Membrane Fouling Rate Research Articles

Comparing the performance of the conventional and fixed-bed membrane bioreactors for treating municipal wastewater.

Membrane bioreactor (MBR) is relatively a new technology in wastewater treatment. It can efficiently remove soluble and suspended organics. However, it may constantly encounter bio-fouling and cannot efficiently remove nutrient pollutants. These two deficiencies have motivated researchers to upgrade the design and operation of conventional MBR (CMBR). This study evaluates the performance of hybrid fixed bed MBR (FBMBR) treating real domestic wastewater in different operational conditions. It also compares the experimental results of FBMBR with the CMBR. For this purpose, two identical reactors are constructed as CMBR and FBMBR. Each module contains the net volume of 140L and is operated continuously in two aerobic (DO > 4mg/L) and anoxic (DO < 1mg/L) conditions with average organic loading rates (OLRs) of 0.58, 0.71 and 1.55 kgCOD/m3d. The pore sizes of flat sheet membranes are 0.2-0.8μm with total surface area of 1.4m2 per module. The experimental results revealed that the removal efficiencies of BOD, COD and TSS are above 95 % in both CMBR and FBMBR in all operating conditions. However, fouling occurs with lower rates in FBMBR. The growing rate of transmembrane pressure (TMP) in aerobic condition is 1.7mBar/day in CMBR, while it reduces to 1.2mBar/day for FBMBR in solid retention time (SRT) of 75 days and OLR of 0.58 and 0.71 kgCOD/m3d. In anoxic condition with SRT of 100 days and OLR of 1.55 kgCOD/m3d, the TMP in FBMBR is 59 % of CMBR. In addition, total nitrogen (TN) removal is between 12 % (aerobic) and 27 % (anoxic) in CMBR, while it is between 25 % (aerobic) and 49 % (anoxic) in FBMBR. Total phosphorous (TP) removal also ranges between 50 and 66 % in CMBR, while it is between 51 and 86 % in FBMBR. Consequently, using hybrid systems of FBMBR can reduce membrane fouling rate and improve nutrient removal efficiency in comparison with CMBR. This approach can reinforce the biological treatment efficiency and preserve permeate quality in higher OLRs or in lower DO level.

Effect of minimal pre-treatment on reverse osmosis using surface water as a source

Reverse osmosis is increasingly used in drinking water supply for treatment of fresh water sources which can directly result in high quality water. In practice reverse osmosis is never applied directly on fresh water sources, predominantly because of the occurrence of membrane fouling. Strategies to control membrane fouling in reverse osmosis without expensive and extensive pre-treatment include low flux operation, increase cross-flow velocities and improved (periodic) hydraulic cleaning. The objective of this research is to technically and economically compare minimal pre-treated reverse osmosis to state-of-the art ultrafiltration pre-treated reverse osmosis in surface water treatment to obtain high quality water. A parallel reverse osmosis system with six parallel 2540-type spiral wound membrane elements has been systematically operated during several months with only screens pre-treatment before reverse osmosis. A minimal pre-treated reverse osmosis system using only screens on surface water did not result in stable reverse osmosis operation, however, the ultrafiltration pre-treated reverse osmosis system also failed in the longer run. Lowering the membrane flux from 25 L/m2.h to 10 L/m2.h in minimal pre-treated RO resulted in an approximately 10-fold decrease of the membrane fouling rate, while not influencing the pressure drop increase. Periodical air water cleaning in minimal pre-treated RO resulted in an approximately 4-fold reduction of the spacer clogging rate, while not affecting the membrane fouling rate. The total cost of a minimal pre-treated low flux (10 L/m2.h) operated RO was significantly lower (0.46 €/m3) compared to state-of-the-art UF pre-treated RO at normal flux (25 L/m2.h) (1.21 €/m3). The cost difference in financial space provides an opportunity to develop minimal pre-treated RO systems with improved control of membrane fouling and spacer clogging.

The effect of composite enzyme catalysis whey protein cross-linking on filtration performance.

