Fouling In Membrane Bioreactors Research Articles

Effect of ferric hydroxide on membrane fouling in membrane bioreactor treating pharmaceutical wastewater

Membrane fouling is considered as a main drawback for MBR technology especially treating industrial wastewater. Therefore, this study aimed to investigate the effect of fouling in membrane bioreactor (MBR) treating pharmaceutical wastewater with the addition of ferric hydroxide. Two identical lab-scale MBRs, namely, a control MBR (Co-MBR) and an enhanced MBR dosed with ferric hydroxide (Fe-MBR), were operated in parallel. The results demonstrate membrane fouling was retarded by 35% with the addition of iron. Further exploration of membrane fouling mechanisms showed iron addition resulted in increase in biomass floc size, enhancement of bacteria activity and reduction of dissolved organic concentration, especially carbohydrate, biopolymer and low molecular weight compounds concentrations in mixed liquor. There was also lower abundance of bacterial associated with biofilm formation in the Fe-MBR compared with the Co-MBR. These findings collectively contributed to the positive impacts on membrane fouling mitigation.

Model-based evaluation of fouling mechanisms in powdered activated carbon/membrane bioreactor system

Identifying the fouling degree of a membrane bioreactor (MBR) provides guidance on the determination of suitable membrane cleaning methods. There is still a lack of knowledge on the effects of powdered activated carbon (PAC) refresh ratio on the MBR fouling mechanism. Major fouling mechanisms of an MBR with constant flow rate at different PAC replenishment ratios were investigated by individual and combined mechanistic fouling models. The root mean square errors were employed to assess the prediction accuracy of the used fouling models. The combined models showed better prediction. The cake-complete model provided far better fits of the transmembrane pressure data, and provided good fits of other individual model predictions regardless of the PAC refreshment ratio. Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy confirmed that the cake layer clogging was the main fouling mechanism followed by complete blockage and standard plugging. The cake-complete model may be used to predict the fouling mechanisms in PAC/MBR systems.

Membrane fouling caused by lipopolysaccharides: A suggestion for alternative model polysaccharides for MBR fouling research

Polysaccharides were identified as key foulants in membrane bioreactors (MBRs) in previous studies. Polysaccharides used for MBR fouling research should represent real foulants, and alginate and dextran have often been used as model polysaccharides. However, their properties are not necessarily similar to those of polysaccharides that actually cause membrane fouling in MBRs. In recent studies, it was shown that polysaccharides causing membrane fouling in MBRs had the structures of lipopolysaccharides (LPSs), which are components of the cell wall of gram-negative bacteria. In the present study, therefore, membrane fouling caused by commercially available LPSs was investigated and was compared with that caused by model polysaccharides. In a series of batch filtration tests using four different microfiltration (MF) and ultrafiltration (UF) membranes, regardless of the membrane used, LPSs caused more severe membrane fouling than did alginate or dextran when they were filtered under the condition of the same organic carbon concentration. The properties of LPSs were found to be considerably different from those of alginate and dextran. In particular, affinity of LPS to PVDF polymer assessed by quartz crystal microbalance (QCM) mass measurement was remarkably high, and it would account for the severe fouling caused by LPSs. In experiments with filtering of mixtures of the model polysaccharides and a biomass suspension collected from a pilot-scale MBR, which were conducted to mimic the sudden increase in dissolved polysaccharides in real MBRs, LPS induced significant irreversible fouling, while alginate and dextran did not. The results obtained in this study clearly demonstrated high fouling potential of LPSs. Use of LPSs in future MBR fouling studies is therefore recommended.

Development of integrated membrane bioreactor and numerical modeling to mitigate fouling and reduced energy consumption in pharmaceutical wastewater treatment

This work focus to alleviate the fouling in Membrane bioreactor (MBR) by integrating electrooxidation, adsorptive cake, bio-film carriers and ozonation referred as Integrated Moving Bed Bioreactor (IMBBR). The total organic carbon (TOC), Chemical Oxygen Demand (COD) and Total Dissolved Solids (TDS) removal were observed as above 95%, 95% and 70% at 300 kPa with the flux increase in 35%. The numerical model was developed which proved less fouling which was in agreement with Scanning electron microscopy (SEM) and Liquid Chromatography and Mass Spectroscopy (LCMS). This study showed less energy consumption without the problem of filamentous bulking.

