Lab-scale Upflow Anaerobic Sludge Blanket Research Articles

Treatment of Slaughterhouse Wastewater through a Series System: Upflow Anaerobic Reactor and Artificial Wetland

Slaughterhouse wastewater is characterized by high concentrations of organic matter. This creates a need to explore methods for its treatment before discharge. This study evaluated the efficiency of an integrated treatment process consisting of a laboratory-scale upflow anaerobic sludge blanket reactor and a pilot-scale horizontal subsurface flow wetland. This treatment was used for (i) the removal of organic matter through anaerobic–aerobic microbiological processes, (ii) the conversion of organic matter from hydraulic processes, and (iii) for bioremediation and phytoremediation. The treatment system was evaluated at hydraulic retention times (HRTs) of 7.5, 5.0, and 2.5 d; during the investigation, the influence of the HRTs on the removal efficiency of the system was evaluated. High efficiencies of 85% and 75% were obtained for CODT and BOD, respectively, at an HRT of 7.5 d. The highest overall efficiency for the removal of total solids was observed at an HRT of 2.5 d. The results obtained confirm the feasibility of implementing the suggested system as an alternative for the adequate and sustainable treatment of slaughterhouse wastewater, and the system can be applied to slaughterhouses with similar conditions to those in this study.

The impact of semi-continuous and alternating microbial feeding patterns on methane yield from UASB reactors

Feeding strategy represents one of the most important bioreactor operation parameters, however, how different feeding patterns impact reactor microbiome development and treatment performance in up-flow anaerobic sludge blanket (UASB) reactors has not been systematically investigated. In the present study, three feeding strategies, including continuous feeding, semi-continuous feeding (with starvation-feast cycles), and alternate feeding (with high loading-low loading cycles) were assessed and compared using three laboratory-scale UASB reactors. It was observed that both long and short starvation-feast cycles provided by a semi-continuous feeding strategy failed to sustain stable anaerobic digestion under the conditions examined in the present study, while alternate feeding with high and low loading cycles supported microbial development. This feeding pattern resulted in an average methane yield of 74 ± 8.5% and an effluent COD removal efficiency of 89 ± 2.8%, which is comparable to the reactor operated under a continuous feeding pattern (Methane yield of 72 ± 2.4% and a COD removal efficiency of 87 ± 7.7%). Interestingly, as compared to continuous operation, reactors experienced starvation/feast stress (i.e., semi-continuous feeding) developed significantly higher methanogenic activities once continuous feeding was presumed, with dominant methanogens shifted from Methanosaeta in continuous feeding UASB to Methanosarcina in reactors undergone semi-continuous feeding. It was concluded that reactor feeding strategies can significantly impact microbiome communities in UASB, and an alternate feeding pattern is preferred, as compared to semi-continuous operation when reactor feeding cannot be continuously supplied.

Treatment of citrus juice process wastewater with UASB and biogas production

A lab-scale up-flow anaerobic sludge blanket (UASB) reactor was used for biogas production from the citrus juice process wastewater (CPWW). The volume of the reactor was 11.5 L. During 200 days of the reactor, the organic loading rate (OLR) value changed from 1.8-21.9 kgCOD./m3.d, upflow velocities (Vup) 0.1-5.2 m/h and hydraulic retention time (HRT) changed from 0.042 to 4.16 days. The reactor showed a stable performance at all organic loadings. Experimental chemical oxygen demand (COD) removal efficiencies were 71.5 ± 21% and 83.3 ± 16.3% for total COD (TCOD) and soluble COD (SCOD), respectively. The acetic acid concentration changed from 135 to 650 mg/L. The temperature was kept in the range of 35.1 ± 1.4 oC, the pH in the range of 6.6 ± 0.2, and the alkalinity was controlled daily and kept in the range of 411 ± 273 CaCO3 mg/L. After anaerobic reactions, 6283 ± 3476 m3/d biogas was produced and the methane concentration in the biogas was 65.5 ± 11.5%. Depending on the methane production, the annual energy value potential that can be obtained from the existing UASB reactor is estimated as 48,768 kWh.

