Search

Mainstream anaerobic wastewater treatment has received increasing attention for the recovery of methane-rich biogas from biodegradable organics, but subsequent mainstream nitrogen and dissolved methane removal at low temperatures remains a critical challenge in practical applications. In this study, granular sludge coupling n-DAMO with Anammox was employed for mainstream nitrogen removal, and the dissolved methane removal potential of granular sludge at low temperatures was investigated. A stable nitrogen removal rate (0.94 kg N m-3 d-1 at 20 °C) was achieved with a high-level effluent quality (

Anaerobic ammonium oxidation (anammox) and nitrification, two common biological ammonium oxidation pathways, are critical for the microbial nitrogen cycle. Short chain alkanes (C

Ammonium (NH4+) oxidation is crucial for nitrogen (N) removal, contributing to regional and global N cycles, but is regarded as limited to a few biological pathways. A novel pathway for NH4+ oxidat...

Nitrogen and phosphorus contamination in wastewater is a serious environmental concern and poses a global threat to sustainable development. In this paper, a comprehensive review of the studies on simultaneous nitrogen and phosphorus removal (SNPR) during 1986-2022 (538 publications) was conducted using bibliometrics, which showed that simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) is the most promising process. To better understand SNDPR, the dissolved oxygen, carbon to nitrogen ratio, carbon source type, sludge retention time, Cu

Methane, a potent greenhouse gas of global importance, has traditionally been considered as an end product of microbial methanogenesis of organic matter. Paradoxically, growing evidence has shown that some microbes, such as cyanobacteria, algae, fungi, purple non-sulfur bacteria, and cryptogamic covers, produce methane in oxygen-saturated aquatic and terrestrial ecosystems. The non-methanogenesis process could be an important potential contributor to methane emissions. This systematic review summarizes the knowledge of microorganisms involved in the non-methanogenesis process and the possible mechanisms of methane formation. Cyanobacteria-derived methane production may be attributed to either demethylation of methyl phosphonates or linked to light-driven primary productivity, while algae produce methane by utilizing methylated sulfur compounds as possible carbon precursors. In addition, fungi produce methane by utilizing methionine as a possible carbon precursor, and purple non‐sulfur bacteria reduce carbon dioxide to methane by nitrogenase. The microbial methane distribution from the non-methanogenesis processes in aquatic and terrestrial environments and its environmental significance to global methane emissions, possible mechanisms of methane production in each open water, water-to-air methane fluxes, and the impact of climate change on microorganisms are also discussed. Finally, future perspectives are highlighted, such as establishing more in-situ experiments, quantifying methane flux through optimizing empirical models, distinguishing individual methane sources, and investigating nitrogenase-like enzyme systems to improve our understanding of microbial methane emission from the non-methanogenesis process.

Currently, the complex mechanism of lipid production in microalgal cells is still unclear, and the platform suitable for microalgal genetic transformation is urgent to be established. In this study, the whole genome of a lipid-rich microalgal mutant strain Scenedesmus sp. Z-4 and a lipid-poor wild strain Scenedesmus sp. MC-1 were sequenced, and results revealed that the sequences of 1,256 genes were changed and 148 differential genes related to glucose and lipid metabolism were identified. Especially, gene differentiation of acetyl-CoA carboxylase (ACCase) and phosphoenolpyruvate carboxylase (PEPC) in mutant strain Z-4 and wild strain MC-1, which played key roles in lipid synthesis, were evaluated. Furthermore, to investigate whether mutated ACCase and PEPC genes affect the lipid production, two genes from mutant strain Z-4 were transformed into the expression system of wild strain MC-1. Nine transformants with higher lipid content were successfully obtained, in which the optimal transformant with 28.6% more intracellular lipid than wild strain MC-1 was isolated by overexpression of mutated ACCase gene, demonstrating the important role of ACCase in lipid accumulation of microalgal cells. These results could provide a better understanding of the superior lipid production of mutant strain Scenedesmus sp. Z-4.

Manganese is a vital heavy metal abundant in terrestrial and aquatic environments. Anaerobic manganese redox reactions mediated by microorganisms have been recognized for a long time, which promote elements mobility and bioavailability in the environment. Biological anaerobic redox of manganese serves two reactions, including Mn(II) oxidation and Mn(IV) reduction. This review provides a comprehensive analysis of manganese redox cycles in the environment, closely related to greenhouse gas mitigation, the fate of nutrients, microbial bioremediation, and global biogeochemical cycle, including nitrogen, sulfur, and carbon. The oxidation and reduction of manganese occur cyclically and simultaneously in the environment. Anaerobic reduction of Mn(IV) receives electrons from methane, ammonium and sulfide, while Mn(II) can function as an electron source for manganese-oxidizing microorganisms for autotrophic denitrification and photosynthesis. The anaerobic redox transition between Mn(II) and Mn(IV) promotes a dynamic biogeochemical cycle coupled to microorganisms in water, soil and sediment environments. The discussion of reaction mechanisms, microorganism diversity, environmental influence bioremediation and application identify the research gaps for future investigation, which provides promising opportunities for further development of biotechnological applications to remediate contaminated environments.

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) is critical for mitigating methane emission and returning reactive nitrogen to the atmosphere. The genomes of n-DAMO archaea show that they have the potential to couple anaerobic oxidation of methane to dissimilatory nitrate reduction to ammonium (DNRA). However, physiological details of DNRA for n-DAMO archaea were not reported yet. This work demonstrated n-DAMO archaea coupling the anaerobic oxidation of methane to DNRA, which fueled Anammox in a methane-fed membrane biofilm reactor with nitrate as only electron acceptor. Microelectrode analysis revealed that ammonium accumulated where nitrite built up in the biofilm. Ammonium production and significant upregulation of gene expression for DNRA were detected in suspended n-DAMO culture with nitrite exposure, indicating that nitrite triggered DNRA by n-DAMO archaea. 15N-labeling batch experiments revealed that n-DAMO archaea produced ammonium from nitrate rather than from external nitrite. Localized gradients of nitrite produced by n-DAMO archaea in biofilms induced ammonium production via the DNRA process, which promoted nitrite consumption by Anammox bacteria and in turn helped n-DAMO archaea resist stress from nitrite. As biofilms predominate in various ecosystems, anaerobic oxidation of methane coupled with DNRA could be an important link between the global carbon and nitrogen cycles that should be investigated in future research.

