Clogging vs. fouling in immersed membrane bioreactors

Integrating artificial intelligence modeling and membrane technologies for advanced wastewater treatment: Research progress and future perspectives

Membrane technologies have become proficient alternatives for advanced wastewater treatment, ensuring high contaminant removal and sustainable resource recovery. Despite significant progress, ongoing research efforts aim to further optimize treatment performance. Among the challenges faced, membrane fouling persists as a relevant obstacle in membrane technologies, necessitating the development of more effective mitigation strategies. Mathematical models, widely employed for predicting treatment performance, generally exhibit low accuracy and suffer from uncertainties due to the complex and variable nature of wastewater. To overcome these limitations, numerous studies have proposed artificial intelligence (AI) modeling to accurately predict membrane technologies' performance and fouling mechanisms. This approach aims to provide advanced simulations and predictions, thereby enhancing process control, optimization, and intensification. This literature review explores recent advancements in modeling membrane-based wastewater treatment processes through AI models. The analysis highlights the enormous potential of this research field in enhancing the efficiency of membrane technologies. The role of AI modeling in defining optimal operating conditions, developing effective strategies for membrane fouling mitigation, enhancing the performance of novel membrane-based technologies, and improving membrane fabrication techniques is discussed. These enhanced process optimization and control strategies driven by AI modeling ensure improved effluent quality, optimized resource consumption, and minimized operating costs. The potential contribution of this cutting-edge approach to a paradigm shift toward sustainable wastewater treatment is examined. Finally, this review outlines future perspectives, emphasizing the research challenges that require attention to overcome the current limitations hindering the integration of AI modeling in wastewater treatment plants.

Novel eco-friendly polylactic acid nanocomposite integrated membrane system for sustainable wastewater treatment: Performance evaluation and antifouling analysis

Water contamination caused by heavy metals, nutrients, and organic pollutants of varying particle sizes originating from domestic and industrial processes poses a significant global challenge. There is a growing concern, particularly regarding the presence of heavy metals in freshwater sources, as they can be toxic even at low concentrations, posing risks to human health and the environment. Currently, membrane technologies are recognized as effective and practical for treating domestic and industrial wastewater. However, these technologies are hindered by fouling issues. Furthermore, the utilization of conventional membranes leads to the accumulation of non-recyclable synthetic polymers, commonly used in their production, resulting in adverse environmental consequences. In light of our previously published studies on environmentally friendly, biodegradable polylactic acid (PLA) nanocomposite mixed matrix membranes (MMMs), we selected two top-performing PLA-based ultrafiltration nanocomposite membranes: one negatively charged (PLA-M-) and one positively charged (PLA-M+). We integrated these membranes into systems with varying arrangements to control fouling and eliminate heavy metals, organic pollutants, and nutrients from raw municipal wastewater collected by the local wastewater treatment plant in Abu Dhabi (UAE). The performance of two integrated systems (i.e., PLA-M+/PLA-M- and PLA-M-/PLA-M+) was compared in terms of permeate flux, contaminant removal efficiencies, and fouling mitigation. The PLA-M+/PLA-M- system achieved removal efficiencies of 79.6 %, 92.6 %, 88.7 %, 85.2 %, 98.9 %, 94 %, 83.3 %, and 98.3 % for chemical oxygen demand (COD), nitrate (NO3--N), phosphate (PO43--P), ammonium (NH4+-N), iron (Fe), zinc (Zn), nickel (Ni), and copper (Cu), respectively. On the other hand, the PLA-M-/PLA-M+ system recorded removal efficiencies of 85.8 %, 95.9 %, 100 %, 81.9 %, 99.3 %, 91.9 %, 72.9 %, and 98.9 % for COD, NO3--N, PO43--P, NH4+-N, Fe, Zn, Ni, and Cu, respectively. Notably, the PLA-M-/PLA-M+ system demonstrated superior antifouling resistance, making it the preferred integrated system. These findings demonstrate the potential of eco-friendly PLA nanocomposite UF-MMMs as a promising alternative to petroleum-based polymeric membranes for efficient and sustainable wastewater treatment.

