MABRs − ten research papers

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Things have moved on quite a long way since the early development of the MABR (membrane aerated-biofilm reactor) process by the pioneering Professor Mike Semmens some 30 years ago. For those au fait with the technology, below is a selection of ten papers provided by a range of research groups, from the start of 2019 onwards.

Apart from the removal of specific recalcitrant pollutants, such as tetracycline, nitroaniline and melamine, the list includes studies of:

  • sulphide removal from AD-treated wastewaters
  • enhancement with bio-carriers
  • nitritation, and
  • a composite membrane-based process.

There’s also a modelling/simulation study and integration into a UCT process. Plus a review, published in 2020, which seems pretty comprehensive. The list below is presented in reverse chronological order and no preference is indicated. This list was compiled in October 2020, and may be updated in future as new papers are published.

For people wondering what the difference is between MBRs and MABRs, you can read our brief explainers What are MABRs? and MABRs vs MBRs as well as our blog Defining MABRs, MBBRs and MBRs − terms and terminology.

Ten MABR research abstracts

'This study investigated the potential of Membrane-Aerated Biofilm Reactors (MABRs) for mainstream nitrogen removal via partial nitration/anaerobic ammonium oxidation (anammox). Four laboratory-scale MABRs were operated with real municipal wastewater characterized by low concentrations of nitrogen (varying between 31 and 120 mg–NH4–N L−1) and the presence of biodegradable organic carbon (soluble COD (sCOD) between 7 and 230 mg-O2 L−1). Two reactors were operated with different aeration strategies (intermittent vs. continuous), the other two with differences in biomass retention (recirculation or removal of detached biomass). Keeping a constant HRT caused instabilities due to difficulties with setting the optimal oxygen flux for the respective surface loadings (1.6–6 g– NH4–N m−2 d−1).

'Operating the MABRs with a constant surface loading (2 g–NH4–N m−2 d−1) resulted in higher and more stable total nitrogen (TN) removal independent of the aeration strategy. The intermittently aerated MABR improved from an average TN removal of 23%–69%, the continuously aerated MABR from 20% to 50% TN removal. Independent of the feeding strategy, the continuously aerated reactor removed slightly more ammonium (80–95%) compared to the intermittently aerated reactor (74–93%). Limiting the oxygen supply by intermittent aeration proofed successful to favor partial nitritation and anammox. Continuous aeration did not achieve stable suppression of nitrite oxidizing bacteria (NOB). Of the removed ammonium, approx. 26% were left in the effluent as nitrate (only 10% with intermittent aeration).

'Recirculation of the detached biomass resulted in reattachment onto the biofilm or membrane surface. This recirculation led to significantly higher biomass retention times and thus to better performance. Removing detached biofilm from the reactor caused a slightly lower TN removal of 33% compared to 45% with reattachment, while average ammonium removal was 58% compared to 63%, respectively. Scouring events had a significant impact on the overall operation, resulting in short term losses of TN removal capacities of 50–100%. The microbial community composition was different depending on the aeration strategy and biomass retention. The continuously aerated reactor contained significantly more AOB than the intermittently aerated MABR. The reactor with biomass retention contained less ammonium oxidizing bacteria (AOB), compared to the reactor with low biomass retention. In all MABRs, anammox bacteria established in the biofilm after an initial drop in abundance.' © 2020 The authors.

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

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'Nitroaniline (NA) is an aniline derivative with high toxicity, potential carcinogenicity and mutagenic effects. At present, the physical, chemical and biological methods used in NA-containing wastewater treatment usually suffer from problems such as low removal efficiency, high energy consumption and secondary pollution generation. In this study, a membrane-aerated biofilm reactor (MABR) was constructed to enhance the treatment of wastewater containing o-nitroaniline (2-NA) and p-nitroaniline (4-NA). The stratified biofilm and counterdiffusion of oxygen in the MABR were conducive to NA degradation. At a lower concentration, NA was primarily removed through direct oxidative degradation in the absence of the co-metabolic substrate acetic acid, while at a higher concentration, NA was predominantly removed through oxidative degradation after reduction of NA in the presence of acetic acid. With an influent NA loading of 0.120 kg/(m3·d), an aeration pressure of 40 kPa and an acetic acid dosing ratio of 2.0, the 2-NA and 4-NA removal loadings reached 0.058 and 0.060 kg/(m3·d), respectively. Additionally, the chemical oxygen demand (COD) and total nitrogen (TN) removal rates were 82.40 and 88.52%, respectively. The MABR technology promoted simultaneous NA degradation and nitrogen removal from NA-containing wastewater treatment, illustrating its prospects for industrial application.' © 2020 Elsevier B.V.

