H2-based Membrane Biofilm Reactor Research Articles

Cooperation and competition between denitrification and chromate reduction in a hydrogen-based membrane biofilm reactor

Competition and cooperation between denitrification and Cr(VI) reduction in a H2-based membrane biofilm reactor (H2−MBfR) were documented over 55 days of continuous operation. When nitrate (5 mg N/L) and chromate (0.5 mg Cr/L) were fed together, the H2−MBfR maintained approximately 100 % nitrate removal and 60 % chromate Cr(VI) removal, which means that nitrate outcompeted Cr(VI) for electrons from H2 oxidation. Removing nitrate from the influent led to an immediate increase in Cr(VI) removal (to 92 %), but Cr(VI) removal gradually deteriorated, with the removal ratio dropping to 14 % after five days. Cr(VI) removal resumed once nitrate was again added to the influent. 16S rDNA analyses showed that bacteria able to carry out H2-based denitrification and Cr(VI) reduction were in similar abundances throughout the experiment, but gene expression for Cr(VI)-reduction and export shifted. Functional genes encoding for energy-consuming chromate export (encoded by ChrA) as a means of bacterial resistance to toxicity were more abundant than genes encoding for the energy producing Cr(VI) respiration via the chromate reductase ChrR-NdFr. Thus, Cr(VI) transport and resistance to Cr(VI) toxicity depended on H2-based denitrification to supply energy. With Cr(VI) being exported from the cells, Cr(VI) reduction to Cr(III) was sustained. Thus, cooperation among H2-based denitrification, Cr(VI) export, and Cr(VI) reduction led to sustained Cr(VI) removal in the presence of nitrate, even though Cr(VI) reduction was at a competitive disadvantage for utilizing electrons from H2 oxidation.

Co-Removal of Perfluorooctanoic Acid and Nitrate from Water by Coupling Pd Catalysis with Enzymatic Biotransformation.

PFAS (poly- and per-fluorinated alkyl substances) represent a large family of recalcitrant organic compounds that are widely used and pose serious threats to human and ecosystem health. Here, palladium (Pd0)-catalyzed defluorination and microbiological mineralization were combined in a denitrifying H2-based membrane biofilm reactor to remove co-occurring perfluorooctanoic acid (PFOA) and nitrate. The combined process, i.e., Pd-biofilm, enabled continuous removal of ∼4 mmol/L nitrate and ∼1 mg/L PFOA, with 81% defluorination of PFOA. Metagenome analysis identified bacteria likely responsible for biodegradation of partially defluorinated PFOA: Dechloromonas sp. CZR5, Kaistella koreensis, Ochrobacterum anthropic, and Azospira sp. I13. High-performance liquid chromatography-quadrupole time-of-flight mass spectrometry and metagenome analyses revealed that the presence of nitrate promoted microbiological oxidation of partially defluorinated PFOA. Taken together, the results point to PFOA-oxidation pathways that began with PFOA adsorption to Pd0, which enabled catalytic generation of partially or fully defluorinated fatty acids and stepwise oxidation and defluorination by the bacteria. This study documents how combining catalysis and microbiological transformation enables the simultaneous removal of PFOA and nitrate.

Optimization of the chemolithotrophic denitrification of ion exchange concentrate using hydrogen-based membrane biofilm reactors

A H2-based membrane biofilm reactor (MBfR) was used to remove nitrate from a synthetic ion-exchange brine made up of 23.8 g L−1 NaCl. To aid the selection of the best nitrate management strategy, our research was based on the integrated analysis of ionic exchange and MBfR processes, including a detailed cost analysis. The nitrate removal flux was not affected if key nutrients were present in the feed solution including potassium and sodium bicarbonate. Operating pH was maintained between 7 and 8. By using a H2 pressure of 15 psi, a hydraulic retention time (HRT) of 4 h, and a surface loading rate of 13.6 ± 0.2 g N m−2 d−1, the average nitrate removal flux was 3.3 ± 0.6 g N m−2 d−1. At HRTs of up to 24 h, the system was able to maintain a removal flux of 1.6 ± 0.2 g N m−2 d−1. Microbial diversity analysis showed that the consortium was dominated by the genera Sulfurimonas and Marinobacter. The estimated cost for a 200 m3/h capacity, coupled ion exchange (IX) + MBfR treatment plant is 0.43 USD/m3. This is a sustainable and competitive alternative to an IX-only plant for the same flowrate. The proposed treatment option allows for brine recycling and reduces costs by 55% by avoiding brine disposal expenses.

