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

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.

A novel strategy for integration of oxidation within advanced thermal hydrolysis of sludge

Due to its environmental impact, the growing production of sewage sludge is a prime concern for wastewater treatment plants. In this study, advanced thermal hydrolysis, the combination of thermal hydrolysis and oxygen, was examined to enhance biogas production and overcome the disadvantages of thermal hydrolysis, including sludge colour, high energy consumption, and high level of ammonia concentration in the treated sludge. A mixture of 55 % primary sludge and 45 % waste activated sludge was pre-treated using advanced thermal hydrolysis at 100, 115, 130, and 145 °C with a processing time varied from 5 to 30 min and oxygen pressure from 10 to 30 bar before anaerobic digestion. Advanced thermal hydrolysis process at 145 °C 15 min 20 bar O₂ is the condition that provided the highest biogas yield (439.6 mL/g VS added). At this treatment condition, the concentration of ammonia nitrogen and propionic acid in the treated sludge was sufficiently low (approximately 302 mg/L and 559.7 mg/L, respectively) to minimise adverse effects on anaerobic digestion.

Advances in nitrogen removal and recovery technologies from reject water: Economic and environmental perspectives

This review critically assesses nitrogen removal technologies applied in the reject water treatment, across different stages of technological development, with a focus on their economic and environmental impacts. The prevalent use of biological processes raises concerns due to potential environmental impacts caused by N2O emissions. However, partial nitritation-anaerobic ammonium oxidation demonstrated economic benefits and the potential for positive environmental outcomes when properly operated and controlled. Furthermore, reject water, in many cases, provides sufficient nitrogen concentrations for nitrogen recovery processes, such as ammonia stripping, substituting production of industrial fertilizers and contributing to a circular economy. Nonetheless, their financial competitiveness is subject to various conditions, including the nitrogen concentration or reject water flow. As the environmental benefits of bioprocesses and economic benefits of nitrogen recovery processes may vary, it is crucial to further optimize both and investigate novel promising technologies such as electrochemical systems, denitrifying anaerobic methane oxidation or direct ammonia oxidation.

Simultaneous anaerobic carbon and nitrogen removal from primary municipal wastewater with hydrogel encapsulated anaerobic digestion sludge and AOA-anammox coated hollow fiber membrane

In this study, a one-stage continuous-flow membrane-hydrogel reactor integrating both partial nitritation-anammox (PN-anammox) and anaerobic digestion (AD) was designed and operated for simultaneous autotrophic nitrogen (N) and anaerobic carbon (C) removal from mainstream municipal wastewater. In the reactor, a synthetic biofilm consisting of anammox biomass and pure culture ammonia oxidizing archaea (AOA) were coated onto and maintained on a counter-diffusion hollow fiber membrane to autotrophically remove nitrogen. Anaerobic digestion sludge was encapsulated in hydrogel beads and placed in the reactor to anaerobically remove COD. During the pilot operation at three operating temperature (25, 16 and 10 °C), the membrane-hydrogel reactor demonstrated stable anaerobic COD removal (76.2 ± 15.5 %) and membrane fouling was successfully suppressed allowing a relatively stable PN-anammox process. The reactor demonstrated good nitrogen removal efficiency, with an overall removal efficiency of 95.8 ± 5.0 % for NH₄⁺-N and 78.9 ± 13.2 % for total inorganic nitrogen (TIN) during the entire pilot operation. Reducing the temperature to 10 °C caused a temporary reduction in nitrogen removal performance and abundances of AOA and anammox. However, the reactor and microbes demonstrated the ability to adapt to the low temperature spontaneously with recovered nitrogen removal performance and microbial abundances. Methanogens in hydrogel beads and AOA and anammox on the membrane were observed in the reactor by qPCR and 16S sequencing across all operational temperatures.

Insights on pretreatment technologies for partial nitrification/anammox processes: A critical review and future perspectives

For almost 20 years, partial nitrification-anammox (PN/A) has been the subject of intensive study and development. Pretreatment of wastewater for PN/A is crucial because the inhibitory substances in the influent may reduce the performance of PN/A. In this review, the current PN/A pretreatment technologies are comprehensively summarized. The selection of pretreatment technology for PN/A depending on the source of the wastewater and its main characteristics (high-strength wastewater or municipal wastewater, organic matters, suspended solids). Comparison of pretreatment technologies through multiple perspectives including wastewater characteristics, the objectives of the wastewater treatment (treating requirement, energy and resource recovery demand), reactor configuration of PN/A. Based on the discussion, two integrated processes, HRAS + one-stage PN/A and advanced AD + two-stage PN/A, are recommended as the preferred processes for treating municipal wastewater and wastewater with a high-strength ammonium, respectively. This review aims to provide guidance for future research and development of PN/A.

