/AMX) and partial denitrification-anammox (PDN/AMX). However, large-scale applications of these deammonification processes for municipal wastewater treatment have been rarely reported thus far. Given such a situation, this review examined the mainstream PN/AMX and PDN/AMX processes with the focus on their engineering feasibility, economic viability and potential challenges. It was revealed that soluble COD and stable nitrite production were the main challenges for mainstream deammonification. Pre-capture of COD was essential for mitigating the competition between denitrifiers and anammox bacteria on nitrite, while NOB suppression and partial denitrification control to nitrite stage were critical issues for stable nitrite production in PN and PDN processes respectively. Compared to nitrification-denitrification, the unit oxygen demand for nitrogen removal in PN/AMX and PDN/AMX could be reduced by 57.3% and 47.7%, while the sludge production could also be cut off by 83.7% and 66.3% in PN/AMX and PDN/AMX respectively. These clearly showed the greater economic viability and environmental sustainability of PN/AMX against PDN/AMX. Consequently, more effort is needed to improve the engineering feasibility of large-scale mainstream deammonification for municipal wastewater treatment.

Comparing two hydrazine addition strategies to stabilize mainstream deammonification: Performance and microbial community analysis

In this study, an expanded granular sludge blanket reactor (EGSB) was proposed to achieve stable mainstream deammonification process by adding hydrazine (N2H4). Two N2H4 addition methods consisted of constant concentration (strategy A) and variable concentration (strategy B) both can inhibit nitrite oxidizing bacteria. A efficient performance was achieved with higher total nitrogen removal efficiency (82 ± 6%) and nitrogen removal rate (0.32 ± 0.02 kg N/(m3·d)) under strategy B. For strategy A, anaerobic ammonia oxidizing bacteria (AnAOB) in-situ activity was decreased from 2.76 to 0.68 mg N/(g VSS·h) at 42 mg/L NH4+-N. Candidatus Brocadia abundance increase from 14.62% to 20.07% under the strategy may indicated the self-regulate mechanism of AnAOB. Aerobic ammonia oxidizing bacteria (AOB, mainly Nitrosomonas) and AnAOB (mainly Candidatus Brocadia) were always dominated under two strategies. Strategy B provided better environment for most microorganisms (mainly Chloroflexri, Planctomycetes, Proteobacteria and Chlorobi).

Integrated upflow anaerobic fixed-bed and single-stage step-feed process for mainstream deammonification: A step further towards sustainable municipal wastewater reclamation

The high energy consumption and excessive waste activated sludge (WAS) production have become the major concerns on the municipal wastewater treatment with conventional biological processes. To tackle these emerging issues, this study demonstrated the feasibility of a novel process integrating an upflow anaerobic fixed-bed reactor (UAFBR) followed by a continuous step-feed reactor for mainstream deammonification towards improved energy efficiency, minimized sludge production and cost-effective ammonium removal. The results showed that 48.8% of the influent chemical oxygen demand (COD) was directly converted to methane gas in UAFBR with minimized sludge production, while 80% of total nitrogen (TN) was removed in the step-feed reactor. Mass balance on the step-feed reactor revealed that the oxic chambers contributed 51.6% of the removed ammonium oxidation to mainly nitrite, while the produced nitrite was immediately removed via anammox with the ammonium supplied by the step-feed in the following anoxic chambers where about 87.1% TN removal occurred. Moreover, it was found that sustainable repression of nitrite oxidizing bacteria (NOB) was achieved without compromising the activity of ammonia oxidizing bacteria (AOB). The anammox bacteria were effectively retained in the anoxic chambers and showed a high specific anammox activity of 0.42 g N/(g VSS·day). These suggest that the step-feed configuration can offer a feasible engineering option towards single-stage mainstream deammonification. It appears that the integrated process developed in this study sheds light on the possible way towards sustainable, energy self-sufficient municipal wastewater reclamation.

Screen versus cyclone for improved capacity and robustness for sidestream and mainstream deammonification

Combining physical and metabolic selection allowed for determination of ideal operational conditions and capacity gain in full-scale deammonification systems.