Effect of EPS production on the performance of membrane-based biofilm reactors

This study explored the effect of extracellular polymeric substance (EPS) production on the performance of membrane-based biofilm reactors. Changing EPS production was induced by eliminating one of the main EPS polysaccharides, i.e., Pel. The studies were carried out using a pure culture of either Pseudomonas aeruginosa or an isogenic P. aeruginosa mutant that was unable to produce the Pel polysaccharide. The biofilm cell density for both strains was compared to confirm the Pel deletion mutant decreased overall EPS production in a bioreactor system. When the Pel-deficient mutant was grown as a biofilm, its cell density, i.e., ratio of cells/(cells + EPS), was 74 % higher than the wild type, showing EPS production was reduced by eliminating pel production. The growth kinetics were determined for both strains. The Pel-deficient mutant had a maximum specific growth rate (μ^) that was 14% higher than the wild type. Next, the effects of EPS reduction on reactor performance were assessed for a membrane aerated biofilm reactor (MABR) and a membrane bioreactor (MBR). For the MABR, the organic removal with the Pel-deficient mutant was around 8% higher than for the wild type. For the MBR, the time to reach the fouling threshold was 65 % greater for the Pel-deficient mutant than for the wild type. These results suggest that amount of EPS production can have significant effects on bacterial growth kinetics and bacterial cell density, which in turn can affect the performance of the membrane-based biofilm reactors. In both cases, lower EPS production correlated with more efficient treatment processes.

Volatile Fatty Acids (VFA) Production and Recovery from Chicken Manure Using a High-Solid Anaerobic Membrane Bioreactor (AnMBR)

Acidogenic fermentation of chicken manure (CM) for production and recovery of volatile fatty acids (VFA) is an interesting biological waste-to-value approach compared to benchmark organic waste management strategies. Considering the wide range of high value applications of VFA, a semi-continuous immersed anaerobic membrane bioreactor (AnMBR) was applied to boost VFA productivity and yield, while reducing downstream processing stages assisting the recovery of VFA. In this regard, the effect of parameters such as pH and organic loading rates (OLR) on the overall bioconversion and filtration performance was investigated. Thermal-shocked CM was applied both as inoculum and substrate. A very high VFA yield (0.90 g-VFA/g-VS) was obtained in the treatment with no pH control (~8.2) at an OLR of 2 g-VS/(L·d), presenting 24% higher yield compared to that of the controlled pH. Batch assays further demonstrated the enhanced hydrolysis and acidogenesis activities at weak alkaline conditions. A long-term (78 days) fermentation and filtration was successfully performed, where stable membrane filtration performance was experienced for about 50 days under high-solid (suspended solid of 37-45 g/L) and high flux (20 L/(m²·h)) conditions. Results suggest that AnMBR of CM is a feasible and promising process for VFA production and recovery.

Low-pressure membrane technology for potable water filtration: true costs

The overall cost, expressed as the present value (PV), of the construction and operation of low-pressure membrane filtration of inland water for potable water supply has been determined for membrane installations across the UK. The analysis was based on 15 full-scale installations installed with hollow fibre and capillary tube polymeric membranes, for which cost and related data were available. The analysis encompassed labour, in addition to energy, chemicals and critical component replacement. PV data were presented as functions of flow capacity (i.e. as cost curves), delineated as capital (CAPEX), operating (OPEX) and total PV normalised against flow rate (PV') the CAPEX excluding the site-specific civil engineering costs. Captured CAPEX data revealed these to be lower than those previously reported, and with a reduced economy of scale. The OPEX PV exceeded the CAPEX by a factor of 3-6 based on a 20-year life cycle, the difference increasing with decreasing flow capacities. Costs associated with unplanned (or "reactive") maintenance, partly associated with the repair of breached membranes and/or permeability recovery following membrane clogging, were found to make up around half the labour costs. Labour costs as a proportion of the flow increased with decreasing flow, exceeding the CAPEX at flows below 30,000 m³/d. Outcomes indicate labour costs associated with process upsets to contribute significantly to the overall cost of the installation over its life cycle, particularly at flows below ~30,000 m³/d. A clear trade-off exists between supplementary capital investment to allay process upsets and the operational costs associated with such events.

Membrane bioreactor-assisted volatile fatty acids production and in situ recovery from cow manure

Cow manure (CM) generation in large volumes has for long been considered a waste management challenge. However, the organic content of CM signals opportunities for the production of value-added bioproducts such as volatile fatty acids (VFAs) through anaerobic digestion (AD). However, a robust VFAs fermentation process requires effective methane formation inhibition and enhance VFAs recovery. In this study, thermal pretreatment was applied to inhibit methanogens for enhanced VFAs production and an immersed membrane bioreactor (iMBR) for in situ recovery of VFAs in a semi-continuous AD. Maximal VFAs yield of 0.41 g VFAs/g volatile solids (VS) was obtained from thermally-treated CM without inoculum addition. The CM was further fed to the iMBR operating at organic loading rates of 0.8-4.7 gVS/L.d. The VFAs concentration increased to 6.93 g/L by rising substrate loading to 4.7 g VS/L.d. The applied iMBR set-up was successfully used for stable long-term (114 days) VFAs production and recovery.