Critical role of extracellular DNA in the establishment and maintenance of anammox biofilms

Anaerobic ammonium oxidation (anammox) has been widely used for the sustainable removal of nitrogen from wastewater. Extracellular DNA (exDNA), as one of the main components of biofilms, not only determines the initial formation process, but also allows the three-dimensional structure to be maintained. Since the effects of exDNA on anammox biofilm formation are still poorly understood, this study elucidated the effects of exDNA on different stages of anammox biofilm establishment and maintenance under static conditions and its mechanism. The results revealed that exDNA mainly affected the maintenance stage of anammox biofilm formation. Compared with the absence of exDNA, nitrogen removal efficiency in the presence of exDNA was 6.17 % higher; the number of bacteria cells attached to the carrier was 2.23 times that in the absence of exDNA. The spatiotemporal distribution of bacteria was revealed by fluorescence in situ hybridization. After 30 days, the relative abundances of anammox in biofilms were 6.19 % and 0.4 % in the presence and absence of exDNA, respectively, indicating its positive role in anammox bacteria (AnAOB) adhesion and biofilm formation. The presence of exDNA in extracellular polymeric substances (EPS) promotes the synthesis of proteins and soluble microbial products. According to the extended Derjaguin-Landau-Verwey-Overbeek (X - DLVO) theory, the presence of exDNA also reduced the Lewis acid-base interaction energy and created favorable thermodynamic conditions for AnAOB adhesion. These findings advance our understanding of the role of exDNA in anammox-mediated biofilm formation and offer insights into the mechanism of exDNA in the establishment and maintenance stages.

Colloidal iron species driven enhanced H2O2 decomposition into hydroxyl radicals for efficient removal of methylene blue from water

Colloids are wide-spread in natural waters and colloid-facilitated transport via adsorption was established as the most important mechanism for the mobilization of aqueous contaminants. This study reports another possible, but reasonable, role of colloids for the contaminants driven by redox reactions. Under the same conditions (pH 6.0, 0.3 ml 30% H₂O₂, and 25 °C), the degradation efficiencies of methylene blue (MB) at 240 min over Fe colloid, Fe ion, Fe oxide and Fe(OH)₃ were 95.38%, 42.66%, 4.42% and 9.40%. We suggested that, Fe colloid can promote the H₂O₂ based in-situ chemical oxidation process (ISCO) compared with other iron species such as Fe(Ⅲ) ion, Fe oxide and Fe(OH)₃ in natural water. Furthermore, the MB removal via adsorption by Fe colloid was only 1.74% at 240 min. Hence, the occurrence, behavior and fate of MB in Fe colloid containing natural water system mainly depends on the reduction-oxidation rather than adsorption-desorption process. Based on the mass balance of colloidal iron species and characterization of iron configurations distribution, Fe oligomers were the active and dominant components for Fe colloid-driven enhanced H₂O₂ activation among three types of Fe species. The quick and steady conversion of Fe(III) to Fe(II) was proven to be reason why Fe colloid can efficiently react with H₂O₂ to produce hydroxyl radicals.

Effect of thermal hydrolyzed sludge filtrate as an external carbon source on biological nutrient removal performance of A2/O system

Thermal hydrolyzed sludge filtrate (THSF) rich in biodegradable organics could be a promising external carbon source for biological nutrient removal (BNR). The use of THSF can effectively reduce wastewater treatment plants operating costs and recover bioresources and bioenergy from the waste activated sludge. In this study, the effect of THSF on the BNR process was investigated using a lab-scale anaerobic/anoxic/oxic (A²/O) system. Total nitrogen (TN) and total phosphorus (TP) removal efficiencies of 74.26 ± 3.36% and 92.20 ± 3.13% at a 0.3% dosing ratio were achieved, respectively. Moreover, 20.42% of the chemical oxygen demand (COD) contained in THSF contributed to denitrification, enhancing nitrogen removal efficiency from 55.30 to 74.26%. However, the effluent COD increased by approximately 36.80%, due to 18.39% of the COD contained in THSF discharged with effluent. In addition, the maximum denitrification rate was approximately 16.01 mg N g VSS^-1 h^-1, while the nitrification rate was not significantly affected by THSF. Nitrosomonas, a common chemoautotrophic nitrifier, was not detected after the introduction of THSF. The aerobic denitrifier Rubellimicrobium was stimulated, and its relative abundance increased from 0.16 to 3.03%. Moreover, the relative abundance of Dechloromonas was 3.93%, indicating that the denitrifying phosphorus removal process was enhanced. This study proposes an engineering application route of THSF, and the chemical phosphate removal pretreatment might be a means to suppress the phosphate recirculation.

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.

Method development for the identification, extraction and characterization of melanoidins in thermal hydrolyzed sludge

Melanoidins, the brown late-stage Maillard reaction products, are responsible for color development and refractoriness in thermal hydrolyzed sludge (THS), causing negative effects on wastewater treatment. This study aimed to develop a methodology for the identification, isolation and preliminary characterization of the THS melanoidins. After thermal hydrolysis, the formation of melanoidins were confirmed by physicochemical indicators and excitation-emission matrix fluorescence analysis. The macroporous resin adsorption method was adopted to successfully extract melanoidins from THS with high recovery and selectivity. The main chemical components of the extracted melanoidins were carbohydrate (23.1 %), protein (43.8 %) and phenol (13.7 %), and the C/N was 4.5. In addition, furans, alcohols and sulfur-containing volatile substances were detected by pyrolysis-gas chromatography-mass spectrometry. Fourier transform infrared spectroscopy determined that functional groups such as CO, CN, NH, C-O-C, amide I and phenyl were present in the structure of THS melanoidins, and nuclear magnetic resonance spectroscopy indicated the formation of heterocyclic macromolecular structures. Their formation pathways were speculated to involve the cross-linkage of low-molecular-weight components (e.g. proteins, Amadori and Schiff base compounds) and the polymerization of heterocyclic units (e.g. furans, pyroles and pyrazines). The above results clarify the fundamental characteristics of the melanoidins formed during sludge thermal hydrolysis and will help improve subsequent research on melanoidins control.

