Deammonification for digester supernatant pretreated with thermal hydrolysis: overcoming inhibition through process optimization

Case study: Bioaugmenting the comammox dominated biomass from B-stage to enhance nitrification in A-stage at Blue Plains AWWTP

A comprehensive case study was undertaken at the Blue Plains wastewater treatment plant (WWTP) to explore the bioaugmentation technique of introducing nitrifying sludge into the non-nitrifying stage over the course of two operational years. This innovative approach involved the return of waste activated sludge (WAS) from the biological nutrient removal (BNR) system to enhance the nitrification in the high carbon removal rate system. The complete ammonia oxidizer (comammox) Nitrospira Nitrosa was identified as the main nitrifier in the system. Bioaugmentation was shown to be successful as nitrifiers returned from BNR were able to increase the nitrifying activity of the high carbon removal rate system. There was a positive correlation between returned sludge from the BNR stage and the specific total kjeldahl nitrogen (TKN) removal rate in A stage. The bioaugmentation process resulted in a remarkable threefold increase in the specific TKN removal rate within the A stage. Result suggested that recycling of WAS is a simple technique to bio-augment a low SRT system with nitrifiers and add ammonia oxidation to a previously non-nitrifying stage. The results from this case study hold the potential for applicable implications for other WWTPs that have a similar operational scheme to Blue Plains, allowing them to reuse WAS from the B stage, previously considered waste, to enhance nitrification and thus improving overall nitrogen removal performance. PRACTITIONER POINTS: Comammox identifying as main nitrifier in the B stage. Comammox enriched sludge from B stage successfully bio-augmented the East side of A stage up to threefold. Bioaugmentation of comammox in the West side of A stage was potentially inhibited by the gravity thickened overflow. Sludge returned from B stage to A stage can improve nitrification with a very minor retrofits and short startup times.

Digesters as heat storage: Effects of the digester temperature on the process stability, sludge liquor quality, and the dewaterability

Variation of the digester temperature during the year enables the operation of digesters as seasonal heat storage contributing to a holistic heat management at water resource recovery facilities. Full- and lab-scale process data were conducted to examine the effect of the digester temperature on process stability, sludge liquor quality, and dewaterability. Both full- and lab-scale digesters show a stable anaerobic degradation process with a hydraulic retention time of more than 20 days and organic load rates up to 2.2-kg COD/(m3 ·day) at temperatures between 33 and 53°C. The concentrations of soluble COD and ammonium-nitrogen in the sludge liquor digested at 53°C are 2.6 to 5.8 times and 1.3 times higher, respectively, than in the sludge liquor digested at 37°C. Dewatering tests show an enhancement of the dewaterability but a clear increase in the polymer demand at increased digester temperature. PRACTITIONER POINTS: Digesters can operate as seasonal heat storage within mesophilic and thermophilic temperatures Stable anaerobic degradation process for HRT above 20 days Maintenance of process stability as well as quantity and quality of biogas Increase of soluble COD in sludge liquor at higher temperatures Better dewaterability but higher demand for polymers with increasing temperature.

Sidestream characteristics in water resource recovery facilities: A critical review

This review compiles information on sidestream characteristics that result from anaerobic digestion dewatering (conventional and preceded by a thermal hydrolysis process), biological and primary sludge thickening. The objective is to define a range of concentrations for the different characteristics found in literature and to confront them with the optimal operating conditions of sidestream processes for nutrient treatment or recovery. Each characteristic of sidestream (TSS, VSS, COD, N, P, Al³⁺, Ca²⁺, Cl^-, Fe^2+/3+, Mg²⁺, K⁺, Na⁺, SO₄^2-, heavy metals, micro-pollutants and pathogens) is discussed according to the water resource recovery facility configuration, wastewater characteristics and implications for the recovery of nitrogen and phosphorus based on current published knowledge on the processes implemented at full-scale. The thorough analysis of sidestream characteristics shows that anaerobic digestion sidestreams have the highest ammonium content compared to biological and primary sludge sidestreams. Phosphate content in anaerobic digestion sidestreams depends on the type of applied phosphorus treatment but is also highly dependent on precipitation reactions within the digester. Thermal Hydrolysis Process (THP) mainly impacts COD, N and alkalinity content in anaerobic digestion sidestreams. Surprisingly, the concentration of phosphate is not higher compared to conventional anaerobic digestion, thus offering more attractive recovery possibilities upstream of the digester rather than in sidestreams. All sidestream processes investigated in the present study (struvite, partial nitrification/anammox, ammonia stripping, membranes, bioelectrochemical system, electrodialysis, ion exchange system and algae production) suffer from residual TSS in sidestreams. Above a certain threshold, residual COD and ions can also deteriorate the performance of the process or the purity of the final nutrient-based product. This article also provides a list of characteristics to measure to help in the choice of a specific process.

