Increase In Transmembrane Pressure Research Articles

Scale-up issues for commercial depth filters in bioprocessing.

Significant increases in cell density and product titer have led to renewed interest in the application of depth filtration for initial clarification of cell culture fluid in antibody production. The performance of these depth filters will depend on the local pressure and velocity distribution within the filter capsule, but these are very difficult to probe experimentally, leading to challenges in both process design and scale-up. We have used a combination of carefully designed experimental studies and computational fluid dynamics (CFD) to examine these issues in both lab-scale (SupracapTM 50) and pilot-scale (StaxTM ) depth filter modules, both employing dual-layer lenticular PDH4 media containing diatomaceous earth. The SupracapTM 50 showed a more rapid increase in transmembrane pressure and a more rapid DNA breakthrough during filtration of a Chinese Hamster Ovary cell culture fluid. These results were explained using CFD calculations which showed very different flow distributions within the modules. CFD predictions were further validated using measurements of the residence time distribution and dye binding in both the lab-scale and pilot-plant modules. These results provide important insights into the factors controlling the performance and scale-up of these commercially important depth filters as well as a framework that can be broadly applied to develop more effective depth filters and depth filtration processes.

Critical Flux and Fouling Analysis of PVDF-Mixed Matrix Membranes for Reclamation of Refinery-Produced Wastewater: Effect of Mixed Liquor Suspended Solids Concentration and Aeration.

Fouling tends to cause a significant increase in hydraulic resistance, decreased permeate flux, or increased transmembrane pressure (TMP) when a process is operated under constant TMP or constant flux conditions. To control membrane fouling and maintain sustainable operation, the concept of critical flux has been discussed by several researchers. Various fouling mechanisms, such as macromolecule adsorption, pore plugging, or cake build-up, as well as hydrodynamic conditions, for example aeration, can take place at the membrane surface. This study aimed to investigate the effects of mixed liquor suspended solid (MLSS) concentration and air bubble flow rate (ABFR) on the critical flux and fouling behavior, when treating refinery-produced wastewater. To determine the critical flux values, the experimental flux-steps were the following: (1) the filtration began with a 30 min step duration at a low flux (10 to 20 L/m2h); (2) at the end of this step (after 30 min), the permeate flux was increased, (3) this step was repeated until the TMP did not remain constant at the constant permeate flux, (4) the critical flux was then achieved. A critical flux model with an R2 of 0.9 was, therefore, derived, which indicates that the particle properties were regulated by the suspended solids. The increase of MLSS concentration, from 3 mg/L to 4.5 mg/L, resulted in a decrease of the permeate flux by 18%. Moreover, an increase in ABFR, from 1.2 mL/min to 2.4 mL/min, increased the permeate flux, but this decreased with a greater flow rate of aeration. To assess the stability and reversibility of fouling during critical flux (Jc) determination using a mixed matrix membrane, flux-step methods were utilized. A step height of 14.3 L/m2h and 30 min duration were arbitrarily chosen. The flux increased to 32.5 L/m2h with a slight increase of trans membrane pressure (TMP), while the rate of increase became significant at a higher flux of 143.6 L/m2h, due to fouling. Overall, this study proved that the response of MLSS concentration and aeration affected the membrane performance, based on the critical flux and fouling behavior.

In-Situ H2O2 Cleaning for Fouling Control of Manganese-Doped Ceramic Membrane through Confined Catalytic Oxidation Inside Membrane.