Biogas purification and ammonia load reduction in sewage treatment by two-stage down-flow hanging sponge reactor

In this study, a two-stage down-flow hanging sponge (TSDHS) reactor was used as biotrickling filter for biogas desulfurization by utilizing the anaerobic digester supernatant (ADS) of sewage sludge of an activated sludge process (ASP). The reactor comprises a closed-type first-stage down-flow hanging sponge (1st DHS) and an open-type second-stage down-flow hanging sponge (2nd DHS) reactors. In the 1st DHS, hydrogen sulfide in biogas was dissolved into the ADS, and then it was oxidized into elemental sulfur and sulfate by microbe using dissolved oxygen and nitrite in the ADS. More than 99.9 % of hydrogen sulfide was removed within 400 s of empty bed residence time, and >50 % of removed hydrogen sulfide was oxidized into elemental sulfur and accumulated at the surface of the sponge carrier in the 1st DHS. The 1st DHS effluent was fed into the 2nd DHS for nitrogen removal via nitrification and sulfur-based denitrification with the recirculation of the 2nd DHS effluent under nonaeration condition. In the 2nd DHS, 36.8 % of ammonia and 5.3 % of total inorganic nitrogen were removed. Sulfurimonas and Halothiobacillus were increased and contributed to the sulfur-based denitrification as well as the accumulation of elemental sulfur in the 1st DHS, respectively. In the 2nd DHS, Nitrosococcus, Nitrobacter, and Sulfuritalea were considered as the contributors of nitrogen removal via nitrification and sulfur-based denitrification. Further, this study shows that a TSDHS reactor can achieve not only desulfurization of biogas in the 1st DHS but also a 3.5 %-15 % reduction of the ammonia load in the 2nd DHS by effective utilization of the ADS during sewage treatment, assuming that the ADS is returned to the ASP.

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.

Principles and potential of thermal hydrolysis of sewage sludge to enhance anaerobic digestion

Sewage sludge is rich source of carbon, nutrients, and trace elements and can be subjected to proper treatment before disposal to fulfill government legislation and protect receiving environments. Anaerobic digestion (AD) is a well-adopted technology for stabilizing sewage sludge and recovering energy-rich biogas and nutrient-rich digestate. However, a slow hydrolysis rate limits the biodegradability of sludge. In the present study we have attempted to explain the potential of thermal hydrolysis to enhance anaerobic digestion of sewage sludge. Thermal pretreatment improves biodegradability and recycling of the sludge as an excellent energy and nutrients recovery source at reasonable capital (CAPEX) and operational (OPEX) costs. Other pretreatments like conventional (below/above 100 °C), temperature-phased anaerobic digestion (TPAD), microwave and chemically mediated thermal pretreatment have also been accounted. This review provides a holistic overview of sludge's characterization and value-added properties, various techniques used for sludge pretreatment for resource recovery, emphasizing conventional and advanced thermal pretreatment, challenges in scale-up of these technologies, and successful commercialization of thermal pretreatment techniques.

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

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

A critical review of exogenous additives for improving the anammox process

Anammox achieves chemoautotrophic nitrogen removal under anaerobic and anoxic conditions and is a low-carbon wastewater biological nitrogen removal process with broad application potential. However, the physiological limitations of AnAOB often cause problems in engineering applications, such as a long start-up time, unstable operation, easily inhibited reactions, and difficulty in long-term strain preservation. Exogenous additives have been considered an alternative strategy to address these issues by retaining microbes, shortening the doubling time of AnAOB and improving functional enzyme activity. This paper reviews the role of carriers, biochar, intermediates, metal ions, reaction substrates, redox buffers, cryoprotectants and organics in optimizing anammox. The pathways and mechanisms of exogenous additives, which are explored to solve problems, are systematically summarized and analyzed in this article according to operational performance, functional enzyme activity, and microbial abundance to provide helpful information for the engineering application of anammox.

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.

Multiple roles of complex organics in polishing THP-AD filtrate with double-line anammox: Inhibitory relief and bacterial selection

Anammox process has been widely regarded as an energy-efficient method for sludge digestion filtrate treatment. However, the complex high-strength organics in the filtrate, especially of Anaerobic Digestion after Thermal Hydrolysis Pretreatment (THP-AD), brings serious threat to anammox bacteria, and the high nitrate residue in effluent remains another significant barrier in operation. In this study, a novel double-line anammox-mediated system, integrating the Partial Nitrification/Anammox (PNA) with Partial Denitrification/Anammox (PDA) processes in separately sequencing batch reactors (SBRs), was developed to polish the THP-AD filtrate. When the real THP-AD filtrate (1946.5 mg NH4+-N/L, 2076.0 mg COD/L) was fed to the front PNA reactor (SBRPNA) with 5-fold dilution, effluent total nitrogen (TN) remained at 93.0 mg/L. Notably, the final effluent TN was effectively polished to as low as 8.8 mg/L by the following PDA reactor (SBRPDA), which was fed with the SBRPNA effluent and real domestic wastewater (71.0 mg NH4+-N/L, 209.1 mg COD/L). More severe inhibition on anammox activity was observed in SBRPNA rather than SBRPDA by refractory organics in filtrate. Fortunately, it could be alleviated with the enhanced degradability of particulate organics and aromatic protein-like compounds, attributed to the enrichment of class Anaerolineae in both SBRPNA and SBRPDA. This further stimulated the electron donor supply for PDA process with much lower external carbon source demand. 16S rRNA sequencing analysis revealed that Candidatus Brocadia as dominant anammox bacteria were efficiently enriched in both SBRPNA and SBRPDA, indicating its unexpected toughness and adaptability to the complex organic compounds in THP-AD filtrate. Overall, this study suggested that the novel double-line anammox would be a promising alternative for cost-efficient nitrogen removal from high-strength wastewater containing complex organic matter.