In this study, enzymatic cross‐linked whey protein coupling ultrafiltration was used to reduce membrane fouling and increase whey protein recovery rate. The filtration efficiency and protein interaction with the membrane surface were investigated. The results showed that the protein recovery rate and relative flux of transglutaminase catalysis protein followed by tyrosinase each increased by approximately 30% during ultrafiltration. The total membrane resistance was reduced by approximately 20%. The shape of the transglutaminase and tyrosinase cross‐linked protein had somewhat spherical and cylindrical structure similar to an elongated shape based on fluorescence microscopy imaging, which indicated membrane resistance reduction. Fluorescence excitation–emission matrix spectroscopy (EEM) showed that the permeation peak intensities of transglutaminase followed by tyrosinase catalysis protein decreased sharply in the tryptophan and aromatic‐like protein fields, indicating that most protein was rejected after ultrafiltration. The repulsive interaction energy was increased between the cross‐linked proteins and membrane based on extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) analysis.

Microalgal exopolymeric substances fouling in submerged vacuum membrane distillation and its mitigation via enhanced air bubbling

This work aims at studying the fouling behaviour of submerged vacuum membrane distillation (S-VMD) in desalinating the algal-blooming seawater. A dynamic microalgal fouling phenomenon and its mitigation via air bubbling was investigated over the time. At the early stage of S-VMD operation, the precipitation of inorganic salts on the membrane surface was responsible for initiating the flux decline. In the later stage, significant amounts of EPS surrounding the microalgae cell aggregates were precipitated on the inorganic scalants and further increased the membrane fouling rate. Based on the exopolymeric substances (EPS) extraction analysis, hydrophilic polysaccharides as a result of the aggregation of microalgal cells was firstly observed, followed by dominating protein fouling over the long run S-VMD operation. Excreted proteins increased the hydrophobicity of the EPS by reducing the surface charge, thus leading to a strong hydrophobic interaction with membrane surface at the 60 h of S-VMD operation. Compared to the non-bubbling S-VMD system, the system subjected to 0.167 m/s air bubbling showed superior and stable flux performance with lower extent of fouling.

Anoxic/oxic membrane bioreactor assisted by electrocoagulation for the treatment of azo-dye containing wastewater

This study investigated the use of an anoxic-oxic electro-membrane bioreactor (A/O-EMBR) for the treatment of an azo-dye containing wastewater. The reactor performance and the bacterial community structure were assessed and compared without (Period I) and with (Period II) the application of the electrocoagulation process under the current density of 10 A m−2. The dye removal performance was substantially improved as the electrocoagulation was applied, increasing from 52% (Period I) to 94.9% (Period II). Respirometric tests showed that the nitrifying activity increased when the membrane bioreactor was exposed to electrocoagulation. Likewise, activity batch tests indicated that both anoxic and anaerobic dye removal rates increased when the electrocoagulation was applied, while aerobic decolorization was not affected and remained invariant. DNA sequencing analysis revealed significant shifts in the microbial community composition upon implementation of electrocoagulation. Janibacter and Lactococcus genus, recognized as azo dye-degrading bacteria, were the most abundant in Period II and accounted for almost 60% and 16% of the classified sequences, respectively. Filtration batch tests revealed better filterability conditions of the mixed liquor when the reactor was assisted by the electrocoagulation. However, the membrane fouling rate became more intense in this period, a result that was attributed to the substantial increment in total suspended solids content. The average energy consumption per mass of dye removed decreased by 17.2% (from 580 to 480 kWh kgdyeremoved−1) when the electrocoagulation was applied, indicating that A/O-EMBR configuration was able to achieve a better energy efficiency in terms of dye removal.

