Fluidized Bed Membrane Bioreactor Research Articles

Understanding key factors determining the effect of particle scouring efficiency on membrane fouling mitigation in AnFMBRs: Correlation analysis via machine learning

Particle scouring methods offer several advantages, including low energy consumption, ease of operation, and effective fouling control. The anaerobic fluidized bed membrane bioreactor is considered to be the most efficient wastewater treatment method with zero energy consumption, as it produces bioenergy and has lower energy requirements compared to conventional processes. However, membrane fouling in AnFMBRs can be affected by various factors such as fluidized particle hydrodynamics, particle properties, and operating conditions. To identify the primary factors affecting membrane fouling control in AnFMBRs, machine learning methods were utilized. Analysis of datasets from previous studies revealed several key findings. The location of the membrane in the reactor, particle momentum, and particle size were identified as the major parameters that govern membrane fouling reduction. Additionally, the optimal condition for AnFMBRs was determined to involve a membrane height-to-reactor height ratio of ≤0.5 and the use of particles with diameters of 1.5–3.0 mm. Furthermore, the use of smaller fluidized particles was shown to decrease particle scouring efficacy, making it less cost-effective. Machine learning models were successfully established to predict fouling, thus providing a comprehensive understanding of the dominant factors influencing membrane fouling control in AnFMBRs and offering an efficient method for optimizing fouling mitigation.

Membrane fouling, methane production and microbial community under fluidization of biocarrier with conductive surface in anaerobic fluidized bed membrane bioreactor for greywater treatment

A comparative study of organic removal efficiency, fouling control, and methane production from synthetic greywater was performed operating three anaerobic fluidized bed membrane bioreactors (AFMBRs). Granular activated carbon (GAC) particles, polyaniline-coated polyethylene terephthalate (PET) beads, and uncoated PET beads were added as scouring agent to control fouling through each AFMBR. The use of PET spherical beads coated with polyaniline as a fluidized medium improved both fouling reduction and methane production kinetics. Although the GAC particles showed the highest organic removal efficiency in AFMBR due to adsorption capability, their progressive fragmentation reduced the methanogenic population and accelerated fouling rate. Microbial activity was adversely affected when the bulk biomass was exposed to the surfactant in the synthetic greywater. Microbiome analysis showed that the methanogenic archaeal population in the GAC bulk biomass reduced significantly from 10 to 0.5%, which corroborates the decrease in methane production rate. The methanogens on the PET beads shifted gradually from acetoclastic Methanosaeta to hydrogenotrophic Methanospirillum presumably because of the detachment of the biofilm that suppressed the slow-growing Methanosaeta. In addition, the key exoelectrogenic microbes were related to Desulfovibrio and Geobacter, which may be associated with direct interspecies electron transfer with the methanogens.

Anaerobic Fluidized-Bed Membrane Bioreactor for Treatment of Liquid Fraction of Sludge Digestate: Performance and Agricultural Reuse Analysis

The treatment of sludge digestion liquid is a big challenge in wastewater treatment. If treated as normal wastewater, large amounts of nitrogen and phosphorus present in the sludge digestion liquid might be wasted when they could be reused in agricultural irrigation and reduce the consumption of artificial fertilizers. Thus, it is of utmost importance to deliver a simple and feasible strategy to treat sludge digestion liquid for agricultural reuse. In this study, a novel type of anaerobic fluidized bed membrane bioreactor system (US-AnFMBR) was developed by combining an ultrasonic processing unit and biochar in AnFMBR. The improvement of sludge properties, removal of pollutants performance and membrane fouling mitigation were achieved in this novel system. The optimal dose of BC (biochar) was 2.5 g·L−1, and the optimal ultrasonic treatment conditions were 30 min at 26 W. The main contribution of ultrasound was to improve the activity of sludge microorganisms to adsorb and degrade more organic matter present in sewage. The system achieved the removal efficiencies of COD, NH4+-N and PO43−-P up to 89.41%, 49.29% and 54.83%, respectively, and had a better mitigation effect in terms of membrane fouling. On the one hand, the biochar addition for COD removal performance was mainly manifested in membrane rejection performance. On the other hand, the combination of low-cost biochar and AnFMBR can also provide new ideas for the recycling of agricultural waste for biochar production. However, regarding the removal efficiency of NH4+-N and PO43−-P, the US-AnFMBR system promoted the activity of starved sludge to preferentially absorb NH4+-N compared with PO43−-P by statistical analysis. The US-AnFMBR can reduce the viscosity of sludge and release more small molecular substances, thus better mitigating membrane fouling. Long-term operation performance also revealed the excellent stability of the sludge digestion liquid treatment. The US-AnFMBR system achieves the recovery of nitrogen and phosphorus resources for subsequent agricultural recycling, and avoids the eutrophication of water ecosystems. Reclaimed water meets the nutrient requirements of typical crops during the growing season. To a certain extent, carbon emission reductions in agriculture can be achieved.