Metagenomics reveals bacterioplankton community adaptation to long-term thermal pollution through the strategy of functional regulation in a subtropical bay

Thermal effluents from coastal nuclear power plants have led to undesirable pollution and subsequent ecological impacts on local marine ecosystems. However, despite the ecological importance, we know little about the impacts on functionality of bacterioplankton subjected in systems with long-term thermal pollution. We used metagenomic sequencing to study of the effect of thermal pollution on bacterioplankton community metagenomics in summer in a subtropical bay located on the northern coast of the South China Sea. Thermal pollution (>15 y), which resulted in an increase in the summer seawater temperature around 8°C and caused seawater temperature up to approximate 39°C, significantly decreased bacterioplankton metabolic potentials in photosynthesis, organic carbon synthesis, and energy production. The bacterioplankton community metagenomics underwent a significant change in its structure from Synechococcus-dominant autotrophy to Alteromonas, Vibrio, and Pseudoalteromonas-dominated heterotrophy, and significantly up-regulated genes involved in organic compound degradation and dissimilatory nitrate reduction for the matter and energy acquisition under thermal pollution. Moreover, the bacterioplankton community metagenomics showed an up-regulation with heating of genes involved in DNA repair systems, heat shock responsive chaperones and proteins, and proteins involved in other biological processes, such as biofilm formation and the biosynthesis of unsaturated fatty acids and glycan, to adapt to the thermal environment. Collectively, it indicates a functional regulation of bacterioplankton adaptation to high-temperature stress, which might advance the understanding of the molecular mechanisms of community adaptation to global extreme warming in aquatic ecosystems.

Bioaugmentation of Anammox Activated Sludge with a Nitrifying Bacterial Community as a Way to Increase the Nitrogen Removal Efficiency

Abstract—

Bioaugmentation, i.e., increasing the abundance of certain microorganisms in the community by adding appropriate cells or establishing the conditions promoting their growth, is widely used in environmental technologies. Its application for launching of the anammox reactors is usually limited to introduction of anammox bacteria. We expected addition of nitrifiers during anammox bioreactor launching to stimulate the anammox process due to rapid production of nitrite, which anammox bacteria use for ammonium oxidation. The present work investigated the effect of introduction of a nitrifying community on the composition and activity of the microbial community in an anammox reactor. At the time of inoculation of a laboratory SBR reactor, an active nitrifying community (5 days old) (ASB) (bioaugmenting activated sludge, ASB) containing group I nitrifiers, primarily Nitrosospira, was added (1 : 100 by biomass) to anammox activated sludge (ASA) stored for 1 month at 4°C and exhibiting low metabolic activity. The use of ASB resulted in increased efficiency of nitrogen removal. While noticeable nitrogen removal in the control (7%) was observed since day 11 of incubation, nitrogen removal in the experimental reactor began on day 4 at the level of 20%. Nitrogen removal after 30 days of incubation was ~60% in the experiment and 20% in the control. The rate of ammonium oxidation in the presence of ASB increased due to activity of nitrifying bacteria (during the first 10 days of operation) and anammox bacteria of the genus Brоcadia, which were already present in ASA (throughout all period of operation). Activity of group II nitrifiers (genera Nitrobacter and Nitrococcus), which were present in ASB, prevented accumulation of nitrite, which in high concentrations is toxic to both nitrifiers and anammox bacteria. High activity of the Nitrosospira nitrifiers introduced with ASB probably provided the anammox bacteria with one of the substrates (nitrite), promoting their rapid growth. During subsequent operation of the reactor, nitrifiers of the genus Nitrosomonas from the initial ASA community were mainly responsible for growth of the anammox bacteria. Thus, ASA bioaugmentation at the loading of the anammox reactor by active nitrifiers resulted in significantly improved efficiency of ammonium removal via the anammox process and accelerated transition of the reactor to the working mode.

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.

Exploring the role of heterotrophs in partial nitritation-anammox process treating thermal hydrolysis process - anaerobic digestion reject water

Heterotrophic bacteria (HB) are generally prevalent in anammox-based processes, but their functional and ecological roles in partial nitritation-anammox (PN/A) process treating high-organics wastewater remained unclear. This study aimed to elucidate HB activities and microbial interactions in a one-stage PN/A treating thermal hydrolysis process (THP) - anaerobic digestion (AD) reject water. The PN/A reactor achieved a satisfactory nitrogen removal rate of 0.58 ± 0.06 g N/(L·d), and around 12% of COD in the THP-AD reject water was removed. N₂O emission factors of the PN/A reactor were 1.15% ± 0.18% treating synthetic wastewater, and 0.95% ± 0.06% treating reject water. A balanced symbiotic relationship was maintained between HB and functional groups (i.e., anammox bacteria and aerobic-ammonia-oxidizing bacteria) over the reactor operation. The relative abundances of Anaerolineae spp. clearly increased, while Denitratisoma, capable of denitrification, slightly decreased when treating THP-AD reject water. The preference for electron donors of heterotrophs explained discrepant growth trends.