Enhancing Biodegradation of Industrial Wastewater into Methane-Rich Biogas Using an Up-Flow Anaerobic Sludge Blanket Reactor

Anaerobic digestion (AD), the oldest technology used for treating waste, converts organic matter into biogas in the absence of oxygen. The current efforts focuses on improving the digestion of a local industrial wastewater to produce biogas and treat water for reuse. A lab-scale up-flow anaerobic sludge blanket (UASB) reactor operated at 37 °C was employed for the biodegradation the industrial wastewater. A one-factor-at-a-time (OFAT) approach was used to study the effects of influent chemical oxygen demand (CODin), hydraulic retention time (HRT), and magnetic nanoparticles (magnetite) on UASB biogas and COD elimination from digestate wastewater. The optimum HRT for the biodegradation of municipal wastewater was found to be 21 days with contaminants’ removals of 94%, 90.1%, and 98.9% for COD, color, and turbidity, respectively. The addition of magnetite resulted in 225 mL of cumulative biogas produced with 73% methane content, and treatability efficiency of 85%. The most influential factor was magnetite load, which stimulated the microbial activity via redox catalytic reaction in degrading the high organic wastewater (9590 mg COD/L) into biogas production. The prospects of upgrading lab-scale of this technological concept for bioenergy production is viable to mitigate wastewater management and fossil fuel environmental challenges.

Microbial dynamics and methanogenic potential of co-digestion of sugarcane vinasse and dairy secondary effluent in an upflow anaerobic sludge blanket reactor

Co-digestion is a strategy that may prevent microbial inhibition during the anaerobic treatment of sugarcane vinasse, a substrate with highly biodegradable organic load, acidity, and toxic compound levels (e.g., sulfates, phenols). In this context, this study evaluated the microbial dynamics and methanogenic potential throughout the co-digestion of sugarcane vinasse and secondary effluent from the dairy industry in a mesophilic lab-scale upflow anaerobic sludge blanket (UASB) reactor. Periodic next-generation sequencing (NGS) analyses revealed an increase in the relative abundance of the phylum Euryarchaeota (+8.6 % after inoculation), predominating hydrogenotrophic methanogens (Methanobacterium and Methanobrevibacter) at the end of the operation. Moreover, the average methane yield was 221 mLCH4 gCODrem-1, with 69 % of organic matter removal. These results evidenced a progressive acclimation of the anaerobic microbial community to the substrate and a stable operation. Therefore, the proposed experiment demonstrates energy advantages for the agro-industrial sector by implementing a similar but full-scale treatment plant.

The effects of caffeine, gliclazide, and prazosin on the performance and microbial diversity in an up-flow anaerobic sludge blanket (UASB) reactor

A laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor was deployed in this study to examine the relationship between pharmaceutical compounds and anaerobic process performance. The reactor successfully biotransformed up to 87–99% of psychostimulant caffeine, anti-diabetic drug gliclazide, and anti-hypertensive drug prazosin during 92 days of operation. At the same time, fluctuations were recorded for the methane gas production, and also the domination of acetic acid and propionic acid in the presence of pharmaceutical compounds was measured. The results from 16s rRNA sequencing revealed that these compounds stimulated the growth of hydrogenotrophic methanogens, mainly Methanobrevibacter and Methanobacterium, while shifting the compositions of hydrolytic and fermentative bacteria. These outcomes proved the capability of the pharmaceutical compounds to influence the process performance by changing the microbial compositions in the anaerobic reactor.

Effect of formic acid inflow on microbial properties of the anaerobic granular sludge in a UASB reactor

In the production of natural rubber, formate or acetate is added to the latex solution to coagulate the rubber; therefore, the wastewater contains high concentrations of organic acids, requiring the application of anaerobic treatment technology. In this study, a two-phase continuous flow experiment using a laboratory-scale upflow anaerobic sludge blanket (UASB) was conducted to investigate the influence of formate inflow on the microbial and physical characteristics of the retained granular sludge. In phase 1, acetate-based wastewater was used as feed, while in phase 2, formate-based wastewater was used as feed. In phase 1, the UASB exhibited high COD removal efficiency (97.2%); in addition, the retained sludge showed increased methane production from acetate and proliferation of acetate-utilizing Methanosaeta species. In phase 2, the UASB performed as well as phase 1, with 98.2% COD removal efficiency. Microbial community structure analysis confirmed that relatives of Methanobacterium formicicum present in the retained sludge were responsible for the degradation of formate in phase 2. However, decreased diameter and slight deterioration of granular sludge settleability were observed. In conclusion, formate inflow has low risk of interference with the process performance of the UASB, but it has negative effects on the physical properties of the granular sludge.