This work presents an effective approach for manganese-doped Al2O3 ceramic membrane (Mn-doped membrane) fouling control by in-situ confined H2O2 cleaning in wastewater treatment. An Mn-doped membrane with 0.7 atomic percent Mn doping in the membrane layer was used in a membrane bioreactor with the aim to improve the catalytic activity toward oxidation of foulants by H2O2. Backwashing with 1 mM H2O2 solution at a flux of 120 L/m2/h (LMH) for 1 min was determined to be the optimal mode for in-situ H2O2 cleaning, with confined H2O2 decomposition inside the membrane. The Mn-doped membrane with in-situ H2O2 cleaning demonstrated much better fouling mitigation efficiency than a pristine Al2O3 ceramic membrane (pristine membrane). With in-situ H2O2 cleaning, the transmembrane pressure increase (ΔTMP) of the Mn-doped membrane was 22.2 kPa after 24-h filtration, which was 40.5% lower than that of the pristine membrane (37.3 kPa). The enhanced fouling mitigation was attributed to Mn doping, in the Mn-doped membrane layer, that improved the membrane surface properties and confined the catalytic oxidation of foulants by H2O2 inside the membrane. Mn3+/Mn4+ redox couples in the Mn-doped membrane catalyzed H2O2 decomposition continuously to generate reactive oxygen species (ROS) (i.e., HO• and O21), which were likely to be confined in membrane pores and efficiently degraded organic foulants.

Low maintenance gravity-driven membrane filtration using hollow fibers: Effect of reducing space for biofilm growth and control strategies on permeate flux

The implementation of centralized drinking water treatment systems necessitates lower operational costs and improved biopolymer removal during ultrafiltration (UF), which can be afforded by gravity-driven membrane (GDM) filtration. However, prior to implementing GDM filtration in centralized systems, biofilm growth in compacted membrane configurations, such as inside-out hollow fiber (HF), and its impact on permeate flux need to be investigated. To this end, we operated modules with distinct limits on available space for biofilm growth: (1) outside-in 1.5 mm 7-capillary HF (non-limited), (2) inside-out 1.5 mm 7-capillary HF (limited), and (3) inside-out 0.9 mm 7-capillary HF (very limited). Here, we observed that the lower the space available for biofilm growth, the lower the permeate flux. To improve GDM performance with inside-out HF, we applied daily shear stress to the biofilm surface with forward flush (FF) or combined relaxation and forward flush (R+FF). We showed that applying shear stress to the biofilm surface was insufficient for controlling flux loss due to low available space for biofilm growth. At the experimental endpoint, we backwashed with a stepwise transmembrane pressure (TMP) increase or a single TMP on all inside-out HF modules, which removed the biofilm from its base. Afterwards, higher fluxes were yielded. We also showed that all modules exhibited a gradual increase in biopolymer removal followed by stabilization between 70 and 90%. Additionally, control of biofilm growth with surface shear stress did not affect biopolymer removal. In summary, the implementation of inside-out HF with GDM filtration is challenged by low available space for biofilm growth, but may be remedied with a regular backwash to remove biofilm from its base. We showed that a wider range of GDM applications are available; making GDM potentially compatible with implementation in centralized systems, if space limitation is taken into consideration for operation optimization.

Applicability of a Combined DAF-MF Process to Respond to Changes in Reservoir Water Quality through a Two-Year Pilot Plant Operation

The optimal operating conditions of a combined dissolved air flotation (DAF)-microfiltration (MF) process to respond to changes in raw water quality were investigated by operating a pilot plant for two years. Without DAF pre-treatment (i.e., MF alone), MF operated stably with a transmembrane pressure (TMP) increase of 0.24 kPa/d when the turbidity of raw water was low and stable (max. 13.4 NTU). However, as the raw water quality deteriorated (max. 76.9 NTU), the rate of TMP increase reached 43.5 kPa/d. When DAF pre-treatment was applied (i.e., the combined DAF-MF process), the MF process operated somewhat stably; however, the rate of TMP increase was relatively high (i.e., 0.64 kPa/d). Residual coagulants and small flocs were not efficiently separated by the DAF process, exacerbating membrane fouling. Based on the particle count analysis of the DAF effluent, the DAF process was optimised based on the coagulant dose and hydraulic loading rate. After optimisation, the rate of TMP increase for the MF process stabilised at 0.17 kPa/d. This study demonstrates that the combined DAF-MF process responded well to substantial changes in raw water quality. In addition, it was suggested that the DAF process must be optimised to avoid excessive membrane fouling.