Performance and microbial analysis of a fluidized bed membrane bioreactor operated in the partial nitrification and anammox (PN/A) mode for polishing anaerobically treated effluent to industrial discharge standard

This study evaluates the performance and microbial dynamics of an ORP-controlled fluidized bed membrane bioreactor impregnated with partial nitrification and anammox culture (FMBRPN/A) for polishing the low COD/NH4+ anaerobically treated effluent of the seafood processing industry. Results showed that the highest average removal of COD and total nitrogen were 68.6% and 75.0% at COD/NH4+ 0.44 and 0.33, respectively. Heterotrophic denitrification accounted for only 3.0–7.1% of the overall nitrogen removals at COD/NH4+ 0.33–0.55. A low nitrite oxidation rate observed indicated that almost all NO3- came from anammox reactions. Data on ammonia oxidation rate, nitrite oxidation rate, and anammox nitrogen removal rate pointed to the competitive advantage between heterotrophic and nitrifying/anammox consortia at higher and lower COD/NH4+ ratios. When salinity threat at 5 g/L NaCl in the influent was imposed to FMBRPN/A, nitrogen removal was almost completely eliminated but quickly recovered to 25.5% as organic removal was not affected. Activities of the nitrogenous autotrophic organisms and heterotrophic microbes were strongly dependent on the presence of organic and salinity in the wastewater. Microbial analysis of biofilm formed on the membrane surface showed a significant difference in the succession of dominant bacteria during the experiments. Next Generation Sequencing indicated the dynamic shifting proportions of ammonium oxidizing bacteria (AOB), nitrite oxidization bacteria (NOB), denitrifying bacteria (DNB), and anammox bacteria (AMX) ranging from 49.4% to 64.2% at various COD/NH4+ ratios, which suggested their syntrophic relationship. Superior membrane retention of FMBRPN/A for heterotrophic and slow-growing autotrophic cells facilitated system stability and efficiency to meet the industrial effluent standard.

Macroalgal biochar synthesis and its implication on membrane fouling mitigation in fluidized bed membrane bioreactor for wastewater treatment

The intensification of biochar into fluidized bed membrane bioreactor was investigated to mitigate membrane fouling. Different biochars from algal biomass were produced and used as biomaterials for wastewater treatment. In this study, different macroalgal biochar was synthesized at different pyrolysis temperatures and characterized using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Brunauer Emmett-Teller (BET) and Fourier transform infrared spectroscopy (FTIR) techniques to implicate their effect on membrane fouling reduction in fluidized bed membrane bioreactor. The combined effect of macroalgal biochars and biocarriers with gas sparging was evaluated for fouling mitigation. Macroalgal biochar curtailed membrane fouling effectively at low gas sparging rate. Transmembrane pressure (TMP) was reduced to 0.053 bar; under the fluidization of biochar-650 and biocarriers with gas sparging; from 0.27 bar (gas sparging only). Combined effect of gas sparging, biocarriers and biochar-650 instigated 92.1% fouling reduction in comparative to gas sparging alone. Mechanical scouring driven by biocarriers could reduce fouling due to removing surface deposit of foulants from membrane surface effectively and biochar can efficiently adsorb foulants because of its active functional groups resulting in reduction of colloidal fouling. The addition of divalent ions (Ca2+) further enhanced the fouling reduction in fluidized bed membrane bioreactor.