Nitrogen removal of thermal hydrolysis-anaerobic digestion liquid: A review

Thermal hydrolysis (TH) pretreatment, as an anaerobic digestion (AD) pretreatment, has not only been verified in the laboratory but also frequently employed in actual engineering. However, the properties of anaerobic digestion liquid (ADL), such as high organic matter concentration, high ammonia nitrogen (NH₄⁺-N) concentration, and low carbon-nitrogen ratio (C/N), have posed some difficulties in the follow-up treatment. To address the above issues, the autotrophic nitrogen removal (ANR) process is developed to treat ADL. Due to the NH₄⁺-N, organic materials, toxic and harmful substances in the ADL that might directly impact the activity of functional bacteria, the ADL should be treated before being fed into the ANR process. This paper provided a focused review of the thermal hydrolysis-anaerobic digestion process (TH-ADP) mechanism and the ANR mechanism, summarized the existing difficulties in the treatment of thermal hydrolysis-anaerobic digestion liquid (TH-ADL), assessed the research status thoroughly, and offered the potential solutions to the problems.

Response of mixed community anammox biomass against sulfide, nitrite and recalcitrant carbon in terms of inhibition coefficients and functional gene expressions

Anaerobic ammonium oxidation (anammox) has evolved as a carbon and energy-efficient nitrogen management bioprocess. However, factors such as inhibitory chemicals still challenge the easy operation of this powerful bioprocess. This research systematically evaluated the inhibition kinetics of sulfide, nitrite, and recalcitrant carbon under a genomic framework. The inhibition at the substrate and genetic levels of sulfide, nitrite and recalcitrant carbon on anammox activity was studied using batch tests. Nitrite inhibition of anammox followed substrate inhibition and was best described by the Aiba model with an inhibition coefficient [Formula: see text] of 324.04 mg N/L. Hydrazine synthase (hzsB) gene (anammox biomarker) expression was increased over time when incubated with nitrite up to 400 mg N/L. However, despite having the highest specific nitrite removal (SNR), the expression of hzsB at 100 and 200 mg N/L of nitrite was more muted than in most other samples with lower SNRs. Sulfide severely inhibited anammox activities. The inhibition was fitted with a Monod-based model with a [Formula: see text] of 4.39 mg S/L. At a sulfide concentration of 5 mg/L, the hzsB expression decreased throughout the experiment from its original value at he beginning. Recalcitrant carbon of filtrate from thermal hydrolysis process pretreated anaerobic digester had a minimal effect on maximum specific anammox activity (MSAA), and thus the value of the inhibition coefficient could not be calculated. At the same time, its hzsB expression profile was similar to that in the control. Resiliency and recovery tests indicated that the inhibition of nitrite (up to 400 mg N/L) and recalcitrant carbon (in 100% filtrate) were reversible. About 32% of MSAA was recovered after repeated exposures to sulfide at 2.5 mg/L, while at 5 mg/L, the inhibition was irreversible. Findings from this study will be helpful for the successful design and implementation of anammox in full-scale applications.