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'Single-stage autotrophic nitrogen removal offers advantages of low energy and carbon consumptions. Based on previous work about a novel composite membrane aerated biofilm (CMAB), two microbial entrapping patterns (mixed and stratified patterns) were evaluated for their applicability to artificially regulate the spatial distribution of distinct microbial aggregates for single-stage autotrophic nitrogen removal. Experimental results showed that the stratified pattern caused little accumulation of NO2and NO3, which leads to a superior nitrogen removal performance compared with the mixed pattern. Candidatus Kuenenia was found to be the major anammox bacterium in the gel film of the mixed pattern and the outer film of the stratified pattern. In contrast, Nitrosomonas, as a representative genus of ammonia-oxidizing bacteria, was substantially enriched in the inner film of the stratified pattern and the gel film of the mixed pattern. Finally, modeling results further confirmed the advantages of the stratified pattern with respect to the formation of rational microbial and nutrient profiles in gel films. The ratio of partial nitrification and anammox film thicknesses should remain below 3:2 to obtain a high fraction of anammox bacteria and to avoid NO2 accumulation. Increasing O2 surface loading does not affect microbial profiles, but can greatly promote the TN removal performance only in the stratified pattern. Overall, the stratified pattern should be employed to achieve optimal microbial profiles and nitrogen removal efficiency.' © 2020, Springer-Verlag.

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'A pilot-scale anaerobic/anoxic/aerobic-membrane aerated biofilm reactor (A2/O-MABR) system was constructed to enhance carbon and nitrogen removal. The effects of major operating parameters including the nitrate recycling ratio (R), sludge recycling ratio (r), and aerobic tank dissolved oxygen (DO) concentration on the system performance were investigated. The average removal efficiencies of the chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), and total nitrogen (TN) were 89.0 ± 3.2%, 98.8 ± 1.3%, and 68.5 ± 4.2%, respectively, and their effluent concentrations were averagely 22.6 ± 7.3, 0.32 ± 0.2, and 13.3 ± 1.2 mg L-1. The suspended sludge and biofilm in aerobic tank facilitated the simultaneous nitrification and denitrification (SND) processes. Indeed, unique biofilm layered structure and abundant microbial community in the biofilm on MABR would enhance nitrogen removal. Compared with the A2/O system, the A2/O-MABR system exhibited higher nitrifying bacteria oxygen uptake rate (OUR) of 58.1 and 54.5 mgO2 per gMLSS per h in suspended sludge and biofilm, respectively, and the lower mixed liquor suspended solid (MLSS) concentration of 1800 mg L-1. Moreover, high-throughput sequencing indicated that putative nitrogen removal bacteria such as Thauera and Paracoccus could be effectively enriched in the biofilm. Since the volume proportions of the anaerobic, anoxic, aerobic and settling tank in the existing A2/O system of the WWTP was not changed, the A2/O-MABR system was simple and practical for the upgrading of A2/O system.' © 2020 The Royal Society of Chemistry.

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'Researchers have observed that the biofilm nitrification rate (NR) in membrane-aerated biofilm reactor (MABR) systems did not deteriorate at low winter temperatures. Using the pilot data, the temperature impacts were studied in two different approaches. A close-to-unity temperature coefficient (θ = 1.007) and a constant half-velocity constant (KN,BF = 5.7 mgN/L) were obtained from the semiempirical kinetic-based approach, indicating that the bulk NH4+-N concentration, rather than temperature, was determining the biofilm NR. The pilot performance was also simulated in GPS-X 7.0 using all typical kinetic values from scientific literatures except the hydrolysis rate constant. A lower hydrolysis rate constant (0.15 day−1) was used to match the data during calibration and it should be considered as a lumped effect of the pilot conditions. While the temperature effects on biological kinetics are well established, they were masked by the dynamic changes in the MABR biofilm. The apparently weak impact of temperature on the biofilm NR distinguishes the MABR technology as a novel solution for nitrification intensification. The two simulation approaches are proved effective as tools for the process design.' © 2020 ASCE