Evaluating performance of nano-Fe3O4 modified granular activated carbon assisted wastewater treatment in anaerobic fluidized membrane bioreactor

Magnetic granular activated carbon (MGAC), a nano-Fe3O4 modified granular activated carbon, was used as the carrier in an anaerobic fluidized-bed membrane bioreactor (AFMBR) to promote domestic wastewater treatment efficiency and alleviate membrane biofouling. Chemical oxygen demand (COD) removal reached 89 ± 2.6% with the effluent concentration of 20 ± 3.9 mg/L in the MGAC-AFMBR, while it was 28 ± 5.2 mg/L in AFMBR at hydraulic retention time (HRT) of 4 h. Total nitrogen (TN) removal was also enhanced by 4.0% with MGAC. An increased proportion of Chloroflexi and Bacteroidetes in the sludge may be responsible for improved treatment performance. MGAC reduced the protein and polysaccharide content in extracellular polymeric substances (EPS) by 9.8% and 8.1%, respectively. Besides, Bacteroidetes and Proteobacteria abundance decreased by 4.0% and 16.6% in the membrane cake layer with MGAC addition. Therefore, the high-quality effluent and low membrane biofouling of AFMBR was sustained by MGAC.

Dissolved Methane Recovery and Trace Contaminant Fate Following Mainstream Anaerobic Treatment of Municipal Wastewater.

Anaerobic treatment of municipal wastewater with the staged anaerobic fluidized bed membrane bioreactor (SAF-MBR) shows promise to transform secondary wastewater treatment into an energy-positive process. However, the dissolved methane in SAF-MBR effluent needs to be recovered to reach net energy positive. To recover this methane for energy generation, an air stripping system was constructed downstream of a pilot-scale SAF-MBR facility and operated for over 80 days. The process removed 98% of effluent dissolved methane, and with the addition of intermittent disinfection recovered an average of 90% of the dissolved methane. The exit gas from air-stripping comprised 1.5-2.5% methane and could be utilized by blending with biogas produced from primary solids digestion and the SAF-MBR in an on-site combustion process. The direct energy costs for air stripping methane are <1% of the energy recoverable from the dissolved methane, not accounting for siloxane or sulfide scrubbing. Only siloxanes were observed at levels impacting combustion in this study, with 1.6 mg Si/m3 present in the blended biogas and air stripping mixture. The fate of a subset of trace organic contaminants was examined across the air stripping unit to check for aerobic degradation by methanotrophs or other opportunistic aerobes. Only 1,4-dioxane and benzotriazole showed statistically significant removal among 17 compounds screened, with 0.53 ± 0.13 and 0.34 ± 0.15 fraction removal, respectively. Our results indicate that air stripping is an energy efficient and robust technology for dissolved methane removal and onsite utilization for heat and electricity generation from anaerobic treatment of municipal wastewater.

C-N-S synergy in a pilot-scale mainstream anammox fluidized-bed membrane bioreactor for treating chemically enhanced primary treatment saline sewage

Seawater for toilet flushing conserves the scarce freshwater resources in Hong Kong and similar densely-populated coastal cities. Saline sewage treatment using energy-efficient anammox-based processes appears to be beneficial, with notable potential for the future. However, the feasibility of this process remains uncharted, especially from its start-up to its steady-state cooperation. In this study, a pilot-scale mainstream anammox process was succeeded in a granular activated carbon fluidized-bed membrane bioreactor (FMBR) with only inoculating saline anaerobic digestion sludge. The FMBR, operating at the dissolved oxygen (DO) of 0.04-0.16 mg/L, achieved comparable nitrogen removal rates of 50.1-78.3 g N/m3/d while treating real chemically enhanced primary treatment saline sewage at 3.2 m3/d. Excluding Scalindua, 16S rRNA gene amplicon sequencing revealed a high abundance of common-freshwater-observed Kuenenia from 0.2% (day 259) to 1.3% (day 332) in biofilms. Nitrosomonas, responsible for ammonium oxidation, dominated in biofilms and accounted for 1.8%-9.2%. Nitrite oxidizing bacteria incursion happened unexpectedly, due to high oxygen exposure/supply from temporary on-site technical difficulties; however, NOB suppression was achieved by controlling DO at <0.16 mg/L, leading the FMBR's stability over the 343-day operation. Sulfate-reducing bacteria and sulfur-dependent denitrifiers propagated with high abundance, representing 14.0±10.6% and 6.0±2.0% in suspensions and 7.2±1.8% and 15.9±2.3% in biofilms, respectively. Further, metagenomic sequencing analysis indicated the C-N-S synergy of nitritation, anammox, sulfate reduction, and mixotrophic denitrification in the FMBR. Importantly, this research found that such a novel C-N-S synergy was made by the scavenges of hydrogen sulfide by Gammaproteobacteria sp. (B01 and B19) and Thioalkalispiraceae sp. (B03 and B04), species having ascendancy subsisting in the presence of oxygen owing to their aptitude of detoxifying reactive oxygen species. Knowledge gleaned from this study, as well as a complete set of pilot experimental data, could serve as a strong technical base for the larger-scale application of this process.