Clogged water bridges for fog harvesting

Capillary water bridges clogged in the holes of mesh-type fog harvesters have previously been considered only as a drawback because they decrease fog-harvesting yield by hindering airflow in front of the clogged mesh in the usual wind conditions. In this study, we show that the role of a clogged water bridge may not be entirely negative and can contribute to increased fog harvesting by increasing the effective shade coefficient in a special condition with high fog inertia. As the fog speed close to the mesh or the plate increases, clogged mesh as well as the impermeable solid plate are found to produce high fog-harvesting efficiency owing to the high inertia of fog particles that impact the blocked wall. For fast fog speeds (∼4 m s^-1) near the mesh, our results show that the fog-harvesting efficiency is proportional to the effective shade coefficient because fog flow circumventing the mesh is limited owing to high fog inertia. We analyzed the clogging effect on fog-harvesting performance by distinguishing between self-clogging and non-self-clogging patterns based on the water bridge stability clogged in mesh holes.

Cultivation of aerobic granular sludge for the treatment of food-processing wastewater and the impact on membrane filtration properties

A laboratory-scale sequencing batch reactor was operated for approximately 300 days, divided into four periods based on the feeding strategy, to develop stable aerobic granular sludge (AGS) while treating chocolate processing wastewater. Application of a prolonged mixed anaerobic feeding was not sufficient to develop AGS and reach stable reactor performance. Through the application of a partially non-mixed and a partially mixed feeding strategy, the reactor performance was increased and stable AGS formation was established characterized by low diluted sludge volume index (D)SVI DSVI_10,30) values of 78 ± 27 mL·g^-1 and 52 ± 17 mL·g^-1, respectively, and a capillary suction time/mixed liquor suspended solids value of 0.9 sec·(g·L^-1)^-1. The membrane bioreactor (MBR) filtration tests showed a reduction of the fouling rate (FR) and an increase of the sustainable flux (SF_0.5) for AGS compared to flocs treating the same industrial wastewater. The SF_0.5 (FR > 0.5 mbar·min^-1) for the flocs was 10 L·(m²·h)^-1 while for AGS the SF_0.5 is higher than 45 L·(m²·h)^-1 because the FR did not exceed 0.1 mbar·min^-1. Additionally, the AGS showed reduced irreversible fouling tendencies due to pore blocking. Our results underline the need for an increased substrate gradient during anaerobic feeding for the development and long-term maintenance of AGS under minimum wash-out conditions. The AGS-MBR filtration performance also shows strong advantages compared to a floccular MBR system due to a high increase of the SF_0.5 and reduced reversible and irreversible fouling.

Development of Polyvinylidene Fluoride Membrane by Incorporating Bio-Based Ginger Extract as Additive

Biofouling on the membrane surface leads to performance deficiencies in membrane filtration. In this study, the application of ginger extract as a bio-based additive to enhance membrane antibiofouling properties was investigated. The extract was dispersed in a dimethyl acetamide (DMAc) solvent together with polyvinylidene fluoride (PVDF) to enhance biofouling resistance of the resulting membrane due to its antibiotic property. The concentrations of the ginger extract in the dope solution were varied in the range of 0–0.1 wt %. The antibacterial property of the resulting membranes was assessed using the Kirby Bauer disc diffusion method. The results show an inhibition zone formed around the PVDF/ginger membrane against Escherichia coli and Staphylococcus aureus demonstrating the efficacy of the residual ginger extract in the membrane matrix to impose the antibiofouling property. The addition of the ginger extract also enhanced the hydrophilicity in the membrane surface by lowering the contact angle from 93° to 85°, which was in good agreement with the increase in the pure water flux of up to 62%.

The Impact of Mechanically-Imposed Shear on Clogging, Fouling and Energy Demand for an Immersed Membrane Bioreactor

The impact of the application of mechanically-imposed shear on the propensity for fouling and clogging (or "sludging"-the agglomeration of sludge solids in the membrane channel) of an immersed flat sheet (iFS) membrane bioreactor (MBR) was studied. The bench-scale test cell used contained a single flat sheet fitted with a crank and motor to allow the membrane to be oscillated (or reciprocated) vertically at a low rate (20 RPM). The membrane was challenged with sludge samples from a local MBR installation treating petroleum industry effluent, the sludge having previously been demonstrated as having a high sludging propensity. Sludging was measured by direct visual observation of membrane surface occlusion by the agglomerated solids, with fouling being notionally represented by the rate of transmembrane pressure increase. Results demonstrated membrane reciprocation to have a more beneficial impact on sludging amelioration than on suppressing fouling. Compared with the stationary membrane, sludging was reduced by an average of 45% compared with only 13% for fouling suppression at the reference flux of 15 L·m^-2·h^-1 applied. The specific energy demand of the mechanical shear application was calculated as being around 0.0081 kWh·m^-3, significantly lower than values reported from a recent pilot scale study on a reciprocated immersed hollow fibre MBR. Whilst results appear promising in terms of energy efficiency, it is likely that the mechanical complexity of applying membrane movement would limit the practical application to low flows, and a correspondingly small number of membrane modules.