Fe(II)-dosed ceramic membrane bioreactor for wastewater treatment: Nutrient removal, microbial community and membrane fouling analysis

Ferrous dosing is used to reduce phosphorus concentration and alleviate polymeric membrane fouling in membrane bioreactor (MBR). However, limited studies have been conducted to investigate the impacts of ferrous dosing on ceramic membrane fouling, nutrient removal efficiency and microbial community. Accordingly, the aim of this study was to investigate the effect of intermittent ferrous dosing with Fe/P molar ratios of 2 and 1 (with a dosing frequency of every two days) on the overall nutrient removal, functional microbial changes and membrane fouling in ceramic membrane bioreactors (CMBR) in treatment of wastewater. TP concentration of 10 mg/L in influent decreased to 1.94 ± 0.62 mg/L (control), 0.38 ± 0.22 mg/L (Fe/P = 1) and 0.31 ± 0.18 mg/L (Fe/P = 2) in the effluent, respectively. Meanwhile, the effluent total nitrogen (TN) concentrations with Fe/P = 1 treatment (6.80 ± 2.02 mg/L) and Fe/P = 2 treatment (5.12 ± 2.28 mg/L) were lower than that of the control (7.72 ± 2.36 mg/L). Compared to Fe/P = 1, the TN removal performance was better for Fe/P = 2 mainly due to the increased abundance of denitrifying bacteria (Zoogloea and Acinetobacter). In addition, excess iron dose might have toxic effects on bacterial physiology, however the Fe concentrations that cause cell damage vary for different bacteria. The relative abundance of Zoogloea (aerobic denitrifying bacteria) continuously increased with ferrous addition (Fe/P = 2), while other bacteria including Dechloromonas, Hyphomicrobium and Thauera (anoxic denitrifying bacteria), Nitrospira (nitrifying bacteria) and Candidatus Accumulibacter (phosphorus accumulating organism) decreased sharply. Furthermore, membrane fouling was effectively moderated by ferrous dosing and Fe/P = 1 treatment showed improved membrane fouling mitigation than Fe/P = 2. Overall, intermittent ferrous addition in CMBR with Fe/P molar ratio of 1 was beneficial to the removal of nutrients (TP, TN and organics), enhanced succession of microbial community and membrane fouling mitigation.

A mechanistic study on electrolytic free chlorine for fouling control in submerged membrane bioreactors

We interrogated the effects of in-situ electrochemical chlorination with Ti/IrO2 anodes on physico-chemical properties of mixed liquor and fouling in membrane bioreactors (MBRs). Linear sweep voltammetry with variable concentrations of model organic foulant (alginic acid) indicated negligible direct oxidation. Batch electrolysis under current densities (j) up to 1.2 mA/cm2 further indicated that free chlorine (FC) primarily mediates transformation of dissolved compounds such as NH4+N and organic carbon (DOC) including protein and soluble microbial product (SMP, as noted in excitation-emission matrix, EEM). Owing to infinitesimal steady-state concentrations of FC under electrolytic generation, diffusion of FC determined the transformation kinetics in bulk, while floc/cell breakage and mineralization of extracellular polymeric substances (EPS) were marginal. Decay of negatively charged functionalities was found to compete with carbonyl generation on aromatic carbons (noted by red shift of EEM peak), which determined the magnitude of floc zeta-potential. A cathodic scale deposition was presumed to bring about PO43− removal and stimulate sludge flocculation. This study evinced that an increased floc size coupled with removal and/or transformation of hydrophobic DOC would contribute to the alleviated membrane fouling. However, significant decreases in microbial utilization rates of DOC under exposure to j > 0.8 mA/cm2 accelerated fouling during continuous operations of MBRs.

Influence of proteins and humic-like substances from soluble microbial products on membrane bioreactor fouling under normal and stress conditions

Soluble microbial products are one of the major fouling agents in membrane bioreactor (MBR). It is accepted that high molecular weights polysaccharides are the main contributors to membrane fouling but the presence in bulk solution of proteins and humic-like substances make fouling layer more complex. To better understand the role of both components in fouling establishment, they were quantified and characterized in bioreactor and permeate under various operating conditions (sludge retention time (SRT), synthetic or real wastewater (SWW or RWW), rapid variation of food to microorganisms (F/M) ratio). With SWW at hydraulic retention time (HRT) of 24 h, a larger part of proteins possessing small molecular weights (< 1 kDa) were obtained with increasing SRT from 20 to 50 d. At 50 d, these proteins present better retention (93%) and could participate in lowering gel layer porosity. MBR operating at SRT of 20 d was then preferable. At respective SRT and HRT of 50 d and 24 h with SWW, F/M ratio decrease (from 0.2 to 0.1 kg (COD).kg(MLVSS)(-1).d(-1) during 24 h) provoked implementation of a compact fouling layer which provoked a high TMP increase (0.83 kPa.h(-1)). Biodegradation of proteins involved in bio clusters structures were implied in this phenomenon.

