Membrane scouring to control fouling under fluidization of non-adsorbing media for wastewater treatment

Anaerobic membrane bioreactors for municipal wastewater: Progress in resource and energy recovery improvement approaches

Anaerobic membrane bioreactor (AnMBR) offer promise in municipal wastewater treatment, with potential benefits including high-quality effluent, energy recovery, sludge reduction, and mitigating greenhouse gas emissions. However, AnMBR face hurdles like membrane fouling, low energy recovery, etc. In light of net-zero carbon target and circular economy strategy, this work sought to evaluate novel AnMBR configurations, focusing on performance, fouling mitigation, net-energy generation, and nutrients-enhancing integrated configurations, such as forward osmosis (FO), membrane distillation (MD), bioelectrochemical systems (BES), membrane photobioreactor (MPBR), and partial nitrification-anammox (PN/A). In addition, we highlight the essential role of AnMBR in advancing the circular economy and propose ideas for the water-energy-climate nexus. While AnMBR has made significant progress, challenges, such as fouling and cost-effectiveness persist. Overall, the use of novel configurations and energy recovery strategies can further improve the sustainability and efficiency of AnMBR systems, making them a promising technology for future sustainable municipal wastewater treatment.

A review of flow field characteristics in submerged hollow fiber membrane bioreactor: Micro-interface, module and reactor

As an important part of the membrane field, hollow fiber membranes (HFM) have been widely concerned by scholars. HFM fouling in the industrial application results in a reduction in its lifespan and an increase in cost. In recent years, various explorations on the HFM fouling control strategies have been carried out. In the current work, we critically review the influence of flow field characteristics in HFM-based bioreactor on membrane fouling control. The flow field characteristics mainly refer to the spatial and temporal variation of the related physical parameters. In the HFM field, the physical parameter mainly refers to the variation characteristics of the shear force, flow velocity and turbulence caused by hydraulics. The factors affecting the flow field characteristics will be discussed from three levels: the micro-flow field near the interface of membrane (micro-interface), the flow field around the membrane module and the reactor design related to flow field, which involves surface morphology, crossflow, aeration, fiber packing density, membrane vibration, structural design and other related parameters. The study of flow field characteristics and influencing factors in the HFM separation process will help to improve the performance of HFM in full-scale water treatment plants.

Low energy-consumption oriented membrane fouling control strategy in anaerobic fluidized membrane bioreactor

Anaerobic fluidized membrane bioreactors (AFMBR) has attracted growing interest as an emerging wastewater treatment technology towards energy recovery from wastewater. AFMBR combines the advantages of anaerobic digestion and membrane bioreactors and shows great potential in overcoming limiting factors such as membrane fouling and low efficiency in treating low-strength wastewater such as domestic sewage. In AFMBR, the fluidized media performs significant role in reducing the membrane fouling, as well as improving the anaerobic microbial activity of AFMBRs. Despite extensive research aimed at mitigating membrane fouling in AFMBR, there has yet to emerge a comprehensive review focusing on strategies for controlling membrane fouling with an emphasis on low energy consumption. Thus, this work overviews the recent progress of AFMBR by summarizing the factors of membrane fouling and energy consumption in AFMBR, and provides targeted in-depth analysis of energy consumption related to membrane fouling control. Additionally, future development directions for AFMBR are also outlooked, and further promotion of AFMBR engineering application is expected. By shedding light on the relationship between energy consumption and membrane fouling control, this review offers a useful information for developing new AFMBR processes with an improved efficiency, low membrane fouling and low energy consumption, and encourages more research efforts and technological advancements in the domain of AFMBR.

A review on the sustainable procurement of microalgal biomass from wastewaters for the production of biofuels

The feasibility of microalgal biomass as one of the most promising and renewable sources for the production of biofuels is being studied extensively. Microalgal biomass can be cultivated under photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic cultivation conditions. Photoautotrophic cultivation is the most common way of microalgal biomass production. Under mixotrophic cultivation, microalgae can utilize both organic carbon and CO2 simultaneously. Mixotrophic cultivation depicts higher biomass productivity as compared to photoautotrophic cultivation. It is evident from the literature that mixotrophic cultivation yields higher quantities of polyunsaturated fatty acids as compared to that photoautotrophic cultivation. In this context, for economical biomass production, the organic carbon of industrial wastewaters can be valorized for the mixotrophic cultivation of microalgae. Following the way, contaminants' load of wastewaters can be reduced while concomitantly producing highly productive microalgal biomass. This review focuses on different aspects covering the sustainable cultivation of different microalgal species in different types of wastewaters.

Selective Capacitive Removal of Pb2+ from Wastewater over Redox-Active Electrodes

Water pollution has become an environmental hazard. Diverse metal cations exist in wastewater; lead is the most common heavy metal pollutant among them. Selective removal of highly toxic and ultradiluted lead ions from wastewater is a major challenge for water purification. Here, selective capacitive removal (SCR) of lead ions from wastewater over redox-active molybdenum dioxide/carbon (MoO₂/C) electrodes was developed by an environment-friendly asymmetric capacitive deionization (CDI) method. The MoO₂/C spheres act as cathodes of an asymmetric CDI device and effectively reduce the concentration of Pb²⁺ from 50 ppm to <0.21 ppb. Moreover, the SCR efficiency of lead ions over redox-active MoO₂/C electrodes is >99% in mixtures of 100 ppm Pb(NO₃)₂ and 100 ppm NaCl solutions. In addition, the electrodes exhibit high regeneration performance in mixtures of NaCl and Pb(NO₃)₂ and high SCR efficiency for lead ions from mixtures of heavy metal ions. The tetrahedral structure of the [MoO₄] lattice is shown to be more favorable for the intercalation of lead ions. In situ Raman spectroscopy further shows that the transition of the crystal interface between [MoO₆] and [MoO₄] cluster lattice could be electrochemically controlled during SCR. Therefore, this study provides a new direction for the SCR of lead ions from wastewater.