Enhancing anaerobic digestion using free nitrous acid: Identifying the optimal pre-treatment condition in continuous operation

Free Nitrous Acid (FNA) pre-treatment is a promising technology demonstrated effective in improving waste activated sludge degradability and anaerobic digestion (AD) performance. Pre-treatment conditions including FNA concentration and treatment duration determine operational and capital cost of full-scale implementation, which have not been studied in long-term experiments. The knowledge of FNA pre-treatment conditions improving the AD performance is urgently required to determine suitable conditions for the technology implementation. In this work, five different FNA concentrations (2.2, 4.4, 7.2, 12 mgN/L and nitrite only without pH adjustment) and three treatment durations (8, 24 and 48 h) were studied in four lab-scale semi-continuous AD reactors for over 300 days. FNA pre-treatment was shown under all tested conditions effective in enhancing AD performances, while its effectiveness and resulted benefits varied substantially amongst different pre-treatment conditions. The long-term experiment demonstrated that the methane production, sludge reduction and digested sludge viscosity of AD are positively correlated with the FNA concentration and durations, until an optimal condition is reached, which was identified in this work to be FNA concentration of 7.2 mgN/L and treatment duration of 24 h. Microbial community changes supported the apparent observation of enhanced sludge degradation at elevating FNA concentrations applied during pre-treatment. The short-term sludge solubilization results were inconsistent with the long-term AD performance, which was potentially caused by inhibitions from stringent FNA pre-treatment conditions applied (FNA = 12 mgN/L with 24-hour treatment & FNA = 7.2 mgN/L with 48-hour treatment). Overall, results suggested FNA pre-treatment at the optimized condition is highly beneficial to WWTPs and competitive with other pre-treatment technologies, e.g., thermal hydrolysis pre-treatment. This work comprehensively evaluated the key design parameters of FNA pre-treatment process, reached a major milestone in the development and applications of FNA technologies.

Optimizing granular anammox retention via hydrocycloning during two-stage deammonification of high-solid sludge anaerobic digester supernatant

High-solid sludge anaerobic digestion leads to increased organic matters in digester supernatant, which promotes heterotrophic competition and reduces anaerobic ammonium oxidation (anammox) retention. This research demonstrated effective anammox retention by hydrocycloning during a two-stage deammonification. Anammox retention was evaluated by dividing large (>0.425 mm), medium (0.25 to 0.425 mm), and small (<0.25 mm) aggregate fractions via a sieve, whereby Candidatus Kuenenia abundance in each size aggregate was measured to be 16.8%, 5.0%, and 0.9% respectively. After hydrocyclone separation, large particles took up only 1.7% to 2.7% in the overflow discharge (upper discharge from the reactor), whereas its initial proportion was 19.4%, indicating limited anammox loss. The volume ratio change of large particles to total aggregates was defined for particle breakdown evaluation. Breakdown (23% to 32% large particles) occurred mainly during pumping (influenced by pump frequency and type), while little happened in the hydrocyclone. This research provided methods to use a sieve to evaluate anammox retention by hydrocyclone during high-solid sludge anaerobic digester supernatant deammonification, and information for reducing particle breakdown, pumping selection, and separation optimization.

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.

Effects of an organic carbon source on the coupling of sulfur(thiosulfate)-driven denitration with Anammox process

The sulfur(thiosulfate)-driven autotrophic denitrification coupled with Anammox (SDDA) process is proposed as an emerging technology for wastewater containing NH₄⁺-N and NO₃^--N. However, the influence of organic matter on the SDDA process is not fully understood. A long-term experiment has shown that a moderate organic (acetate) (＜140 mg/L COD) can accelerate the heterotrophic/autotrophic denitrification and Anammox activity, to reach as high as 92.8% ± 0.3% total nitrogen at a loading rate of 1.34 kg-N/(m³·d). Batch test results showed that Anammox made the largest contribution to the removal of nitrogen, even in an SDDA system with COD addition. Additionally, organics can promote the bioavailability of solid sulfur through reaction with sulfide to form polysulfides, which increased nitrite accumulation to forward Anammox process. Sulfur-oxidizing bacteria (e.g., Thiobacillus and Denitratisoma) coexisted with Anammox bacteria (e.g., Ca. Brocadia and Ca. Kuenenia) in the SDDA system despite the addition of exogenous COD.

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.

Combining numerical simulation with response surface modelling for optimization of reject water partial nitritation/anammox in moving bed biofilm reactor

Optimization of a single-stage, partial nitritation/anammox (PN/A) process for a reject water treatment in a continuous-flow, moving bed biofilm reactor (MBBR) was presented. Response surface method (RSM) was combined with simulation experiments conducted with the validated mathematical model of PN/A in MBBR. The total inorganic nitrogen (TIN) removal efficiency was the response parameter. Eight independent variables were taken into consideration: reject water flow rate (Q), inflow concentrations of the total ammonium nitrogen (TAN), chemical oxygen demand (COD), alkalinity (ALK), pH, temperature (T), dissolved oxygen concentration in the bulk liquid (DO) and aeration time within 60 min intermittent aeration cycle (AERON). Eleven interactions between independent variables were found as significant (p < 0.05). The interaction of AERON*DO had the highest impact on the PN/A process. Optimal values of the controlled variables were found for two cases of MBBR operation. Verification of the optimization was done by the simulation and comparison with the data from the empirical experiments. Under the conditions of the fixed hydraulic retention time of about 38 h, volumetric nitrogen loading rate of 0.48 kgN/m³d, T of 22.5°C, TAN of 750 gN/m³ and optimized values of DO = 3.0 gO₂/m³, AERON = 0.54 h, pH = 7.5, ALK = 80 molHCO₃/m³, COD = 775 gO₂/m³, the predicted TINrem was 78% which is consistent with PN/A performance observed in the technical-scale MBBR systems.