Polyaniline-coated conductive media promotes direct interspecies electrons transfer (DIET) and kinetics enhancement of low-strength wastewater treatment in anaerobic fluidized bed membrane bioreactor (AFMBR)

Polyaniline (PANI) was applied as coating materials to develop conductive surface on polyethylene terephthalate (PET) bead and polyvinylidene fluoride (PVDF) pellet termed as C-PET and C-PVDF as fluidized media in anaerobic fluidized bed membrane bioreactor (AFMBR). Parallel operation with AFMBRs showed that the fouling rate was lower for the C-PET and C-PVDF media than uncoated ones to scour membrane, and this was more pronounced as the organic loading rate was higher. Methane production rate was about 50% faster for the C-PET and C-PVDF media, and their use in the AFMBR system promoted methane yield by 14 to 190% higher than uncoated ones. 16S rRNA gene analysis revealed predictable results for methanogenic archaeal community structure (high abundance in Methanothrix), in line with the reactor performance observed, and suggestive of known Direct Interspecies Electron Transfer (DIET) metabolism. The bacterial analysis revealed common syntrophic species typically seen in anaerobic reactors, however, few known DIET species were also found, suggesting that more works are needed to elucidate pathways and syntrophies which may be activated by the PANI coating. Our results supported that conductive polymeric fluidized media should have great potential to promote kinetic enhancement in AFMBR treating low-strength wastewater.

Wastewater Treatment Using Anaerobic Fluidized Bed Membrane Bioreactor Coupled with Microbial Fuel Cells for Circular Economy

Wastewater treatment has been a problem in modern society due to negligence. It has led to the depletion of freshwater resources for human consumption and it is inevitable to search for ways to treat the wastewater effectively and economically. Domestic and industrial wastewaters are not treated well before letting into the freshwater sources. The freshwater gets polluted due to the presence of organic and inorganic substances that are known to be mutagenic, carcinogenic, and harmful to the environment. The conventional wastewater treatment systems are energy-intensive and inefficient. The use of membrane bioreactors is one of the breakthroughs in the field of wastewater treatment, where microorganisms are used to produce energy from the biomass present in the wastewater and utilize it as a substrate for their growth and development. The metabolic cycles of these microbes produce electrons/ions that are utilized in electricity/energy generation respectively. Wastewater usage to produce energy promotes circular economy, but this method alone is not very effective in treating the wastewater. Anaerobic fluidized bed membrane bioreactor with suspended granular activated carbon serves the purpose of a bio sorbent that facilitates the adsorption of low concentration pollutants and reduce the COD levels making it suitable for release into the freshwater resources. Coupling these two methods together seems to be effective and can be scaled up. This review article concentrates on coupling the two mechanisms to promote circular economy.

Long-term performance evaluation of granular activated carbon fluidization and biogas sparging in anaerobic fluidized bed membrane bioreactor: Membrane fouling and micropollutant removal

In this study, fluidization of granular activated carbon (GAC) by the recirculation of a bulk suspension through an anaerobic fluidized bed membrane bioreactor (AFMBR) and biogas sparging from the bottom of an anaerobic membrane bioreactor (G-AnMBR) for treating low-strength wastewater were compared to investigate organic removal and fouling rate. The chemical oxygen demand (COD) removal efficiency obtained by both the AFMBR and G-AnMBR exceeded 90 %, and the proportion of methane in the biogas produced was 60 % at the same hydraulic retention time (HRT). In the AFMBR, the transmembrane pressure (TMP) gradually increased, but a rapid TMP jump was not observed during operational period. In the G-AnMBR, the TMP increased rapidly as the biogas flowrate was 2 and 3 L/min (LPM) at 8 h of HRT while the TMP below 0.1 bar was maintained over 90 d at 4 LPM. Our results also indicated that organic micropollutants, such as Bisphenol A (BPA), Sulfamethoxazole (SMX), and Methylparaben (MeP), were removed by AFMBR almost completely. However, the G-AnMBR showed relatively low SMX and MeP removal efficiencies of 47.6 % and 74.9 %, respectively. The estimated energy required to operate the G-AnMBR was 1.37 kW h/m3, while it was only 0.06 kW h/m3 for AFMBR.

