Comparison of sulfate-reducing and conventional Anammox upflow anaerobic sludge blanket reactors

Sulfate-reducing ammonium oxidation: A promising novel process for nitrogen and sulfur removal

Sulfate-reducing ammonium oxidation (sulfammox), a novel and promising process that has emerged in recent years, is essential to nitrogen and sulfur cycles and offers significant potential for the elimination of ammonium and sulfate. This review discussed the development of sulfammox process, the mechanism, characteristics of microbes, potential influencing factors, applicable bioreactors, and proposed the research needs and future perspective. The sulfammox process could be affected by many factors, such as the NH4+/SO42- ratio, carbon source, pH, and temperature. However, these potential influencing factors were only obtained based on what has been seen in papers studying related processes such as denitrification, sulfate-reduction, etc., and have to be further tested in bioreactors carrying out the sulfammox process in the future. Currently, sulfammox is predominantly used in granular activated carbon anaerobic fluidized beds, up-flow anaerobic sludge blanket reactors, anaerobic expanded granular bed reactors, rotating biological contact reactors, and moving bed biofilm reactors. In the future, the operating parameters of sulfammox should be further optimized to improve the processing performance, and the system can be further scaled up for actual wastewater treatment. In addition, the isolation, identification, and characterization of key functional microbes and the analysis of microbial interrelationships will also be focused on in future studies to enable an in-depth analysis of the sulfammox mechanism.

Simultaneous nitrogen and sulfur removal through synergy of sulfammox, anammox and sulfur-driven autotrophic denitrification in a modified bioreactor enhanced by activated carbon

Anaerobic ammonium (NH₄⁺ - N) oxidation coupled with sulfate (SO₄^2-) reduction (sulfammox) is a new pathway for the autotrophic removal of nitrogen and sulfur from wastewater. Sulfammox was achieved in a modified up-flow anaerobic bioreactor filled with granular activated carbon. After 70 days of operation, the NH₄⁺ - N removal efficiency almost reached 70%, with activated carbon adsorption and biological reaction accounting for 26% and 74%, respectively. Ammonium hydrosulfide (NH₄SH) was found in sulfammox by X-ray diffraction analysis for the first time, which confirmed that hydrogen sulfide (H₂S) was one of the sulfammox products. Microbial results indicated that NH₄⁺ - N oxidation and SO₄^2- reduction in sulfammox were carried out by Crenothrix and Desulfobacterota, respectively, in which activated carbon may operate as electron shuttle. In the ¹⁵NH₄⁺ labeled experiment, ³⁰N₂ were produced at a rate of 34.14 μmol/(g sludge·h) and no ³⁰N₂ was detected in the chemical control group, proving that sulfammox was present and could only be induced by microorganisms. The ¹⁵NO₃^- labeled group produced ³⁰N₂ at a rate of 88.77 μmol/(g sludge·h), demonstrating the presence of sulfur-driven autotrophic denitrification. In the adding ¹⁴NH₄⁺ and ¹⁵NO₃^- group, it was confirmed that NH₄⁺ - N was removed by the synergy of sulfammox, anammox and sulfur-driven autotrophic denitrification, where the main product of sulfammox was nitrite (NO₂^-) and anammox was the main cause of nitrogen loss. The findings showed that SO₄^2- as a non-polluting species to environment may substitute NO₂^- to create a new "anammox" process.

Integration of the sulfate reduction and anammox processes for enhancing sustainable nitrogen removal in granular sludge reactors

The Anammox and Sulfate Reduction Ammonium Oxidation processes were compared in two granular sequencing batch reactors operated for 160 days under anammox conditions. It was hypothesized that increasing the concentration of SO₄^2- may positively influence the rate of N removal under anaerobic conditions and it was tested whether SO₄^2- reduction and anammox occur independently or are related to each other. The cooperation of N-S cycles by increasing the concentration of influent SO₄^2- to 952 mg S/L in the second reactor, a higher ammonium utilization rate and sulfate utilization rate was achieved compared to the first reactor, i.e., 2.1-fold and 15-fold, respectively. Nitrosomonas played the dominant role in the N metabolism, while Thauera - in the S metabolism. This study highlights the benefits of linking the N-S cycles as an effective approach for the treatment of NH₄⁺ and SO₄^2- - rich wastewater, including lower substrate removal cost and reduced energy consumption.

Lactate as an effective electron donor in the sulfate reduction: impacts on the microbial diversity

The competition between sulfate-reducing bacteria and methane-producing archaea has a major influence on organic matter removal, as well as the success of sulfidogenic systems. This study investigated the performance of six batch sulfidogenic reactors in response to different COD/sulfate ratios (1.0 and 2.0) and electron donors (cheese whey, ethanol, and sodium lactate) by evaluating the biochemical mechanisms of sulfate reduction, organic matter oxidation, and microbial structure modification. A COD/sulfate ratio of 1.0 resulted in high sulfidogenic activity for all electron donors, thereby achieving a nearly 80% sulfate removal. Lactate provided high sulfate removal rates at COD/sulfate ratios of 1.0 (80%) and 2.0 (90%). A COD/sulfate ratio of 2.0 decreased the sulfate removal rates by 25 and 28% when ethanol and cheese whey were used as substrates. The sulfate-reducing bacteria populations increased using ethanol and lactate at a COD/sulfate ratio of 1.0. Particularly, Desulfovibrio, Clostridium, and Syntrophobacter were predominant. Influent composition and COD/sulfate ratio influenced the relative abundance of the microbial communities. Therefore, controlling these parameters may facilitate the wastewater treatment with high sulfate levels through bacterial activity.