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'Membrane aerated biofilm bioreactors (MABRs), a relatively new innovation in biological wastewater treatment technology, have received much attention in recent years. In the past two decades, the emphasis has focused on exploring and verifying the advantages of MABRs for wastewater treatment through experimental and modeling studies. In-depth fundamental understanding of MABRs and their design have been achieved. Pilot-scale studies and full-scale applications of MABRs have been reported. MABR technology has been successfully applied for high strength industrial wastewater treatment and refractory pollutant removal, simultaneous removal of chemical oxygen demand (COD) and nitrogen (N) in municipal wastewater treatment, and retrofitting of existing activated sludge plants. The advantages of MABRs include high oxygen transfer efficiency, effective COD/N removal, improved energy efficiency, and the relative ease in scale-up. The importance of biofilm thickness control, potential for new applications, and design of low-cost and high efficient membrane materials and modules call for further studies to advance MABR technology. Recent advances in physico-chemical properties of membranes, factors affecting MABR performance, microbial communities, and modeling in MABRs are systematically reviewed. A number of important challenges and unexplored opportunities remain pointing in the direction of future research and development needs.' © Taylor & Francis 2020.

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'The Membrane Aerated Biofilm Reactor (MABR) is an attractive alternative for the removal of nitrogen from wastewater because of its ability to overcome the inherent limitations of conventional systems. But in MABR, the denitrification performance is low at low Hydraulic Retention Times (HRT). Therefore, a modified MABR which uses Polyvinyl Alcohol (PVA) gel beads as bio-carriers was used in this study to enhance the Total Nitrogen (TN) removal efficiency when treating domestic wastewater. By adding PVA-Gel in the MABR, the nitrification and TN removal performances increased by 14% and 13.4% respectively. At 12 h HRT and COD/N = 6, it had a maximum TN removal efficiency of 68.63%. The COD removal performance was always above 90.2%. Moreover, in contrast to a conventional MABR, the nitrification rate had an upward trend when the COD/N ratio was increased and/or when the HRT was reduced. Above results concluded that PVA-Gel addition enhanced the MABR performance.' © 2019 Elsevier Ltd.

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'The membrane aerated biofilms reactor (MABR) is an emerging technology in wastewater treatment with particular advantages including high rate nitrification, and very high oxygen transfer efficiencies. In this study a synthetic feed water incorporating tetracycline (TC) was investigated in a MABR. Simultaneous removal of ammonium and tetracycline (TC) in the reactor, formation of TC transformation products (TPs), and microbial community analysis in the biofilm growing on the membrane were performed. A range of TC and ammonium loading rates and the effect of different intra-membrane oxygen pressures were on treatment performance were systematically investigated. Successful nitrification and TC degradation were achieved with the highest TC removal (63%) obtained at a HRT of 18 h HRT and 0.41 bar gas pressure. It has shown that different operating conditions (HRT and gas pressure) do not cause a significant change in ammonium removal. The concentration of TPs such as ETC, EATC, and ATC was determined to be at the ppb level. Molecular results showed that MABR reactor was mainly dominated by β-proteobacteria. The relative abundance of this group decreased in parallel with the increasing ammonium and TC loading.' © 2019 Elsevier B.V.

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'A upflow anaerobic sludge blanket reactor was operated combined to a membrane aerated biofilm reactor for sulfate removal and for elemental sulfur reclamation. A commercial silicon tube was used as an oxygen delivery diffuser. The process achieved high rates of sulfide removal from the liquid phase (90%). The hydrogen sulfide removal was influenced by the pH value and at pH value of 7.5, 98% of the H2S was removed. The elemental sulfur was observed inside the membrane, with content in the biomass of 21%. Through the massive sequencing of the samples, the microbial community diversity and the stratification of biomass inside the silicon tube was demonstrated, confirming the presence of sulfide-oxidizing bacteria on the membrane wall. The most important genera found related to the sulfur cycle were Sulfuricurvum, Geovibrio, Flexispira and Sulforospirillum.' © Taylor & Francis 2019.

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