Inert gas is often used in the deoxygenation of microbial electrolysis cells (MECs) to maintain growth and viability of anaerobes. However, the effects of the gas atmosphere on hydrogen production and microbial community of MECs are often neglected. Here, the performances and biofilm microbiomes of MECs pre-sparged with different gases were compared. MECs pre-sparged with argon gas (Ar) yielded more hydrogen (3.73 ± 0.13 mol-H2/mol-acetate) and a higher hydrogen production rate (2.99 ± 0.17 L-H2/L-reactor-day) than MECs pre-sparged with N2 (3.41 ± 0.13 mol-H2/mol-acetate and 2.27 ± 0.28 L-H2/L-reactor-day, respectively). Microbiome analysis indicated that the relative abundance of Geobacter increased from 59.25% to 77.79% when the gas atmosphere in MECs shifted from N2 to Ar. Hydrogen production may have been catalyzed by nitrogenase from Geobacter and photosynthetic bacteria in MECs pre-sparged with Ar. These findings suggested that the gas atmosphere substantially influences the microbiome of anode biofilms and Ar sparging is most effective for enhancing hydrogen production in MECs.

Sulfate dependent ammonium oxidation (Sulfammox) is a potential microbial process coupling ammonium oxidation with sulfate reduction under anaerobic conditions, which provides a novel link between nitrogen and sulfur cycle. Recently, Sulfammox was detected in wastewater treatments and was confirmed to occur in natural environments, especially in marine sediments. However, knowledge gaps in the mechanism of Sulfammox, functional bacteria, and their metabolic pathway, make it challenging to estimate its environmental significance and potential applications. This review provides an overview of recent advances in Sulfammox, including possible mechanisms, functional bacteria, and main influential factors, and discusses future challenges and opportunities. Future perspectives are outlined and discussed, such as exploration of microbial community structure and metabolic pathways, possible interactions with other microbes, environmental significance, and potential applications for nitrogen and sulfate removal, to inspire more researches on the Sulfammox process.

A novel method for fabricating air-cathodes was developed by assembling an activated carbon (AC) catalyst together with a waterproof breathable membrane (WBM) and stainless steel mesh (SSM) to reduce manufacturing costs of bioelectrochemical systems (BESs). WBMs made of different materials were tested in the assembly, including a hybrid of polypropylene and polyolefin (PPPO), polyethylene (PE), and polyurethane (PU), and compared against poly tetrafluoroethylene (PTFE)-based cathodes. Results showed that the maximum power density of the activated carbon-stainless steel mesh-polyurethane (AC@SSM/PU) assembly was 2.03 W/m2 while that of conventional carbon cloth cathode assembly (Pt@CC/PTFE) was 1.51 W/m2. Compared to conventional cathode fabrication, AC@SSM/PU had a much lower cost and simpler manufacturing process. Illumina Miseq sequencing of 16S rRNA gene amplicons indicated that microbiomes were substantially different between anode and cathode biofilms. There was also a difference in the community composition between different cathode biofilms. The predominant population in the anode biofilms was Geobacter (38–75% relative abundance), while Thauera and Pseudomonas dominated the cathode biofilms. The results demonstrated that different types of air-cathodes influenced the microbial community assembly on the electrodes.

Denitrifying anaerobic methane oxidation (DAMO) coupled to anaerobic ammonium oxidation (anammox) is a promising technology for complete nitrogen removal with economic and environmental benefit. In this work, a model framework integrating DAMO and anammox process was constructed based on suspended-growth systems. The proposed model was calibrated and validated using experimental data from a sequencing batch reactor and a membrane aerated membrane bioreactor (MAMBR). The model managed to describe removal rates of ammonium (NH4+), nitrite (NO2-), and total nitrogen, as well as biomass changes of DAMO archaea, DAMO bacteria, and anaerobic ammonium oxidizing bacteria (AnAOB) in both reactors. The estimated parameter values revealed that DAMO archaea possessed properties of faster growth and higher biomass yield in suspended-growth systems compared to those in attached-growth systems (e.g., biofilm). Model simulation demonstrated that solid retention time (SRT) was effective in washing out DAMO bacteria, but retaining DAMO archaea and AnAOB in the MAMBR. The optimal SRT and nitritation efficiency (the ratio of the NO2- to the sum of NH4+ and NO2- in the MAMBR influent) were simulated so that 99% of total nitrogen was removed to meet the discharge standard. MAMBR further suggested to be operated with SRT between 15 and 30 days so that the optimal nitritation efficiency could be minimized to 49% for cost savings.

Since there is high lignocellulose content in the cotton straw and cow manure mixture (MCC), the appropriate MCC pretreatment is important to promote the anaerobic digestion (AD) hydrolysis. This study mainly explored the effect of potassium ferrate (PF) and peroxymonosulfate (PMS) pretreatments on MCC decomposition. PMS + PF co-treatment showed a higher reduction of total solid and volatile solid than PF pretreatment and PMS pretreatment. Hydrolysis of treated MCC indicated that the PF pretreatment was more effective to the release of organics than the PMS pretreatment and the PMS + PF co-treatment. However, the PMS + PF co-treatment resulted in a higher lignin removal rate (40.4%–50.5%) than the PMS pretreatment (30.8%) and the PF pretreatment (21.4%). The PMS1 + PF2 co-treatment (molar ratio of 1:2) acquired the optimal lignin removal rate and the release of organics among the PMS + PF co-treatment with different dosing ratio. Potential mechanism was that PF reduction products activated PMS to produce free radicals (SO4 −, OH), which attacked lignocellulosic components and promoted MCC decomposition. The PMS1 + PF2 co-treatment was deduced to be the optimal pretreatment method when considering MCC decomposition, biodegradability, and mass transfer in the bioreactor.

Bisphenols (BPs) are distributed in worldwide as typical environmental hormones, which potentially harm the ecological environment and human health. In this study, four BPs, i.e., bisphenol A, bisphenol F, bisphenol S, and bisphenol AF, were used as prototypes to identify the intrinsic differences in degradation mechanisms correlated with the molecular structures in peroxydisulfate (PDS)-based advanced oxidation processes (AOPs). Electron transfer was the main way of modified biochar to trigger the heterogenous catalysis of PDS, which can cause the degradation of BPs. Phenolic hydroxyl groups on bisphenol pollutants were considered as possible active sites, and the existence of substituents was the main reason for the differentiation in the degradation efficiency of various bisphenols. Results of ecotoxicity prediction showed that most intermediates produced by the degradation of BPs in the β-SB/PDS system, which was dominated by the electron transfer pathway, had a lower toxicity than the parent molecules, while the toxicity of several ring cleavage intermediates was higher. This study presents a simple modification scheme for the conversion of biochar into functional catalysts and provides insights into the mechanism of heterogeneous catalytic degradation mediated by modified biochar as well as the degradation differences of bisphenol pollutants and their potential ecotoxicity.