Development of a novel periodic venting-controlled membrane biofilm reactor for hydrogenotrophic denitrification: Process performance and microbial mechanism

The performance of anaerobic membrane biofilm reactor (MBfR) has long been underexploited due to the limited delivery of active gas to the biofilm on the close-end hollow fiber membranes (HFMs). Here, to establish a valid scheme for overcoming this obstacle, we coupled a denitrifying H2-based MBfR to an automatic venting unit for intermittently updating intramembrane gas, and a microsensor unit for investigating the H2 diffusion behavior. In short-term experiments, at the HFM length of 60 cm and H2 supplying pressure of 1.2 atm, the periodic venting strategy, in which the venting time and interval were set as 30 s and 17 min, respectively, was validated to be capable of improving the denitrification performance of H2-based MBfR. The results of long-term experiment show that compared to the conventional close-end operation, the around 50% increase in denitrification flux was achieved in the periodic venting-controlled system, which was found to be associated with the increased biofilm thickness and the evolution of denitrifying bacteria (DNB) and functional genes in the biofilm at the HFM distal end. Model outputs manifest that regardless of the HFM length, the biofilm regions with high DNB activity at the distal end were much narrower than those at the proximal end of the close-end HFMs; owing to the improved H2 delivery, the active biofilm region at the distal end of 60 cm HFM was significantly enlarged from 0–225 µm in the case of close-end operation to 0–450 µm in the venting-controlled system. The proposed periodic venting strategy opens a new avenue for the management of anaerobic MBfR.

Biological conversion of sulfisoxazole in an autotrophic hydrogen-based membrane biofilm reactor

Sulfisoxazole (SIZ), a common antimicrobial prescribed for treating infections in livestock, is frequently detected in surface water and groundwater along with nitrate. The interactions of SIZ biotransformation and nitrate removal were investigated in a H2-based membrane biofilm reactor (H2-MBfR) through long-term reactor operation augmented by short-term batch experiments in serum bottles. Denitrification in the H2-MBfR was not influenced by SIZ when its input concentration was ≤5 mg L−1, although SIZ removal was inhibited by nitrate. Transformation products identified by mass spectrometry were formed via hydrogenation (reduction) reactions. The addition of SIZ shaped the microbial community structure, leading to the relative abundance of denitrifiers decreasing with the highest SIZ loading. Sulfate-reducing bacteria (SRB) were present in all stages, as the biofilms had relatively high abundances of the dsrA gene and its transcription products, while sulfide was generated in the final stage. SRB also appeared to be important in SIZ biotransformation, perhaps using SIZ as an electron donor, electron acceptor, or both. Concurrent SIZ removal and stable denitrification make the H2-MBfR a prospective technology for the treatment of wastewaters polluted with nitrate and SIZ.

Model Evaluation of the Microbial Metabolic Processes in a Hydrogen-Based Membrane Biofilm Reactor for Simultaneous Bromate and Nitrate Reduction

