Influence of biofilm thickness on the removal of thirteen different organic micropollutants via a Membrane Aerated Biofilm Reactor (MABR)

Membrane aerated biofilm reactor system driven by pure oxygen for wastewater treatment

Pure oxygen is proposed for wastewater treatment due to its advantages over conventional air aeration. This study investigates a Pure Oxygen-based Membrane Aerated Biofilm Reactor (PO-MABR) for the first time under various operating conditions. The PO-MABR employs a gas-permeable membrane for direct diffusion of low-pressurized pure oxygen to the biofilm, ensuring exceptional carbon and nitrogen removal. The effectiveness of PO-MABR was investigated by varying operational conditions, including temperature, carbon-to-nitrogen ratio, gas pressure, and flow rate. Results indicate superior performance, with a 97% chemical oxygen demand removal and 19% higher total nitrogen removal than Air-Ventilated MABR (A-MABR) due to thicker biofilm and unique microbial structures in PO-MABR. Also, PO-MABR demonstrated resilience to low temperatures and effectively treated both high and low-strength wastewater. The findings emphasize the efficiency of PO-MABR in wastewater treatment, advocating for its adoption due to superior carbon and nitrogen removal across diverse operational conditions.

Preparation of PDMS and PDMS-UiO-66 oxygen-rich membranes and modules for membrane-aerated biofilm reactors

A membrane-aerated biofilm reactor (MABR) combines membrane technology with biofilm processes and has unique advantages in the treatment of organic wastewater and volatile wastewater. The common membranes for MABR systems usually have relatively uneven pore structures and low bubble point pressure, resulting in unsatisfactory O2 utilization and wastewater treatment efficiency. In this work, polydimethylsiloxane (PDMS) and UiO-66 (a Zr-based metal organic framework) were coated on the surface of a commercial polypropylene (PP) hollow fiber membrane to prepare oxygen-rich MABR membranes and modules, which showed an attractive O2 utilization rate and wastewater treatment efficiency. The bubble points of the PDMS and PDMS-UiO-66 membranes were significantly higher than those of the PP membranes, and the PDMS-UiO-66 membranes had better oxygen enrichment capacity and biological affinity. The optimal PDMS-UiO-66 membrane modules had an O2 permeance of 31.65 GPU (1 GPU = 3.35 × 10-10 mol m-2 s-1 Pa-1), with O2/N2 selectivity of 2.21. The membrane hanging effect and processing capacity for domestic sewage were greatly improved. This study may provide insights and guidelines to fabricate porous mixed matrix membranes and modules in the industry for MABR. The developed products are expected to be applied in the actual separation process.

Biofilm reactors for the treatment of used water in space:potential, challenges, and future perspectives

Water is not only essential to sustain life on Earth, but also is a crucial resource for long-duration deep space exploration and habitation. Current systems in space rely on the resupply of water from Earth, however, as missions get longer and move farther away from Earth, resupply will no longer be a sustainable option. Thus, the development of regenerative reclamation water systems through which useable water can be recovered from "waste streams" (i.e., used waters) is sorely needed to further close the loop in space life support systems. This review presents the origin and characteristics of different used waters generated in space and discusses the intrinsic challenges of developing suitable technologies to treat such streams given the unique constrains of space exploration and habitation (e.g., different gravity conditions, size and weight limitations, compatibility with other systems, etc.). In this review, we discuss the potential use of biological systems, particularly biofilms, as possible alternatives or additions to current technologies for water reclamation and waste treatment in space. The fundamentals of biofilm reactors, their advantages and disadvantages, as well as different reactor configurations and their potential for use and challenges to be incorporated in self-sustaining and regenerative life support systems in long-duration space missions are also discussed. Furthermore, we discuss the possibility to recover value-added products (e.g., biomass, nutrients, water) from used waters and the opportunity to recycle and reuse such products as resources in other life support subsystems (e.g., habitation, waste, air, etc.).