Electro-fermentation systems (EFSs) are an emerging technology capable of regulating microbial fermentation pathways by tuning oxidation-reduction potentials and electron flow. However, there is limited understanding of the bioenergy conversion and metabolic regulation of fermentative bacteria in EFSs. In this study, we investigated how electrode potentials in EFSs affect the metabolic products and global transcriptome expression of Ethanoligenens harbinense. The E. harbinense-inoculated anodic EFS (AEFS) with a poised potential of 0 V or the cathodic EFS (CEFS) with a poised potential of 0 V (vs. Ag/AgCl reference electrode) obtained the maximum H2 production of 1888–1986 mL/L-medium, which increased by 23–26% compared with open-circuit fermentation (OC-EFSs). The highest H2 yield of 1.190 ± 0.009–1.197 ± 0.001 mol-H2/mol-glucose was obtained by the AEFS0 and the OC-EFS. Ethanol production of AEFS-0.4 increased by 30.7 ± 13.3% compared with OC-EFSs. In addition, glucose uptake and cell growth in the EFS were enhanced with an increase in cellular energy supply. Transcriptome analysis revealed that overexpression of the [FeFe]-hydrogenase, ferredoxin, and rubredoxin genes in the AEFS with a poised potential of 0 V promoted the H2 production rate. Genes involved in electron transfer and reduced nicotinamide adenine dinucleotide (NADH) regeneration were upregulated in the AEFS, leading to more ethanol production. In addition, substrate transmembrane transport was suppressed by underexpression of adenosine triphosphate (ATP)-binding cassette (ABC) transporter system-related genes at lower or higher potentials. These results confirm that an EFS effectively regulates the metabolite spectrum of H2-producing bacteria by coordinating electron transfer, NADH regeneration, and substrate transmembrane transport to provide a flexible approach for improving bioenergy production by fermentative bacteria.

At present, the bioproduction of short-chain fatty acids (SCFAs) from waste activated sludge (WAS) has attracted worldwide attention due to the demand of carbon neutrality during waste treatment. Calcium peroxide (CaO2) has been reported to be an effective method for the solubilization of WAS and the accumulation of SCFAs, but the high reagent cost limits its industrial application. Therefore, free nitrous acid (FNA) was introduced into the WAS pretreatment system to assist with CaO2 for enhancing the disruption of extracellular polymeric substances (EPS) and the subsequent acidogenesis process. The results showed that FNA and CaO2 synergistically enhanced EPS decomposition and the release of biodegradable organic compounds during pretreatment. The highest soluble chemical oxygen demand (3.1- and 2.6-fold higher compared to individual pretreatments at the same concentrations) after pretreatment and the highest SCFAs accumulation (2.0- and 6.4-fold compared to individual pretreatments at the same concentrations) after a 2-day fermentation period was observed in the FNA + CaO2 (0.15 g/g VSS) co-treated group. Therefore, the FNA + CaO2 (0.15 g/g VSS) co-treatment was determined to be the optimal strategy for ensuring the disintegration of the EPS matrix and enhancing the accumulation of SCFAs in pretreated sludge during anaerobic digestion.

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) is an important process linking nitrogen and carbon cycle. It is recently demonstrated that n-DAMO archaea are able to couple n-DAMO to dissimilatory nitrate reduction to ammonium (DNRA). In this work, a mathematical model is developed to describe DNRA by n-DAMO archaea for the first time. The anabolic and catabolic processes of n-DAMO archaea, n-DAMO bacteria and anaerobic ammonium oxidation (Anammox) bacteria are involved. The different impacts of exogenous and endogenous nitrite on DNRA and n-DAMO microbes are considered. The developed model is calibrated and validated using experimental data collected from a sequencing batch reactor (SBR) and a counter-diffusion membrane biofilm bioreactor (MBfR). The model outputs fit well with the profiles of nitrogen (N) dynamics and biomass changes in both reactors, demonstrating its good predictive ability. The developed model is further used to simulate the counter-diffusion MBfR incorporating n-DAMO and Anammox process to treat sidestream wastewater. The simulated distribution profiles of N removal/production rates by different microbes along biofilm depth reveal that DNRA by n-DAMO archaea plays an important role in N transformation of the integrated n-DAMO and Anammox process. It is further suggested that the counter-diffusion MBfR under the investigated conditions should be operated at proper hydraulic retention times (HRTs) (i.e. 6h and 8h) with exogenous NO2− in the range of 0–10 mg N/L or at HRTs >3h with the absence of exogenous NO2− in order to achieve dischargeable effluent.

Bacterial Mn(II) oxidation plays an important role in the biogeochemical cycling of manganese and many trace metals. This study describes Mn(II) oxidation by two isolated manganese (Mn)-oxidizing strains that were identified and assigned as Brevibacillus brevis MO1 and Brevibacillus parabrevis MO2 based on physiochemical and phylogenetic characterizations. The ecological conditions influenced Mn(II) oxidation by both strains. Mn(II) stimulated the growth of strain MO2 while slightly inhibiting strain MO1. Mn(II)-oxidizing activity of two strains was enhanced with increase of initial pH, and maximum Mn(II)-oxidizing activity occurred at pH 8 for both strains (93.5%-94.0%). Brevibacillus showed the capability of mesophilic and psychrophilic Mn(II) oxidation. X-ray photoelectron spectroscopy (XPS) analysis indicated that the biogenic manganese oxides had an intermediate valence between 3 and 4. These results demonstrated that Brevibacillus, which is capable of oxidizing dissolved Mn(II), will be a suitable strain for exploring the mechanism of manganese oxidation in engineered and natural environments.

This study investigated the potential of improving methane production from algal sludge anaerobic digestion by peroxydisulfate (PDS) pretreatment. The results show that with PDS dosage at 0.02 g PDS/g algal sludge TSS, PDS added system has highest accumulative methane production after 60 days fermentation. The accumulative methane production was 1.08, 1.15, 1.14, 1.13, 1.08, 0.76, and 0.15 times as compared with control, at 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1 g PDS/g algal sludge TSS added, respectively. The SCOD in the system was keep increasing with the increment of PDS dosage after 120 min pretreatment. The algal sludge dewatering rate was increased with adding of PDS as pretreatment. The addition of PDS has inhibited the activities of microbes involved in digestion, while the short chain fatty acids production was improved after 3 days digestion. One-substrate model can be used to simulate the methane yield. The hydrolysis rate was decreased after dosing with PDS, while highest actual and predicted accumulative methane yield was occurred at 0.02 g PDS/g algal sludge TSS. Proteobacteria has higher percentage when the PDS was not higher than 0.1 g PDS/g algal sludge TSS, Acetothermia has higher percentage at 0.01 g PDS/g algal sludge TSS. The microcystin-LR (MC-LR) in algal sludge was largely removed after digestion, including the intracellular MC-LR. The higher PDS dosage could cause heavy metal release from algae cell to the digestate during fermentation. The addition of PDS to algal sludge can improve the accumulative methane production and mitigate microcystin concentration.