Aeration and non-aeration cycles (AE/NA) time: influence in combined organic matter and nitrogen removal and features of biofilm

This research aimed the performance evaluation of a structured bed reactor with different cycles of Intermittent Aeration (IA)(SBRRIA) in the municipal sewage treatment and the verification of the effect of IA cycles on the total nitrogen (TN) removal and organic matter (COD). Three IA cycles were evaluated: phase I (4 h AE (aeration on) - 2 h NA (aeration off)); II (2 h AE-1 h NA) and III (2 h AE-2 h NA), with Hydraulic Retention Time of 16 h. The best nitrogen removal was obtained during phase II, with the lowest non-aeration time: efficiency of nitrification, denitrification, TN and COD removal of 80 ± 15%, 82 ± 12%, 67 ± 6% and 94 ± 7%, respectively. The mean cell residence time was 19, 26 and 33 d in phases I, II and III, respectively. The statistical analysis applied to the AE/NA profiles showed that the time of AE and NA in the cycles did not influence nitrogen and organic matter removal. Thus, this indicates the recirculation and the gradient formed in the support material facilitate the process of Simultaneous Nitrification and Denitrification. The lowest concentration of nitrifying and denitrifying microorganisms was obtained in effluent and sludge at the end of phase III. From the TP (Total Proteins)/TPS (Total Polysaccharides) ratio obtained (0.8 ± 0.1, 1.3 ± 0.1 e 1.5 ± 0.1 in phases I, II and III), it was possible to conclude that the biofilm in phase I was more porous, with a thin layer if compared to that in phase II and III.

Effect of organic matter on the anammox performance of constructed rapid infiltration systems

Anaerobic ammonia oxidation (anammox) process was achieved in a constructed rapid infiltration (CRI) system and the effect of organic matter on the anammox performance and microbial community structure was investigated. The results showed that the removal efficiencies of NH4+-N, NO2-N and TN were 99.7 ± 0.3%, 99.8 ± 0.2% and 91.3 ± 0.2% respectively after 83 days of acclimation without the presence of organic matter in the influent. The average TN removal efficiency increased by 3.2%-7.7% due to the synergistic effect of anammox and denitrification at a low level of organic matter concentration (10-30 mg COD/L). At medium or high organic matter concentration (50-100 mg COD/L), denitrification gradually replaced anammox as the predominant nitrogen removal route due to its stronger ability to compete with substrate, resulting in a significant decline in anammox activity. The contribution rate of anammox to nitrogen removal dropped by 70.3% with the influent COD increased from 0 to 100 mg/L, and the TN removal efficiency decreased to 68.4 ± 3.6% since the anammox was seriously suppressed. 16S rRNA high-throughput sequencing analysis illustrated that the genus Candidatus Kuenenia was the predominant anammox bacteria (AAOB) with a relative abundance of 12.63% when no organic matter was applied. While the heterotrophic denitrifying bacteria (DNB) Thauera gradually dominated the community with the elevated organic matter introduction. The findings of this study provide useful information for the stable operation and optimal regulation of anammox in the CRI system when the influent contains organic matter.

Systematic evaluation of PDA/PAM/MAH-modified basalt fibre as biofilm carrier for wastewater treatment

In this study, three kinds of modified basalt fibre (MBF) were used as biofilm carrier to treat wastewater, mainly for the removal of organic matter and nutrient pollutants, which was evaluated the feasibility of modification by pollutants removal performance. Polydopamine modified basalt fibre (PAD-BF) via the surface coating method were obtained. Polyacrylamide modified basalt fibre (PAM-BF) and maleic anhydride-modified basalt fibre (MAH-BF) via the surface grafting method were prepared. The surface physicochemical properties, biomass attachment capacity and pollutants removal efficiency of MBF were systematically investigated. Electron microscope scanning (SEM) revealed that the surface roughness of BF was obviously improved by modification. Besides, fourier transform infrared (FTIR) suggested that the MBF had more surface-active functional groups. The results of sludge immobilization tests showed that PDA/PAM/MAH-BF had higher bio-affinity than ordinary BF with 1.5∼2.3 times on immobilization ratio of microorganisms (IRM). Furthermore, the performances of PDA/PAM/MAH-BF as biofilm carrier for pollutants were significantly higher than that of ordinary BF group. Among them, the highest removal efficiency of COD in PAD-BF biofilm reactor was 95.29 ± 0.99%, while that of BF group was 86.30 ± 3.09%. PAM-BF group had the best removal effect of nutrients with the removal efficiency of 90.83 ± 7.69% for TP and 91.25 ± 6.43% for TN, respectively, while the removal rate of BF group was only about 70%. The improvement of dissolved oxygen (DO) in the MBF reactors was consistent with the enhancement of contaminant removal. Therefore, PDA/PAM/MAH-BF can be used as promising biological carrier fillers in wastewater treatment engineering.

Sulfidation forwarding high-strength Anammox process using nitrate as electron acceptor via thiosulfate-driven nitrate denitratation

A single up-flow thiosulfate-driven nitrate denitratation coupled with the sulfurized Anammox (TDSA) with the core-shell structure (S⁰@ Anammox granules) provided a chemical/energy-saving way for the removal of high-content ammonium with nitrate as electron acceptor. Approximately 83.66% total nitrogen removal efficiency (TNRE) could be achieved by the sulfurized Anammox encrusted by S⁰/S_n^2- at a high loading rate (2.6 kg-N/(m³·d)) via resisting high concentration of free ammonia (FA) (22.35 mg/L), mainly through S₂O₃^2-, S⁰/S_n^2- -driven partial denitrification-Anammox (PDN-Anammox) process. Moreover, S⁰/S_n^2--PDN-Anammox was largely restricted when intermittently aerated, but still resulting in 74.47% TNRE due to the partial nitrification-Anammox (PN-Anammox). The sequencing analysis revealed that Anammox bacterium (Candidatus_Kuenenia) and sulfur-oxidizing bacterium (Thiobacillus) coexisted, in which Anammox process occurred mainly via NO instead of NH₂OH. This study provided a new perspective for high concentration nitrogen wastewater removal in engineering applications.