Monitoring biofilm thickness using the membrane aerated biofilm reactor (MABR) fingerprint soft sensor to optimize nitrogen removal

The ongoing commercialization and installation of full-scale membrane aerated biofilm reactors (MABRs) stimulate the increasing need to monitor biofilm development. Biofilm thickness in MABRs can be assessed indirectly by plotting the exhaust oxygen purity versus bulk ammonia concentration, defined here as the MABR fingerprint soft sensor. Dynamic simulations with diurnal flow variations of an MABR unit model were implemented over a broad range of biofilm thicknesses and influent conditions consisting of variable C/N ratios and applied ammonia fluxes to assess the utility of the MABR fingerprint. Results show that the continuously decreasing trend of the MABR fingerprint plot slopes can be employed as a useful signal for biofilm thickness control in nitrogen removal processes. This technique is useful in a wide range of influent conditions and is helpful for MABR operators and designers to arrange biofilm thickness control events efficiently and determine where in an overall treatment process the technique can be applied to control biofilm thickness and optimize process performance. PRACTITIONER POINTS: The linear relationship between exhaust oxygen purity and bulk ammonia concentration is defined as the MABR fingerprint plot. MABR fingerprint plots are generated for a given biofilm thickness with diurnal flow or short-term loading variations implemented. Continuously decreasing trends of the MABR fingerprint plot slopes are useful signals for biofilm control in nitrogen removal. The MABR fingerprint is useful over a wide range of influent conditions regarding C/N ratios and applied ammonia fluxes. MABR practitioners can use the fingerprint plots to determine when biofilm control measures should be taken.

Biofilm formation in xenobiotic-degrading microorganisms

The increased presence of xenobiotics affects living organisms and the environment at large on a global scale. Microbial degradation is effective for the removal of xenobiotics from the ecosystem. In natural habitats, biofilms are formed by single or multiple populations attached to biotic/abiotic surfaces and interfaces. The attachment of microbial cells to these surfaces is possible via the matrix of extracellular polymeric substances (EPSs). However, the molecular machinery underlying the development of biofilms differs depending on the microbial species. Biofilms act as biocatalysts and degrade xenobiotic compounds, thereby removing them from the environment. Quorum sensing (QS) helps with biofilm formation and is linked to the development of biofilms in natural contaminated sites. To date, scant information is available about the biofilm-mediated degradation of toxic chemicals from the environment. Therefore, we review novel insights into the impact of microbial biofilms in xenobiotic contamination remediation, the regulation of biofilms in contaminated sites, and the implications for large-scale xenobiotic compound treatment.

Understanding the role of sorption and biodegradation in the removal of organic micropollutants by membrane aerated biofilm reactor (MABR) with different biofilm thickness

The role of sorption and biodegradation in a membrane aerated biofilm reactor (MABR) were investigated for the removal of 10 organic micropollutants (OMPs) including endocrine disruptors and pharmaceutical active compounds. The influence of the biofilm thickness on the mechanisms of removal was analyzed via kinetic test at three different stages. At all biofilm stages, biodegradation was demonstrated to dominate the removal of selected OMPs. Higher OMPs rates of removal via biodegradation (K_biol) were achieved when biofilm increased its thickness from (stage T1) 0.26 mm, to (stage T2) 0.58 mm and (stage T3) 1.03 mm. At stage T1 of biofilm, heterotrophs contribute predominantly to OMPs degradation. Hydrophilic compounds removal (i.e., acetaminophen) continue to be driven by heterotrophic bacteria at the next stages of biofilm thickness. However, for medium hydrophobic neutral and charged OMPs, the combined action of heterotrophic and enriched nitrifying activity at stages T2 and T3 enhanced the overall removal. A degradation pathway based on heterotrophic activity for acetaminophen and combined action of nitrifiers-heterotrophs for estrone was proposed based on identified metabolites. Although biodegradation dominated the removal of most OMPs, sorption was also observed to be essential in the removal of biologically recalcitrant and lipophilic compounds like triclosan. Furthermore, sorption capacity of apolar compound was enhanced as the biofilm thickness grew and increased in EPS protein fraction. Microbial analysis confirmed the higher abundance of nitrifying and denitrifying activity at stage T3 of biofilm, which not only facilitated near complete ammonium removal but also enhanced degradation of OMPs.