A-stage and high-rate contact-stabilization performance comparison for carbon and nutrient redirection from high-strength municipal wastewater

This study performed a parallel comparison of the A-stage (adsorption) and high-rate contact-stabilization (CS) technology for carbon and nutrient redirection, operating both systems at similar sludge retention time (SRT) of 0.16–0.3 d and treating high-strength raw wastewater. Overall at the average 0.22 d SRT condition, both A-stage and CS had similar carbon capture behavior (42–43%) and thus the similar potential for energy recovery. However, the A-stage had better effluent quality (67 mg VSS/L) through the growth of more heterotrophic biomass leading to increased oxidation (22% vs 18%), and increased fraction of nitrogen (26% vs 19%) and phosphorous (36% vs 30%) redirection compared to the CS. At biomass limited conditions and at lower SRT, CS maintained better performance, potentially through a better extracellular polymeric substance management under feast-famine conditions. Full-scale plant energy calculations based on this study results showed that chemically enhanced primary treatment (CEPT), A-stage, CS, primary treatment + CS and CEPT + CS could all lead to energy neutral plants as enough carbon can be redirected to generate the energy needed to support wastewater treatment. Given the superior performance of CS under lower loading or SRT limitation, the best energy gain (200%) could be potentially reached with a combination of CEPT and CS in series to enhance carbon capture up to 68% in combination with mainstream deammonification.

Two-stage partial nitritation-anammox process for high-rate mainstream deammonification.

Increasing information supported that achieving high-rate mainstream deammonification through two-stage partial nitritation (PN)-anammox process should be a better option than through single-stage process. However, direct experimental evidence was limited so far. Herein, a two-stage PN-anammox process was successfully operated for nitrogen removal from low-strength wastewater in winter. Influent shift from synthetic wastewater to actual anaerobically pretreated sewage had little impact on the process performance. Promising nitrogen removal rates (NRRs) of 0.28-0.07kgNm-3d-1 with an average effluent concentration of 5.2mg TNL-1 were achieved for the anaerobically pretreated sewage treatment at 15-7°C. Moreover, nearly all the degradable COD in the pretreated sewage was steadily removed in the first-stage PN reactor, despite the varied influent COD concentrations of 22-78mgL-1 and the operating temperature decrease, suggesting the positive role of the first-stage PN in protecting anammox bacteria. The low temperature seemingly was the only deterministic factor inhibiting the anammox activity, and hence made the anammox reaction to be the rate-limiting step for nitrogen removal in the two-stage PN-anammox process. Unexpectedly, nearly all the anammox bacteria remained active at low temperatures with the process actual anammox activity reached about 76-85% of their maximum potential, implying that higher NRRs would be easily realized through bioaugmentation or enrichment of anammox bacteria. Overall, the present investigation provides direct and valuable information for implementing the two-stage PN-anammox process to treat mainstream municipal wastewater. A control strategy was also proposed to optimize the operation of the two-stage mainstream deammonification process.

Microbial community response to influent shift and lowering temperature in a two-stage mainstream deammonification process

The effects of influent shift from synthetic wastewater to anaerobically pretreated actual sewage coupling with lowering temperature on microbial community of a two-stage partial nitritation (PN)-anammox process were evaluated through high-throughput sequencing. Venn diagrams and Hill numbers showed the significantly increased bacterial diversity both in the PN and anammox reactor. However, taxonomic analysis indicated that outstanding enrichment of heterotrophic bacteria and reduction of autotrophic species mainly occurred in the PN reactor, while nearly all of the dominant bacteria in the anammox reactor only slightly decreased in abundance. Moreover, immigrant bacteria from the PN reactor to the following anammox reactor had no negative effect on the anammox function. These results implied the positive role of the first-stage PN in maintaining the stability of the following anammox community. Nitrosomonas europaea (17.9–52.9%) and one cluster (19.2–27.7%) within Candidatus Brocadia remained as the dominant functional species in the PN and anammox reactor, respectively.