Performance of the UASB reactor during wastewater treatment and the effect of the biogas bubbles on its hydrodynamics

ABSTRACT A lab-scale Upflow Anaerobic Sludge Blanket (UASB) reactor was used as a model for evaluating synthetic and complex industrial wastewater treatment, using a solar heater to control temperature. Also, hydrodynamics was assessed using the Computational Fluid Dynamics (CFD) method. Initially, the UASB reactor was operated with synthetic wastewater at Hydraulic Retention Time (HRT) of 24 h in 20 ± 2 °C and 30 ± 2 °C to measure the biogas bubbles production for CFD study. COD removal efficiencies of 85 ± 3% and 95 ± 3%, respectively, with production of 27 and 39 ml CH4/h, correspondingly, were observed. After that, the reactor was fed with complex industrial wastewater. It was evaluated at 24 h in both temperatures. At 30 °C, low COD removal efficiency was observed, being 48 ± 13%, with methane production of 20 ± 3 ml CH4/h. The plug flow pattern was observed in the CFD modelling at HRT of 24 h and 20 °C without considering biogas bubbles interaction. Similar hydrodynamic behaviour was observed at HRT of 24 h and 30 °C. Nonetheless, when biogas bubbles were considered in the CFD modelling, hydrodynamics significantly changed, passing from a plug flow to a complete mix flow pattern.

Roles of granular activated carbon (GAC) and operational factors on active microbiome development in anaerobic reactors

Ambient temperature municipal sewage was treated using two laboratory-scale up-flow anaerobic sludge blanket reactors for 225 days. Granular activated carbon (GAC) was added to one reactor to facilitate the development of direct interspecies electron transfer (DIET). The GAC addition increased total chemical oxygen demand removal by 5% − 18%. In addition to assessing the relative abundance of active amplicon sequence variants (ASVs), the mass balance model, the Mantel test, and the generalized linear models were applied to evaluate the dynamics of the active ASVs and the key operational factors controlling the bioreactor microbial community. These results demonstrated that, in addition to the GAC addition, extrinsic engineering operational factors played important roles in controlling (active) microbial communities. This study underlines the importance of taking a wholistic approach to assess microbial population dynamics. Reactor design and performance prediction should consider key engineering parameters when using DIET-based AD reactors in the future.

Microaeration improves the removal/biotransformation of organic micropollutants in anaerobic wastewater treatment systems

This work assessed the effect of increasing microaeration flow rates (1–6 mL min−1 at 28 °C and 1 atm, equivalent to 0.025–0.152 L O2 L−1 feed) on the removal/biotransformation of seven organic micropollutants (OMPs) (three hormones, one xenoestrogen, and three pharmaceuticals), at 200 μg L−1 each, in a lab-scale upflow anaerobic sludge blanket reactor operated at a hydraulic retention time (HRT) of 7.4 h. Additionally, the operational stability of the system and the evolution of its microbial community under microaerobic conditions were evaluated. Microaeration was demonstrated to be an effective strategy to improve the limited removal/biotransformation of the evaluated OMPs in short-HRT anaerobic wastewater treatment systems. The rise in the airflow rate considerably increased the removal efficiencies of all OMPs. However, there seems to be a saturation limit for the biochemical reactions. Then, the best results were obtained with 4 mL air min−1 (0.101 L O2 L−1 feed) (~90%) because, above this flow rate, the efficiency increase was negligible. The long-term exposure to microaerobic conditions (249 days) led the microbiota to a gradual evolution. Consequently, there was some enrichment with species potentially associated with the biotransformation of OMPs, which may explain the better performance at the end of the microaerobic term even with the lowest airflow rate tested.