Mitigation of membrane biofouling using quorum-quenching bacteria in a continuously operated membrane bioreactor

Quorum-quenching (QQ) has become an attractive strategy for the mitigation of membrane biofouling known as biocake or biofilm. In this study, a QQ system, which exploited two QQ bacteria (Serratia sp. Z4 and Klebsiella sp. Q2) and γ-caprolactone (GCL), was established and used to effectively mitigate biofouling. This system could delay the increase in transmembrane pressure by half during a 40-day operation in a continuous membrane bioreactor (MBR) with low effluent chemical oxygen demand and ammonium nitrogen. GCL improved the biofouling-mitigation ability of the QQ bacteria without stimulating bacterial growth. The reduction in soluble microbial products was consistent with the delay in transmembrane pressure increase. Furthermore, soluble microbial products (SMP) in the reactors were significantly influenced by the QQ system, suggesting that SMP was important for the occurrence of biofouling. Microbial community analysis showed that the relative abundance of some main genera was not greatly influenced by the QQ system. The two most abundant genera of quorum sensing (QS)-related bacteria found in the sludge mixture were Alicycliphilus and Thauera. The results indicated that a QQ strategy based on the disturbance of QS among the microbes should be effective for biofouling mitigation in MBR.

Deacidification through calcium carbonate dosing in combination with ultrafiltration

Abstract Soft acidic waters are often treated for drinking water purposes by using limestone filters to attain chemical equilibrium. The present study investigated the process parameters of a relatively new process combination in which powdered calcium carbonate (CaCO3) was added prior to an ultrafiltration (UF). In order to reach the targeted pH value (≥7.8), dosing concentration, type of material and retention time were evaluated in pilot-scale experiments. The deacidification followed the same kinetics as for limestone filtration and yielded similar filtrate characteristics with dosing concentrations of 20 and 40 g/L CaCO3. No significant increase in transmembrane pressure was observed during the operation of a pilot-scale UF module at low flux (34 L m−2 h−1). Critical flux was determined in a laboratory scale to evaluate the potential impact of CaCO3 particles on the UF operation. Stepping-flux experiments revealed the presence of fouling only at high-dosing concentrations, resulting in a critical flux of 55 L m−2 h−1. At a higher flux, a CaCO3-fouling layer was formed, which decreased the membrane's permeability by 20% over 5 h. Considering that effective air-enhanced backwash and acidic chemical cleanings will be implemented in large-scale applications, the investigated process combination promises to be an appropriate treatment technology for turbid and soft acidic waters.

Identification of sustainable filtration mode of an anaerobic membrane bioreactor for wastewater treatment towards low-fouling operation and efficient bioenergy production

The application of anaerobic membrane bioreactor (AnMBR) process for low-carbon and sustainable municipal wastewater (MWW) treatment is still hindered by membrane fouling and dissolved methane issues, while optimizing operational mode for efficient fouling mitigation and modelling the liquid-gaseous phase equilibrium of multicomponent biogas are still not well understood. To address this gap, a 20-L submerged AnMBR was operated for the treatment of real MWW over a 200 d operation period, divided into three phases according to the variations of operational flux (5, 8 and 11 L/m2h) and intermittent filtration mode (filtration to relaxation time (F/R) ratios of 3:1, 4:1, 5:1 and 9:1). The AnMBR showed a stable COD removal (∼85%), satisfactory methane production (∼0.07 LCH4/L-wastewater), and a high methane content of 80% regardless of filtration mode. A theoretical model was successfully developed to simulate the liquid-gaseous phase equilibrium of the multicomponent biogas, which can quantitatively predict the origin and phase distribution of biogas with high accuracy and also determine the saturation index of dissolved methane in the range of 0.8–1.1. At low-flux conditions (5 and 8 LMH), the transmembrane pressure (TMP) remained at low values of 0.5–1.0 kPa, and was not affected by changed F/R ratios. However, at the higher flux of 11 LMH, the TMP increase was obvious at F/R ratios of 3:1 and 9:1, and larger than that at F/R ratios of 4:1 and 5:1. A higher instantaneous flux and shorter relaxation time resulted in substantial irreversible fouling caused by a high-flux induced drag force and insufficient detachment of foulants, while periodical in-situ chemical cleaning allowed a sustainable operation with irreversible fouling successfully mitigated. The results recommended optimized filtration mode for cost-effective fouling control and highlighted the importance of dissolved methane management, which are expected to support large-scale AnMBR implementations for mainstream MWW treatment towards low fouling operation and efficient bioenergy recovery.