Integrated thermal hydrolysis pretreated anaerobic digestion centrate and municipal wastewater treatment via partial nitritation/anammox process: A promising approach to alleviate inhibitory effects and enhance nitrogen removal

Two-stage Partial nitritation/Anammox (PN/A) was firstly performed for recalcitrant organics (RO)-rich thermal hydrolysis pretreated anaerobic digestion (THP-AD) centrate treatment with municipal wastewater (MW) as co-substrate. Results indicated the inhibitory effects of RO was alleviated and high nitrate issue in PN/A effluent was addressed by cotreatment strategy. Stable PN with nitrite accumulation ratio of 95% and N removal efficiency of 97.1% were well maintained at MW of 80%. Nevertheless, nitrate accumulation and anammox activity loss were observed with lowering MW proportion owing to the weakened denitrification activity and aggravated inhibitory effect. Microbial analysis revealed Nitrosomonas was the major ammonium oxidizing bacteria and the ideal PN performance was due to the effective out-selection of nitrite oxidizing bacteria. Candidatus Kuenenia was identified as the primary bacteria for nitrogen removal (82.7%), and the controlled abundance of heterotrophic denitrifiers in anammox system ensured the enhanced nitrogen removal regardless of high COD loading from THP-AD centrate.

Mitigation of inhibitory effect of THP-AD centrate on partial nitritation and anammox: Insights into ozone pretreatment

Anaerobic digestion centrate produced from thermal hydrolysis pretreated sludge (THP-AD centrate) has serious inhibitory effect on ammonium oxidizing bacteria (AOB) and anammox bacteria. This imposes huge challenge to employ partial nitritation/anammox (PN/A) process to treat THP-AD centrate. This study, for the first time, presented an effective strategy, ozone pretreatment, to alleviate such inhibitory effect. The activities of AOB and anammox bacteria increased with increasing ozone dosage, which were likely related to the transformation of organic compounds including humic acid-like and fulvic acid-like substances as well as high molecular weight (HMW) protein. Long-term operation of PN/A system further demonstrated the improved performance in term of nitrogen removal, organics degradation as well as sludge settleability and effluent solids. Nitrogen removal rate (NRR) of 0.64 Kg N/m³/d was achieved (1.38 g O₃/ g COD), which was 42.2% higher compared to treating untreated THP-AD centrate. Effluent nitrate, the by-product of PN/A process, was reduced by 39.7% despite of its release in ozonation. This was due to the enhanced denitrification activity, humic acid-like and fulvic acid-like substances as well as HMW protein were significantly reduced. Overall, this study provides a promising method to improve PN/A performance and final effluent quality when treating organic-rich THP-AD centrate.

Effects of sludge thermal hydrolysis pretreatment on anaerobic digestion and downstream processes: mechanism, challenges and solutions

Thermal hydrolysis pretreatment (THP), as a step prior to sludge anaerobic digestion (AD), is widely applied due to its effectiveness in enhancing organic solids hydrolysis and subsequent biogas productivity. However, THP also induces a series of problems including formation of refractory compounds in THP cylinder, high residual ammonia and organic in the AD centrate, inhibition on downstream nitrogen removal process and reduction in UV-disinfection effectiveness during post-treatment. More attention should be paid on how to mitigate these negative effects. Despite intensive studies were carried out to reduce refractory compounds formation and enhance biological performance, there is limited effort to discuss the solutions to tackle the THP associated problems in a holistic manner. This paper summarizes the solutions developed to date and analyzes their technology readiness to assess application potential in full-scale settings. The content highlights the limitations of THP and proposes potential solutions to address the technological challenges.

Challenges of THP-AD centrate treatment using partial nitritation-anammox (PN/A) - inhibition, biomass washout, low alkalinity, recalcitrant and more