Lessons Learned from 10 Years of ANITA Mox for Sidestream Treatment

When a wastewater treatment plant (WWTP) uses anaerobic digestion (AD) on its sludge treatment line, the opportunity to install a sidestream deammonification process for the cost-effective removal of the N-rich reject water load generated by the sludge digester should be considered. In this context, the ANITA™ Mox process based on the moving bed biofilm reactor (MBBR) technology has been implemented at more than 30 full-scale facilities over the last 10 years to treat reject water from conventional AD or after thermal hydrolysis process (THP) to reduce the N-load and associated treatment costs on the WWTP. This paper reviews the lessons learned in the implementation of the ANITA™ Mox process at several WWTP in the US, Europe, and Australia.

Impacts of organics on the microbial ecology of wastewater anammox processes: Recent advances and meta-analysis

Anaerobic ammonium oxidation (anammox) represents a promising technology for wastewater nitrogen removal. Organics management is critical to achieving efficient and stable performance of anammox or integrated processes, e.g., denitratation-anammox. The aim of this systematic review is to synthesize the state-of-the-art knowledge on the multifaceted impacts of organics on wastewater anammox community structure and function. Both exogenous and endogenous organics are discussed with respect to their effects on the biofilm/granule structure and function, as well as the interactions between anammox bacteria (AnAOB) and a broad range of coexisting functional groups. A global core community consisting of 19 taxa is identified and a co-occurrence network is constructed by meta-analysis on the 16S rDNA sequences of 149 wastewater anammox samples. Correlations between core taxa, keystone taxa, and environmental factors, including COD, nitrogen loading rate (NLR) and C/N ratio are obtained. This review provides a holistic understanding of the microbial responses to different origins and types of organics in wastewater anammox reactors, which will facilitate the design and operation of more efficient anammox-based wastewater nitrogen removal process.

Assessment of sludge management strategies in wastewater treatment systems using a plant-wide approach

The objective of this paper is to use plant-wide modeling to assess the net impacts of varying sludge management strategies. Special emphasis is placed on effluent quality, operational cost and potential resource recovery (energy, nutrients). The study is particularly focused on a centralized bio-solids beneficiation facility (BBF), which enables larger, more capital intensive sludge management strategies. Potential barriers include the ability to process reject streams from multiple donor plants in the host plant. Cape Flats (CF) wastewater treatment works (WWTW) (Cape Town, South Africa) was used as a relevant test case since it is currently assessing to process sludge cake from three nearby facilities (Athlone, Mitchells Plain and Wildevoelvlei). A plant-wide model based on the Benchmark Simulation Model no 2 (BSM2) extended with phosphorus transformations was adapted to the CF design / operational conditions. Flow diagram and model parameters were adjusted to reproduce the influent, effluent and process characteristics. Historical data between January 2014 and December 2019 was used to compare full-scale measurements and predictions. Next, different process intensification / mitigation technologies were evaluated using multiple criteria. Simulation values for COD, TSS, VSS/TSS ratio, TN, TP, NH₄⁺/NH₃, H_xPO4^3-x, NO_x alkalinity and pH fall within the interquartile ranges of measured data. The effects of the 2017 severe drought on influent variations and biological phosphorus removal are successfully reproduced for the entire period with dynamic simulations. Indeed, 80% of all dynamically simulated values are included within the plant measurement uncertainty ranges. Sludge management analysis reveals that flow diagrams with thermal hydrolysis pre-treatment (THP) result in a better energy balance in spite of having higher heat demands. The flow diagram with THP is able to i) increase biodegradability/solubility, ii) handle higher sludge loads, iii) change methanogenic microbial population and iv) generate lower solids volumes to dispose by improving sludge dewaterability. The study also reveals the importance of including struvite precipitation and harvesting (SPH) technology, and the effect that pH in the AD and the use of chemicals (NaOH, MgO) may have on phosphorus recovery. Model-based results indicate that the current aerobic volume in the water line (if properly aerated) would be able to handle the returns from the sludge line and the contribution of a granular partial nitritation/Anammox (PN/ANX) reactor on the overall nitrogen removal would be marginal. However autotrophic N denitrification generates a much lower sludge production and therefore increases AD treatment capacity. The study shows for the very first time in Africa how the use of a (calibrated) plant-wide model could assist water utilities to decide between competing plant layouts when upgrading a WWTW.

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.

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.