Giant sulfur bacteria (Beggiatoaceae) from sediments underlying the Benguela upwelling system host diverse microbiomes

Due to their lithotrophic metabolisms, morphological complexity and conspicuous appearance, members of the Beggiatoaceae have been extensively studied for more than 100 years. These bacteria are known to be primarily sulfur-oxidizing autotrophs that commonly occur in dense mats at redox interfaces. Their large size and the presence of a mucous sheath allows these cells to serve as sites of attachment for communities of other microorganisms. But little is known about their individual niche preferences and attached microbiomes, particularly in marine environments, due to a paucity of cultivars and their prevalence in habitats that are difficult to access and study. Therefore, in this study, we compare Beggiatoaceae strain composition, community composition, and geochemical profiles collected from sulfidic sediments at four marine stations off the coast of Namibia. To elucidate community members that were directly attached and enriched in both filamentous Beggiatoaceae, namely Ca. Marithioploca spp. and Ca. Maribeggiatoa spp., as well as non-filamentous Beggiatoaceae, Ca. Thiomargarita spp., the Beggiatoaceae were pooled by morphotype for community analysis. The Beggiatoaceae samples collected from a highly sulfidic site were enriched in strains of sulfur-oxidizing Campylobacterota, that may promote a more hospitable setting for the Beggiatoaceae, which are known to have a lower tolerance for high sulfide to oxygen ratios. We found just a few host-specific associations with the motile filamentous morphotypes. Conversely, we detected 123 host specific enrichments with non-motile chain forming Beggiatoaceae. Potential metabolisms of the enriched strains include fermentation of host sheath material, syntrophic exchange of H₂ and acetate, inorganic sulfur metabolism, and nitrite oxidation. Surprisingly, we did not detect any enrichments of anaerobic ammonium oxidizing bacteria as previously suggested and postulate that less well-studied anaerobic ammonium oxidation pathways may be occurring instead.

Novel biotechnologies for nitrogen removal and their coupling with gas emissions abatement in wastewater treatment facilities

Wastewaters contaminated with nitrogenous pollutants, derived from anthropogenic activities, have exacerbated our ecosystems sparking environmental problems, such as eutrophication and acidification of water reservoirs, emission of greenhouse gases, death of aquatic organisms, among others. Wastewater treatment facilities (WWTF) combining nitrification and denitrification, and lately partial nitrification coupled to anaerobic ammonium oxidation (anammox), have traditionally been applied for the removal of nitrogen from wastewaters. The present work provides a comprehensive review of the recent biotechnologies developed in which nitrogen-removing processes are relevant for the treatment of both wastewaters and gas emissions. These novel processes include the anammox process with alternative electron acceptors, such as sulfate (sulfammox), ferric iron (feammox), and anodes in microbial electrolysis cells (anodic anammox). New technologies that couple nitrate/nitrite reduction with the oxidation of methane, H₂S, volatile methyl siloxanes, and other volatile organic compounds are also described. The potential of these processes for (i) minimizing greenhouse gas emissions from WWTF, (ii) biogas purification, and (iii) air pollution control is critically discussed considering the factors that might trigger N₂O release during nitrate/nitrite reduction. Moreover, this review provides a discussion on the main challenges to tackle towards the consolidation of these novel biotechnologies.

Nitrogen removal from ammonium- and sulfate-rich wastewater in an upflow anaerobic sludge bed reactor: performance and microbial community structure

Autotrophic ammonium removal by sulfate-dependent anaerobic ammonium oxidation (S-Anammox) process was studied in an upflow anaerobic sludge bed reactor inoculated with Anammox sludge. Over an operation period of 371 days, the reactor with a hydraulic retention time of 16 h was fed with influent in which NH₄⁺ concentration was fixed at 70 mg N L^-1, and the molar ratio of NO₂^-:NO₃^-:SO₄^2- was 1:0.2:0.2, 0.5:0.1:0.3 and 0:0:0.5 in stages I, II and III, respectively. As the NO₂^- in influent was entirely replaced by SO₄^2-, the NH₄⁺ removal rate was 31.02 mg N L^-1 d^-1, and the conversion rate of SO₄^2- was 8.18 mg S L^-1 d^-1. On grounds of the high NH₄⁺:SO₄^2- removal ratio (8.67:1), the S^2- accumulation and pH drop in effluent, as well as the analysis results of microbial community structure, the S-Anammox process was speculated to play a dominant role in stage III. The NH₄⁺ over-transformation was presumably as a consequence of the cyclic regeneration of SO₄^2-. Concerning the microbial characteristics in the system, the Anammox bacteria (Candidatus Brocadia), sulfate-reducing bacteria (SRB) (Desulfatiglans and Desulfurivibrio) and sulfur-oxidizing bacteria (SOB) (Thiobacillus) in biomass was enriched in the case of without addition of NO₂^- in influent. Sulfate reduction driven ammonium anaerobic oxidation was probably attributed to the coordinated metabolism of nitrogen- and sulfur-utilizing bacteria consortium, in which Anammox bacteria dominates the nitrogen removal, and the SRB and SOB participates in the sulfur cycle as well as accepts required electrons from Anammox bacteria through a direct inter-species electron transfer (DIET) pathway.