Impact of NaOCl ageing on reinforced PVDF hollow fiber membranes used in membrane bioreactor

Reinforced hollow fiber membranes are commercially available but its information is limited on open literature. Its notable mechanical properties due to the reinforced layer makes it suitable for membrane bioreactor (MBR) application. On the other hand, polyvinylidene fluoride (PVDF) is an increasingly popular material choice for membrane used in MBR due to its good chemical resistance against chlorine present in sodium hypochlorite (NaOCl), which is commonly used as a cleaning agent. The impact of NaOCl on the PVDF membrane characteristics was reported in literature, but little information is available about the membrane performance of the aged PVDF membrane caused by NaOCl in MBR operation. In this study, the membrane performance of a reinforced PVDF hollow fiber membranes after NaOCl ageing were investigated thoroughly in MBR operations. A series of characterization on virgin and fouled membranes with/without NaOCl exposure were carried out. The accelerated NaOCl ageing experiments revealed that reinforced hollow fiber membranes have notable mechanical strength, which is not significantly affected by NaOCl ageing as compared to their non-reinforced counterpart. Additionally, there was no significant effect on the membrane behaviours in MBR after the membranes were exposed to a 5000 ppm NaOCl solution at pH 7 for 48 h, which is equivalent to 246,000 ppm.hr (~6.1 years) NaOCl exposure using a normal dose of NaOCl for regular membrane cleaning. However, after 524,000 ppm.hr (~13.1 years) of NaOCl exposure, the membrane failed to perform and a sharp transmembrane pressure (TMP) increase during MBR operation was observed. The severe fouling of aged membranes was found to be attributed to the changes in hydrophobicity, pore size and the foulants left on the membrane despite cleaning. Even though the membrane was fouled quickly after 524,000 ppm.hr (~13.1 years) of NaOCl exposure, the permeate quality was not affected much as indicated by >90% removal for dissolved organic carbon (DOC) and soluble chemical oxygen demand (sCOD), which suggests that the reinforced PVDF hollow fiber membranes used in current study exhibit considerable chemical resistance against chlorine and can be used in the MBR system for a long period of operation.

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The impact of sludge discharge on membrane fouling during ultrafiltration of surface water was investigated in this study. Discharge sludge and without discharge during UF were compared by measuring the increase of transmembrane pressure (TMP) and the accumulation of foulants with running time was studied. It was found that turbidity and dissolved organic carbon of retentate solution apparently increased as UF proceeded. Three-dimensional excitation/emission matrix fluorescence spectroscopy analyses of raw water and retentate solution demonstrated that UF could lead to the accumulation of humic and protein-like substances. Filtration experiments showed that membrane fouling could be alleviated by discharging the retentate solution after physical cleaning due to the reduced cake layer formation and concentration polarization. In addition, effects of sludge discharge intervals on the TMP and fouling characteristics were further investigated. Results indicated that short SDI would benefit control of both reversible and irreversible fouling. However, frequent discharge of retentate solution may increase the self-use water and decrease the water production rate of the UF system, leading to an expansion of running cost. In general, SDI was a critically important factor for both membrane fouling and water production rate.