The centrate produced from a thermal hydrolysis pretreatment coupled anaerobic digestion (THP-AD) system is generally characterized by high concentrations of ammonium and recalcitrant organics. In this study, a cost-effective partial nitritation-anammox (PN/A) process was developed to evaluate the potential challenges in THP-AD centrate treatment. The results show ammonium oxidizing bacteria (AOB) and anammox bacteria were seriously inhibited by THP-AD centrate, while long-term acclimation together with aeration optimization can mitigate such inhibition. A nitrogen removal rate (NRR) of 0.55 kg N/m³/d was obtained and maintained with 60% THP-AD centrate as feed. However, 100% THP-AD centrate caused sludge wash-out from PN reactor due to excessive polymer and high solids in influent. The alkalinity deficit also reduced the AOB activity. Moreover, anammox activity and overall NRR also declined (to 0.37 kg N/m³/d). The organics transformation mainly occurred in PN reactor with very low removal efficiency due to their recalcitrant characteristics. The humic acid-like, fulvic acid-like substances and building blocks were revealed as the major organic compounds in THP-AD centrate (51.5-53.8% TOC), which likely contributed to the recalcitrant. Nitrosomonas and Candidatus Brocadia were the major AOB and anammox bacteria in the PN and anammox reactors respectively. With the increased THP-AD centrate proportion in the feed, the abundance of both population declined. Interestingly, Denitratisoma, being the major denitrifying bacteria in anammox reactor, had relatively stable abundance (7.0-7.9%) when THP-AD centrate was improved from 3 and 100%, suggesting the inhibition on anammox bacteria was not due to the overgrowth of denitrifying microorganism despite the high organics loading rate. Overall, this study provides a guide to develop the energy-saving PN/A process for THP-AD centrate treatment by pointing out potential challenges and mitigating strategies.

Application of Anammox-Based Processes in Urban WWTPs: Are We on the Right Track?

The application of partial nitritation and anammox processes (PN/A) to remove nitrogen can improve the energy efficiency of wastewater treatment plants (WWTPs) as well as diminish their operational costs. However, there are still several limitations that are preventing the widespread application of PN/A processes in urban WWTPs such as: (a) the loss of performance stability of the PN/A units operated at the sludge line, when the sludge is thermally pretreated to increase biogas production; (b) the proliferation of nitrite-oxidizing bacteria (NOB) in the mainstream; and (c) the maintenance of a suitable effluent quality in the mainstream. In this work, different operational strategies to overcome these limitations were modelled and analyzed. In WWTPs whose sludge is thermically hydrolyzed, the implementation of an anerobic treatment before the PN/A unit is the best alternative, from an economic point of view, to maintain the stable performance of this unit. In order to apply the PN/A process in the mainstream, the growth of ammonia-oxidizing bacteria (AOB) should be promoted in the sludge line by supplying extra sludge to the anaerobic digesters. The AOB generated would be applied to the water line to partially oxidize ammonia, and the anammox process would then be carried out. Excess nitrate generated by anammox bacteria and/or NOB can be removed by recycling a fraction of the WWTP effluent to the biological reactor to promote its denitrification.

Ammonia removal from thermal hydrolysis dewatering liquors via three different deammonification technologies

The benefits of deammonification to remove nitrogen from sidestreams, i.e., sludge dewatering liquors, in municipal wastewater treatment plants are well accepted. The ammonia removal from dewatering liquors originated from thermal hydrolysis/anaerobic digestion (THP/AD) are deemed challenging. Many different commercial technologies have been applied to remove ammonia from sidestreams, varying in reactor design, biomass growth form and instrumentation and control strategy. Four technologies were tested (a deammonification suspended sludge sequencing batch reactor (S-SBR), a deammonification moving bed biofilm reactor (MEDIA), a deammonification granular sludge sequencing batch reactor (G-SBR), and a nitrification suspended sludge sequencing batch reactor (N-SBR)). All technologies relied on distinct control strategies that actuated on the feed flow leading to a range of different ammonia loading rates. Periods of poor performance were displayed by all technologies and related to imbalances in the chain of deammonification reactions subsequently effecting both load and removal. The S-SBR was most robust, not presenting these imbalances. The S-SBR and G-SBR presented the highest nitrogen removal rates (NRR) of 0.58 and 0.56 kg N m^-3 d^-1, respectively. The MEDIA and the N-SBR presented an NRR of 0.17 and 0.07 kg N m^-3 d^-1, respectively. This study demonstrated stable ammonia removal from THP/AD dewatering liquors and did not observe toxicity in the nitrogen removal technologies tested. It was identified that instrumentation and control strategy was the main contributor that enabled higher stability and NRR. Overall, this study provides support in selecting a suitable biological nitrogen removal technology for the treatment of sludge dewatering liquors from THP/AD.