The H2-based membrane biofilm reactor (H2-MBfR) has been acknowledged as a cost-effective microbial reduction technology for oxyanion removal from drinking water sources, but it remains unknown how the evolution of biofilm characteristics responds to the changing critical operating parameters of the H2-MBfR for simultaneous bromate (BrO3−) and nitrate (NO3−) elimination. Therefore, an expanded multispecies model, applicable to mechanistically interpret the bromate-reducing bacteria (BRB)- and denitrifying bacteria (DNB)-dominated metabolic processes in the biofilm of the H2-MBfR, was developed in this study. The model outputs indicate that (1) increased BrO3− loading facilitated the metabolism of BRB by increasing BRB fraction and BrO3− gradients in the biofilm, but had a marginal influence on NO3− reduction; (2) H2 pressure of 0.04 MPa enabled the minimal loss of H2 and the extension of the active region of BRB and DNB in the biofilm; (3) once the influent NO3− concentration was beyond 10 mg N/L, the fraction and activity of BRB significantly declined; (4) BRB was more tolerant than DNB for the acidic aquatic environment incurred by the CO2 pressure over 0.02 MPa. The results corroborate that the degree of microbial competition for substrates and space in the biofilm was dependent on system operating parameters.

Enhanced removal of diclofenac via coupling Pd catalytic and microbial processes in a H2-based membrane biofilm reactor: Performance, mechanism and biofilm microbial ecology

Diclofenac (DCF) is a most widely used anti-inflammatory drug, which has attracted worldwide attention given its low biodegradability and ecological damage, especially toxic effects on mammals including humans. In this study, a H2-based membrane biofilm reactor (H2-MBfR) was constructed with well-dispersed Pd nanoparticles generated in situ. The Pd-MBfR was applied for catalytic reductive dechlorination of DCF. In batch tests, DCF concentration had significantly effect on the rate and extent DCF removal, and NO3− had negative impact on DCF reductive dechlorination. Over 67% removal of 0.5 mg/L DCF and 99% removal of 10 mg/L NO3−-N were achieved in 90 min, and the highest removal of 97% was obtained at 0.5 mg/L DCF in the absence of NO3−. Over 78 days of continuous operation, the highest steady-state removal flux of DCF was 0.0097 g/m2/d. LC-MS analysis indicated that the major product was 2-anilinephenylacetic acid (APA). Dechlorination was the main removal process of DCF mainly owing to the catalytic reduction by PdNPs, microbial reduction, and the synergistic reduction of microbial and PdNPs catalysis using direct delivery of H2. Moreover, DCF reductive Dechlorination shifted the microbial community in the biofilms and Sporomusa was responsible for DCF degradation. In summary, this work expands a remarkable feasibility of sustainable catalytic removal of DCF.

New insight into CO2-mediated denitrification process in H2-based membrane biofilm reactor: An experimental and modeling study

The H2-based membrane biofilm reactor (H2−MBfR) is an emerging technology for removal of nitrate (NO3−) in water supplies. In this research, a lab-scale H2−MBfR equipped with a separated CO2 providing system and a microsensor measuring unit was developed for NO3− removal from synthetic groundwater. Experimental results show that efficient NO3− reduction with a flux of 1.46 g/(m2⋅d) was achieved at the optimal operating conditions of hydraulic retention time (HRT) 80 min, influent NO3− concentration 20 mg N/L, H2 pressure 5 psig and CO2 addition 50 mg/L. Given the complex counter-diffusion of substrates in the H2−MBfR, mathematical modeling is a key tool to both understand its behavior and optimize its performance. A sophisticated model was successfully established, calibrated and validated via comparing the measured and simulated system performance and/or substrate gradients within biofilm. Model results indicate that i) even under the optimal operating conditions, denitrifying bacteria (DNB) in the interior and exterior of biofilm suffered low growth rate, attributed to CO2 and H2 limitation, respectively; ii) appropriate operating parameters are essential to maintaining high activity of DNB in the biofilm; iii) CO2 concentration was the decisive factor which matters its dominant role in mediating hydrogenotrophic denitrification process; iv) the predicted optimum biofilm thickness was 650 µm that can maximize the denitrification flux and prevent loss of H2.

Influence of operating conditions on sulfate reduction from real mining process water by membrane biofilm reactors.