Characterizing the roles of pretreatment methods for model suspensions in the membrane fouling process: The case of yeast and kaolin

Model suspensions are important substances for characterizing fouling processes to study the mechanism of membrane fouling, thus, choosing a suitable standard suspension is critical for researches on membrane fouling processes. The pretreatment methods of model suspensions have long been neglected, which can alter the physical and chemical properties and affect fouling results. This study compared four different pretreatment methods (centrifuging and drying, magnetic stirring, ultrasonic processing, and dissolving in buffer solution) and found effects on size distribution, dispersion stability, pH variation over time, and fouling properties. Among the characterization of model suspensions, different pretreatment methods led to various changes in physical and chemical properties in this study. Membrane filtration experiments showed that these four pretreatments changed the rate of membrane fouling. The results of the analysis of filtration flux for suspensions indicated that for ultrasonic processing of all suspensions and magnetic stirring of kaolin suspensions, pore blocking was the main mechanism, while cake formation was dominant for the others. Therefore, special attention should be placed on different pretreatment methods and selecting appropriate model foulants. Finally, some guidance on selecting appropriate model foulants was given in the study.

Modelling the critical roles of zeta potential and contact angle on colloidal fouling with a coupled XDLVO - collision attachment approach

A coupled XDLVO-collision attachment (CA) model is proposed to quantitatively evaluate the critical roles of zeta potential ζ and contact angle θ of foulant on colloidal fouling. In this model, the XDLVO theory is applied to relate ζ and θ to foulant-membrane interaction energy barrier (ΔEb). The latter is further bridged to membrane fouling rate (dmf/dt) by the CA theory, recognizing fouling as foulant colliding with a membrane surface followed by its attachment. XDLVO-CA model predictions agree well with the experimental water flux declines under various solution pHs. Modelling results show that severe fouling occurs at low ζ2, and increasing ζ2 can substantially lower dmf/dt as a result of the increased ΔEb. Interestingly, a negative linear relationship is observed between ζ2 and logarithm of dmf/dt at high ζ2. For the role of contact angle for water, glycerol and diiodomethane, there exists a critical θ, below (or above) which little fouling occurs owing to the dramatically increased ΔEb and thus decreased dmf/dt by orders of magnitude. Furthermore, the threshold θ corresponds to the acid-base interaction energy transiting from attraction to repulsion. Our modelling results reveal the importance of optimally tailoring foulant ζ and θ for fouling control.

Application of Error Function in Dead-end/cross-flow Microfiltration Mode

In this study, error function was used to analyze the membrane fouling behavior (flux decay) for bovine serum album (BSA) solution in dead-end mode and for kaolin suspension in cross-flow mode under constant pressure. The results showed that the predictions of error function had good agreements with experimental data both in dead-end mode and cross-flow mode. Meanwhile, both higher concentration and higher TMP could accelerate the membrane fouling rate. In addition, the parameter k in error function decreased with the increase of concentration or TMP. Thus, smaller parameter k represented more serious membrane fouling.

A novel electro-cleanable PAN-ZnO nanofiber membrane with superior water flux and electrocatalytic properties for organic pollutant degradation

Nanofiber membranes (NFMs) prepared with electrostatic spinning have attracted more and more attention in wastewater treatment owing to its unique advantages of high porosity and large specific surface area. However, the low removal rate of small molecular weight dyes and membrane fouling are the main obstacles for its large-scale application. Therefore, new polyacrylonitrile (PAN)-ZnO NFM was prepared simply and efficiently combined with electrostatic spinning technology and magnetron sputtering. Under the action of electrocatalysis, PAN-ZnO NFM exhibited not only high removal rate (>95%) for Congo red (CR), rhodamine B (RhB), sunset yellow (YS), methyl orange (MO) and methylene blue (MB), but also excellent water flux (1016 L m−2 h−1 Bar−1). Moreover, the electrocatalytic stability investigation of PAN-ZnO NFM showed that the membrane still maintained an excellent dye removal rate (>90%) after 10 h of continuous electrocatalytic filtration. Apart from, PAN-ZnO NFM also displayed excellent mechanical properties (252 MPa of Young's modulus) and antifouling ability. The permeate flux recovery rate of more than 90% after electrocatalytic cleaning for 5 min. Due to its excellent properties in dye removal rate, water flux, electrocatalytic stability, and antifouling, PAN-ZnO NFM exhibited an excellent application prospect in textile wastewater treatment.