Is the ammonia stripping pre-treatment suitable for the nitrogen removal via partial nitritation-anammox of OFMSW digestate?

Treating the organic fraction of municipal solid waste (OFMSW) can be performed by coupling the anaerobic digestion (AD) and partial nitritation-anammox (PN-AMX) processes for organic matter and nitrogen removal, respectively. Besides, an ammonia stripping (AS) step before the AD benefit the removal of organic matter. In the present study, the operation of two PN-AMX sequencing batch reactors with and without AS pre-treated OFMSW digestate (AS-SBR and nAS-SBR, respectively) was assessed. The specific anammox activity decreased by 90 % for increasing proportions of fed OFMSW in both cases, indicating no differences over the anammox activity whether the AS pre-treatment is implemented or not. For 100 % OFMSW proportion, the AS-SBR achieved better effluent quality than the nAS-SBR (127 ± 88 vs. 1050 ± 23 mg N/L) but with lower nitrogen removal rates (58 ± 8 vs. 687 ± 32 g N/(L·d)). Still, the latter required successive re-inoculations to obtain higher removal rates. Changes in the microbial communities were mainly correlated to sCOD/N ratios in the OFMSW, being Candidatus Brocadia the dominant anamnmox species. The results proved the AS to be a suitable pre-treatment, despite the higher sCOD/N ratios in the OFMSW digestate, achieving good synergy between the PN-AMX and heterotrophic denitrification processes.

Robust Nitritation of Anaerobic Digester Centrate Using Dual Stressors and Timed Alkali Additions

Nitrogen is commonly removed from wastewater by nitrification to nitrate followed by nitrate reduction to N₂. Shortcut N removal saves energy by limiting ammonia oxidation to nitrite, but nitrite accumulation can be unstable. We hypothesized that repeated short-term exposures of ammonia-oxidizing communities to free ammonia (FA) and free nitrous acid (FNA) would stabilize nitritation by selecting against nitrite-oxidizing bacteria (NOB). Accordingly, we evaluated ammonium oxidation of anaerobic digester centrate in two bench-scale sequencing batch reactors (SBRs), seeded with the same inoculum and operated identically but with differing pH-control strategies. A single stressor SBR (SS/SBR) using pH set-point control produced HNO₃, while a dual stressor SBR (DS/SBR) using timed alkalinity addition (TAA) produced HNO₂ (ammonium removal efficiency of 97 ± 2%; nitrite accumulation ratio of 98 ± 1%). The TAA protocol was developed during an adaptation period with continuous pH monitoring. After adaptation, automated TAA enabled stable nitritation without set-point control. In the SS/SBR, repeatedly exposing the community to FA (8-10 h/exposure, one exposure/cycle) selected for FA-tolerant ammonia-oxidizing bacteria (Nitrosomonas sp. NM107) and NOB (Nitrobacter sp.). In the DS/SBR, repeatedly exposing the community to FA (2-4 h/exposure, three exposures/cycle) and FNA (4-6 h/exposure, two exposures/cycle) selected for FA- and FNA-resistant AOB (Nitrosomonas IWT514) and against NOB, stabilizing nitritation.