Microbial electrolysis cells (MECs) provide effective approaches for hydrogen production from wastewater and renewable biomass. Improving the efficiency of energy recovery from wastes remains a challenge. Here we report the cross-feeding interactions between the hydrogen-producing Ethanoligenens harbinense and electroactive Geobacter sulfurreducens in MECs and anaerobic fermentation using glucose as electron donor. Results showed that G. sulfurreducens could oxidize acetate produced by E. harbinense and transfer electrons extracellularly to the electrode of MECs, which also enhanced hydrogen production by E. harbinense via mitigation of metabolic feedback inhibition and enhancement of interspecies electron transfer. The defined co-cultures showed 2.5–2.9 times higher hydrogen production rates compared to the mono-cultures, while the MECs further enhanced the substrate conversion efficiency and converted electrical energy into hydrogen energy. The molar ratio of ethanol to acetic acid in co-cultured MECs doubled compared to mono-cultures, indicating that G. sulfurreducens steered the fermentation products of E. harbinense towards ethanol. The co-cultures formed dense aggregates or biofilms, in which close physical interactions by intercellular pili-like nanowire structures were observed between E. harbinense and G. sulfurreducens in the co-culture biofilms of both anode and cathode. These findings provide new insight into syntrophic interactions, beyond that previously reported on fermentative hydrogen-producing bacteria with electroactive bacteria or methanogens, and offer an effective strategy to enhance H2 production and steer metabolic products of fermentative bacteria.

Anaerobic ammonium oxidation (anammox) is an important pathway in the nitrogen cycle and for autotrophic nitrogen removal of wastewater. However, the slow granulation or biofilm formation of anammox bacteria in a continuous-flow reactor without anammox inoculum is still a challenge. To accelerate granulation or biofilm formation, an approach of sequential immobilization and granulation of anammox (SIGA) and an internal circulation immobilized blanket (ICIB) with non-granular activated sludge inoculum was investigated. Pre-immobilizing the biofilm with carriers showed higher efficiencies of nitrite removal and enrichment of Candidatus Kuenenia than anaerobic sludge without immobilization. An ICIB with pre-immobilized anaerobic biofilm and an up-flow anaerobic sludge bed (UASB) with pre-acclimated anaerobic sludge were operated for 180 d. The ICIB reactor achieved a nitrogen removal rate of 1.11 kg·N/(m3·d) whereas the UASB reactor only obtained 0.29 kg·N/(m3·d). Illumina HiSeq sequencing of 16S rRNA gene amplicons indicated that the relative abundance of anammox bacteria (Candidatus Kuenenia, Candidatus Brocadia, and Candidatus Jettenia) achieved 42.5–50.6% in biofilm and 45.3–47.1% in granules in the ICIB reactor. By contrast, no anammox bacteria were enriched in the sludge of the UASB reactor. These findings showed that the granulation and the biofilm formation of abundant anammox bacteria occurred in a single ICIB. The anammox biofilm and internal circulation facilitate the granulation of anammox bacteria, as the planktonic anammox cells escaped from the biofilm on the carrier provides parent cells for the formation of anammox granules under suitable hydraulic shear conditions. This study provides a new strategy for a faster start-up of anammox using activated sludge inoculum based on ICIB and SIGA.

High purity ammonia-oxidizing archaea (AOA) culture containing a single AOA strain was enriched from the filtering materials of biological aerated filter. The concentration of AOA reached 3.27 × 10 7 copies/mL, while its proportion was 91.40%. The AOA amoA gene sequence belonged to Nitrososphaera cluster. Ammonia concentration significantly influenced the growth of AOA in culture, while total organic carbon (TOC) concentration had no obvious effect. The optimum ammonia concentration, temperature, pH and DO concentration for growth of AOA were 1 mM, 30 °C, 7.5 and 2.65 mg/L, respectively. Under the optimum growth conditions, the AOA abundance and ammonia oxidation rate were 3.53 × 10 7 copies/mL and 2.54 × 10 −10 mg/(copies·d).

Partial nitritation-anammox (PNA) is a promising and energy-efficient process for the sustainable nitrogen removal. However, its wide applications are still limited by the long start-up period and instability of long-term operation. Quorum sensing (QS), as a way of cell-to-cell communication generally regulating various microbial behaviors, has been increasingly investigated in PNA process, because QS may substantially manipulate the metabolism of microorganisms and overcome the limitations of PNA process. This critical review provides a comprehensive analysis of QS in PNA systems, and identifies the challenges and opportunities for the optimization of PNA process based on QS. The analysis is grouped based on the configurations of PNA process, including partial nitritation, anammox and single-stage PNA systems. QS is confirmed to regulate various properties of PNA systems, including microbial activity, microbial growth rate, microbial aggregation, microbial interactions and the robustness under adverse conditions. Major challenges in the mechanisms of QS, such as QS circuits, target genes and the response to environmental inputs, are identified. Potential applications of QS, such as short-term addition of certain acyl-homoserine lactones (AHLs) or substances containing AHLs, transient unfavorable conditions to stimulate the secretion of AHLs, are also proposed. This review focuses on the theoretical and practical cognation for QS in PNA systems, and serves as a stepping stone for further QS-based strategies to enhance nitrogen removal through PNA process.

ANaerobic MEthanotrophic (ANME) archaea are critical microorganisms mitigating methane emission from anoxic zones. In previous studies, sulfate-dependent anaerobic oxidation of methane (AOM) and nitrate-dependent AOM, performed by different clades of ANME archaea, were detected in marine sediments and freshwater environments, respectively. This study shows that simultaneous sulfate- and nitrate-dependent AOM can be mediated by a clade of ANME archaea, which may occur in estuaries and coastal zones, at the interface of marine and freshwater environments enriched with sulfate and nitrate. Long-term (~1,200 days) performance data of a bioreactor, metagenomic analysis and batch experiments demonstrated that ANME-2d not only conducted AOM coupled to reduction of nitrate to nitrite, but also coupled to the conversion of sulfate to sulfide, in collaboration with sulfate-reducing bacteria (SRB). Sulfide was oxidized back to sulfate by sulfide-oxidizing autotrophic denitrifiers with nitrate or nitrite as electron acceptors, in turn alleviating sulfide accumulation. In addition, dissimilatory nitrate reduction to ammonium performed by ANME-2d was detected, providing substrates to Anammox. Metatranscriptomic analysis revealed significant upregulation of flaB in ANME-2d and pilA in Desulfococcus, which likely resulted in the formation of unique nanonets connecting cells and expanding within the biofilm, and putatively providing structural links between ANME-2d and SRB for electron transfer. Simultaneous nitrate- and sulfate-dependent AOM as observed in this study could be an important link between the carbon, nitrogen and sulfur cycles in natural environments, such as nearshore environments.