Combined Effect of Activated Carbon Particles and Non-Adsorptive Spherical Beads as Fluidized Media on Fouling, Organic Removal and Microbial Communities in Anaerobic Membrane Bioreactor.

The combined effect of acrylonitrile butadiene styrene (ABS) spherical beads and granular activated carbon (GAC) particles as fluidized media on the performance of anaerobic fluidized bed membrane bioreactor (AFMBR) was investigated. GAC particles and ABS beads were fluidized together in a single AFMBR to investigate membrane fouling and organic removal efficiency as well as energy consumption. The density difference between these two similarly sized media caused the stratified bed layer where ABS beads are fluidized above the GAC along the membrane. Membrane relaxation was effective to reduce the fouling and trans-membrane pressure (TMP) below 0.25 bar could be achieved at 6 h of hydraulic retention time (HRT). More than 90% of soluble chemical oxygen demand (SCOD) was removed after 80 d operation. Biogas consisting of 65% of methane was produced by AFMBR, suggesting that combined use of GAC and ABS beads did not have any adverse effect on methane production during the operational period. Scanning Electron Microscope (SEM) examinations showed the adherence of microbes to both media. However, 16S rRNA results revealed that fewer microbes attached to ABS beads than GAC. There were also compositional differences between the ABS and GAC microbial communities. The abundance of the syntrophs and exoelectrogens population on ABS beads was relatively low compared to that of GAC. Our result implied that syntrophic synergy and possible occurrence of direct interspecies electron transfer (DIET) might be facilitated in AFMBR by GAC, while traditional methanogenic pathways were dominant in ABS beads. The electrical energy required was 0.02 kWh/m3, and it was only about 13% of that produced by AFMBR.

Microbial fuel cells for municipal wastewater treatment: From technology fundamentals to full-scale development

Microbial fuel cells (MFCs) in municipal wastewater treatment plants (M-WWTPs) have garnered increasing interest in terms of attaining energy self-sufficiency due to their theoretical superiority to conventional M-WWTP processes. Despite being widely studied, pertaining literature primarily focuses on the fundamentals and configurations of the MFCs while overlooking their targeted application niche. Therefore, the adoption of MFCs in many niches (i.e., M-WWTPs) has not been adequately reviewed yet. This study aims to critically review the adoption of MFCs for carbon handling in the liquid stream of M-WWTPs with an emphasis on MFC's scalability, use of municipal wastewater (M-WW) as the substrate, and MFC's capital cost. The review includes the scaled-up results and other efforts to engineer MFCs. Three key challenges stymie MFC's adoption in M-WWTPs: low power generation, wide range of reported carbon removal efficiencies, and high capital cost. Accordingly, MFCs should be adopted in M-WWTPs with the goal of energy neutrality, not extra electricity production. To meet the effluent discharge standards, MFCs should be preceded by primary treatment, followed by an anaerobic fluidized bed membrane bioreactor. However, breakthroughs are still required to make this technology cost-efficient and energy-efficient. These efforts should take into consideration the multivariate nature of the MFCs. Additionally, the development of bioelectrochemically assisted anaerobic technologies has shown great prominence as an alternative technology that can be integrated into M-WWTPs. However, validation based on larger-scale applications, cost, and energy estimations is still needed.