Organic compounds evolution and sludge properties variation along partial nitritation and subsequent anammox processes treating reject water

Reject water contains complex components of organic compounds, which have significant influences on the nitrogen removal performance when treated using biological autotrophic nitrogen removal technology. In this study, a two-stage partial nitritation (PN)-anammox (floc-granule) system was established to treat reject water (COD/NH₄⁺-N = 0.97 ± 0.15), and the evolution of organic compounds along PN and annamox bioreactors was investigated using gas chromatography-mass spectrometry and excitation-emission matrix. Also, the variation of PN and anammox sludge properties relating to COD reduction was examined. The PN-anammox system removed approximately 80% of total inorganic nitrogen and COD with hydraulic reaction time of 16 h. The influent organics (330-600 mg COD/L) in reject water were primarily composed of volatile, protein-like and humic acid-like organic compounds. PN process contributed 53 ± 18% of the overall COD removal, primarily including oxygen-containing organics (e.g. phenol), proteins and humic acids. Anammox process contributed 22 ± 15% of the overall COD removal, but large molecule acids (e.g. lactic acid) and small molecule alcohols (e.g. glycerol) were reoccurred, contributing to the effluent COD with recalcitrant hydrocarbons (e.g. n-Octadecane). Reject water increased the extracellular proteins/polysaccharides ratio of PN and anammox sludge, promoting the adsorption and degradation of organic compounds. High-throughput sequencing results showed that denitrifying bacteria of Ottowia increased from 0.03% to 14.4% in PN reactor, and of Denitratisoma increased from 9.6% to 15.4% in anammox reactor. The occurrence of these denitrifiers might mitigate the negative impact of organics to functional organisms. This study highlights the organics fate during PN-anammox treatment system, which is important to maintain the robust nitrogen removal when treating organics-containing and high ammonium concentration wastewater.

Process performance and anammox community diversity in a deammonification reactor under progressive nitrogen loading rates for swine wastewater treatment

The performance of a deammonification reactor fed with increasing nitrogen loading rates (NLR) was evaluated. The digestate from a continuous stirred tank reactor (CSTR) treating sludge from a swine production unit was diluted to provide different ammonia concentrations. The biomass samples from the end of each experimental phase were analyzed for microorganism community evaluation. The results proved that deammonification system supported a NLR up to 3.27 ± 0.13 g N L^-1 d^-1 with nitrogen removal efficiency of 83%. The specific ammonia consumption rate (µ_NH3-N) did not decrease up to this NLR proving the stability of reactor performance. Anammox bacteria genus shifted along the experiment and at the end the predominant anammox bacteria found in the reactor was candidatus Brocadia. Finally, it was proved that a deammonification reactor for nitrogen removal from CSTR digestate could be easily controlled only by monitoring pH and dissolved oxygen.

Assessment of a fast method to predict the biochemical methane potential based on biodegradable COD obtained by fractionation respirometric tests

The biochemical methane potential test (BMP) is the most common analytical technique to predict the performance of anaerobic digesters. However, this assay is time-consuming (from 20 to over than 100 days) and consequently impractical when it is necessary to obtain a quick result. Several methods are available for faster BMP prediction but, unfortunately, there is still a lack of a clear alternative. Current aerobic tests underestimate the BMP of substrates since they only detect the easily biodegradable COD. In this context, the potential of COD fractionation respirometric assays, which allow the determination of the particulate slowly biodegradable fraction, was evaluated here as an alternative to early predict the BMP of substrates. Seven different origin waste streams were tested and the anaerobically biodegraded organic matter (COD_met) was compared with the different COD fractions. When considering adapted microorganisms, the appropriate operational conditions and the required biodegradation time, the differences between the COD_met, determined through BMP tests, and the biodegradable COD (COD_b) obtained by respirometry, were not significant (COD_met (57.8026 ± 21.2875) and COD_b (55.6491 ± 21.3417), t (5) = 0.189, p = 0.853). Therefore, results suggest that the BMP of a substrate might be early predicted from its COD_b in only few hours. This methodology was validated by the performance of an inter-laboratory studyconsidering four additional substrates.

Full-scale partial nitritation/anammox (PN/A) process for treating sludge dewatering liquor from anaerobic digestion after thermal hydrolysis

In this study, a full-scale partial nitritation/anammox (PN/A) process was successfully established to treat dewatering liquor (filtrate) from the activated sludge after thermal hydrolysis (THP) - anaerobic digestion (AD). The filtrate had an average ammonium of 1407 mg/L with a COD/N ratio of 1.43 ± 0.3. Under limited anammox biofilm inoculation, PN/A was started-up in an integrated fixed - biofilm activated sludge (IFAS) reactor. During the stable period, 2500 m³ of THP - AD sludge filtrate was treated daily and an average nitrogen removal rate of 0.21 kg N/(m³·d) was maintained with a removal efficiency over 85%. The application of PN/A reduced mainstream total inorganic nitrogen in effluent by 4.4 mg/L, saving $3.5 million in operational costs annually due to the reduction of organics addition. Overall, IFAS - PN/A process can be an efficient and economical method to treat THP - AD sludge filtrate and improve mainstream nitrogen removal performance.