Robust Nitritation Sustained by Acid-Tolerant Ammonia-Oxidizing Bacteria

Oxidation of ammonium to nitrite rather than nitrate, i.e., nitritation, is critical for autotrophic nitrogen removal. This study demonstrates a robust nitritation process in treating low-strength wastewater, obtained from a mixture of real mainstream sewage with sidestream anaerobic digestion liquor. This is achieved through cultivating acid-tolerant ammonia-oxidizing bacteria (AOB) in a laboratory nitrifying bioreactor at pH 4.5-5.0. It was shown that nitrite accumulation with a high NO₂^-/(NO₂^- + NO₃^-) ratio of 95 ± 5% was stably maintained for more than 300 days, and the obtained volumetric NH₄⁺ removal rate (i.e., 188 ± 14 mg N L^-1 d^-1) was practically useful. 16S rRNA gene sequencing analyses indicated the dominance of new AOB, "Candidatus Nitrosoglobus," in the nitrifying guild (i.e., 1.90 ± 0.08% in the total community), with the disappearance of typical activated sludge nitrifying microorganisms, including Nitrosomonas, Nitrospira, and Nitrobacter. This is the first identification of Ca. Nitrosoglobus as key ammonia oxidizers in a wastewater treatment system. It was found that Ca. Nitrosoglobus can tolerate low pH (<5.0), and free nitrous acid (FNA) at levels that inhibit AOB and nitrite-oxidizing bacteria (NOB) commonly found in wastewater treatment processes. The in situ inhibition of NOB leads to accumulation of nitrite (NO₂^-), which along with protons (H⁺) also produced in ammonium oxidation generates and sustains FNA at 3.0 ± 1.4 mg HNO₂-N L^-1. As such, robust PN was achieved under acidic conditions, with a complete absence of NOB. Compared to previous nitritation systems, this acidic nitritation process is featured by a higher nitric oxide (NO) but a lower nitrous oxide (N₂O) emission level, with the emission factors estimated at 1.57 ± 0.08 and 0.57 ± 0.03%, respectively, of influent ammonium nitrogen load.

Towards mainstream deammonification: Comprehensive review on potential mainstream applications and developed sidestream technologies

Deammonification (partial nitritation-anammox) process is a favorable and innovative process, for treatment of nitrogen-rich wastewater due to decreased oxygen and carbon requirements at very high nitrogen loadings. The bacterial groups responsible for this process are anaerobic ammonium oxidation (anammox) bacteria in symbiosis with ammonium oxidizing bacteria (AOB) which have an active role in development of nitrogen removal biotechnology in wastewater. Development and operation of sidestream deammonification processes has augmented since the initial full-scale systems, yet there are several aspects which mandate additional investigation and deliberation by the practitioners, to reach the operating perspective, set for the facility. Process technologies for treatment of streams with high ammonia concentrations continue to emerge, correspondingly, further investigation towards feasibility of applying the deammonification concept, in the mainstream treatment process is required. Mainstream deammonification can potentially improve the process of achieving more sustainable and energy-neutral municipal wastewater treatment, however feasible applications are not accessible yet. This critical review focuses on a comprehensive assessment of the worldwide lab-scale, pilot-scale and full-scale sidestream applications as well as identifying the major issues obstructing the implementation of mainstream processes, in addition to the designs, operational factors and technology advancements at both novel and/or conventional levels. This review aims to provide a novel and broad overview of the status and challenges of both sidestream and mainstream deammonification technologies and installations worldwide to assess the global perspectives on deammonification research in the recent years. The different configurations, crucial factors and overall trends in the development of deammonification research are discussed and conclusively, the future needs for feasible applications are critically reviewed.

Evaluation of a Full-Scale Suspended Sludge Deammonification Technology Coupled with an Hydrocyclone to Treat Thermal Hydrolysis Dewatering Liquors

Suspended sludge deammonification technologies are frequently applied for sidestream ammonia removal from dewatering liquors resulting from a thermal hydrolysis anaerobic digestion (THP/AD) process. This study aimed at optimizing the operation, evaluate the performance and stability of a full-scale suspended sludge continuous stirred tank reactor (S-CSTR) with a hydrocyclone for anaerobic ammonia oxidizing bacteria (AMX) biomass separation. The S-CSTR operated at a range of nitrogen loading rates of 0.08–0.39 kg N m−3 d−1 displaying nitrogen removal efficiencies of 75–89%. The hydrocyclone was responsible for retaining 56–83% of the AMX biomass and the washout of ammonia oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was two times greater than AMX. The solid retention time (SRT) impacted on NOB washout, that ranged from 0.02–0.07 d−1. Additionally, it was demonstrated that an SRT of 11–13 d was adequate to wash-out NOB. Microbiome analysis revealed a higher AMX abundance (Candidatus scalindua) in the reactor through the action of the hydrocyclone. Overall, this study established the optimal operational envelope for deammonification from THP/AD dewatering liquors and the role of the hydrocyclone towards maintaining AMX in the S-CSTR and hence obtain process stability.