Innovative encapsulated self-forming dynamic bio-membrane bioreactor (ESFDMBR) for efficient wastewater treatment and fouling control

The concept of a novel living encapsulated self-forming dynamic bio-membranes (ESFDM) for an innovative wastewater treatment in membrane bioreactor (MBR) is presented in the current study. The active filtering membrane is encapsulated, and thus stabilized, between two support meshes with pore in micrometer size. The combination of activated sludge, the ESFDM and the cake layer formed external to the filtering module contributed to the treatment of municipal wastewater. COD concentration reductions (average value of 95.55 ± 1.44%) by ESFDM bioreactor (ESFDMBR) were comparable to those obtained with a previously reported membrane bioreactor (MBR), where a conventional membrane was studied under the same operating conditions. The ESFDMBR, compared to the conventional MBR, obtained higher reductions of NH3-N, NO3–N and PO43–P concentrations. Increased removals of nitrogen-containing nutrients were ascribed to anoxic conditions reached in the ESFDM layer protected from the aeration by the external cake layer. Rate of increase of transmembrane pressure (TMP) per day in the ESFDMBR (0.03 kPa/day) was lower than the value obtained in the previously reported conventional MBR (8.08 kPa/day). Lower concentrations of fouling precursors in combination with the effective filtration capacity of the porous living ESFDM resulted in the reduction of the fouling rate. Analysis of microbiological community revealed that the microbial community structures in the mixed liquor and ESFDM were different. The ESFDM layer promoted growth of bacteria as indicated by the higher total cell count and higher microbial diversity compared to those observed in the mixed liquor.

Modulation of reduced graphene oxide membrane for low-fouling wastewater filtration: Membrane structure, wastewater property, and DFT calculation

Membrane fouling is a major hurdle impeding real-world application of membranes for advanced wastewater treatment. In this study, a GO membrane and a reduced GO (rGO) membrane were examined in parallel for their anti-fouling propensities and ability to remove pharmaceutical compounds from realistic wastewater effluents. The effects of membrane properties and wastewater characteristics on the two aspects were also assessed by experiments and DFT simulation. The results showed that the transmembrane pressure (TMP) of the rGO membrane increased by 0–3.5 kPa after filtering a secondary wastewater effluent from an activated sludge system (SW), as compared to 201.6–292.1 kPa for the GO membrane. Meanwhile, slightly greater TMP increases were observed for both membranes after filtering a secondary wastewater effluent from a partial nitrification and denitrification system (PND), but the fouling remained low for the rGO membrane. Overall, chemical reduction of GO to rGO led to larger SSA and reduced negative charge, which promoted adsorptive filtration of pharmaceutical compounds. Also, the diminishing of functional groups possessed by the GO membrane mitigated attractive interlayer polar interaction and expanded membrane pore dimension, thus enhancing the permeability and anti-fouling propensity of GO membranes.

Comparison between novel vibrating ceramic MBR and conventional air-sparging MBR for domestic wastewater treatment: Performance, fouling control and energy consumption

Two crucial themes emerge from the growing application of MBRs treating domestic wastewater so far: fouling control and energy demand. The significance of in-situ shear-enhanced methods for fouling control in MBRs has been widely acknowledged with air sparging over decades. However, it is still a challenge to develop energy-efficient ways to replace energy-intensive air sparging for effective fouling control during long-term real domestic wastewater treatment. A novel vibrating flat-sheet ceramic MBR (VMBR) was established for investigating the effects of different shear rates on treatment performance, fouling control and specific energy demand compared with air-sparging MBR (ASMBR). Three levels of shear rates with vibration speed of 120, 80, and 40 RPM in the VMBR, versus specific aeration rate of 1.5, 1.0 and 0.5 LPM in the ASMBR were examined as high-, middle- and low-shear phases. Results showed that the VMBR removed over 78.35% TOC, 89.89% COD and 99.9% NH4-N over three phases, and retarded initial increases in transmembrane pressure to control membrane fouling effectively with average fouling rate around 2.31 kPa/d, 3.59 kPa/d and 10.15 kPa/d, almost 70% lower than the ASMBR in Phase 1, 2 and 3, respectively. Particle size distribution of mixed liquor revealed that colloids and biopolymer clusters were significantly reduced in the VMBR showing less propensity for foulant formation. DOM characteristics further indicated that lower production of polysaccharides and protein (by approximately half in Phases 1 and 2) of SMP and EPS in the VMBR generated lower biopolymer content, promoting better fouling mitigation and enhanced dewaterability compared to the ASMBR. Moreover, the VMBR showed superior energy efficiency for fouling control and could save 51.7% to 78.5% energy of the ASMBR under similar-shear condition. The combination of excellent treatment performance, fouling control and energy efficiency from the VMBR makes this an attractive strategy for future improvement of MBR designs in full-scale application with the potential to replace conventional ASMBR.