Greener and sustainable production of bioethylene from bioethanol: current status, opportunities and perspectives

The economic value of bioethylene produced from bioethanol dehydration is remarkable due to its extensive usage in the petrochemical industry. Bioethylene is produced through several routes, such as steam cracking of hydrocarbons from fossil fuel and dehydration of bioethanol, which can be produced through fermentation processes using renewable substrates such as glucose and starch. The rise in oil prices, environmental issues due to toxic emissions caused by the combustion of fossil fuel and depletion of fossil fuel resources have led a demand for an alternative pathway to produce green ethylene. One of the abundant alternative renewable sources for bioethanol production is biomass. Bioethanol produced from biomass is alleged to be a competitive alternative to bioethylene production as it is environmentally friendly and economical. In recent years, many studies have investigated catalysts and new reaction engineering pathways to enhance the bioethylene yield and to lower reaction temperature to drive the technology toward economic feasibility and practicality. This paper critically reviews bioethylene production from bioethanol in the presence of different catalysts, reaction conditions and reactor technologies to achieve a higher yield and selectivity of ethylene. Techno-economic and environmental assessments are performed to further development and commercialization. Finally, key issues and perspectives that require utmost attention to facilitate global penetration of technology are highlighted.

Influence of salinity on the biological treatment of domestic ship sewage using an air-lift multilevel circulation membrane reactor

Recently, strict standards for ship domestic sewage discharge have been implemented by the International Maritime Organization (IMO). The high salinity of ship sewage was considered a key factor influencing the removal efficiency of ship sewage treatment systems. In the present study, the salinity effect on the removal of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N) from ship domestic sewage was investigated by using a novel air-lift multilevel circulation membrane reactor (AMCMBR). Enzyme activity analysis and wavelet neural network (WNN) models were built to determine the mechanisms of the process. The experimental results indicate that high salinity levels (> 21 g/L) had a negative impact on COD and NH₄⁺-N removal efficiencies, and low saline concentrations (≤ 21 g/L) caused a negligible effect. The COD and NH₄-N removal efficiencies were 84% and 97%, respectively, at a salinity of 21 g/L, which were higher than those at low salinities (i.e., 7 g/L and 14 g/L). Invertase and nitrate reductase had a close relationship with removal performance, and they can be considered important indicators reflecting the operation effort under saline environments. With high predictive accuracies, the constructed WNN models simulated the complex COD and NH₄⁺-N removal processes well under different saline concentrations, ensuring the long-term stable operation of the AMCMBR under different salinities.

Anaerobic membrane bioreactors for wastewater treatment: Novel configurations, fouling control and energy considerations

Water shortage, public health and environmental protection are key motives to treat wastewater. The widespread adoption of wastewater as a resource depends upon development of an energy-efficient technology. Anaerobic membrane bioreactor (AnMBR) technology has gained increasing popularity due to their ability to offset the disadvantages of conventional treatment technologies. However there are several hurdles, yet to climb over, for wider spread and scale-up of the technology. This paper reviews fundamental aspects of anaerobic digestion of wastewater, and identifies the challenges and opportunities to the further development of AnMBRs. Membrane fouling and its implications are discussed, and strategies to control membrane fouling are proposed. Novel AnMBR configurations are discussed as an integrated approach to overcome technology limitations. Energy demand and recovery in AnMBRs is analyzed. Finally key issues that require urgent attention to facilitate global penetration of AnMBR technology are highlighted.

Investigating membrane fouling associated with GAC fluidization on membrane with effluent from anaerobic fluidized bed bioreactor in domestic wastewater treatment

Effect of mechanical scouring driven by granular activated carbon (GAC) fluidization on membrane fouling was investigated using a laboratory-scaled, fluidized membrane reactor filtering the effluent from anaerobic fluidized bed bioreactor (AFBR) in domestic wastewater treatment. The GAC particles were fluidized by recirculating a bulk solution only through the membrane reactor to control membrane fouling. The membrane fouling was compared with two different feed solutions, effluent taken from a pilot-scaled, AFBR treating domestic wastewater and its filtrate through 0.1-μm membrane pore size. The GAC fluidization driven by bulk recirculation through the membrane reactor was very effective to reduce membrane fouling. Membrane scouring under GAC fluidization decreased reversible fouling resistance effectively. Fouling mitigation was more pronounced with bigger GAC particles than smaller ones as fluidized media. Regardless of the fluidized GAC sizes, however, there was limited effect on controlling irreversible fouling caused by colloidal materials which is smaller than 0.1 μm. In addition, the deposit of GAC particles that ranged from 180 to 500 μm in size on membrane surface was very significant and accelerated fouling rate. Biopolymers rejected by the membranes were thought to play a role as binding these small GAC particles on membrane surface strongly.