Anammox Bacteria Are Potentially Involved in Anaerobic Ammonium Oxidation Coupled to Iron(III) Reduction in the Wastewater Treatment System

Anaerobic ammonium oxidation coupled to nitrite reduction (termed as Anammox) was demonstrated as an efficient pathway to remove nitrogen from a wastewater treatment system. Recently, anaerobic ammonium oxidation was also identified to be linked to iron(III) reduction (termed Feammox) with dinitrogen, nitrite, or nitrate as end-product, reporting to enhance nitrogen removal from the wastewater treatment system. However, little is known about the role of Anammox bacteria in the Feammox process. Here, slurry from wastewater reactor amended with ferrihydrite was employed to investigate activity of Anammox bacteria in the Feammox process using the ¹⁵N isotopic tracing technique combined with 16S rRNA gene amplicon sequencing. A significantly positive relationship between rates of ¹⁵N₂ production and iron(III) reduction indicated the occurrence of Feammox during incubation. Relative abundances of Anammox bacteria including Brocadia, Kuenenia, Jettenia, and unclassified Brocadiaceae were detected with low relative abundances, whereas Geobacteraceae dominated in the treatment throughout the incubation. ¹⁵N₂ production rates significantly positively correlated with relative abundances of Geobacter, unclassified Geobacteraceae, and Anammox bacteria, revealing their contribution to nitrogen generation via Feammox. Overall, these findings suggested Anammox bacteria or cooperation between Anammox bacteria and iron(III) reducers serves a potential role in Feammox process.

Solar-driven, self-sustainable electrolysis for treating eutrophic river water: Intensified nutrient removal and reshaped microbial communities

River ecosystems are the most important resource of surface freshwater, but they have frequently been contaminated by excessive nutrient input of nitrogen (N) and phosphorus (P) in particular. An efficient and economic river water treatment technology that possesses the capacity of simultaneous N and P removal is urgently required. In this study, a solar-driven, self-sustainable electrolytic treatment was conducted in situ to intensify N and P removal from eutrophic river water. Solar panel was applied to provide the electrolysis setups with energy (voltage 10 ± 0.5 V), and the current density was controlled to be 0.06 ± 0.02 mA cm^-2. Results indicated that the average removal efficiencies of total N (TN) and total P (TP) under electrolysis conditions reached 72.4 ± 11.7 and 13.8 ± 5.3 mg m^-2 d^-1, which were 3.7- and 4.7-fold higher compared to untreated conditions. Enhanced TN removal mainly reflected the abatement of nitrate N (NO₃^--N) (80.6 ± 4.1%). The formation of ferric ions through the electro-dissolution of the sacrificial iron anode improved TP removal by coprecipitation with SPS. Combined high-throughput sequencing and statistical analyses revealed that electrolysis significantly reshaped the microbial communities in both the sediment-water interface and suspended sediment (SPS), and hydrogenotrophic denitrifiers (e.g., Hydrogenophaga) were highly enriched under electrolysis conditions. These findings indicated that in situ electrolysis is a feasible and effective technology for intensified nutrient removal from river water.

Sludge ratio affects the start-up performance and functional bacteria distribution of a hybrid CANON system

To investigate the effect of sludge ratio on the hybrid CANON system, autotrophic nitrogen removal sludge was inoculated with different granule/floc ratios to initiate the CANON system, and maintained the sludge ratio during the operation process. The start-up performances were compared, and the distribution characteristics of functional bacteria were investigated. The results show that the Equivalent system (granules:flocs = 1:1-1:1.5) successfully started-up on day 19, and the nitrogen removal rate (NRR) reached 0.299 kgN m^-3·d^-1 on day 63. At the same time, it was less affected by the load shock than High-granules and High-flocs systems. Therefore, the Equivalent system had the strongest start-up performance. The activities of the functional bacteria conformed to spatial heterogeneity, unlike the abundance. With the increased floc proportion, the difference in the activity and abundance of anaerobic ammonium-oxidizing bacteria (AAOB) between the granules and flocs increased, while there was a decrease in the difference in aerobic ammonium-oxidizing bacteria (AOB). However, the abundance of Nitrosomonas in the granules was higher than in the flocs when the proportion of flocs was higher than 50%. This study provides new ideas and insights for the fast start-up of the CANON system and can conform to the varying needs of engineering applications.

Sulfate dependent ammonium oxidation: A microbial process linked nitrogen with sulfur cycle and potential application

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.

Unclassified Anammox bacterium responds to robust nitrogen removal in a sequencing batch reactor fed with landfill leachate

Treatment of landfill leachate was conducted in a lab-scale sequencing batch reactor (SBR). The SBR was started through inoculating activated sludge with controlling dissolved oxygen of 0.5-1.0 mg/L. Anammox reaction took place within around three months. The SBR established robust nitrogen removal with incremental NLRs of 0.25-2.17 kg N/m³/d. At the final phase, it achieved elevated nitrogen removals of 1.68-1.91 kg N/m³/d. 16S rRNA gene amplicon sequencing analysis revealed Nitrosomonas, unclassified Anammox bacterium, and diverse denitrifying populations coexisted and accounted for 4.02%, 20.05% and 34.69%, respectively. Phylogenic analysis and average nucleotide identity comparison jointly suggested the unclassified Anammox bacterium potentially pertained to a novel Anammox lineage. The functional profiles' prediction suggested sulfate reduction, arsenate reduction and eliminations of antibiotics and drugs likely occurred in the SBR. The finding from this study suggests contribution of unclassified Anammox bacteria in influencing nitrogen budget in natural and engineering systems is currently being underestimated.

Indoor generated PM2.5 compositions and volatile organic compounds: Potential sources and health risk implications

The aim of the present study was to investigate the potential sources of heavy metals in fine air particles (PM_2.5) and benzene, toluene, ethylbenzene, and isomeric xylenes (BTEX) in gas phase indoor air. PM_2.5 samples were collected using a low volume sampler. BTEX samples were collected using passive sampling onto sorbent tubes and analyzed using gas chromatography-mass spectrometry (GC-MS). For the lower and upper floors of the evaluated building, the concentrations of PM_2.5 were 96.4 ± 2.70 μg/m³ and 80.2 ± 3.11 μg/m³, respectively. The compositions of heavy metals in PM_2.5 were predominated by iron (Fe), zinc (Zn), and aluminum (Al) with concentration of 500 ± 50.07 ng/m³, 466 ± 77.38 ng/m³, and 422 ± 147.38 ng/m³. A principal component analysis (PCA) showed that the main sources of BTEX were originated from vehicle emissions and exacerbate because of temperature variations. Hazard quotient results for BTEX showed that the compounds were below acceptable limits and thus did not possess potential carcinogenic risks. However, a measured output of lifetime cancer probability revealed that benzene and ethylbenzene posed definite carcinogenic risks. Pollutants that originated from heavy traffic next to the sampling site contributed to the indoor pollution.