Zero-valent iron and biochar composite (ZVI/BC) is a prospective catalyst for activating persulfate and specific surface area (SSA) of ZVI/BC is one of the most important factors affecting its efficacy in the removal of environmental contaminants. However, the green fabrication of ZVI/BC with large SSA remains a challenge. In this study, ZVI/BC with a highly porous structure and large SSA fabricated by co-pyrolysis of K2FeO4 and bamboo was prepared and characterized. The large SSA stemmed from the catalytic and corrosive functions of K and the oxidation of K2FeO4 onto bamboo. ZVI/BC fabricated with 0.05 mol/L K2FeO4 (BC-Fe0.05) showed optimal sulfadiazine (SDZ) removal performance in the peroxydisulfate (PDS) activation system with complete removal after 10 min, as it showed the highest adsorptive ability of SDZ. Moreover, BC-Fe0.05 was able to remain stable after four cycles or 80 days of storage. Higher temperature, lower pH, and Cl− were beneficial to SDZ removal efficiency, whereas CO32– and HPO42− had inhibitory effects. Non-radical species (1O2) and radical species (SO4 −, OH, and O2 −) both contributed to SDZ degradation, and 1O2 was the most important reactive oxygen species. Four degradation pathways were proposed based on ten identified intermediates. Potential eco-toxicity analysis by ECOSAR suggested that most intermediates were less toxic than their parent compound. Overall, this study describes a green fabrication method for ZVI/BC with large SSA using K2FeO4 as the iron precursor. Generally, ZVI/BC with large SSA is an effective catalyst for activating persulfate to degrade antibiotics.

Methane emission has contributed greatly to the global warming and climate change, and the pollution of heavy metals is an important concern due to their toxicity and environmental persistence. Recently, multiple heavy metals have been demonstrated to be electron acceptors for methane oxidation, which offers a potential for simultaneous methane emission mitigation and heavy metal detoxification. This review provides a comprehensive discussion of heavy metals reduction coupled to methane oxidation, and identifies knowledge gaps and opportunities for future research. The functional microorganisms and possible mechanisms are detailed in groups under aerobic, hypoxic and anaerobic conditions. The potential application and major environmental significances for global methane mitigation, the elements cycle and heavy metals detoxification are also discussed. The future research opportunities are also discussed to provide insights for further research and efficient practical application.

Understanding the metabolic function of psychrophilic electroactive bacteria is important for the investigation of extracellular electron transfer (EET) mechanisms under low temperatures (4–15 °C). In this study, Raman activated cell ejection coupled high throughput sequencing was used to accurately generate a mini-metagenome of psychrophilic bacterial community. Hierarchical cluster analysis of the Raman spectrum could accurately select the target Geobacter cluster. The high relative abundance of the membrane transport functional genes ftsEX in the biofilm community indicated an adaptation to reduced temperature, which aided survival of the electroactive bacteria under low temperature. The basal metabolism such as citrate cycle and glycolytic pathway maintained the electron pool for the EET process. The identification of iron (III) transport system genes in high abundance indicated their presence in an active metabolic reaction for potential electron transfer process. It showed the potential involvement c-type cytochromes (coxA and cox1) activity in EET. These results indicated that psychrophilic Geobacter had effective EET mediated by c-type cytochromes at low temperatures.

The granular bioreactor, characterized by excellent settling velocity, high rate and low cost is an ideal choice for achieving coupled nitrate/nitrite dependent denitrifying anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) process. To fundamentally understand its underlining mechanisms and provide suggestions for process optimization, a granule-based model framework was developed to describe simultaneous anaerobic methane and ammonium oxidation by functional microbes. The proposed model was evaluated based on long-term experimental data from two membrane granular sludge reactors (MGSRs) with different operational conditions. The model possessed of good predictive ability to reproduce removal rates and effluent concentrations of nitrogen species. The predicted biomass abundance in two MGSRs and stratified microbial distribution along granule depth were consistent with experimental observations. The estimated parameter values, with good identifiability and reliability indicated a stimulated growth of DAMO archaea in MGSRs. Both hydraulic retention times (HRTs) and granule sizes have influences on microbial abundance in the MGSR and community distribution inside granules. Within the investigated HRTs from 1.4 h to 20 h and granule sizes from 500 μm to 2900 μm, it was revealed that a proper control of relatively short HRTs and small granule sizes resulted in an increased fraction of DAMO archaea and a reduced DAMO bacteria abundance with AnAOB less impacted, which would lower the required nitrite nitrogen to ammonium nitrogen ratio in the nitritation reactor (prior unit) and thus minimize operational cost in sidestream treatment lines.

Microplastics (MPs) have been widely detected in wastewater treatment plants (WWTPs) due to their small particle size, wide distribution, and difficulty in removal. Previous studies, however, mostly focused on MPs in wastewater, thereby neglecting sludge. To comprehensively understand the changes of MPs in WWTPs, we investigated the quantity and characteristics of MPs in wastewater and sludge of a WWTP in Harbin, a typical inland city in China, and calculated the MPs removal rate. The results showed that there were 126.0 ± 14.0 particles/L MPs in the influent and 30.6 ± 7.8 particles/L in the effluent, about 75.7% MPs were removed and transferred to the sludge during this WWTP. The abundance of MPs in dewatered sludge and sludge filter cake was 36.3 ± 5.7 and 46.3 ± 6.2 particles/g (dry sludge), the sludge disposal scale of this WWTP can reach 1300 tons/day, which was equivalent to about 7.74 × 1012 microplastic particles accumulated in sludge per year. These sludges were used as fertilizers in the soil, which will cause secondary pollution of MPs. Raman spectroscopic analysis showed that about 89.5% of particles were plastic polymers, such as polyesters, polyamide (PA), polyethylene terephthalate (PET) and polyethylene (PE), which suggested that MPs may be derived from laundry and personal care products. Therefore, we recommend that more work should be devoted to how to control the release of MPs at the source and the reuse of sludge after treatment by WWTPs.

© 2020 Elsevier Ltd Membrane aerated biofilm reactor (MABR) system is excellent in developing slow growing microorganisms and treating micropollutants prior to entering the aquatic environment. In this work, a mathematical biofilm model was developed to assess melamine biodegradation under different conditions and to predict the profiles of melamine, nitrogen species and microbial biomass in the MABR system. Comtabolism linked to growth of ammonia oxidizing bacteria (AOB) or heterotrophic bacteria (HB) and their respective metabolism were involved in the model to contribute to melamine biodegradation. Results demonstrated the good predictive performance of the developed model in describing dynamic profiles of melamine, COD and nitrogen species in the MABR system. The relative contribution by AOB-induced cometabolism and metabolism by AOB and HB varied depending on the stratification of the biofilm system with AOB prevalent in the inner layer of the biofilm. Metabolism by AOB and HB played more important roles than AOB-induced cometabolism in melamine removal. Controlling optimal biofilm thickness in the suitable range (e.g., more than 750 μm) might realize better simultaneous removal of melamine and nitrogen. This work might provide further insight on efficient removal of melamine from wastewater.