Study of membrane fouling mechanism during the phenol degradation in microbial fuel cell and membrane bioreactor coupling system

This study evaluated the feasibility of phenol degradation in microbial fuel cell (MFC) and membrane bioreactor (MBR) coupling system, and explored the mechanism of MBR membrane fouling. Four aspects were researched in open and closed circuit conditions: the degradation capacity of the coupling system, the increase of trans-membrane pressure (TMP), and the adhesion of phenol degradation products and microorganisms on the membrane. The results showed that the degradation of phenol and COD in the closed circuit coupling system was higher than that in the open circuit. The micro-electric field can inhibit the growth of TMP and keep dodecamethylcyclohexasiloxane away from the membrane, meanwhile can also reduce the abundance and species diversity of microorganisms. Nevertheless, the micro-electric field could not completely eliminate the membrane fouling due to the fact that the phenol degradation product of ethanethiol, microorganisms of Proteobacteria and Actinobacteria were more favorable on the membrane.

Treatment of the Supernatant of Anaerobically Digested Organic Fraction of Municipal Solid Waste in a Demo-Scale Mesophilic External Anaerobic Membrane Bioreactor.

Conventional aerobic biological treatments of digested organic fraction of municipal solid waste (OFMSW) slurries–usually conventional activated sludge or aerobic membrane bioreactor (AeMBR)–are inefficient in terms of energy and economically costly because of the high aeration requirements and the high amount of produced sludge. In this study, the supernatant obtained after the anaerobic digestion of OFMSW was treated in a mesophilic demo-scale anaerobic membrane bioreactor (AnMBR) at cross flow velocities (CFVs) between 1 and 3.5 m⋅s–1. The aim was to determine the process performance of the system with an external ultrafiltration unit, in terms of organic matter removal and sludge filterability. In previous anaerobic continuous stirred tank reactor (CSTR) tests, without ultrafiltration, specific gas production between 40 and 83 NL CH4⋅kg–1 chemical oxygen demand (COD) fed and removals in the range of 10–20% total COD (tCOD) or 59–77% soluble COD (sCOD) were obtained, for organic loading rates (OLR) between 1.7 and 4.4 kg COD⋅m–3reactor d–1. Data helped to identify a simplified model with the aim of understanding and expressing the process performance. Methane content in biogas was in the range of 74–77% v:v. In the AnMBR configuration, the COD removal has been in the ranges of 15.6–38.5 and 61.3–70.4% for total and sCOD, respectively, with a positive correlation between solids retention time (SRT, ranging from 7.3 to 24.3 days) and tCOD removal. The constant used in the model expressing inhibition, attributable to the high nitrogen content (3.6 ± 1.0 g N-NH4+⋅L–1), indicated that this inhibition decreased when SRT increased, explaining values measured for volatile fatty acids concentration, which decreased when SRT increased and OLR, measured per unit of volatile suspended solids in the reactor, decreased. The alkalinity was high enough to allow a stable process throughout the experiments. Constant CFV operation resulted in excessive fouling and sudden trans-membrane pressure (TMP) increases. Nevertheless, an ultrafiltration regime based on alternation of CFV (20 min with a certain CFVi and then 5 min at CFVi + 1 m⋅s–1) allowed the membranes to filter at a flux (standardized at 20°C temperature) ranging from 2.8 to 7.3 L⋅m–2⋅h–1, over 331 days of operation, even at very high suspended solids concentrations (>30 g total suspended solids⋅L–1) in the reactor sludge. This flux range confirms that fouling is the main issue that can limit the spread of AnMBR potential for the studied stream. No clear correlation was found between CFV or SRT vs. fouling rate, in terms of either TMP⋅time–1 or permeability⋅time–1. As part of the demo-scale study, other operational limitations were observed: irreversible fouling, scaling (in the form of struvite deposition), ragging, and sludging. Because ragging and sludging were also observed in the existing AeMBR, it can be stated that both are attributable to the stream and to the difficulty of removing existing fibers. All the mentioned phenomena could have contributed to the high data dispersion of experimental results.