Two H2-based membrane biofilm reactor (H2-MBfR) systems, differing in membrane type, were tested for sulfate reduction from a real mining-process water having low alkalinity and high concentrations of dissolved sulfate and calcium. Maximum sulfate reductions were 99%, with an optimum pH range between 8 and 8.5, which minimized any toxic effect of unionized hydrogen sulfide (H2S) on sulfate-reducing bacteria (SRB) and calcite scaling on the fibers and in the biofilm. Although several strategies for control of pH and gas back-diffusion were applied, it was not possible to sustain a high degree of sulfate reduction over the long-term. The most likely cause was precipitation of calcite inside the biofilm and on the surface of fibers, which was shown by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) analysis. Another possible cause was a decline in pH, leading to inhibition by H2S. A H2/CO2 mixture in the gas supply was able to temporarily recover the effectiveness of the reactors and stabilize the pH. Biomolecular analysis showed that the biofilm was comprised of 15-20% SRB, but a great variety of autotrophic and heterotrophic genera, including sulfur-oxidizing bacteria, were present. Results also suggest that the MBfR system can be optimized by improving H2 mass transfer using fibers of higher gas permeability and by feeding a H2/CO2 mixture that is automatically adjusted for pH control.

Model-based evaluation of selenate and nitrate reduction in hydrogen-based membrane biofilm reactor

A biofilm model was developed to describe the simultaneous NO3− and SeO42− reduction in a H2-based membrane biofilm reactor (MBfR). Model calibration and validation was conducted using the experimental data of a reported H2-based MBfR. With a good level of identifiability, the SeO42− affinity constant and the SeO32− affinity constant were estimated at 9.80 ± 0.51 g Se m−3 and 1.83 ± 0.38 g Se m−3, respectively. The model was then applied to evaluate the effects of key operating conditions on the single-stage H2-based MBfR and the role of reactor configuration through comparing two-stage to single-stage MBfR systems. The results showed that (i) high SeO42− or low NO3− concentration in the influent favored the growth of selenate-reducing bacteria (SeRB) and therefore benefited the Se removal, (ii) the influent dissolved oxygen slightly inhibited the Se removal through enhancing the aerobic microbial respiration on H2, (iii) the H2 supply should be controlled at a proper level to avoid SeRB suppression and H2 wastage, (iv) thin biofilm should be avoided to ensure a protected niche for SeRB and therefore a promising Se removal, and (v) the two-stage MBfR configuration offered relatively higher efficiency in removing Se and NO3− simultaneously under the same loading condition.

Total electron acceptor loading and composition affect hexavalent uranium reduction and microbial community structure in a membrane biofilm reactor

Molecular microbiology tools (i.e., 16S rDNA gene sequencing) were employed to elucidate changes in the microbial community structure according to the total electron acceptor loading (controlled by influent flow rate and/or medium composition) in a H2-based membrane biofilm reactor evaluated for removal of hexavalent uranium. Once nitrate, sulfate, and dissolved oxygen were replaced by U(VI) and bicarbonate and the total acceptor loading was lowered, slow-growing bacteria capable of reducing U(VI) to U(IV) dominated in the biofilm community: Replacing denitrifying bacteria Rhodocyclales and Burkholderiales were spore-producing Clostridiales and Natranaerobiales. Though potentially competing for electrons with U(VI) reducers, homo-acetogens helped attain steady U(VI) reduction, while methanogenesis inhibited U(VI) reduction. U(VI) reduction was reinstated through suppression of methanogenesis by addition of bromoethanesulfonate or by competition from SRB when sulfate was re-introduced. Predictive metagenome analysis further points out community changes in response to alterations in the electron-acceptor loading: Sporulation and homo-acetogenesis were critical factors for strengthening stable microbial U(VI) reduction. This study documents that sporulation was important to long-term U(VI) reduction, whether or not microorganisms that carry out U(VI) reduction mediated by cytochrome c3, such as SRB and ferric-iron-reducers, were inhibited.