Use of polymeric scouring agent as fluidized media in anaerobic fluidized bed membrane bioreactor for wastewater treatment: System performance and microbial community

New attempts using polymeric media with a tubular shape consisting of polyvinylidene fluoride (PVDF) were made as fluidized agent for anaerobic fluidized bed membrane bioreactor (AFMBR) in wastewater treatment. The AFMBR added with PVDF media was operated at room temperature and hydraulic retention time (HRT) from 4 to 16 h to investigate membrane fouling, organic removal efficiency, and microbial structure. Results showed that the PVDF media reduced membrane fouling effectively due to their scouring actions to clean the membrane. Transmembrane pressure (TMP) was maintained less than 0.1 bar during the operational period. More than 90% of chemical oxygen demand (COD) removal was achieved, yielding 10 mg/L of COD in membrane permeate. The energy required to operate the AFMBR using PVDF media was only 1.09×10−2 kWh/m3. The electrical energy produced by AFMBR was 0.246 kWh/m3, which is much higher than that required for system operation. Microbial community analysis based on 16S rRNA gene sequencing showed that the microbial community on PVDF biofilm was distinct from that in the suspended microbes. Importantly, it was found that dominant propionate-catabolizing bacteria on PVDF media include Desulfobulbus and syntroph Syntrophobacter while the key methanogenic player shifted from hydrogenotrophic Methanolinea to acetoclastic Methanothrix during the operation.

Fluidized bed membrane bioreactor achieves high sulfate reduction and filtration performances at moderate temperatures

The study explored the potential of an up-flow sulfate reducing fluidized-bed membrane bioreactor (SR-FMBR) for biogenic sulfide generation at room temperature together with evaluation of filtration and fouling characteristics developed under various operational conditions. The SR-FMBR was tested at different COD/sulfate (mg/mg) ratios for a total of 127 days, initially at 35 °C and then at 23 °C. SR-FMBR was able to achieve COD oxidation and sulfate reduction efficiencies up to 98%, and allowed for biogenic sulfide generation up to 600 mg/L (97% of theoretical value) at room temperature. Alkalinity was generated as a result of sulfate reduction and averaged around 1900 mgCaCO3/L in the permeate. Hence, starting the bioreactor operation at 35 °C and then decreasing it to 23 °C did not adversely affect the process performance. High filtration fluxes up to 9.3 L/m2/h (LMH) could be maintained at employed hydraulic retention times between 24 h and 6 h. Observing relatively high filtration performance was due to keeping a high fraction of biomass attached to the carrier material, which decreased the cake formation potential on the membrane surface compared to conventional MBR operation. The SR-FMBR performance may further be tested for heavy metal removal under sulfidogenic conditions for acid mine drainage treatment.

Beyond Energy Balance: Environmental Trade-Offs of Organics Capture and Low Carbon-to-Nitrogen Ratio Sewage Treatment Systems.

Several life-cycle assessments (LCAs) have evaluated the environmental impacts (EIs) of different wastewater treatment (WWT) configurations, attempting resource recovery and energy efficiency. However, a plant-wide LCA considering up-concentration primary treatment and low carbon-to-nitrogen (C/N) ratio sewage at the secondary biological treatment (SBT) has not yet been conducted. This study identifies the environmental trade-offs and hotspots for the chemically enhanced primary treatment (CEPT) and low C/N ratio SBT emerging processes compared to conventional WWT. The life-cycle inventories were calculated using a stoichiometric life-cycle inventory framework that couples stoichiometry and kinetics to obtain site-specific water, air, and soil emissions. The midpoint results of LCA show that CEPT with anaerobic digestion (AD) for sludge treatment achieves energy self-sufficiency, but increases marine eutrophication (MEu) by 1 order of magnitude compared to conventional WWT. A mainstream anaerobic fluidized-bed bioreactor and a partial nitritation-anammox fluidized-bed membrane bioreactor which can reduce all environmental impacts by 17-47%, including MEu, are proposed as the SBT of the low-carbon CEPT settled sewage. Integrating the standardized S-LCI framework resulted in a site-specific LCA that aids decision-makers on choosing between higher reductions in most EIs at the expense of high MEu or less but consistent reductions in all EI categories.

Swirling fluidization in an anoxic membrane bioreactor as an antifouling technique

Scarce attention has been placed on the geometry of anoxic fluidized bed membrane bioreactors (AFMBR) affecting the hydrodynamic pattern inside the reactor and, consequently, on the mechanical cleaning driven by granular carbon (GC) around the membrane. The present work evaluated the application of a swirling fluidization, produced by a tangential inlet in a reactor with hydrocyclone geometry, with the aim to avoid membrane fouling during the performance of a denitrification process. The study includes 3D-hydrodynamic description of the flow and particles fluidization through computation fluid dynamics (CFD), experimentally validated with the particle image velocimetry (PIV) technique. Water shear stress and GC particles momentum acting over the membranes were also assessed, in addition to monitoring filtration and denitrification performance. The conical section showed higher shear stress and particles momentum as compared to the cylindrical zone. Soluble microbial products (SMP) accumulated on the membrane walls with lower shear stress and particles momentum. The operation of the AFMBR was maintained with a continuous permeate flow without any change in suction pressure and the nitrate removal efficiency was above 90% with negligible accumulation of NO2− and N2O in the denitrifying process. This novel reactor configuration could be suitable for the treatment of industrial wastewaters.