FeOx@GAC catalyzed microbubble ozonation coupled with biological process for industrial phenolic wastewater treatment: Catalytic performance, biological process screening and microbial characteristics

Phenolic compounds are common ccontaminants in industrial effluents. In this study, a combined catalytic microbubble ozonation and biological process was developed and applied for efficient industrial phenolic wastewater (PWW) treatment. Catalytic activity of an iron-oxides (FeOx) doped granular activated carbon (GAC) catalyst (FeOx@GAC) in microbubble ozonation for PWW treatment was investigated. The results demonstrated that the FeOx@GAC catalyzed microbubble ozonation (O3/FeOx@GAC) obtained significantly higher reaction rate constant (k1 = 0.023 min−1) in TOC removal compared to the bare GAC catalyzed microbubble ozonation (O3/GAC, k1 = 0.013 min−1) and ordinary microbubble ozonation (k1 = 0.008 min−1). Destruction rate constant of phenolic compounds (k2) was improved from 0.014 min−1 (ordinary microbubble ozonation) to 0.025 min−1 (O3/FeOx@GAC). The 60-min pretreatment of PWW by O3/FeOx@GAC process enhanced BOD5/COD ratio from 0.31 to 0.76 and reduced the acute bio-toxicity by 79.2%. Screening and characterization of biological post-treatment processes were conducted among activated sludge process (ASP), up-flow anaerobic sludge blanket (UASB) and membrane bioreactor (MBR). UASB and ASP showed limited phenolic compounds removal of 35.4% and 57.0% with lower bio-toxicity resistance than MBR (94.9% phenolic compounds removal). The combined process O3/FeOx@GAC-MBR was thus developed and achieved high COD removal (98.0%) and phenolic compounds degradation (99.4%). PWW pretreatment by O3/FeOx@GAC process decreased membrane fouling rate of MBR by 88.2% by reducing proteins/polysaccharides accumulation in both extracellular polymeric substances and soluble microbial products. 16S rRNA high-throughput sequencing revealed the predominance of phylum Proteobacteria, class Alphaproteobacteria and genera Mycobacterium, Gordonia, Pedomicrobium & Defluviimonas in biological PWW treatment bio-systems. Pearson correlation coefficient and ANOVA analysis verified that Mycobacterium possessed high bio-toxicity resistance and was the main contributor to the biodegradation of phenolic compounds.

The effect of sludge retention time and organic loading rate on performance and membrane fouling in membrane bioreactor

AbstractBACKGROUNDMembrane bioreactor (MBR) is commonly considered a promising technology for wastewater treatment due to its outstanding effluent quality, low sludge production, and smaller environmental footprint. However, membrane biofouling is regarded as the bottleneck of MBR processes preventing their universal application. Optimizing operating conditions and improving the antifouling properties of membranes have a substantial impact on the rate and characteristics of membrane fouling in MBR systems.RESULTSIn this study, a two‐step process was performed to mitigate membrane fouling by optimizing sludge retention time (SRT) and organic loading rate (OLR) and improving membrane characteristics in an MBR system developed for the treatment of pharmaceutical wastewater. At first, pure membrane fouling and sludge characteristics were examined in three identical MBRs at different OLRs (40, 100, and 160 mg chemical oxygen demand(COD)/L.d) under various SRTs (7.5, 22.5, and 37.5 days). The investigation indicated that high protein concentration in loosely bound extracellular polymeric substances (LB‐EPS) caused more irreversible fouling at the OLR and SRT of 40 mgCOD/L.d and 7.5 days, respectively. In the second stage, a modified anti‐biofouling membrane was installed into the optimized submerged MBR at OLR = 100 mgCOD/L.d and SRT of 22.5 days for further mitigation of membrane fouling. Membrane fouling significantly reduced as the protein and gram negative bacteria on the surface of the modified membrane decreased.CONCLUSIONThe results showed that the reversible and irreversible membrane fouling were controlled successfully through the proposed optimization of operational conditions and by improving the membrane characteristics in MBR. Finally, the protein of LB‐EPS is a vitally important factor affecting the irreversible membrane fouling. © 2020 Society of Chemical Industry (SCI)

Polyethylene-supported nanofiltration membrane with in situ formed surface patterns of millimeter size in resisting fouling