Perchlorate, nitrate, and sulfate reduction in hydrogen-based membrane biofilm reactor: Model-based evaluation

A biofilm model was developed to evaluate the key mechanisms including microbially-mediated ClO4−, NO3−, and SO42− reduction in the H2-based membrane biofilm reactor (MBfR). Sensitivity analysis indicated that the maximum growth rate of H2-based denitrification (μ1) and maximum growth rate of H2-based SO42− reduction (μ3) could be reliably estimated by fitting the model predictions to the experimental measurements. The model was first calibrated using the experimental data of a single-stage H2-based MBfR fed with different combinations of ClO4−, NO3−, and/or SO42− together with a constant dissolved oxygen (DO) concentration at three operating stages. μ1 and μ3 were determined at 0.133h−1 and 0.0062h−1, respectively, with a good level of identifiability. The model and the parameter values were further validated based on the experimental data of a two-stage H2-based MBfR system fed with ClO4−, NO3−, SO42−, and DO simultaneously but at different feeding rates during two running phases. The validated model was then applied to evaluate the quantitative and systematic effects of key operating conditions on the reduction of ClO4−, NO3−, and SO42− as well as the steady-state microbial structure in the biofilm of a single-stage H2-based MBfR. The results showed that i) a higher influent ClO4− concentration led to a higher ClO4− removal efficiency, compensated by a slightly decreasing SO42− removal; ii) the H2 loading should be properly managed at certain critical level to maximize the ClO4− and NO3− removal while limiting the growth of sulfate reducing bacteria which would occur in the case of excessive H2 supply; and iii) a moderate hydraulic retention time and a relatively thin biofilm were required to maintain high-level removal of ClO4− and NO3− but restrict the SO42− reduction.

Concomitant Cr(VI) reduction and Cr(III) precipitation with nitrate in a methane/oxygen-based membrane biofilm reactor

A continuously stirred methane (CH4) and oxygen (O2)-based membrane biofilm reactor (MBfR) was investigated for removing chromium (Cr) from nitrate (NO3−)-contaminated drinking water. Cr(VI) at an initial concentration of 100μg/L was rapidly reduced to Cr(III) with a removal rate of 89% and a hydraulic retention time of 48h under normal denitrifying conditions in a methane/oxygen-based MBfR. A microbial community analysis indicated that Comamonadaceae, Cytophagaceae, Hyphomicrobiaceae and Alcaligenaceae were effective denitrifiers, Methylophilaceae and Methylococcaceae were functional methanotrophic bacteria, and Comamonadaceae was a kind of Cr(VI) reducers in the reactor. Cr(VI) was reduced to Cr(III), which precipitated and adsorbed onto the biofilm as Cr(OH)3, due to the alkaline produced during denitrification. When the CH4 pressure increased from 0.02 to 0.03MPa, the Cr(VI) reduction increased by 40.3%, and the NO3− reduction increased by 30.2%. Although the effluent Cr(VI) concentration increased with increasing influent loading, the removal efficiency of Cr(VI) reached the highest level of 99.8% under a high daily loading of 5.76mg/d. Unlike a H2-based MBfR, it is possible to remove Cr from water without post-processing, such as precipitation, in a CH4/O2-based MBfR.

Palladium Recovery in a H2-Based Membrane Biofilm Reactor: Formation of Pd(0) Nanoparticles through Enzymatic and Autocatalytic Reductions.

Recovering palladium (Pd) from waste streams opens up the possibility of augmenting the supply of this important catalyst. We evaluated Pd reduction and recovery as a novel application of a H2-based membrane biofilm reactor (MBfR). At steady states, over 99% of the input soluble Pd(II) was reduced through concomitant enzymatic and autocatalytic processes at acidic or near neutral pHs. Nanoparticulate Pd(0), at an average crystallite size of 10 nm, was recovered with minimal leaching and heterogeneously associated with microbial cells and extracellular polymeric substances in the biofilm. The dominant phylotypes potentially responsible for Pd(II) reduction at circumneutral pH were denitrifying β-proteobacteria mainly consisting of the family Rhodocyclaceae. Though greatly shifted by acidic pH, the biofilm microbial community largely bounced back when the pH was returned to 7 within 2 weeks. These discoveries infer that the biofilm was capable of rapid adaptive evolution to stressed environmental change, and facilitated Pd recovery in versatile ways. This study demonstrates the promise of effective microbially driven Pd recovery in a single MBfR system that could be applied for the treatment of the waste streams, and it documents the role of biofilms in this reduction and recovery process.