Influence of hydraulic retention time and temperature on the performance of an anaerobic ammonium oxidation fluidized bed membrane bioreactor for low-strength ammonia wastewater treatment

The feasibility of anaerobic ammonium oxidation (Anammox) process with a fluidized bed membrane bioreactor (Anammox-FMBR) was evaluated for 561 days treating synthetic wastewater containing 35 mg/L of NO2−-N and 25 mg/L of NH4+-N. During start-up periods, higher nitrogen loading rate (NLR) induced faster stabilization than the low NLR. Total nitrogen (TN) removal efficiency was over 82% even with short hydraulic retention time (HRT) of 0.75 h at 25 °C conditions but decreased to below 30% at 15 °C. Pronounced effect of operating temperature at lower range was supported by high activation energy (Ea) value. The membrane fouling was controlled well, as evidenced from negligible fouling rates when the systems were operated at less than 13 L/m2/h flux with granular activated carbon (GAC) fluidization as cleaning media. With the estimated low energy requirements of 0.0005 kWh/kg Nremoved, the Anammox-FMBR could be successfully applied in mainstream operation for the energy efficient treatment of low ammonia wastewater.

Integration of an anaerobic fluidized-bed membrane bioreactor (MBR) with zeolite adsorption and reverse osmosis (RO) for municipal wastewater reclamation: Comparison with an anoxic-aerobic MBR coupled with RO.

This study compared the performance of an anaerobic fluidized bed membrane bioreactor (AFMBR)-zeolite adsorption-reverse osmosis (RO) system and an anoxic-aerobic MBR-RO system for municipal wastewater reclamation. Both MBR-RO systems were operated in parallel with the same operating conditions. The results showed that the MBR systems achieved excellent organic removals (>95%) and the anoxic-aerobic MBR could also remove ∼57% of soluble total nitrogen. Compared to the aerobic MBR, the AFMBR displayed better membrane performance with less energy consumption, attributed to effective membrane scouring by liquid-fluidized GAC particles. Furthermore, a zeolite column was employed to remove ammonia in the AFMBR permeate, which ensured comparable organic and nitrogen levels in the feeds to RO units in the two processes. Although less organic substances and microbial cells were accumulated on the RO membrane fed with AFMBR-zeolite column effluent, its fouling rate (∼6.5±2.2bar/day) was significantly greater than that fed with anoxic-aerobic MBR permeate (∼1.1±1.5bar/day). This may be associated with more severe inorganic colloidal fouling on the RO membrane, illustrated by an electrical impedance spectroscopy fouling monitoring system.

CFD-DEM study of geometry changes in an AnFMBR towards particle momentum

An anaerobic fluidized bed membrane bioreactor (AnFMBR) with granular activated carbon (GAC) particles as a scouring material was numerically investigated with the use of a CFD-DEM approach. After validation of the numerical solver, two different shapes of impediments, i.e., linear decreasing of the gap and linear de-/increasing of the gap, with variable impediment lengths were introduced to the geometry. The effects of built-in impediments, different fluid inlet velocities and particle sizes on the hydrodynamics, resulting particle momentum and required power input were evaluated and compared to the reactor geometry without an impediment. The disadvantage of reactor geometry without an impediment, i.e., the non-uniform distribution of particle momentum across the height, can be compensated with the use of built-in impediments depending on the fluid inlet velocity, particle diameter and impediment lengths. Furthermore, with the introduction of impediments the maximum achievable particle momentum can be increased or the optimum of particle momentum in regards to the power input can be shifted towards lower power inputs. The latter case is especially important for collisional- and scouring-sensitive membranes. The most promising effect towards particle momentum in terms of uniform distribution and magnitude was observed with small scouring particles (1.25 and 1.55 mm) for both impediments.