Membrane surface properties play important roles in determining the rate and severity of membrane fouling. This paper reported an innovative nanofiltration (NF) membrane called PENF which had a poly(piperazine-amide) active layer formed on a polyethylene (PE) support layer. The PENF membrane was very attractive in that millimeter-sized surface patterns could be automatically formed by the pressing effect of applied pressure for which permeate spacer acted as the in situ imprinter. This was attributed to the thin and tough PE support layer, which could be easily deformed under the applied pressure for NF applications. The surface-patterned PENF membrane (PENF-P) demonstrated greatly enhanced resistance to organic, inorganic and scaling fouling as well as combined fouling, when compared to either the original PENF membrane or commercial NF membranes like NF270. Without surface patterns, the PENF membrane along with other NF membranes followed a same general rule in resisting membrane fouling; a more hydrophilic NF membrane was generally more resistant to fouling. Membrane integrity breaches caused by surface deformation and patterning were negligible in terms of glucose rejection and water permeability coefficient. The PENF-P membrane could reject glucose by >80% at an applied pressure of 3.5 bar and had a water permeability coefficient of >11 L/m2/h/bar. A continuous running of a small-size spiral-wound element of the membrane (0.85 m2) for over 3000 h confirmed that the PENF membrane had a long-time consistently high performance in terms of water permeation and solute rejection. The innovative PENF membrane and the involved surface patterning technique are expected to have a bright application prospect for water treatment and wastewater reclamation.

Effects of electrocoagulation on membrane fouling and treatment performance of a membrane bioreactor operated without sludge discharge

This study evaluated the effects of the electrocoagulation on membrane fouling and treatment performance in a membrane bioreactor operated with prolonged solids retention time. The membrane bioreactor was fed with synthetic wastewater, and its operation was conducted at three different experimental runs. Initially, the reactor was operated without electric current application (run 1), named as control period, and subsequently using electric current density of 5 A m−2 (run 2) and 15 A m−2 (run 3). Hence, the reactor performance was evaluated for the impact of electrocoagulation on fouling mitigation and pollutant removal (chemical oxygen demand, phosphorus and ammonium) as well as for the use of two different current densities. The results showed that the use of the lower current density (run 2) was able to significantly improve the membrane bioreactor performance on organic matter and phosphorus removal, showing average efficiencies of 95 and 99%, respectively. Particularly for ammonium removal, the membrane bioreactor exhibited a gradual increase from run 1 to 3, attaining the highest ammonium removal efficiency (86%) during run 3. Compared to run 1 and 3, the use of 5 A m−2 resulted in a better mixed liquor filterability conditions and consequently in a lower membrane fouling rate (0.107 bar d−1). Therefore, the integration of electrocoagulation with the membrane bioreactor technology proved to be an interesting alternative to improve the treatment performance and attenuate the fouling process, even operating the reactor without sludge discharge.

Probing effects of additives on the filterability of oncolytic viruses via a microfiltration process

One major part of therapeutic oncolytic viruses (OV) manufacturing is a membrane-based process with a major challenge of membrane fouling and consequent product loss. A small-scale microfiltration setup was developed, allowing online transmembrane pressure (TMP) measurement through a constant flux filtration using a low volume of a representative OV solution (< 3 mL). Using this setup, the effects of different additives including various proteins (bovine serum albumin and alpha-lactalbumin) and organic polymers (polyethylene glycol and polyvinylpyrrolidone) on microfiltration of the OV solution were screened. Results demonstrated that examined proteins significantly decreased membrane fouling rates and increased the virus recoveries. An addition of 5% bovine serum albumin (BSA) to the virus solution increased the virus recovery about 6-times compared to microfiltration of the virus solution without any additive. In contrast, none of the organic polymers could imitate effects of the protein additives. In a separate set of experiment, to study effect of protein on the membrane surface, the membrane surface was pre-blocked using a BSA protein solution and then subsequently utilized to filter the virus solution. This result also demonstrated a significant increase in virus recovery through the blocked membrane, about 4-times higher virus recovery compared to a non-blocked membrane.