The efficient degradation of pollutants in river sediments is essential for the bioremediation of contaminated rivers. In the present study, sediment microbial fuel cells (SMFCs) with manganese dioxide/tourmaline composite modified cathodes (MnO2/T-SMFCs) were developed to simultaneously produce electricity and degrade organic matter in contaminated river sediment and water. The MnO2/T-SMFCs exhibited a higher power density of 368.99 mW/m3, which was 1.26 and 2.06 times that of SMFCs with MnO2 cathode and open-circuit SMFCs (OC-SMFCs), respectively. Moreover, MnO2/T-SMFCs exhibited the highest total organic carbon (TOC) removal of 55.7 %, which was 1.76 times that of the OC-SMFCs. It also obtained the highest NH4+-N removal of 93.7 %, 40 % higher than OC-SMFCs. The high oxidation reduction reaction (ORR) associated with the MnO2/T cathode is partly attributed to the synergetic effect between MnO2 and tourmaline to change the electronic structure of MnO2 electrode and modify its adsorption/desorption behaviors. PacBio sequencing of 16S rRNA gene amplicons showed that volatile fatty acid- and alcohol-oxidizing Syntrophus and Smithella, and electroactive Geobacter dominated the anode biofilms in the MnO2/T-SMFCs. These results indicated that MnO2/T-SMFCs are effective for sediment bioelectroremediation in contaminated rivers.

Poor flocculation of photo fermentative bacteria resulting in continuous biomass washout from photobioreactor is a critical challenge to achieve rapid and stable hydrogen production. In this work, the aggregation of Rhodopseudomonas faecalis RLD-53 was successfully developed in a photobioreactor and the effects of different carbon sources on hydrogen production and aggregation ability were investigated. Extracellular polymeric substances (EPS) production by R. faecalis RLD-53 cultivated using different carbon sources were stimulated by addition of L-cysteine. The absolute ζ potentials of R. faecalis RLD-53 were considerably decreased with addition of L-cysteine, and aggregation barriers based on DLVO dropped to 15–43 % of that in control groups. Thus, R. faecalis RLD-53 flocculated effectively, and aggregation abilities of strain RLD-53 cultivated with acetate, propionate, lactate and malate reached 29.35, 32.34, 26.07 and 24.86 %, respectively. In the continuous test, hydrogen-producing activity was also promoted and reached 2.45 mol H2/mol lactate, 3.87 mol H2/mol propionate and 5.10 mol H2/mol malate, respectively. Therefore, the aggregation of R. faecalis RLD-53 induced by L-cysteine is independent on the substrate types, which ensures the wide application of this technology to enhance hydrogen recovery from wastewater dominated by different organic substrates.

Biological wastewater treatment process generates large amounts of sludge, the treatment and disposal of which incur substantial costs. Enhancement of sludge dewaterability is of great importance for decreasing the sludge disposal cost in a wastewater treatment plant (WWTP). This study proposes an innovative conditioning approach to improve the dewaterability of the anaerobically digested sludge (ADS) collected from a full-scale WWTP for the first time. The ADS dewaterability was significantly improved in the presence of persulfate (0–1.0 g/g TS; TS: total solids) and zero valent iron (ZVI) (0–4.0 g/g TS) at neutral pH. The largest improvement of ADS dewaterability was obtained at 2.0 g ZVI/g TS and 0.5 g persulfate/g TS, under which the capillary suction time (an indicator of sludge dewaterability) was decreased by approximately 90%. Compared with the traditional Fenton process (Fe2+ + H2O2 at pH 2.0), economic analysis indicated that the ZVI–persulfate conditioning process is more economically attractive for enhancing ADS dewaterability.

Methane in biogas has been proposed to be an electron donor to facilitate complete nitrogen removal using denitrifying anaerobic methane oxidizing (DAMO) microorganisms in an anaerobic ammonium oxidation (anammox) reactor, by reducing the nitrate produced. However, the slow growth and the low activity of DAMO microorganisms cast a serious doubt about the practical usefulness of such a process. In this study, a previously established lab-scale membrane biofilm reactor (MBfR), with biofilms consisting of a coculture of DAMO and anammox microorganisms, was operated to answer if the DAMO reactor can achieve a nitrate reduction rate that can potentially be applied for wastewater treatment. Through progressively increasing nitrate and ammonium loading rates to the reactor, a nitrate removal rate of 684 ± 10 mg-N L(-1) d(-1) was achieved after 453 days of operation. This rate is, to our knowledge, by far the highest reported for DAMO reactors, and far exceeds what is predicted to be required for nitrate removal in a sidestream (5.6-135 mg-N L(-1) d(-1)) or mainstream anammox reactor (3.2-124 mg-N L(-1) d(-1)). Mass balance analysis showed that the nitrite produced by nitrate reduction was jointly reduced by anammox bacteria at a rate of 354 ± 3 mg-N L(-1) d(-1), accompanied by an ammonium removal rate of 268 ± 2 mg-N L(-1) d(-1), and DAMO bacteria at a rate of 330 ± 9 mg-N L(-1) d(-1). This study shows that the nitrate reduction rate achieved by the DAMO process can be high enough for removing nitrate produced by anammox process, which would enable complete nitrogen removal from wastewater.

The integration of nitrate/nitrite dependent anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) provides sustainable solution to simultaneously remove nitrate, nitrite and ammonium. This study demonstrated the sludge granulation process coupling n-DAMO and Anammox from mixed inoculum including river sediment, return activated sludge and crushed anaerobic granule sludge in a novel membrane granular sludge reactor (MGSR). Flocculent biomass gradually turned into compact aggregates and retained as granular sludge with an average diameter of 2.2 mm in MGSR after 684 days’ operation. When steady state with a hydraulic retention time of 1.19 days was reached, the MGSR achieved a nitrogen removal rate of 1.77 g N L−1 d−1. Granules with density of 1.043 g mL−1, settling velocity of 72 m h−1 and sludge volume index of 22 mL g−1 leaded to excellent biomass retention (42 g VSS L−1). Pyrosequencing analysis revealed that two dominant microbial groups, n-DAMO archaea and Anammox bacteria, in the microbial community of the granule were enriched to 31.09% and 12.45%. Fluorescence in situ hybridization revealed a homogenous distribution of n-DAMO archaea and Anammox bacteria throughout the granule. The granular sludge coupling n-DAMO and Anammox microorganisms provides significant potential for high rate nitrogen removal from wastewater.