Micro-graphite particles accelerate denitrification in biological treatment systems

Accelerated denitrification is an essential problem in the biological treatment of nitrogenous wastewater. In this study, we report that denitrification is accelerated by micro-graphite particles (MGPs). The denitrification rate was increased by 83.4% or 11.1% in synthetic (with 0.16 g/L MGPs) or industrial nitrogenous wastewater (with 0.12 g/L MGP), respectively. The mechanism was revealed via a quantitative polymerase chain reaction (q-PCR), high-throughput sequencing, and scanning electron microscopy (SEM). The abundance of denitrifying bacteria Paracoccus in the sludge was increased by micro-graphite particles. The number of denitrifying bacteria with the nirS gene was increased significantly (75.6%). To the best of our knowledge, this is the first report that MGP could enhance denitrification via the sludge. MGP can denitrify in industrial applications.

Use of a low-cost and energy-efficient device for treating low-strength wastewater at low temperatures focusing on nitrogen removal and microbial community

Treating wastewater at low temperatures has always been challenging. In this study, an anoxic filter (ANF)/multi-stage waterwheel driving rotating biological contactors (ms-wdRBCs) device was investigated as a potential solution for treatment of low-strength domestic wastewater at low temperatures (6-18 °C). Parameters, including the recirculation ratio (RR) and hydraulic retention time (HRT), were regulated to identify the optimum operating conditions. Using the optimum parameters of 200% RR, 10.67 h HRT_ANF, and 1.33 h HRT_wdRBC, 75.37% ± 4.43% COD, 44.81% ± 3.67% TN, 75.05% ±1.86% NH₄⁺-N, and 35.46% ± 4.87% TP were removed. The microbial communities in eight different sections of the device were investigated through the 16s rRNA analysis. The microbial results helped to explain the device performance. Denitrification-related bacteria were present in great abundance in both the ANF and the ms-wdRBCs. Anammox-related bacteria were also in significant abundance in ANF and some parts of ms-wdRBCs, which suggested a potential solution for improving the device performance by expanding the role of these anammox bacteria. Considering both the pollutant removal efficiency and investment costs, this device is acceptable as part of a low-strength domestic wastewater treatment solution at low temperatures.

Investigating COD and Nitrate-Nitrogen Flow and Distribution Variations in the MUCT Process Using ORP as a Control Parameter

This study aimed to reveal the flow and distribution lows of chemical oxygen demand (COD) and nitrate-nitrogen under different main anoxic stage oxidation-reduction potential (ORPan) conditions based on the analysis of material balance in each reaction stage of the modified university of cape town (MUCT) process, combined with the biochemical reaction principles of activated sludge. The rule of the carbon source saving effect was also clarified. The study adopted the programmable logic controller automatic control system and the feedback control structure using the inner circulation flow of nitrate as the controlled variable. The ORPan setting values of control parameters were -140, -125, -110, -95, -70, and -60 mV, respectively. The results showed that when the ORPan setting value was -95 mV, COD distribution ratios of phosphorus-accumulating bacteria reached the highest in the anaerobic stage and preanoxic stage, with the values of 51.74 and 7.70%, respectively. The COD was distributed between heterotrophic bacteria and denitrifying bacteria in the main anoxic stage, and the distribution ratios were 4.40 and 7.19%, respectively, when the ORPan setting value was -95 mV. The study also showed the distribution of nitrate-nitrogen between denitrifying bacteria and denitrifying phosphorus-accumulating bacteria in the main anoxic stage, and when ORPan increased from -140 to -60 mV, the distribution ratios of denitrifying phosphate-accumulating bacteria increased from 76.46 to 86.32%. When there was no denitrification and phosphorus absorption, the acetic acid dosage increased from 20.33 g/d at -140 mV to 24.76 g/d at -95 mV, and the carbon source saving rate increased from 23.19 to 26.56% under similar conditions. Therefore, in the MUCT process, the regulation of ORPan changed the material flow direction and mass quality distribution of COD and nitrate nitrogen. When ORPan set value was -95 mV, COD and nitrate-nitrogen got the best distribution and the carbon source saving effect was the most significant.

Response of nitrogen removal performance, functional genes abundances and N-acyl-homoserine lactones release to carminic acid of anammox biomass

Carminic acid (CA) can serve as a redox mediator and influence the electron transfer process. CA dosages of 0-5 mg/L were added to anaerobic ammonia oxidation (anammox) biomass. The results illustrated that CA not only reduced the inorganic nitrogen removal efficiency, but also decreased the nitrogen removal rate. The deterioration of nitrogen removal performance was due to the excess production of nitrate-nitrogen. The concentration of extracellular polymeric substances showed a decrease together with a decline in N-acyl-homoserine lactones release. CA addition decreased the activity of anammox bacteria while increasing the nitrifying potential. Quantitative reverse transcription polymerase chain reaction showed a decrease in anammox functional genes (nirS, hzo, and hzsB) and promotion of the expression of the nxrB gene, which corresponded with a decrease in anammox bacteria activity and the improvement of nitrifying potential. As a result, CA should not be added to anammox biomass.