Evaluating the effect of air flow rate on hybrid and conventional membrane bioreactors: Implications on performance, microbial activity and membrane fouling

This study addressed the impact of air flow rate on the performance, membrane fouling behaviour and microbial community of a sequencing batch conventional membrane bioreactor (SB-MBR) and a sequencing batch hybrid membrane bioreactor (SB-HMBR) with carrier media for biofilm growth. Two different scenarios were evaluated: high (6.4 L min−1) and low (1.6 L min−1) air flow rates, associated with high (4.5 mg L−1) and low (1.5 mg L−1) dissolved oxygen (DO) concentrations and specific aeration demand per membrane area (SADm) of 0.426 and 0.106 m3 m−2 h−1, respectively. Both reactors were subjected to alternating non-aerated and aerated conditions for organic matter (as chemical oxygen demand - COD), nitrogen and phosphate removal from a municipal wastewater. From the bacterial community analysis, the key players in nutrient removal processes were assessed. The results showed that COD removal efficiencies were above 95% in both MBRs, regardless of the aeration intensity, while complete ammonium removal was observed at the higher DO. However, nitrifying activity was adversely affected under low DO levels. High nitrification levels were re-established faster in the hybrid MBR, thanks to the presence of biofilm, where nitrifying activity was favoured and the bacterial community profile did not exhibit substantial changes upon DO reduction. A higher denitrification potential was found for the carrier-based MBR, resulting in lower effluent nitrate concentrations. Regarding phosphorus removal, a slight improvement was observed in the SB-HMBR at reduced DO, while in the SB-MBR it remained practically constant. Moreover, the specific phosphate uptake rate exhibited a significant increase, especially in the hybrid MBR, reaching 44.6 mgP gVSS−1 h−1. At lower aeration rate, however, worse filterability and higher membrane fouling rates were observed, especially in the conventional MBR. Overall, the results demonstrated that the hybrid MBR better withstood the reduced air flow rate and DO as compared to the conventional counterpart.

Impacts of sulfadiazine on the performance and membrane fouling of a hybrid moving bed biofilm reactor-membrane bioreactor system at different C/N ratios

The performance and membrane fouling of a hybrid moving bed biofilm reactor-membrane bioreactor (MBBR-MBR) system was evaluated when exposed to 0.5 mg/L of antibiotic sulfadiazine (SDZ). Results indicated that although SDZ reduced the removal efficiency of NH4+-N and TN (up to 12%) and TOC (up to 6%) at low C/N (2.5 and 4), it had no significant effect at high C/N (6 and 9). It was found that SDZ was removed 75% and 58% at high C/N of 9 and low C/N of 2.5, respectively. SDZ decreased the ratio of volatile biomass/total biomass and sludge particle size and increased the concentrations of extracellular polymeric substance (EPS) and soluble microbial product (SMP) in MBR. Consequently, this accelerated the membrane fouling rates, with an average increase of 6.85 kPa/d at low C/N (2.5) and 0.513–0.701 kPa/d at medium and high C/N (4, 6 and 9).

Role of dissolved air flotation (DAF) and liquid ferrate on mitigation of algal organic matter (AOM) during algal bloom events in RO desalination

Harmful Algal Blooms (HABs) are considered a major contributor to membrane biofouling in Seawater Reverse Osmosis (SWRO) desalination plants. The presence of HABs in the raw feed water leads to an increase in membrane fouling rate, increase of chemical consumption, and can cause temporary shutdown of plants. Effective pretreatment can reduce the amount of organic foulants reaching the RO membrane and alleviate the problem of flux decline during RO operation and frequent membrane cleaning using chemicals. This study compared the effect of in-situ generated liquid ferrate and ferric chloride in combination with dissolved air flotation (DAF) as a pretreatment strategy to remove algal cells and algal organic matter (AOM) during algal bloom events. Experiments were performed using a bench-scale DAF unit. HABs conditions were simulated by harvesting AOM from cultivating Chaetoceros affinis (CA) in raw seawater to a concentration of around 10 mg C/L of dissolved organic carbon (DOC). The liquid ferrate was generated in-situ by wet oxidation of ferric chloride in an alkaline media. The best performance was achieved with the combined use of liquid ferrate and DAF, removing up to 100% of algal cells, 99.99% of adenosine tri-phosphate (ATP), and up to 92% of AOM.