The characterization of dissolved organic matter in alkaline fermentation of sewage sludge with different pH for volatile fatty acids production

Sewage sludge (SS) alkaline fermentation (especially at pH 10) can efficiently enhance volatile fatty acids (VFAs) production. VFAs are considered an excellent carbon source for the biological nutrient removal (BNR) process. Dissolved organic matter (DOM) in fermentation liquid is the direct substrate used for producing VFAs and can greatly influence the effluent quality of BNR process. However, knowledge of DOM characteristics in sludge alkaline fermentation is limited. This study focused on the functional groups, fluorescent components and molecular features of DOM as well as molecular weight of proteins in SS alkaline fermentation (at pH uncontrolled, 7, 8, 9 and 10). Results showed a significantly improved generation of tryptophan-like and tyrosine-like substances as well as molecular weight <1 kDa proteins (381.5 ± 38.4 mg/L) was observed at pH 10 (p < 0.05). Further analysis of DOM molecular characteristics indicated that pH 10 resulted in the highest molecular diversity and the generation or degradation of easily biodegradable lipid-like and proteins/amino sugars-like formulas. The improved solubilization of DOM contributed to VFAs production. Meanwhile, increasing pH to 10 also promoted the release of hard-biodegradable organic matter, e.g., humic-like and lignin-like substances. Additionally, a high diversity of resistant N-containing organic molecules was generated at pH 10. Fermentation of SS at pH 10, is favored to enhance VFAs production and, can also result in a higher content of refractory DOM. This study helps to achieve a comprehensive understanding of SS alkaline fermentation and provides fundamental information for further treatment.

Single- and multi-component chiral supraparticles as modular enantioselective catalysts

Nanoscale biological assemblies exemplified by exosomes, endosomes and capsids, play crucial roles in all living systems. Supraparticles (SP) from inorganic nanoparticles (NPs) replicate structural characteristics of these bioassemblies, but it is unknown whether they can mimic their biochemical functions. Here, we show that chiral ZnS NPs self-assemble into 70–100 nm SPs that display sub-nanoscale porosity associated with interstitial spaces between constituent NPs. Similarly to photosynthetic bacterial organelles, these SPs can serve as photocatalysts, enantioselectively converting L- or D-tyrosine (Tyr) into dityrosine (diTyr). Experimental data and molecular dynamic simulations indicate that the chiral bias of the photocatalytic reaction is associated with the chiral environment of interstitial spaces and preferential partitioning of enantiomers into SPs, which can be further enhanced by co-assembling ZnS with Au NPs. Besides replicating a specific function of biological nanoassemblies, these findings establish a path to enantioselective oxidative coupling of phenols for biomedical and other needs.

Nanoscale biological assemblies play crucial roles in all living systems and display a variety of chemical functionalities. Here the authors show that it is possible to replicate some of the biochemical functions in similarly-sized assemblies made from inorganic nanoparticles.

Characterization of the refractory dissolved organic matters (rDOM) in sludge alkaline fermentation liquid driven denitrification: Effect of HRT on their fate and transformation

Enhanced biological denitrification for nitrogen removal using sludge alkaline fermentation liquid (SAFL) as an alternative carbon source has been widely reported in previous studies, while limited studies focused on the degradation of the organics presented in SAFL. In this study, an SAFL driven anoxic denitrification sequencing batch reactor (SBR) was established, the mechanism of organics utilization was characterized and the refractory dissolved organic matters (rDOM) was identified. Denitrification could rapidly proceed with the presence of volatile fatty acids (VFAs) initially, while the denitrification rate largely decreased after the VFAs depleted. A great deal of rDOM, which was hard to be utilized by denitrifying microorganism, was found in the effluent. A prolonged hydraulic retention time (HRT) led to the further transformation of particles and colloids to smaller colloids and soluble organics. Extended HRT promoted the degradation of soluble microbial by-product (SMP), but had minor effect on the removal of humic-like, and fulvic acid-like substances. The characterization of the effluent demonstrated the building blocks, were dominated in the rDOM (43.79%-48.78%), followed by high molecular weight protein (HMW-PN) (13.37%-17.39%), HMW polysaccharide (HMW-PS) (12.84%-15.9%), low molecular weight (LMW) neutrals (11.28%-13.65%), and hydrophobic dissolved organic carbon (HO-DOC) (8.0%-12.62%). Moreover, it was found that the building blocks were relatively easy to be degraded with the extension of HRTs, followed by LMW-PS, LMW-PN, LMW neutrals, HMW-PN, and HMW-PS. However, further extended HRT >24 h could not improve the removal of building blocks, LMW-PS and LMW neutrals. This study, for the first time, provided insights into the transformation of organic matters produced by SAFL in a denitrification system and acted as a guide for the subsequent advanced treatment.

Achieving completely anaerobic ammonium removal over nitrite (CAARON) in one single UASB reactor: Synchronous and asynchronous feeding regimes of organic carbon make a difference

At least 11% of total nitrogen (TN) remains in the anammox effluent, making it difficult to meet increasingly stringent discharge standards. To overcome this bottleneck, an innovative process to achieve completely anaerobic ammonium removal over nitrite (CAARON) in one single up-flow anaerobic sludge blanket reactor was proposed in this study. The synchronous feeding of acetate at a C/N (nitrite) ratio of 0.6 significantly reduced the nitrogen removal capacity of anammox reactor by limiting the abundance and metabolism of anammox bacteria. In contrast, the asynchronous feeding of acetate optimized the partition of the reactor column into two specific compartments: the lower half favoring anammox and the upper half dominated by DEAMOX (DEnitrifying AMmonium Oxidation). A high TN removal efficiency of 96.2±0.4% and a low effluent TN concentration of 9.3±0.9mgL^-1 were obtained under a high TN loading rate of 9.0kgNm^-3d^-1. The dominant functional microbes in the CAARON process were identified as Candidatus Kuenenia and Thauera, which were responsible for the anammox and denitratation reactions, respectively. Overall, the results in this study provide valuable insight into the coupling of anammox with denitratation, which is a cost-efficient approach for treating ammonium-rich wastewaters.