Anammox-based processes: How far have we come and what work remains? A review by bibliometric analysis

Nitrogen contamination remains a severe environmental problem and a major threat to sustainable development worldwide. A systematic analysis of the literature indicates that the partial nitritation-anammox (PN/AMX) process is still actively studied as a viable option for energy-efficient and feasible technology for the sustainable treatment of N- rich wastewaters, since its initial discovery in 1990. Notably, the mainstream PN/AMX process application remains the most challenging bottleneck in AMX technology and fascinates the world's attention in AMX studies. This paper discusses the recent trends and developments of PN/AMX research and analyzes the results of recent years of research on the PN/AMX from lab-to full-scale applications. The findings would deeply improve our understanding of the major challenges under mainstream conditions and next-stage research on the PN/AMX process. A great deal of efforts has been made in the process engineering, PN/AMX bacteria populations, predictive modeling, and the full-scale implementations during the past 22 years. A series of new and excellent experimental findings at lab, pilot and full-scale levels including good nitrogen removal performance even under low temperature (15-10 °C) around the world were achieved. To date, pilot- and full-scale PN/AMX have been successfully used to treat different types of industrial sewage, including black wastewater, sludge digester liquids, landfill leachate, monosodium glutamate wastewater, etc. Supplementing the qualitative analysis, this review also provides a quantitative bibliometrics study and evaluates global perspectives on PN/AMX research published during the past 22 years. Finally, general trends in the development of PN/AMX research are summarized with the aim of conveying potential future trajectories. The current review offers a valuable orientation and global overview for scientists, engineers, readers and decision makers presently focusing on PN/AMX processes.

Effect of nitrite and nitrate on sulfate reducing ammonium oxidation

The effects of nitrite and nitrate on the integration of ammonium oxidization and sulfate reduction were investigated in a self-designed reactor with an effective volume of 5 L. An experimental study indicated that the ammonium oxidization and sulfate reduction efficiencies were increased in the presence of nitrite and nitrate. Studies showed that a decreasing proportion of N/S in the presence of NO₂ ^- at 30 mg·L^-1 would lead to high removal efficiencies of NH₄ ⁺-N and SO₄ ^2--S of up to 78.13% and 46.72%, respectively. On the other hand, NO₃ ^- was produced at approximately 26.89 mg·L^-1. Proteobacteria, Chloroflexi, Bacteroidetes, Chlorobi, Acidobacteria, Planctomycetes and Nitrospirae were detected in the anaerobic cycle growth reactor. Proteobacteria was identified as the dominant functional bacteria removing nitrogen in the reactor. The nitritation reaction could promote the sulfate-reducing ammonium oxidation (SRAO) process. NH₄ ⁺ was converted to NO₂ and other intermediates, for which the electron acceptor was SO₄ ^2-. These results showed that nitrogen was converted by the nitrification process, the denitrification process, and the traditional anammox process simultaneously with the SRAO process. The sulfur-based autotrophic denitration and denitrification in the reactor were caused by the influent nitrite and nitrate.

Study of sulfate-reducing ammonium oxidation process and its microbial community composition

In this study, the simultaneous removal of ammonium and sulfate was detected in a self-designed circulating flow reactor, in which ammonium oxidization was combined with sulfate reduction. The highest removal efficiencies of NH₄ ⁺-N and SO₄ ^2-S were 92% and 59.2%. NO₂ ^- and NO₃ ^- appeared in the effluent, and experimental studies showed that increasing the proportion of N/S in the influent would increase the NO₂ ^- concentration in the effluent. However, N/S [n(NH₄ ⁺-N)/n(SO₄ ^2-S)] conversion rates during the experiment were between 2.1 and 12.9, which may have been caused by the experiment's complex process. The microbial community in the sludge reactor included Proteobacteria, Chloroflexi, Bacteroidetes, Chlorobi, Acidobacteria and Planctomycetes after 187 days of operation. Proteobacteria bacteria had a more versatile metabolism. The sulfate-reducing ammonium oxidation (SRAO) was mainly due to the high performance of Proteobacteria. Nitrospirae has been identified as the dominant functional bacteria in several anammox reactors used for nitrogen removal. Approximately 12.4% of denitrifying bacteria were found in the sludge. These results show that a portion of the nitrogen was converted by nitrification-denitrification, and that traditional anammox proceeds simultaneously with SRAO.

Mitigating adverse impacts of varying sulfide/nitrate ratios on denitrifying sulfide removal process performance

Complete removal of nitrogen, sulfur and carbon in wastewaters by denitrifying sulfide removal (DSR) process can be achieved at stoichiometry sulfide to nitrate ratio (S/N) of 1:1 in expanded granular sludge bed reactor. Wastewaters with varying S/N ratios can adversely impact the DSR performances with deterioration of synergetic cooperation between autotrophic and heterotrophic denitrifiers. DO (dissolved oxygen) serves effectively as supplementary electron receiver for sulfide oxidation, leaving more nitrate for heterotrophic denitrifiers to utilize acetate. The optimal oxygen to sulfide molar ratio (DO/S) is 0.5:1 for complete removal of sulfide, nitrate and acetate at different S/N ratios. The heterotrophic denitrification rate was decreased to 0.03 ± 0.002, 0.24 ± 0.011 and 0.35 ± 0.027 NO₃^--N·h^-1·gVSS^-1 at S/N ratio of 5:2, 5:5 and 5:8, respectively, when DO/S of 3:1 was performed. This optimal condition was proposed as an easy-to-implement control criterion for subsiding the adverse impact by varying S/N ratios in handling real wastewaters.