Critical Analysis of Biomass Retention Strategies in Mainstream and Sidestream ANAMMOX-Mediated Nitrogen Removal Systems

ANAMMOX (anaerobic ammonium oxidation) represents an energy-efficient process for biological nitrogen removal, particularly from wastewater streams with low chemical oxygen demand (COD) to nitrogen (C/N) ratios. Its widespread application, however, is still hampered by a lack of access to biomass-enriched with ANAMMOX bacteria (AMX), slow growth rates of AMX, and their sensitivity to inhibition. Although the coupling of ANAMMOX processes with partial nitrification is already widespread, especially for sidestream treatment, maintaining a functional population density of AMX remains a challenge in these systems. Therefore, strategies that maximize retention of AMX-rich biomass are essential to promote process stability. This paper reviews existing methods of biomass retention in ANAMMOX-mediated systems, focusing on (i) granulation; (ii) biofilm formation on carrier materials; (iii) gel entrapment; and (iv) membrane technology in mainstream and sidestream systems. In addition, the microbial ecology of different ANAMMOX-mediated systems is reviewed.

The occurrence and role of Nitrospira in nitrogen removal systems

Application of the modern microbial techniques changed the paradigm about the microorganisms performing nitrification. Numerous investigations recognized representatives of the genus Nitrospira as a key and predominant nitrite-oxidizing bacteria in biological nutrient removal systems, especially under low dissolved oxygen and substrate conditions. The recent discovery of Nitrospira capable of performing complete ammonia oxidation (comammox) raised a fundamental question about the actual role of Nitrospira in both nitrification steps. This review summarizes the current knowledge about morphological, physiological and genetic characteristics of the canonical and comammox Nitrospira. Potential implications of comammox for the functional aspects of nitrogen removal have been highlighted. The complex meta-analysis of literature data was applied to identify specific individual variables and their combined interactions on the Nitrospira abundance. In addition to dissolved oxygen and influent nitrogen concentrations, temperature and pH may play an important role in enhancing or suppressing the Nitrospira activity.

Impacts of feed dilution and lower solids retention time on performance of thermal hydrolysis/anaerobic digestion

The goal of this study was to evaluate using feed dilution/solids retention time (SRT) control to manage potential ammonia inhibition in highly loaded anaerobic digesters after thermal hydrolysis. The study compared three digesters operated at the same target volatile solids (VS) loading rate of 5.5 kg VS/d-m³ , but at different feed concentrations resulting in SRTs of 10, 15, and 18 days. Lowering the feed concentration decreased the digester total ammonia nitrogen concentrations which averaged 1,580, 2,610, and 3,080 mg NH 4 + -N/L for the 10-, 15-, and 18-day digesters. The VS reduction and methane yields were equivalent for the 15- and 18-day digesters and about 4% lower for the 10-day digester. Ammonia inhibition of the 18-day digester occurred early in the study, but the system acclimated over time. Feed dilution reduced the viscosity and the potential for volume expansion due to gas holdup and foaming. PRACTIONER POINTS: Feed dilution reduces digester ammonia concentrations and inhibition potential without sacrificing digester performance at lower SRTs. Feed dilution greatly reduces digester viscosity and associated issues with digester volume expansion due to gas holdup and foaming. Operating at the lower SRT does not impact cake solids after dewatering and substantially decreases polymer demand for conditioning.

Inhibition of anammox by sludge thermal hydrolysis and metagenomic insights

Anaerobic ammonium oxidation (anammox) would be a feasible treatment method for thermal hydrolysis processed sidestream (THPS). Short-term study revealed that the 1/20 diluted THPS caused a 28% decrease of specific anammox activity. The MBR achieved a volumetric nitrogen loading rate of 3.64 kg/(m³·d) with undiluted regular sidestream (RS) fed, while the reactor crashed with 70% diluted THPS as feed. The ratio of produced NO₃^--N to consumed NH₄⁺-N also decreased compared with RS feeding. Candidatus brocadia was the major anammox bacteria species with the average abundance of 33.3% (synthetic wastewater), 6.42% (RS) and 2.51% (THPS). The abundances of metagenome bins for dissimilatory nitrate reduction to ammonium (DNRA) increased in the system with THPS compared with RS. The reason for the inhibition of anammox by THPS could be the high content of organic carbon in THPS, which caused the over-population of heterotrophic bacteria, i.e. DNRA bacteria, leading to anammox bacteria washout.