The threshold of influent ammonium concentration for nitrate over-accumulation in a one-stage deammonification system with granular sludge without aeration

Low-strength ammonium is still a challenge for the mainstream deammonification because of nitrate over-accumulation. In this study, the threshold of influent ammonium concentration of one-stage deammonification system with granular sludge was investigated, by stepwise decreasing influent ammonium from high concentrations (280mg/L to 140mg/L) to the low concentration (70mg/L) in 108d at 32°C without aeration. Results showed that, under 70mg/L NH4+-N, ΔNO3−-N/ΔNH4+-N ratio increased to 0.2, deviated from the theoretical value of 0.11, with ammonium and TN removal efficiencies of 91% and 71%, respectively. However, under both high ammonium concentrations (280mg/L and 140mg/L), nitrate production stabilized at only 13%. Chloroflexi, Planctomycetes and Proteobacteria contributed >70% of the communities under all three ammonium concentrations. As influent ammonium decreasing, the relative abundances of bacteria for anammox, aerobic oxidizing and denitrifying decreased, while NOB (nitrite oxidizing bacteria) abundance increased greatly. So 70mg/L was the threshold of influent ammonium concentration for stable deammonification without organic influent. It was the decrease of functional bacteria and overgrowth of NOB that worsen the deammonification performance under low-strength ammonium.

Redesigning C and N mass flows for energy-neutral wastewater treatment by coagulation adsorption enhanced membrane (CAEM)-based pre-concentration process

From the perspective of mass flow, the conventional municipal wastewater treatment based on active sludge process (CAS) removes pollutants by aerobically converting organic carbon (C) into useless CO2 with excess sludge as a by-product and removing nitrogen (N) in the form of N2 by nitrification/denitrification with aeration energy and the carbon source input. To improve sustainability, in this paper, we propose a novel process based on the coagulation adsorption enhanced membrane (CAEM) method, which redesigns the C and N mass flows for energy-neutral wastewater treatment. A pilot-scale operation conducted over two months demonstrated that up to 85.6% chemical oxygen demand (COD) was rejected by CAEM, which could be directed into the anaerobic energy recovery unit in a concentrated form with high biodegradability. Meanwhile, 74.9% nitrogen was kept in the mainstream for the subsequent autotrophic deammonification. Modelling results based on steady-state mass balance and stoichiometric calculations indicated the changes in the C and N mass flows induced by CAEM. The amount of organics (COD) used for energy production increased remarkably compared with that in the CAS process. Combined with mainstream deammonification, this CAEM-based process also avoided the COD consumed by denitrification and heterotrophic oxidation, leading to less aeration and energy consumption (0.22 kWh/t in the CAS process vs. 0.05 kWh/t in the CAEM-based process). The proposed CAEM-based process redesigned a larger C mass flow to the anaerobic energy recovery unit than energy-intensive aerobic oxidation and more N removal by autotrophic deammonification than by heterotrophic deammonification, making it feasible to achieve energy neutrality.

Achieving sustainable and long term NOB repression for shortcut nitrogen removal and mainstream deammonification

Achieving sustainable and long term NOB repression for shortcut nitrogen removal and mainstream deammonification

Achieving Mainstream Deammonification with Biological Phosphorus Removal via Sidestream RAS Fermentation in an A/B Process

Achieving Mainstream Deammonification with Biological Phosphorus Removal via Sidestream RAS Fermentation in an A/B Process

Simulation of dissolved oxygen-and ammonia-based aeration control strategies in a mainstream deammonification biofilm process

Simulation of dissolved oxygen-and ammonia-based aeration control strategies in a mainstream deammonification biofilm process

Model extension, calibration and validation of partial nitritation–anammox process in moving bed biofilm reactor (MBBR) for reject and mainstream wastewater