Purification of polyphenols from apple skins by membrane electro-filtration

Dead-end electro-filtration of polyphenols extracted from apple skin was studied. The influence of membrane pore size (dm = 3.02–50 nm), transmembrane pressure (ΔP = 1–6 bar) and direct current (DC) electric field (U = 5–15 V) on the purification efficiency was investigated. The sieving ratios R of selected membrane UH030 (dm = 4.35 nm) towards the polyphenols, proteins, total solutes, and colour intensity increased with increase of transmembrane pressure. It was demonstrated that utilization of this membrane for the DC electro-filtration allowed more effective rejection of proteins at the anode part of the filter. Such effects can be attributed to the large size of protein molecules and their positive charge. Obtained data evidenced the possibility of selective purification of polyphenols by membrane electro-filtration.

Effects of large salinity fluctuations on an anaerobic membrane bioreactor treating phenolic wastewater

High salinity is becoming more common in industrial process water and final effluents, particularly when striving to close water loops. There is limited knowledge on the anaerobic treatment of chemical wastewaters characterized by distinct salinity fluctuations. This study investigates the high and fluctuating salinity effects on the conversion capacity and membrane filtration performance of an anaerobic membrane bioreactor (AnMBR) in treating phenol-containing wastewater. The AnMBR operated for 180 days with sodium concentrations between 8 and 37 gNa+.L−1. At ≤ 26 gNa+.L−1, approximately 99% COD and phenol removal efficiencies were achieved. At 37 gNa+.L−1, phenol and COD removal efficiencies decreased to 86 and 82%, respectively, while the biomass specific methanogenic activity was 0.12 ± 0.05 gCOD-CH4.gVSS−1.d−1. Due to large salinity fluctuations, phenol and COD removal efficiencies reduced to ≤ 45% but recovered to ≥ 88%. Compared to phenol conversion, methanogenesis was more severely affected. Calculations showed a maximum in-situ phenol conversion rate of 25.5 mgPh.gVSS−1.d−1. Concomitantly, biomass integrity was compromised, and the median particle size severely dropped from 65.6 to 4.3 μm, resulting in a transmembrane pressure increase above 400 mbar. Cake layer resistance to filtration contributed to 85% of the total resistance. Nonetheless, all biomass was effectively retained in the AnMBR. A change in salinity ≥ 14 gNa+.L−1 substantially reduced the microbial richness and diversity. The microbial community was dominated by Bacteria belonging to Clostridiales and Archaea of the orders Methanosarcinales and Methanobacteriales. Our findings demonstrate AnMBRs as suitable techniques for treating chemical process water, with possible subsequent reclamation, characterized by high phenols concentrations and largely fluctuating salinity levels.

The combination effect of preozonation and CNTs layer modification on low-pressure membrane fouling control in treating NOM and EfOM