Nitrogen removal via nitritation pathway for low-strength ammonium wastewater by adsorption, biological desorption and denitrification

Stable nitritation for low-strength ammonium wastewater was the key obstacle for cost-effective and low-carbon biological nitrogen removal. A zeolite biological fixed bed (ZBFB) and an anoxic sequencing batch reactor (ASBR) were successfully applied for achieving nitritation-denitrification of low-strength ammonium wastewater by adsorption, biological desorption and denitrification. Based on free ammonia inhibition on biofilm, stable nitrite accumulation could be realized with suitable operational time and aeration in biological desorption. During cycle operation, adsorption effluent NH₄⁺-N kept at 3.0-4.0 mg/L, biological desorption effluent NO₂^--N maintained at 226.8-243.2 mg/L with average nitrite accumulation ratio of 97.18%, and nitrite removal rate was about 0.628-0.672 kg NO₂^--N·m^-3·day^-1, revealing obvious feasibility of ZBFB and ASBR for low-strength ammonium wastewater treatment. High-throughput sequencing analysis results further presented significant microbial community variations happened after cycle operation, with ammonia oxidizing bacteria enrichment and nitrite oxidizing bacteria inhibition in ZBFB and dominance of denitrifiers in ASBR.

Effect of air flow rate and C/N ratio on biological nitrogen removal through the CANON process treating reject water

The CANON process is a promising method for nitrogen removal in wastewaters with low organic carbon content like reject water. This study investigated the effect of important factors for optimization of the CANON process through inhibition of nitrite-oxidizing bacteria (NOB). In the acclimation period, complete ammonium removal and 43.3% total N removal were obtained at hydraulic retention time of 12 h, temperature of 30°C ± 0.5°C and DO equal to 7-9 mg/L. The effects of air flow rate (AFR) (representative of DO), SRT and C/N were evaluated. Air flow rate was the most important factor for controlling the process, but the effect of SRT was negligible. When AFR was increased from 100 to 500 mL/min, both ammonium removal efficiency (33-43% to 81-83%) and nitrite accumulation (nitritation, 40 mgN/L to 100-120 mgN/L) were increased, but with increasing AFR to 1000 mL/min only ammonium removal efficiency was increased and because of better condition (high DO) for NOBs, nitritation was decreased. C/N had an effect like AFR of 1000 and only increased ammonium removal efficiency and total N removal. With increasing AFR and C/N, both OUR and AUR were increased, but SVI was decreased.

New insight into sludge reduction induced by different substrate allocation strategy between oxygen and nitrate/nitrite as terminal electron acceptor

Sludge reduction based on regulating substrate allocation between catabolism and anabolism as a strategy is proposed to reduce energy and chemicals consumption during wastewater treatment. The results indicated that a sludge reduction of 14.8% and excellent nutrient removal were simultaneously achieved in the low dissolved oxygen (LDO) activated sludge system with a hydraulic retention time of 24 h at 25 °C. Denitrifiers comprised nearly 1/4 of all microorganisms in the system. These denitrifiers converted NO_x^- to N₂ obtaining a lower biomass yield. The oxidoreductase activity proteins in the LDO sample was more than twice that of the normal DO sample, indicating that catabolism was stimulated by NO_x^- when replacing O₂ as electron acceptor. Less substrate was used for cell synthesis in the LDO system. Stable sludge reduction without extra energy and chemicals inputs was achieved by regulating the substrate allocation by inducing the bacteria to utilize NO_x^- instead of O₂.

Novel design and optimisation of a nitritation/anammox set-up for ammonium removal from filtrate of digested sludge

Although the anammox process is extensively applied for the treatment of NH4-rich wastewater, new technical solutions overcoming the operational difficulties remain an important task. An innovative design of anammox-based set-up was employed to improve sludge settling under high ammonium load. The set-up included a completely mixed bioreactor with suspended and immobilised activated sludge. To prevent sludge flotation, recycled suspended sludge was additionally treated in an aerated tank at dissolved oxygen (DO) concentration of 1.5 ± 0.2 mg/l followed by processing in a flow-homogeniser. Introduction of these elements resulted in a 3.5-fold increase in total nitrogen removal efficiency (TNRE). The bioreactor achieved maximal TNRE of 86% corresponding to total nitrogen removal rate of 0.77 kg N/m3/d under defined optimal conditions: temperature of 35 ± 2°C, DO of 0.6 ± 0.2 mg/l, hydraulic retention time of 12 h, and dose of suspended sludge of 1.5 ± 0.1 g total suspended solids (TSS)/l. A weakly attached sludge was first described as a technologically important factor. Suspended, weakly and firmly attached sludge exhibited the highest heterotrophic, nitrifying, and anammox activities, respectively. New probes were constructed to detect anammox bacteria by fluorescence in situ hybridisation. Probe for Candidatus 'Jettenia' could be recommended for widespread use.

Improvement of start-up and nitrogen removal of the anammox process in reactors inoculated with conventional activated sludge using biofilm carrier materials

The start-up of the anaerobic ammonium oxidation (anammox) process in three up-flow column reactors seeded with common mixed activated sludge and added with three materials, sponge (R1), sponge + volcanic rock (R2) and sponge + charcoal (R3), as carriers for biofilm formation were comparatively investigated in this study. The supplement of volcanic rock and charcoal could significantly shorten the start-up time of the anammox process, which primarily occurred in the activity-enhanced phase, with ammonium and nitrite removal efficiencies stabilized above 92.5% and 93.4% after an operation period of 145, 105 and 121 d for R1, R2 and R3, respectively. After the successful anammox start-up, R2 performed significantly better in TN removal (p < .05), achieving an average rate of 91.0% and 191.5 g N m^-3 d^-1 compared to R1 of 88.4% and 172.1 g N m^-3 d^-1, and R3 of 89.9% and 180.1 g N m^-3 d^-1 in the steady running phase. The ratios of consumed [Formula: see text] and generated [Formula: see text]/consumed [Formula: see text] after anammox start-up were lower than the theoretical values, probably suggesting the simultaneous existences of anammox, denitrification as well as nitrification processes in the reactors. A reddish brown biofilm was wrapped on the carriers and morphological detection of biofilm displayed the presentations of thick and compact floc aggregates and some filamentous bacteria on the sponge, and spherical-, ovoid- and shortrod-shaped microorganisms on the volcanic rock and charcoal. Using porous material as carrier for biofilm development is an effective strategy for practical application of the anammox reactor.