ABSTRACTIn the paper, the extension of mathematical model of partial nitritation–anammox process in a moving bed biofilm reactor (MBBR) is presented. The model was calibrated with a set of kinetic, stoichiometric and biofilm parameters, whose values were taken from the literature and batch tests. The model was validated with data obtained from: laboratory batch experiments, pilot-scale MBBR for a reject water deammonification operated at Himmerfjärden wastewater treatment and pilot-scale MBBR for mainstream wastewater deammonification at Hammarby Sjöstadsverk research facility, Sweden. Simulations were conducted in AQUASIM software. The proposed, extended model proved to be useful for simulating of partial nitritation/anammox process in biofilm reactor both for reject water and mainstream wastewater at variable substrate concentrations (influent total ammonium–nitrogen concentration of 530 ± 68; 45 ± 2.6 and 38 ± 3 gN/m3 – for reject water – and two cases of mainstream wastewater treatment, respectively), temperature (24 ± 2.8; 15 ± 1.1 and 18 ± 0.5°C), pH (7.8 ± 0.2; 7.3 ± 0.1 and 7.4 ± 0.1) and aeration patterns (continuous aeration and intermittent aeration with variable dissolved oxygen concentrations and length of aerated and anoxic phases). The model can be utilized for optimizing and testing different operational strategies of deammonification process in biofilm systems.

Mainstream Deammonification: Preliminary Experience Employing Granular AOB-Enriched Biomass at Low DO Values

The deammonification process represents one of the most convenient pathways for nitrogen removal from wastewater. A great deal of scientific articles dwells on the treatment of sidestream fluxes, whereas applications to mainstream waters represent a novel field. Among the general challenges of deammonification, one of the most important is the effective selection of ammonia oxidizers (AOB) over nitrite oxidizers (NOB), but also the typical slow start-up periods. In addition to such issues, mainstream deammonification has to face water temperatures and alkalinity reserves lower than those of sidestream fluxes and higher content of organic matter. An attempt was made to tackle such challenges by employing a lab-scale plant; low dissolved oxygen (DO) values (average 0.78 mg/L) and granular AOB-enriched biomass were used in order to address exclusion of nitrite oxidizers. The granules also allowed better biomass retention. The hydraulic retention time (HRT) was established initially at 24 h and later decreased to 12 h, as to possibly enhance the performance of the reactor. After 52 days of operation, Anammox biomass was also inoculated to the reactor. The results showed a maximum nitrogen removal efficiency of 54%. Moreover, little quantities of nitrates were observed throughout the experiment (<5 mg N/L twice, under the limit of quantification the rest of the sampling days), meaning that NOB out-selection techniques worked properly. Retention of biomass was also positively addressed and yielded a final SRT value of 15.6 days. Therefore, the proposed solution for mainstream deammonification was demonstrated to be promising and more research would be necessary to optimize it.

Dual substrate limitation modeling and implications for mainstream deammonification

Substrate limitation occurs frequently in wastewater treatment and knowledge about microbial behavior at limiting conditions is essential for the use of biokinetic models in system design and optimization. Monod kinetics are well-accepted for modeling growth rates when a single substrate is limiting, but several models exist for treating two or more limiting substrates simultaneously. In this study three dual limitation models (multiplicative, minimum, and Bertolazzi) were compared based on experiments using nitrite-oxidizing bacteria (limited by dissolved oxygen and nitrite) and ANaerobic AMMonia-OXidizing bacteria or Aanammox (limited by ammonium and nitrite) within mixed liquor from deammonification pilots. A deterministic likelihood-based parameter estimation followed by Bayesian inference was used to estimate model-specific parameters. The minimum model outperformed the other two by a slight margin in three separate analyses. 1) Parameters estimated using the minimum model were closest to parameters estimated from single limitation batch tests. 2) Among simulations based on each model's own estimated parameters, the minimum model best described the experimental observations. 3) Among simulations based on parameters estimated from single limitation, the minimum model best described the experimental observations. The dual substrate model selected among the three studied can effect a 75% process performance variation based on simulations of a full-scale mainstream deammonification system.