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) coupling to Anaerobic ammonium oxidation (Anammox) provides an opportunity for simultaneous nitrogen removal and methane emissions mitigation from wastewater. However, to achieve high nitrogen removal rate in such a process remains a critical challenge in practical application. This work investigated the interactions between n-DAMO and Anammox in membrane biofilm reactor (MBfR) and then developed operational strategies of MBfR for high rate nitrogen removal from landfill leachate. Initially, influent containing nitrate and ammonium facilitated the development of n-DAMO and Anammox microorganisms in MBfR, but nitrogen removal performance is hard to be further improved even deteriorated. Detailed investigations of interactions among n-DAMO and Anammox microorganisms confirmed that extra addition of nitrite into MBfR fed with nitrate and ammonium not only stimulated the activities of Anammox bacteria, but also enhanced the activities of n-DAMO archaea from 172.3 to 356.9 mg NO3−-N L−1 d−1. Functional gene analysis also indicated that mcrA and hzsA genes increased after nitrite addition. Based on this finding, influent containing NO3−, NO2− and NH4+ enabled nitrogen removal rates of MBfR increase from 224.9 to 888.2 mg N L−1 d−1. Finally, nitrate in the influent was gradually replaced with nitrite to mimic the effluent from partial nitriation of landfill leachate, but maintain the nitrate availability for n-DAMO archaea through increasing nitrate production from Anammox. These operation strategies enabled MBfR achieve the steady state with a nitrogen removal rate of 6.1 kg N m−3 d−1. Microbial community analysis revealed n-DAMO archaea, n-DAMO bacteria and Anammox bacteria jointly dominated the biofilm, and their relative abundance dynamically shifted with feeding regime. This work provides promising operational strategies for high rate of nitrogen removal from landfill leachate through integrating n-DAMO and Anammox process.

Copyright © 2018 American Chemical Society. Free ammonia (FA) could accumulate at high levels in the sludge anaerobic fermentation, especially under alkaline fermentation conditions, which might significantly affect the anaerobic fermentation. However, its role in the sludge fermentation process has not been revealed fundamentally. This work therefore aims to fill the knowledge gap through the integration of experimental and mathematical approaches. Experimental results showed that when the initial ammonium concentration increased from 20 to 300 mg/L, the maximal short-chain fatty acid (SCFA) yield from fermentation systems with different pH values varied from 91.2 to 296.7 mg of chemical oxygen demand/g volatile suspended solids (VSS). The increasing SCFA production was observed to correlate with the FA level rather than the ammonium level, suggesting that FA, instead of ammonium, is likely the true contributor to enhance SCFA production. Batch tests confirmed that ammonium in the fermentation-strength range (e.g., 0-300 mg/L) did not affect any process of sludge fermentation, but all the processes were affected significantly by FA, pH, or combined FA-pH. It was found that FA facilitated sludge disintegration but inhibited the processes of hydrolysis, acidification, and methanogenesis. When FA and alkaline conditions were combined, synergistic effects on all these processes were observed. The significant contribution of FA to SCFA production was finally confirmed by a sludge fermentation mathematical model proposed recently. The findings reported here revealed the actually existing, yet previously unrecognized contributor to the sludge fermentation, which help engineers better understand the role of FA in sludge anaerobic fermentation.

Different pretreatment approaches enhance hydrolysis and biogas production of waste activated sludge (WAS). However, the best WAS pretreatment method may vary for different purposes. The aim of this study was to compare different combined treatments using potassium ferrate, alkali, and ultrasonication treatment in terms of hydrolysis, biogas production, and microbial community structure during subsequent anaerobic digestion. The soluble chemical oxygen demand (SCOD) increased sharply during sludge pretreatment. Co-treatment with potassium ferrate and ultrasonication (PF + ULT) provided the highest concentration of SCOD (10,206 mg/L) and volatile fatty acids (VFAs) (9160 mg/L). Maximum cumulative methane production, 752.6 mL during 21 days of subsequent anaerobic digestion, was achieved for alkali and ultrasonication (ALK + ULT) co-treated sludge, a 39.3% improvement compared with raw sludge. Our results indicate that PF + ULT and ALK + ULT co-treatments are suitable for methanogenesis in subsequent anaerobic digestion. Co-treatment typically improves biogas production and sludge hydrolysis relative to a single pretreatment. Illumina sequencing of 16S rRNA genes showed that sludge subjected to ALK pretreatment and ALK + ULT co-treatment contained the same predominant populations, and the community structure of PF was similar to PF + ULT. Principal coordinate analysis (PCoA) based on weighted UniFrac distance indicated differences in the microbial communities of the pretreated and raw sludges. The predominant archaeal populations were Methanomassiliicoccus and Methanobacterium in the ALK + ULT and ALK pretreated sludges, and the majority were Methanomassiliicoccus (76.82%) in PF + ULT co-treated sludge, indicating that different pretreatment methods could substantially shape archaeal communities of pretreated sludge. These results reveal that sludge pretreatment not only impacts sludge hydrolysis and biogas production, but also significantly influences the microbial community in subsequent anaerobic digestion.

Ammonia oxidation is the rate-limiting step in nitrification process and dominated by ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). In the present study, a highly enriched culture of AOA was obtained from urban polluted water in Shahe River, Shenzhen, China. The optimum growth conditions were identified by orthogonal analysis as 37 °C, with pH 7.0 and initial ammonia concentration of 1.0 mM. Under these conditions, the highest abundance of AOA was obtained as 4.6 × 107 copies/ng DNA. Growth of AOA in polluted river water showed significant reduction in ammonia concentration in AOA-enriched cultures without antibiotics after 10 days of incubation, while synchronous increase in nitrate concentration was up to 12.7 mg/L. However, AOA-enriched by antibiotic showed insignificant changes in ammonia or nitrite concentration. This study showed that AOB play an important role in ammonia oxidation of polluted river water, and AOA alone showed insignificant changes in ammonia or nitrite concentrations. Therefore, the ammonia oxidation performance of natural water could not be improved by adding high concentration AOA bacterial liquid.

© 2018 In this work, a kinetic model was proposed to evaluate the simultaneous removal of arsenite (As (III)), chlorate (ClO3−) and nitrate (NO3−) in a granule-based mixotrophic As (III) oxidizing bioreactor for the first time. The autotrophic kinetics related to growth-linked As (III) oxidation and ClO3− reduction by As (III) oxidizing bacteria (AsOB) were calibrated and validated based on experimental data from batch test and long-term reactor operation under autotrophic conditions. The heterotrophic kinetics related to non-growth linked As (III) oxidation and ClO3− reduction by heterotrophic bacteria (HB) were evaluated based on the batch experimental data under heterotrophic conditions. The existing kinetics related to As (III) oxidation with NO3− as the electron acceptor together with heterotrophic denitrification were incorporated into the model framework to assess the bioreactor performance in treatment of the three co-occurring contaminants. The results revealed that under autotrophic conditions As (III) was completely oxidized by AsOB (over 99%), while ClO3− and NO3− were poorly removed. Under mixotrophic conditions, the simultaneous removal of the three contaminants was achieved with As (III) oxidized mostly by AsOB and ClO3− and NO3− removed mostly by HB. Both hydraulic retention time (HRT) and influent organic matter (COD) concentration significantly affected the removal efficiency. Above 90% of As (III), ClO3− and NO3− were removed in the mixotrophic bioreactor under optimal operational conditions of HRT and influent COD.