Insights into the roles of membrane pore size and feed foulant concentration in ultrafiltration membrane fouling based on collision-attachment theory.

Membrane property and feed characteristics play critical roles in membrane fouling. This paper aims to clarify the roles of membrane pore size (φ) and feed foulant concentration (Cb ) in ultrafiltration fouling induced by polysaccharides. The fouling behaviors were expounded by collision-attachment theory, where the rate of membrane fouling is mainly determined by collision frequency (JCb ) and attachment efficiency (γ). At the initial fouling stage, rapid flux decline was observed at large φ or high Cb due to the great JCb and/or γ. At the later fouling stage, there existed a nearly identical maximum stable flux attributing to the same JCb and γ, which was independent of φ and Cb . Moreover, the smaller φ can lead to less foulants passed through the membrane and thus more foulants attaching on the membrane, while the higher Cb can give rise to more foulants on both the membrane surface and in the permeate. The results presented in current study provide fundamental basis in understanding membrane fouling. PRACTITIONER POINTS: Collision-attachment theory was employed to expound the UF fouling behavior. Rapid flux decline occurred at large membrane pore size or high feed foulant concentration in the initial fouling stage. Membranes with different pore size or feed foulant concentration had an identical flux at the latter fouling stage. Lowering membrane pore size or increasing feed foulant concentration can lead to more foulants attaching on the membrane surface.

Long-Term Investigation into the Membrane Fouling Behavior in Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment Operated at Two Different Temperatures.

In this study, the characteristics of activated sludge flocs were investigated and their effects on the evolution of membrane fouling were considered in the anaerobic membrane bioreactors (AnMBR), which were operated at 25 and 35 °C for municipal wastewater treatment. It was found that the membrane fouling rate of the AnMBR at 25 °C was more severe than that at 35 °C. The membrane fouling trends were not consistent with the change in the concentration of soluble microbial product (SMP). The larger amount of SMP in the AnMBR at 35 °C did not induce more severe membrane fouling than that in the AnMBR at 25 °C. However, the polysaccharide and protein concentration of extracellular polymeric substance (EPS) was higher in the AnMBR at 25 °C in comparison with that in the AnMBR at 35 °C, and the protein/polysaccharide ratio of the EPS in the AnMBR at 25 °C was higher in contrast to that in the AnMBR at 35 °C. Meanwhile, the fouling tendencies measured for the AnMBRs could be related to the characteristics of loosely bound EPS and tightly bound EPS. The analysis of the activated sludge flocs characteristics indicated that a smaller sludge particle size and more fine flocs were observed at the AnMBR with 25 °C. Therefore, the membrane fouling potential in the AnMBR could be explained by the characteristics of activated sludge flocs.

Optimization of nitrogen and carbon removal with simultaneous partial nitrification, anammox and denitrification in membrane bioreactor.

In this study, a membrane bioreactor (MBR) was used to achieve both nitrogen and carbon removal by a simultaneous partial nitrification, anammox and denitrification (SNAD) process. During the entire experiment, the intermittent aeration (non-aerobic time : aeration time, min min−1) cycle was controlled by a time-controlled switch, and the aeration rate was controlled by a gas flowmeter, and the optimal operating parameters as determined by response surface methodology (RSM) were a C/N value of 1.16, a DO value of 0.84 mg l−1 and an aerobic time (Tae) of 15.75 min. Under these conditions, the SNAD process achieved efficient and stable nitrogen and carbon removal; the total inorganic nitrogen removal efficiency and chemical oxygen demand removal efficiency were 92.31% and 95.67%, respectively. With the formation of granular sludge, the membrane fouling rate decreased significantly from 35.0 Pa h−1 at SNAD start-up to 19.9 Pa h−1 during stable operation. Fluorescence in situ hybrid analyses confirmed the structural characteristics and the relative ratio of aerobic ammonia-oxidizing bacteria, anaerobic ammonia-oxidizing bacteria and denitrifying bacteria in the SNAD system.