Precipitation of Heavy Metal Ions (Cu, Fe, Zn, and Pb) from Mining Flotation Effluents Using a Laboratory-Scale Upflow Anaerobic Sludge Blanket Reactor

Metal mining extraction and concentration need water. The recycling of liquid effluents reduces its consumption. This recycled water must contain low concentrations of metals. This project’s first objective was to start up a laboratory-scale upflow anaerobic sludge blanket (UASB) reactor for biotransforming metal sulfates into metal sulfides of effluent from flotation units of a mining plant (FE). The second objective was to determine the effect of pH and chemical oxygen demand:sulfate ratio (COD:SO42−) in the precipitation of heavy metal sulfides. The third objective, which is the subject of this part of the research, was to evaluate the feasibility of this proposal through a mass balance of the metals separated by precipitation through the formation of sulfides by sulfate-reducing microorganisms (SRM), using as energy source carbonaceous compounds from flotation residual organic reagents enriched with lactic acid. To monitor bioconversion effectiveness, various parameters were used: pH-alkalinity factor (α), temperature (T), COD, SO42−, and sulfides (S2−). Four metals were considered for this part of the research: Cu, Pb, Zn, and Fe. The UASB system achieved a sulfate bioconversion of 69% and an organic matter removal as COD of 88% after transient state with the best COD:SO42− ratio found. Using a statistical analysis by clusters, metal sulfide production of 74 mg L−1 and removals of 39, 70, 79, and 65%, for Pb, Cu Zn, and Fe, respectively, were obtained. These values were calculated with an initial ratio of COD:SO42− of 0.66 ± 0.2 and pH values around 6 inside the reactor, through anaerobic microbial biomass, indicating that the solution proposed to recycle water in the metal extraction and concentration is feasible after using these systems.

Adaption strategy of up-flow anaerobic sludge blanket reactor on tetracycline stress during tetracycline antibiotic wastewater treatment

Tetracycline antibiotic wastewater with high chemical oxygen demand (COD) concentration and containing bio-refractory compounds was investigated in a lab-scale up-flow anaerobic sludge blanket (UASB) and anoxic-oxic (A/O) reactor. Specific methanogenic activity (SMA) was determined to reveal the inhibition levels of methane production and volatile fatty acid (VFA) accumulation. The results showed that microorganisms can adapt to tetracycline or oxytetracycline when the concentration of antibiotics is less than 400 mg/L. Acetic acid, propanoic acid, and n-butyric acid accounted for more than 90% of VFA with increasing antibiotic concentration from 50 mg/L to 600 mg/L. During the 215 d of operation, the concentration of tetracycline antibiotic increased from 0 to 95 mg/L, and the COD concentration from 3,500 to 6,500 mg/L. The average COD and tetracycline antibiotic removal rates of the reactors were maintained above 90%. The methane production of the UASB reactor achieved 0.32 L/g COD. VFA accumulation was observed when tetracycline antibiotic concentration increased to 47.5 mg/L. The sludge granule diameter increased from 0–300 μm to 300–1,500 μm during the operation. Rod-shaped and coccus-shaped organisms with pores and internal channels on the granule surface were observed using scanning electron microscopy. In the internal space, methanogenic filamentous bacteria constitute a rock-steady structure.

Microbial properties of the granular sludge in a psychrophilic UASB reactor fed with electronics industry wastewater containing organic chemicals

In this study, a lab-scale upflow anaerobic sludge blanket (UASB) reactor was applied to the treatment of artificial electronics industry wastewater containing tetramethylammonium-hydroxide (TMAH), monoethanolamine (MEA), and isopropyl-alcohol (IPA) in order to evaluate process performance and degradation properties. During 800 days of operation, 96% efficiency of chemical oxygen demand (COD) removal was stably achieved at an organic loading rate of 8.5 kgCOD/m3/day at 18–19 °C. MEA degradation, carried out by acid-forming eubacteria, was confirmed within a week. The physical properties of the retained granular sludge were degraded by feeding with TMAH wastewater, but maintained by feeding with MEA wastewater due to an accumulation of species from the genus Methanosaeta and family Geobacteraceae. Analysis of the microbial community structure via SEM and 16S rRNA genes showed a proliferation of Methanomethylovorans-like cells and Methanosaeta-like cells at the surface and in the core of the granular sludge with TMAH, MEA and IPA acclimation. Furthermore, a batch degradation experiment confirmed that process inhibition due to increasing chemical concentration was relatively stronger for TMAH than for MEA or IPA. Thus, controlling the TMAH concentration of the influent to below 1 gCOD/L will be important for the stable treatment of electronics industry wastewater by UASB technology.