The discovery of denitrifying anaerobic methane oxidation (DAMO) processes enables the complete nitrogen removal from wastewater by utilizing the methane produced on site from anaerobic digesters. This model-based study investigated the mechanisms and operational window for efficient nitrogen removal by coupling nitritation-anaerobic ammonium oxidation (Anammox) and methane-dependent denitrification in membrane biofilm reactors (MBfRs). A mathematical model was applied to describe the microbial interactions among Anammox bacteria, DAMO archaea, and DAMO bacteria. The model sufficiently described the batch experimental data from an MBfR containing an Anammox-DAMO biofilm with different feeding nitrogen compositions, which confirmed the validity of the model. The effects of process parameters on the system performance and microbial community structure could therefore be reliably evaluated. The impacts of nitritation produced NO2(-)/NH4(+) ratio, methane supply, biofilm thickness and total nitrogen (TN) surface loading were comprehensively investigated with the model. Results showed that the optimum NO2(-)/NH4(+) ratio produced from nitritation for the Anammox-DAMO biofilm system was around 1.0 in order to achieve the maximum TN removal (over 99.0%), independent on TN surface loading. The corresponding optimal methane supply increased while the associated methane utilization efficiency decreased with the increase of TN surface loading. The cooperation between DAMO organisms and Anammox bacteria played the key role in the TN removal. Based on these results, the proof-of-concept feasibility of a single-stage MBfR coupling nitritation-Anammox-DAMO for complete nitrogen removal was also tested through integrating the model with ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) processes whilst controlling the dissolved oxygen (DO) concentration in the simulated system. The maximum TN removal was found to be achieved at the bulk DO concentration of around 0.17 g m(-3) under the simulation conditions, with the AOB, Anammox bacteria and DAMO organisms coexisting in the biofilm.

The importance of enhancing sludge dewaterability is increasing due to the considerable impact of excess sludge volume on disposal costs and on overall sludge management. This study presents an innovative approach to enhance dewaterability of anaerobic digestate (AD) harvested from a wastewater treatment plant. The combination of zero valent iron (ZVI, 0-4.0g/g total solids (TS)) and hydrogen peroxide (HP, 0-90mg/g TS) under pH3.0 significantly enhanced the AD dewaterability. The largest enhancement of AD dewaterability was achieved at 18mg HP/g TS and 2.0g ZVI/g TS, with the capillary suction time reduced by up to 90%. Economic analysis suggested that the proposed HP and ZVI treatment has more economic benefits in comparison with the classical Fenton reaction process. The destruction of extracellular polymeric substances and cells as well as the decrease of particle size were supposed to contribute to the enhanced AD dewaterability by HP+ZVI conditioning.

Integrating denitrifying anaerobic methane oxidation (DAMO) with Anammox provides alternative solutions to simultaneously remove nitrogen and mitigate methane emission from wastewater treatment. However, the practical application of DAMO has been greatly limited by slow-growing DAMO microorganisms living on low-solubility gaseous methane. In this work, DAMO and Anammox co-cultures were fast enriched using high concentration of mixed sludges from various environments, and achieved nitrogen removal rate of 76.7 mg NH4+-N L−1 d−1 and 87.9 mg NO3−-N L−1 d−1 on Day 178. Subsequently, nitrogen removal rate significantly decreased but recovered quickly through increasing methane flushing frequency, indicating methane availability could be the limiting factor of DAMO activity. Thus, this work developed a novel Membrane Aerated Membrane Bioreactor (MAMBR), which equipped with gas permeable membrane for efficient methane delivery and ultrafiltration membrane for complete biomass retention. After inoculated with enriched sludge, nitrogen removal rates of MAMBR were significantly enhanced to 126.9 mg NH4+-N L−1 d−1 and 158.8 mg NO3−-N L−1 d−1 by membrane aeration in batch test. Finally, the MAMBR was continuously fed with synthetic wastewater containing ammonium and nitrite to mimic the effluent from partial nitritation. When steady state with nitrogen loading rate of 2500 mg N L−1 d−1 was reached, the MAMBR achieved total nitrogen removal of 2496.7 mg N L−1 d−1, with negligible nitrate in effluent (~6.5 mg NO3−-N L−1). 16S rRNA amplicon sequencing and fluorescence in situ hybridization revealed the microbial community dynamics during enrichment and application. The high performance of nitrogen removal (2.5 kg N m−3 d−1) within 200 days operation and excellent biomass retention capacity (8.67 kg VSS m−3) makes the MAMBR promising for practical application of DAMO and Anammox in wastewater treatment. Keywords: Nitrogen removal, Anammox, Denitrifying anaerobic methane oxidation, Membrane aerated membrane bioreactor, Application

Post aerobic digestion of anaerobically digested sludge (ADS) has been extensively applied to the wastewater treatment plants to enhance sludge reduction. However, the degradation of ADS in the post aerobic digester itself is still limited. In this work, an innovative free nitrous acid (HNO2 or FNA)-based pretreatment approach is proposed to improve full-scale ADS degradation in post aerobic digester. The post aerobic digestion was conducted by using an activated sludge to aerobically digest ADS for 4 days. Degradations of the FNA-treated (treated at 1.0 and 2.0 mg N/L for 24 h) and untreated ADSs were then determined and compared. The ADS was degraded by 26% and 32%, respectively, in the 4-day post aerobic digestion period while being pretreated at 1.0 and 2.0 mg HNO2–N/L. In comparison, only 20% of the untreated ADS was degraded. Economic analysis demonstrated that the implementation of FNA pretreatment can be economically favourable or not depending on the sludge transport and disposal cost.

© 2015 Elsevier Ltd. The presence of a high level of dissolved methane (e.g., 20-26 g m-3) in the anaerobic sludge digestion liquor represents a major challenge to the treatment of this stream, as its emission to the atmosphere contributes significantly to the carbon footprint of wastewater treatment. Here we propose a new approach to simultaneous ammonium and dissolved methane removal from the anaerobic digestion liquor through integrating partial nitritation-Anammox and denitrifying anaerobic methane oxidation (DAMO) processes in a single-stage membrane biofilm reactor (MBfR). In such an MBfR, the anaerobic digestion liquor is provided in the bulk liquid, while oxygen is supplied through gas-permeable membranes to avoid dissolved methane stripping. A previously developed model with appropriate extensions was applied to assess the system performance under different operational conditions and the corresponding microbial interactions. Both influent surface loading (or hydraulic retention time) and oxygen surface loading are found to significantly influence the total nitrogen (TN) and dissolved methane removal, which jointly determine the overall system performance. The counter diffusion and concentration gradients of substrates cause microbial stratification in the biofilm, where ammonia-oxidizing bacteria (AOB) attach close to the membrane surface (biofilm base) where oxygen and ammonium are available, while Anammox and DAMO microorganisms jointly grow in the biofilm layer close to the bulk liquid where methane, ammonium, and nitrite are available with the latter produced by AOB. These results provide first insights and useful information for the design and operation of this new technology for simultaneous ammonium and dissolved methane removal in its potential future applications.