In this study, the combination effect of preozonation and carbon nanotubes (CNTs) layer modification on low-pressure membrane (LPM) fouling control was systematically investigated. To understand the alleviation mechanism of the hybrid process, natural organic matter (NOM) from IHSS and effluent organic matter (EfOM) from actual sewage effluent were both selected as the typical organic foulants presented in actual surface water and wastewater. A dead-end continuous flow model combined with programmable logic control system was used to operate four membrane filtration units and their backwash processes. With a constant permeates flux, the fouling resistant of CNT modified LPM after preozonation could be evaluated according to the increase in transmembrane pressure (TMP). The results revealed that the hybrid approach of preozonation and CNTs modification could significantly improve the anti-fouling ability of LPM, reduce the backwash frequency, and improve the reversibility of membrane fouling. During the filtration of EfOM and NOM, preozonation improved the water treatment capacity of the CNTs modified membranes. The experiment of mass balance revealed that preozonation enhanced the recoverability of CNTs modified membrane and greatly increased its operation time in treating EfOM and NOM. The molecular weight distribution as well as EEM analysis demonstrated the dissimilar characteristics of EfOM and NOM, which caused the different treatment efficiency by preozonation and CNT modification. The mechanism of EfOM/NOM fouling on LPM was summarized as the primary blocking by medium-MW EfOM/NOM. CNTs modification had a better effect on the control of LPM fouling when treating EfOM, as it removed the medium-MW EfOM by adsorption and prevented the pores blockage of the original PVDF membrane. Preozonation had a better effect on the control of LPM fouling when treating NOM, as it greatly changed the MWD of NOM by removing medium-MW NOM. The combination effect of the hybrid preozonation and CNTs modification resulted in the most effective fouling control of LPM by both decreasing the medium-MW and large-MW EfOM/NOM. At the same time, it decreased irreversible fouling related with membrane pore blocking. The hybrid approach demonstrated its promising application for LPM fouling control in actual sewage water and surface water treatment process.

Considering the Prospect of Utilizing Anaerobic Membrane Biofouling Layers Advantageously for the Removal of Emerging Contaminants

Membrane biofilm formation has traditionally been perceived as a wholly negative occurrence in membrane filtration-based wastewater treatment systems due to its resultant effect on transmembrane pressure and energy expenditure. This is the case for both membrane bioreactor (MBR) systems, generally, and anaerobic membrane bioreactors (AnMBRs), specifically. Insight gained through recent research, however, has revealed a potentially positive aspect to biofouling in AnMBR systems—namely, the improved removal of certain emerging contaminants (both microbial and chemical) from wastewater that would not otherwise be retained by the microfiltration/ultrafiltration membranes that are commonly used. Although the exact reasons behind this are not yet understood, the biofilm-specific anaerobic microbial communities that develop on membrane surfaces may play a key role in the phenomenon. Mechanisms of biofouling development in AnMBRs have recently been proven distinctly different from those that govern fouling in aerobic MBR systems. Based on these differences, it may be possible to devise operational strategies that promote the development of anaerobic biofilms on membranes while also minimizing transmembrane pressure increases. If achievable, this would serve as a sustainable basis for reducing the release of emerging contaminants such as organic micropollutants (OMPs) and antibiotic resistance genes (ARGs) with treated wastewater effluents.

Evaluating the impact of pretreatment processes on fouling of reverse osmosis membrane by secondary wastewater

Pretreatment of secondary effluents, containing relatively high concentrations of colloidal particles, suspended solids, dissolved organics and high level of biological activity, is required to reduce fouling of reverse osmosis (RO) membranes treating these effluents. Various indices are used to evaluate pretreatment efficacy. The effect of two different pretreatments for secondary effluent (BCMF - biofiltration, coagulation and microfiber filtration) vs. ultrafiltration (UF) were evaluated for their effect in reducing the fouling potential of the effluent as expressed by the indices of BOD (biofouling), TOC (organic and biofouling), and MFI0.45 (colloidal fouling). Actual RO fouling tests were conducted using identical RO flow cells at constant flux conditions. Fouled membrane autopsies were subsequently carried out at the end of each test run. The actual fouling based on real-time performance and post-operation autopsies were then correlated to the fouling indices.The results showed that BCMF pretreatment significantly reduced the fouling potential as reflected in all three indices, but UF pretreatment process reduced BOD and MFI0.45 to a significantly greater extent. RO membranes were in general fouled more severely by BCMF treated effluents as reflected in increased transmembrane pressure (TMP). This correlated with BOD and MFI0.45 analyses of the treated effluents and with membrane autopsies at the end of the run. For both treatments, the calculated biofilm porosity dropped as the experiments were carried out for longer periods. As expected, the hydraulic resistance of the fouling layer was found to contribute significantly more to deterioration of RO performance than biofilm-enhanced osmotic pressure for both BCMF-RO and UF-RO.