Approaches and processes for ammonia removal from side-streams of municipal effluent treatment plants

The main objective of this review article is to provide a comprehensive view on various conventional and emerging side-stream ammonia removal treatment options for municipal wastewater treatment plants (WWTPs). Optimization of wastewater treatment facilities from an energy and emissions stand-point necessitates consideration of the impact of the various internal side-streams. Side-streams from anaerobic sludge digesters in particular have the potential to be a significant ammonium load to the mainstream treatment process. However, the literature suggests that managing side-streams through their treatment in the mainstream process is not the most energy efficient approach, nor does it allow for practical recovery of nutrients. Furthermore, as effluent criteria become more stringent in some jurisdictions and sludge hydrolysis pre-treatment for digesters more common, an understanding of treatment options for ammonia in digester supernatant becomes more important. Given these considerations, a variety of side-stream treatment processes described in the literature are reviewed.

Supernatant organics from anaerobic digestion after thermal hydrolysis cause direct and/or diffusional activity loss for nitritation and anammox

Treatment of sewage sludge with a thermal hydrolysis process (THP) followed by anaerobic digestion (AD) enables to boost biogas production and minimize residual sludge volumes. However, the reject water can cause inhibition to aerobic and anoxic ammonium-oxidizing bacteria (AerAOB & AnAOB), the two key microbial groups involved in the deammonification process. Firstly, a detailed investigation elucidated the impact of different organic fractions present in THP-AD return liquor on AerAOB and AnAOB activity. For AnAOB, soluble compounds linked to THP conditions and AD performance caused the main inhibition. Direct inhibition by dissolved organics was also observed for AerAOB, but could be overcome by treating the filtrate with extended aerobic or anaerobic incubation or with activated carbon. AerAOB additionally suffered from particulate and colloidal organics limiting the diffusion of substrates. This was resolved by improving the dewatering process through an optimized flocculant polymer dose and/or addition of coagulant polymer to better capture the large colloidal fraction, especially in case of unstable AD performance. Secondly, a new inhibition model for AerAOB included diffusion-limiting compounds based on the porter-equation, and achieved the best fit with the experimental data, highlighting that AerAOB were highly sensitive to large colloids. Overall, this paper for the first time provides separate identification of organic fractions within THP-AD filtrate causing differential types of inhibition. Moreover, it highlights the combined effect of the performance of THP, AD and dewatering on the downstream autotrophic nitrogen removal kinetics.

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.

The transformation from anammox granules to deammonification granules in micro-aerobic system by facilitating indigenous ammonia oxidizing bacteria

Granular deammonification process is a good way to retain aerobic and anaerobic ammonia oxidizing bacteria (AOB and anammox bacteria) and exhaust flocculent nitrite oxidizing bacteria (NOB). In this study, to facilitate indigenous AOB growth on anammox granules, by stepwise reducing influent nitrite, anammox granules were effectively transformed into deammonification granules in a micro-aerobic EGSB in 100 days. Total nitrogen removal efficiency of 90% and nitrogen removal rate of 2.3 g N/L/d were reached at stable deammonification stage. High influent FA and limited oxygen supply contributed suppression for Nitrospira-like NOB. In transition stages, Proteobacteria and Chloroflexi were always dominated. Anammox abundance decreased, while AOB abundance grew fast. Anammox bacteria and AOB were dominated by Brocadia fulgida and Nitrosomonas europaea, respectively. Denitrification activity and bacteria existed although without influent organic. The final AOB abundance was about 4.55-13.8 times more than anammox bacteria abundance, with almost equal potential activities.

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.