Actual Application of a H2-Based Polyvinyl Chloride Hollow Fiber Membrane Biofilm Reactor to Remove Nitrate from Groundwater

To evaluate the actual performance of the H2-based polyvinyl chloride hollow fiber membrane biofilm reactor (HF-MBfR), we used HF-MBfR to remove nitrate from the nitrate contaminated groundwater with the dissolved oxygen (~6.2 mg/L) in Zhangqiu city (Jinan, China). The reactor was operated over 135 days with the actual nitrate contaminated groundwater. The result showed that maximum of nitrate denitrification rate achieved was over 133.8 gNO3--N/m3d (1.18 gNO3--N/m2d) and the total nitrogen removal was more than 95.0% at the conditions of influent nitrate 50 mg/L, hydrogen pressure 0.05 MPa, and dissolved oxygen (DO) 6.2 mg/L, with the nitrate in effluent under the value limits of drinking water. The fluxes analysis showed that the electron-equivalent fluxes of nitrate, sulfate, and oxygen account for about 81.2%, 15.2%, and 3.6%, respectively, which indicated that nitrate reduction could consume more electrons than that of sulfate reduction and dissolved oxygen reduction. The nitrate reduction was not significantly influenced by sulfate reduction and the dissolved oxygen reduction. Based on the actual groundwater quality on site, the Langelier Saturation Index (LSI) was 0.4, and the membrane could be at the risk of surface scaling.

Bio-reduction of tetrachloroethen using a H2-based membrane biofilm reactor and community fingerprinting

Chlorinated ethenes in drinking water could be reductively dechlorinated to non-toxic ethene by using a hydrogen based membrane biofilm reactor (H2-MBfR) under denitrifying conditions as it provides an appropriate environment for dechlorinating bacteria in biofilm communities. This study evaluates the reductive dechlorination of perchloroethene (PCE) to non-toxic ethene (ETH) and comparative community analysis of the biofilm grown on the gas permeable membrane fibers. For these purposes, three H2-MBfRs receiving three different chlorinated ethenes (PCE, TCE and DCE) were operated under different hydraulic retention times (HRTs) and H2 pressures. Among these reactors, the H2-MBfR fed with PCE (H2-MBfR 1) accomplished a complete dechlorination, whereas cis-DCE accumulated in the TCE receiving H2-MBfR 2 and no dechlorination was detected in the DCE receiving H2-MBfR 3. The results showed that 95% of PCE dechlorinated to ETH together with over 99.8% dechlorination efficiency. Nitrate was the preferred electron acceptor as the most of electrons generated from H2 oxidation used for denitrification and dechlorination started under nitrate deficient conditions at increased H2 pressures. PCR-DGGE analysis showed that Dehalococcoides were present in autotrophic biofilm community dechlorinating PCE to ethene, and RDase genes analysis revealed that pceA, tceA, bvcA and vcrA, responsible for complete dechlorination step, were available in Dehalococcoides strains.