An experimental model of COD abatement in MBBR based on biofilm growth dynamic and on substrates' removal kinetics

In this study, the performance of a lab-scale Moving Bed Biofilm Reactor (MBBR) under different operating conditions was analysed. Moreover, the dependence of the reaction rates both from the concentration and biodegradability of substrates and from the biofilm surface density, by means of several batch kinetic tests, was investigated. The reactor controls exhibited an increasing COD (Chemical Oxygen Demand) removal, reaching maximum yields (close to 90%) for influent loadings of up to12.5 gCOD/m(2)d. From this value, the pilot plant performance decreased to yields of only about 55% for influent loadings greater than 16 gCOD/m(2)d. In response to the influent loading increase, the biofilm surface density exhibited a logistic growing trend until reaching a maximum amount of total attached solids of about 9.5 g/m(2). The kinetic test results indicated that the COD removal rates for rapidly biodegradable, rapidly hydrolysable and slowly biodegradable substrates were not affected by the organic matter concentrations. Instead, first-order kinetics were detected with respect to biofilm surface density. The experimental results permitted the formulation of a mathematical model to predict the MBBR organic matter removal efficiency. The validity of the model was successfully tested in the lab-scale plant.

Model-Based Feasibility Assessment of Membrane Biofilm Reactor to Achieve Simultaneous Ammonium, Dissolved Methane, and Sulfide Removal from Anaerobic Digestion Liquor

In this study, the membrane biofilm reactor (MBfR) is proposed to achieve simultaneous removal of ammonium, dissolved methane, and sulfide from main-stream and side-stream anaerobic digestion liquors. To avoid dissolved methane stripping, oxygen is introduced through gas-permeable membranes, which also from the substratum for the growth of a biofilm likely comprising ammonium oxidizing bacteria (AOB), anaerobic ammonium oxidation (Anammox) bacteria, denitrifying anaerobic methane oxidation (DAMO) microorganisms, aerobic methane oxidizing bacteria (MOB), and sulfur oxidizing bacteria (SOB). A mathematical model is developed and applied to assess the feasibility of such a system and the associated microbial community structure under different operational conditions. The simulation studies demonstrate the feasibility of achieving high-level (>97.0%), simultaneous removal of ammonium, dissolved methane, and sulfide in the MBfRs from both main-stream and side-stream anaerobic digestion liquors through adjusting the influent surface loading (or hydraulic retention time (HRT)) and the oxygen surface loading. The optimal HRT was found to be inversely proportional to the corresponding oxygen surface loading. Under the optimal operational conditions, AOB, DAMO bacteria, MOB, and SOB dominate the biofilm of the main-stream MBfR, while AOB, Anammox bacteria, DAMO bacteria, and SOB coexist in the side-stream MBfR to remove ammonium, dissolved methane, and sulfide simultaneously.

Effects of substrate shock on extracellular polymeric substance (EPS) excretion and characteristics of attached biofilm anammox granules

The production mechanism of an extracellular polymeric substance (EPS) and its effects on the performance of anammox granules were evaluated.

The effect of magnetite on the start-up and N2O emission reduction of the anammox process

A reactor combined with magnetite could enhance the anammox performance and enrich morePlanctomycetesbacteria.

ANAMMOX-like performances for nitrogen removal from ammonium-sulfate-rich wastewater in an anaerobic sequencing batch reactor

Ammonium removal by the ANaerobic AMonium OXidation (ANAMMOX) process was observed through the Sulfate-Reducing Ammonium Oxidation (SRAO) process. The same concentration of ammonium (100 mg N L(-1)) was applied to two anaerobic sequencing batch reactors (AnSBRs) that were inoculated with the same activated sludge from the Vermicelli wastewater treatment process, while nitrite was fed in ANAMMOX and sulfate in SRAO reactors. In SRAO-AnSBR, in substrates that were fed with a ratio of NH4(+)/SO4(2-) at 1:0.4 ± 0.03, a hydraulic retention time (HRT) of 48 h and without sludge draining, the Ammonium Removal Rate (ARR) was 0.02 ± 0.01 kg N m(-3).d(-1). Adding specific ANAMMOX substrates to SRAO-AnSBR sludge in batch tests results in specific ammonium and nitrite removal rates of 0.198 and 0.139 g N g(-1) VSS.d, respectively, indicating that the ANAMMOX activity contributes to the removal of ammonium in the SRAO process using the nitrite that is produced from SRAO. Nevertheless, the inability of ANAMMOX to utilize sulfate to oxidize ammonium was also investigated in batch tests by augmenting enriched ANAMMOX culture in SRAO-AnSBR sludge and without nitrite supply. The time course of sulfate in a 24-hour cycle of SRAO-AnSBR showed an increase in sulfate after 6 h. For enriched SRAO culture, the uptake molar ratio of NH4(+)/SO4(2-) at 8 hours in a batch test was 1:0.82 lower than the value of 1:0.20 ± 0.09 as obtained in an SRAO-AnSBR effluent, while the stoichiometric ratio of 1:0.5 that includes the ANAMMOX reaction was in this range. After a longer operation of more than 2 years without sludge draining, the accumulation of sulfate and the reduction of ammonium removal were observed, probably due to the gradual increase in the sulfur denitrification rate and the competitive use of nitrite with ANAMMOX. The 16S rRNA gene PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) and PCR cloning analyses resulted in the detection of the ANAMMOX bacterium (Candidatus Brocadia sinica JPN1) Desulfacinum subterraneum belonging to the genus Desulfacinum and bacteria that are involved in sulfur metabolism (Pseudomonas aeruginosa strain SBTPe-001 and Paracoccus denitrificans strain IAM12479) in SRAO-AnSBR.