Laboratory-Scale Investigation of Integrated Biological Phosphorus Removal and Mainstream Deammonification at the Terrence J. O’Brien Water Reclamation Plant

Laboratory-Scale Investigation of Integrated Biological Phosphorus Removal and Mainstream Deammonification at the Terrence J. O’Brien Water Reclamation Plant

Uncoupling the solids retention times of flocs and granules in mainstream deammonification: A screen as effective out-selection tool for nitrite oxidizing bacteria

This study focused on a physical separator in the form of a screen to out-select nitrite oxidizing bacteria (NOB) for mainstream sewage treatment. This separation relied on the principle that the NOB prefer to grow in flocs, while anammox bacteria (AnAOB) reside in granules. Two types of screens (vacuum and vibrating) were tested for separating these fractions. The vibrating screen was preferred due to more moderate normal forces and additional tangential forces, better balancing retention efficiency of AnAOB granules (41% of the AnAOB activity) and washout of NOB (92% activity washout). This operation resulted in increased NOB out-selection (AerAOB/NOB ratio of 2.3) and a total nitrogen removal efficiency of 70% at influent COD/N ratio of 1.4. An effluent total nitrogen concentration <10mgN/L was achieved using this novel approach combining biological selection with physical separation, opening up the path towards energy positive sewage treatment.

Achieving Stable Nitritation for Mainstream Deammonification by Combining Free Nitrous Acid-Based Sludge Treatment and Oxygen Limitation.

Stable nitritation is a critical bottleneck for achieving autotrophic nitrogen removal using the energy-saving mainstream deammonification process. Herein we report a new strategy to wash out both the Nitrospira sp. and Nitrobacter sp. from the treatment of domestic-strength wastewater. The strategy combines sludge treatment using free nitrous acid (FNA) with dissolved oxygen (DO) control in the nitritation reactor. Initially, the nitrifying reactor achieved full conversion of NH4+ to NO3−. Then, nitrite accumulation at ~60% was achieved in the reactor when 1/4 of the sludge was treated daily with FNA at 1.82 mg N/L in a side-stream unit for 24 h. Fluorescence in-situ hybridization (FISH) revealed FNA treatment substantially reduced the abundance of nitrite oxidizing bacteria (NOB) (from 23.0 ± 4.3 to 5.3 ± 1.9%), especially that of Nitrospira sp. (from 15.7 ± 3.9 to 0.4 ± 0.1%). Nitrite accumulation increased to ~80% when the DO concentration in the mainstream reactor was reduced from 2.5–3.0 to 0.3–0.8 mg/L. FISH revealed the DO limitation further reduced the abundance of NOB (to 2.1 ± 1.0%), especially that of Nitrobacter sp. (from 4.9 ± 1.2 to 1.8 ± 0.8%). The strategy developed removes a major barrier for deammonification in low-strength domestic wastewater.

Impact of carbon to nitrogen ratio and aeration regime on mainstream deammonification.

While deammonification of high-strength wastewater in the sludge line of sewage treatment plants has become well established, the potential cost savings spur the development of this technology for mainstream applications. This study aimed at identifying the effect of aeration and organic carbon on the deammonification process. Two 10 L sequencing bath reactors with different aeration frequencies were operated at 25°C. Real wastewater effluents from chemically enhanced primary treatment and high-rate activated sludge process were fed into the reactors with biodegradable chemical oxygen demand/nitrogen (bCOD/N) of 2.0 and 0.6, respectively. It was found that shorter aerobic solids retention time (SRT) and higher aeration frequency gave more advantages for aerobic ammonium-oxidizing bacteria (AerAOB) than nitrite oxidizing bacteria (NOB) in the system. From the kinetics study, it is shown that the affinity for oxygen is higher for NOB than for AerAOB, and higher dissolved oxygen set-point could decrease the affinity of both AerAOB and NOB communities. After 514 days of operation, it was concluded that lower organic carbon levels enhanced the activity of anoxic ammonium-oxidizing bacteria (AnAOB) over denitrifiers. As a result, the contribution of AnAOB to nitrogen removal increased from 40 to 70%. Overall, a reasonably good total removal efficiency of 66% was reached under a low bCOD/N ratio of 2.0 after adaptation.