Modeling trichloroethene reduction in a hydrogen-based biofilm

We constructed a multispecies biofilm model for simultaneous reduction of trichloroethene (TCE) and nitrate (NO3(-)) in the biofilm of a H2-based membrane biofilm reactor (MBfR). The one-dimensional model includes dual-substrate Monod kinetics for a steady-state biofilm with multiple solid and dissolved components. The model has five solid components: autotrophic denitrifying bacteria (ADB), heterotrophic denitrifying bacteria (HDB), Dehalococcoides (DHC), inert biomass (IB), and extracellular polymeric substances (EPS). The model has eight dissolved components: NO3(-), TCE, dichloroethene (DCE), vinyl chloride (VC), ethene, hydrogen (H2), substrate-utilization-associated products (UAP), and biomass-associated products (BAP). We used this model to simulate a bench-scale experiment in a H2-based MBfR. The model simulated the trends well: almost complete removal of nitrate, incomplete reduction of TCE, and almost no accumulation of DCE and VC. To gain insight into reductive dehalogenation in a H2-based MBfR, we also simulated the concentrations of nitrate, TCE, DCE, VC, and ethene in the reactor effluent while varying the influent nitrate concentration. Simultaneous low concentrations of nitrate and the three chlorinated ethenes can occur as long as the influent ratio of NO3(-) to TCE is not too large, so that DHC are a significant fraction of the biofilm.

Hydrogen permeability of the hollow fibers used in H2-based membrane biofilm reactors

Abstract We developed and used steady-state permeation tests and a mathematical model to determine the H2 permeabilities of three hollow fibers (composite, polyester, and polypropylene) commonly used in the H2-based membrane biofilm reactor (MBfR). The H2 permeabilities spanned a wide range: 1.6 × 10−6, 1.8 × 10−7, and 6.6 × 10−8 m3 H2 @ standard temperature and pressure m membrane thickness/m2 hollow fiber surface area d bar for the composite, polypropylene, and polyester hollow fibers, respectively; this represents a ratio of the maximum H2 flux for composite:polypropylene:polyester hollow fibers = 32:3.3:1. The H2 permeabilities were then used to correlate hollow-fiber type to contaminant-removal flux in previous MBfR experiments. Only the experiments with composite hollow fibers were not routinely limited by H2 delivery, although fouling by mineral precipitates lowered the H2 flux in some cases. Since existing contaminant-removal data for the polyester hollow fibers were not adequate, we did special experiments to investigate the effect of H2 pressure on contaminant removal in the MBfR with the polyester hollow fibers. We confirmed that this hollow fiber was operated at its maximum H2-delivery capacity based on its H2 permeability.

Comparing heterotrophic and hydrogen-based autotrophic denitrification reactors for effluent water quality and post-treatment

This work compares a pilot-scale H2-based membrane biofilm reactor (MBfR) and a pilot-scale packed-bed heterotrophic reactor (PBHR) for denitrification of nitrate-contaminated groundwater. The comparison includes the effluent water quality of the denitrification reactors (NO3−, NO2−, dissolved oxygen, SO42−, (biodegradable) dissolved organic carbon, heterotrophic plate counts (HPC), turbidity, NH4+, and pH), and the impact of post-treatment on water quality. At the same nitrate carrier-surface loading, effluent water quality was generally better directly from the MBfR than from the PBHR. However, post treatment including an ozone-contact tank and a post-filter brought the finished-water quality for both systems to roughly the same level, which met all drinking water standards except for HPC.

Effect of NaCl on nitrate removal from ion-exchange spent brine in the membrane biofilm reactor (MBfR)

The H(2)-based membrane biofilm reactor was used to remove nitrate from synthetic ion-exchange brine at NaCl concentrations from ∼3 to 30 g/L. NaCl concentrations below 20 g/L did not affect the nitrate removal flux as long as potassium was available to generate osmotic tolerance for high sodium, the H(2) pressure was adequate, and membrane fouling was eliminated. Operating pHs of 7-8 and periodic citric acid washes controlled membrane fouling and enabled reactor operation for 650 days. At 30 psig H(2) and high nitrate loading rates of 15 to 80 g/m(2) d, nitrate removal fluxes ranged from 2.5 to ∼6 g/m(2) d, which are the highest fluxes observed when treating 30 g/L IX brine. However, percent removals were low, and the H(2) pressure probably limited the removal flux.