Soybean molasses as feedstock for sustainable generation of biomethane using high-rate anaerobic reactor

Anaerobic digestion of agro-industrial wastes is an environmentally friendly green biotechnology of significant interest in order to facilitate sustainable development of bioenergy production. Thus, it becomes important to invest in management processes for agro-industrial wastes, particularly low-cost ones. In this paper, the main purposes were to investigate the performance of a high-rate reactor and biogas generation potential by anaerobic digestion of soybean molasses, which is a viscous liquid of brown color obtained as a byproduct from processing of the soy protein industry concentrate. A lab-scale up-flow anaerobic sludge blanket reactor (UASB reactor), with a total volume of 12 L, was operated at six different organic loading rates (OLR) ranging from 0.28 to 6.98kgCODm−3d−1 (COD of 500–4000 mg L−1). The reactor was fed with soybean molasses for 134 days and maintained under mesophilic conditions. Different values were tested for the hydraulic retention time (HRT of 48, 24 and 12 h). After the fast startup period (52 days), the mean values of removal efficiencies (CODTotal) ranged from 70% to 83% in all experimental periods. In a UASB reactor, a higher organic loading rate of 6.98kgCODm−3d−1 could be tolerated, but it resulted in a lower biomethane yield of 356.1mLCH4gCOD−1. In addition, for all the tested COD concentrations and HRT, high concentrations of methane in the biogas were obtained from 72.5% to 82.1%. Based on the experimental results, it can be verified that this high-rate anaerobic configuration can be used for the biomethane generation of soybean molasses and the produced effluent can be reutilized in the dilution of soybean molasses for reactor feed.

Start-up study of biohydrogen production from palm oil mill effluent in a lab-scale up-flow anaerobic sludge blanket fixed-film reactor

A start-up study of lab-scale up-flow anaerobic sludge blanket fixed-film reactor (UASFF) was conducted to produce biohydrogen from palm oil mill effluent (POME). The reactor was fed with POME at different hydraulic retention time (HRT) and organic loading rate (OLR) to obtain the optimum fermentation time for maximum hydrogen yield (HY). The results showed the HY, volumetric hydrogen production rate (VHPR), and COD removal of 0.5–1.1 L H2/g CODconsumed, 1.98–4.1 L H2 L−1 day−1, and 33.4–38.5%, respectively. The characteristic study on POME particles was analyzed by particle size distribution (PSD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX). The microbial Shannon and Simpson diversity indices and Principal Component Analysis assessed the alpha and beta diversity, respectively. The results indicated the change of bacterial community diversity over the operation, in which Clostridium sensu stricto 1 and Lactobacillus species were contributed to hydrogen fermentation.

Ecogenomics Reveals Microbial Metabolic Networks in a Psychrophilic Methanogenic Bioreactor Treating Soy Sauce Production Wastewater.

An ecogenomic analysis of the methanogenic microbial community in a laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor treating soy sauce-processing wastewater revealed a synergistic metabolic network. Granular sludge samples were collected from the UASB reactor operated under psychrophilic (20°C) conditions with a COD removal rate >75%. A 16S rRNA gene amplicon sequencing-based microbial community analysis classified the major microbial taxa as Methanothrix, Methanobacterium, Pelotomaculaceae, Syntrophomonadaceae, Solidesulfovibrio, and members of the phyla Synergistota and Bacteroidota. Draft genomes of dominant microbial populations were recovered by metagenomic shotgun sequencing. Metagenomic- and metatranscriptomic-assisted metabolic reconstructions indicated that Synergistota- and Bacteroidota-related organisms play major roles in the degradation of amino acids. A metagenomic bin of the uncultured Bacteroidales 4484-276 clade encodes genes for proteins that may function in the catabolism of phenylalanine and tyrosine under microaerobic conditions. Syntrophomonadaceae and Pelotomaculaceae oxidize fatty acid byproducts presumably derived from the degradation of amino acids in syntrophic association with aceticlastic and hydrogenotrophic methanogen populations. Solidesulfovibrio organisms are responsible for the reduction of sulfite and may support the activity of hydrogenotrophic methanogens and other microbial populations by providing hydrogen and ammonia using nitrogen fixation-related proteins. Overall, functionally diverse anaerobic organisms unite to form a metabolic network that performs the complete degradation of amino acids in the psychrophilic methanogenic microbiota.

Anaerobic co-digestion of landfill leachate and acid mine drainage using up-flow anaerobic sludge blanket reactor.

A laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor was developed and constructed for the treatment of landfill leachate and acid mine drainage (AMD). The removal of chemical oxygen demand (COD), sulfate, and metal ions was studied. The maximum COD and sulfate removal efficiency reached 75% and 69%, respectively, during the start-up phase of the UASB. The hydraulic retention time (HRT) had a significant influence on the system. The maximum removal efficiency for COD and sulfate reached 83% and 78%, respectively, at an HRT of 20 h. The methane production process competed with the sulfate reduction process in the UASB. The fractionation of metals in the sludge was analyzed to facilitate metal recovery in a later processing stage. The most abundant sulfate-reducing bacteria was Desulfobulbus, and the methanogen archaeal community in the reactor was mainly composed of Methanobacterium.

Enhanced anaerobic treatment of azo dye wastewater via direct interspecies electron transfer with Fe3O4/sludge carbon

In this study, enhancement of anaerobic treatment of azo dye wastewater with Fe3O4/SC is investigated. Fe3O4/sludge carbon (SC) is prepared from waste activated sludge using a simple impregnation method. Two identical laboratory-scale upflow anaerobic sludge blanket reactors with a working volume of 1.5 L are filled with 2 g/L of SC (reactor 1) and 2 g/L of Fe3O4/SC (reactor 2). Another reactor (reactor 0) is operated as a control. FTIR, XPS, SEM, and BET results indicate that Fe3O4 is successfully loaded on the SC. Addition of Fe3O4/SC to the reactor results in high chemical oxygen demand (78.13%) and color (97.60%) removal rates. Furthermore, Fe3O4/SC effectively decreases the amount of aniline generated and increases CH4 production. The Fe3O4/SC anaerobic system is stable with fast recovery in terms of both organic matter removal and aniline control with high toxic substance concentrations and fluctuating organic loads. Moreover, Fe3O4/SC greatly enhances enzymatic activity and sludge granulation, which could greatly improve anaerobic reactor stability. High electron transport system and conductivity values and the enrichment of Geobacter and Methanosaeta species confirm that direct interspecies electron transfer occurs with Fe3O4/SC in the reactor. These results provide a scientific basis for further applications to azo dye wastewater treatment and promote resource utilization of waste sewage sludge.

Approaches in Design of Laboratory-Scale UASB Reactors

Up-flow Anaerobic Sludge Blanket (UASB) reactors are popular tools in wastewater treatment systems due to the ability to work with high feed rates and wastes with high concentration of organic contaminants. While full-scale industrial applications of UASB reactors are developed and described in the available literature, laboratory-scale designs utilized for treatability testing are not well described. The majority of published studies do not describe the laboratory UASB construction details or do use reactors that already had developed a trophic network in microbial consortia under laboratory environment and therefore are more stable. The absence of defined guidelines for geometry design, selection of materials, construction, operation rules, and, especially, the start-up conditions, significantly hamper researchers who desire to conduct treatability testing using UASB reactors in laboratory scale. In this article, we compiled and analyzed the information available in the refereed literature concerning UASB reactors used in laboratory environment, where information on geometry and/or operational conditions were provided in detail. We utilized the information available in the literature and the experience gained in our laboratory (Sustainable Waste to Bioproducts Engineering Center) to suggest a unified operation flowchart and for design, construction, operation, and monitoring for a laboratory-scale UASB reactors.

Performance of a high-rate anammox reactor under high hydraulic loadings: Physicochemical properties, microbial structure and process kinetics

In this study, a lab-scale upflow anaerobic sludge blanket (UASB) reactor was applied to studying the high-rate nitrogen removal of granule-based anammox process. The nitrogen removal rate (NRR) finally improved to 15.77 kg/m3/d by shortening hydraulic retention time (HRT) to 1.06 h. Well-shaped red anammox granules were extensively enriched inside the reactor. The results of nitrogen removal kinetics indicated that the present bioreactor has great nitrogen removal potential, because the maximum rate of substrate utilization (Umax) predicted by Stover-Kincannon model is suggested as 55.68 kg/(m3·d). Analysis of the microbial community showed that the anammox genus Candidatus Kuenenia dominated the bacterial communities. The relative abundance of Candidatus Kuenenia rose from 12.29% to 36.95% after progressively shorter HRT and higher influent substrate concentrations, illustrating the stability of nitrogen removal performance and biomass enrichment offered by the UASB in carrying out high-rate anammox process.