Membrane-aerated biofilm reactor (MABR): recent advances and challenges

Membrane-aerated biofilm reactor (MABR) has been considered as an innovative technology to solve aeration issues in conventional bioreactors. MABR uses a membrane to supply oxygen to biofilm grown on the membrane surface. MABR can perform bubbleless aeration with high oxygen transfer rates, which can reduce energy requirements and expenses. In addition, a unique feature of counter-diffusion creates a stratified biofilm structure, allowing the simultaneous nitrification–denitrification process to take place in a single MABR. Controlling the biofilm is crucial in MABR operation, since its thickness significantly affects MABR performance. Several approaches have been proposed to control biofilm growth, such as increasing shear stress, adding chemical agents (e.g., surfactant), using biological predators to suppress microorganism growth, and introducing ultrasound cavitation to detach biofilm. Several studies also showed the important role of membrane properties and configuration in biofilm development. In addition, MABR demonstrates high removal rates of pollutants in various wastewater treatments, including in full-scale plants. This review presents the basic principles of MABR and the effect of operational conditions on its performance. Biofilm formation, methods to control its thickness, and membrane materials are also discussed. In addition, MABR performance in various applications, full-scale MBRs, and challenges is summarized.

Effects mechanism of bio-carrier filling rate on rotating biofilms and the reactor performance optimization method

Benefited from the massive filling bio-carriers, the packed cage rotating biological contactors (RBCs) have better performance and application potentiality in wastewater treatment. Investigating the effects mechanism of bio-carrier filling rate is crucial for such reactors management. In this study, the pollutants removal performance, biofilms physical characteristics, and microbial communities of the biofilms under a series of bio-carrier filling rates were analyzed. The results shown, the pollutant removal rate and amount were quite different under different filling rates, and biofilms structure and microbial composition were the main factors affecting the pollutants removal performance. With the increasing filling rates, the biofilms were more mass increased (dry weight from 0.066 to 0.148 g/per carrier), thicker (from 340.30 to 850.84 μm) and lower dense (from 0.068 to 0.060 g/cm³). The microbial community composition of those biofilms was also quite different at the genus level. The effects mechanism of bio-carrier filling rate can be summarized: the filling rates affect the physical and biological characteristics of biofilms, which will further affect the microenvironment and microbial distribution in biofilms, and then determines the pollutant metabolic rate and metabolic pathway. This study will contribute to design better bio-carrier filling rate according to different wastewater treatment scenario, and promote the performance optimization of packed cage RBCs.

Available online sensors can be used to create fingerprints for MABRs that characterize biofilm limiting conditions and serve as soft sensors

Membrane aerated biofilm reactors (MABRs) are a promising biological wastewater treatment technology, whose industrial applications have dramatically accelerated in the last five years. Increased popularity and fast industrial adaptation are coupled with increased needs to monitor, optimize, and control MABRs with available online sensors. Observations of commercial scale MABR installations have shown a distinctive and repetitive pattern relating oxygen purity in MABR exhaust gas to reactor ammonia concentrations. This provides an obvious opportunity for process monitoring and control which this paper investigates with the help of modeling. The relationship plots between the bulk ammonia concentration and the oxygen purity are defined as MABR fingerprint plots, which are described in the form of steady-state curves and dynamic trajectories. This study systematically investigated, analyzed, and explained the behaviors and connections of steady-state curves and dynamic trajectories with a MABR model in SUMO^®, and proposed a hypothesis about utilizing the MABR fingerprint plots to characterize MABR system performance, identify the limiting factor of biofilms, and possibly develop a soft senor for MABR biofilm thickness monitoring and control.

Application of moving bed biofilm reactor - nanofiltration - membrane bioreactor with loose nanofiltration hollow fiber membranes for synthetic roxithromycin-containing wastewater treatment: Long-term performance, membrane fouling and microbial community

The present study operated the novel moving bed biofilm reactor-nanofiltration-membrane bioreactor (MBBR-NF-MBR) with loose polyamide NF membranes for the first time to treat roxithromycin (ROX) wastewater. Results showed that both MBBR-NF-MBRs achieved superior COD removal of 98.4% and 97.2% and excellent removal of ROX at 74.1% and 65.5%, respectively. The main membrane fouling mechanism was reversible fouling caused by the combination of abundant polysaccharides, proteins and Ca-P precipitates, which could be effectively removed by acidic cleaning. Sorption and biodegradation were the main removal routes of ROX in MBBR. Partial retention of loose NF membrane contributed to microbial metabolism and increased microbial diversity, especially the genera Hyphomicrobium in attached biofilm, which was reasonable for ROX removal. The cleavage of cladinose, demethylation, phosphorylation and β-oxidation in macrolactone ring were the main biotransformation reactions of ROX. This study provides novel insights for micropollutants wastewater treatment by using loose NF membrane in MBR.