Municipal Wastewater Treatment Using Membrane Aerated Biofilm Reactor (MABR): Mechanisms, Performance and Microbial Community
Creators: Ukaigwe, Sandra A
Publisher: name: University of Alberta Library
Year: 2024

<p>The current drive for energy neutrality, drastic reduction in energy costs and increasingly stringent wastewater discharge rules has led to the quest for the development of more energy efficient and effective wastewater treatment technologies. MABR is one of these developing technologies. MABR is a biofilm-based technology that offer improved performance with regards to pollutants removal from wastewater, energy efficiency and environmental sustainability. Currently, MABR is garnering wide acceptance due to process and operational advantages that have accrued during many years of investigation. But despite these achievements, the challenge of MABR biofilm thickness management still persists.<br><br>
    Additional benefits in terms of energy efficiency and savings in operational costs for wastewater treatment could also be realized by combining the MABR advantages with nitritation. However, the range of operational factors and substrate conditions, that can be manipulated to suppress NOB for stable nitritation are absent both in MABR and mainstream wastewater. Consequently, for the treatment of conventionally collected sewage, establishing nitritation in MABR is challenging. This work was therefore designed to expand the current knowledge of MABR operations, particularly with respect to biofilm thickness management, performance stability and the establishment of nitritation in MABR for municipal wastewater treatment. Municipal wastewater remains one of the largest sources of environmental degradation as well as eutrophication of receiving water bodies. Eutrophication alters waterbody ecosystems equilibrium, leads to secondary water pollution and limits the possibilities of wastewater reuse.<br>
    In this study, two parallel MABRs; R1 and R2 were operated continuously for more than 250 days, using real and synthetic wastewaters.  R1 was a municipal wastewater system, applied in the optimization of MABR performance, study of structural and microbial community dynamics analysis of MABR biofilm, and the potential of the MABR to perform stable nitritation under mainstream conditions. While R2 was a high strength synthetic wastewater system, applied in the study of performance and stability of MABR under high strength wastewater conditions and the impact of inoculum on MABR performance and microbial community ecology. <br>
To optimize the performance of MABR for real municipal wastewater treatment, graduated HRT was applied with biomass recirculation until organic carbon, ammonia nitrogen and total nitrogen removal efficiencies reached 98, 96 and 67% respectively with acceptable effluent quality at a low HRT of 3h and operating pressure of 2psia. <br>
For MABR biofilm management and performance stability study, a protocol involving biomass recirculation and intermittent membrane cleaning induced by a drop in DO to set-point of 0.2 mg/L was developed. When applied in the treatment of municipal wastewater, the MABR demonstrated average organic carbon, ammonia nitrogen and total inorganic nitrogen removal efficiencies of 92 ± 2%, 100 ± 7.8% and 84 ± 5% respectively, at mean surface loading rates of 10 ± 0.7 gCOD/m2/d and 0.93 ± 0.07 gN/m2/d within a low hydraulic retention time of 2.5 h. Microbial population at each stage of investigation indicated sufficient biodiversity and relative abundance for stable reactor performance. <br>
The potentiality of nitritation development and sustenance in MABR for mainstream wastewater treatment was also investigated. This aspect of the study was accomplished in four phases using a combination of continuous and intermittent aeration modes with aerated and non-aerated cycles of 10 (5 on: 5 off), 20 (10 on: 10 off) and 25 (10 on: 15 off) minutes respectively, and a constant hydraulic retention time (HRT) of 2.5h. Nitrite accumulation rate (NAR), nitrate production rate (NPR) and ammonium nitrogen removal efficiency (ANRE) achieved in Phases II - IV were, 35%, 12% and 99%; 76%, 3.4% and 98%; 94%, 1% and 98% respectively.  Between the initiation of intermittent aeration and termination of the study, ammonia oxidizing bacteria (AOB) activities within the reactor increased by &gt;150%. In contrast, NOB activities declined by &gt;60 %.<br>
Finally, the impact of combined inocula on MABR biofilm properties was explored in a 4-stage study using HRTs of 24, 10, 6 and 4h for high strength wastewater treatment. Microscopy analysis of the biofilm at stage four of the study using; cells viability analysis, SEM and TEM revealed low viable cells and low biofilm concentration on membrane surface. Biofilm thickness was determined to be 0.357mm, thus simultaneous nitrification-denitrification was inhibited, leading to poor total inorganic nitrogen removal. Mean COD removal efficiency was estimated to be &gt;80% while the mean removal efficiencies for NH4+–N and TIN were 60 and 13 % respectively. Further investigations are required to collaborate these results and optimize the study parameters. </p>