Novel insights into membrane fouling caused by gel layer in a membrane bioreactor: Effects of hydrogen bonding

Gel layer formation in some cases directly determines membrane fouling extent in membrane bioreactors (MBRs). While hydrogen bonding interactions extensively exist in gelling foulants and sludge suspension, their exact roles in fouling remain unveiled. Filtration results in this study showed that, specific filtration resistance (SFR) of a gel layer formed in the MBR was as high as 2.06 × 1019 m−1·kg−1 at 20 °C, and moreover, SFR of both the real gel and model gel (Poly(N-isopropylacrylamide) (PNIPAM)) decreased with temperature. Fourier-transform infrared spectroscopy (FTIR) analysis indicated that gel samples were abundant of good hydrogen bonding donors/acceptors to form hydrogen bonding, and hydrogen bonding strength decreased with temperature. From viewpoint of free energy, mathematical models depicting roles of hydrogen bonding were proposed. For the first time, contribution level of hydrogen bonding effects to total gel SFR was quantified to be around 20%. These results offered in-depth insights into membrane fouling in MBRs.

Sludge characteristics and membrane fouling in membrane bioreactors with various sludge retention times

Sludge characteristics and membrane fouling in membrane bioreactors with various sludge retention times

Gradual PVP leaching from PVDF/PVP blend membranes and its effects on membrane fouling in membrane bioreactors

Improving the hydrodynamics on the membrane surface in a magnetically induced membrane vibration system (MMV) has been proven efficient for membrane fouling control in membrane bioreactors. This advantage can be further extended by using an optimized membrane. This was realized in this study by preparing porous polyvinylidene fluoride membranes via polyvinylpyrrolidone (PVP) blending and later by leaching out the PVP from the membrane matrix via post-treatment using NaOCl. Results show that increasing the PVP content in the casting solution increases membrane fouling resistance. Slowly leaching of PVP after several periodic NaOCl cleanings increased membrane permeance. No advantage of NaOCl post-treatment was observed. The long-term filtration confirmed the superiority of the highly porous membrane that complemented the advantages offered by the MMV system. This suggests that despite the small quantity of the remaining PVP, its leaching offered a substantial gain to improve membrane filterability.

Study on Operational Conditions to Minimize Membrane Fouling in Membrane Bioreactor (MBR) System for Wastewater Treatment-Preliminary Pilot Tests

In this study, effect of antiscalant usage on minimizing of membrane fouling due to high water hardness during wastewater treatment tests run by a pilot-scale membrane bioreactor (MBR) system. The membranes used in these studies were Kubota flat sheet MBR membranes made from polyethylene with a pore size of 0.4 micrometer. Preliminary tests were carried out with tap water for sixty days of operation. To investigate the applicability and the effect of antiscalant usage, four experiments (two experiments with tap water and two experiments with wastewater) were carried out and each experiment lasted for 29 days. The tests were carried out in the presence and in the absence of antiscalant. Fouling on MBR membranes was investigated by monitoring flux decline versus time. In tap water tests, unstable flux was observed initially then a flux decline due inorganic scaling. On the other hand, the flux was almost constant up to end of the experiment in the presence of antiscalant. During wastewater tests (in the absence of antiscalant), the flux decline was observed within ten days of operation while during wastewater tests in presence of antiscalant, the flux did not decline until twenty days of operation. The use of antiscalant did not influencethe efuent quality. According to the quality analyses results for MBR efuent, removal efciencies for COD, PO4-P, and total N were 95%, 98% and 40%, respectively. In addition,99% of total suspended solid rejection and 98% of color rejection were obtained in the presence or absence of antiscalant.

Fouling mitigation through maghemite particles in membrane bioreactor

In this study, there were two parallel membrane bioreactors (MBR) were operated to verify the influence of maghemite addition on membrane fouling in municipal wastewater treatment at maghemite addition of 0.54 gL−1. Mesoporous maghemite particles was prepared via hydrothermal method. The average COD removal was 95% involving in effluent with COD ranging from 12-55 mg/L. The turbidity of both MBR effluent values ranged from 0.4 to 1.5 NTU. The feed and operating conditions were similar in both MBR, and COD, turbidity, TMP, flow rate, SVI, MLSS and EPS were monitored over 60-day period. Maghemite was able to adsorp the proteins and after maghemite addition, the rate of membrane fouling was decreased. Detailed studies on the effect of maghemite addition in MBR indicated that maghemite dosage of 0.54 gL−1 was able to reduce fouling in membrane bioreactors.

Differences in the colloid properties of sodium alginate and polysaccharides in extracellular polymeric substances with regard to membrane fouling

Microbial extracellular polymeric substances (EPS) with a high polysaccharides content contribute to membrane fouling in membrane bioreactors. Sodium alginate (Alg) has been widely used as a substitute for polysaccharides in EPS to study membrane fouling; however, the rational for such a substitute is unclear and remains to be verified. In this work, the differences in the colloid properties of Alg-Ca2+ and EPS-Ca2+ were explored by integrating rheometry and dynamic light scattering with regard to distinct membrane fouling behaviors. The Alg-Ca2+ exhibited a larger hydrodynamic diameter and higher colloidal stability, which were attributed to its more solidified complexation compared with the electrostatic interactions in EPS-Ca2+. As a result, the gel layer of Alg-Ca2+ that formed on the membrane surface was denser and more impermeable, leading to a faster flux decline in the membrane filtration process. These results indicate that it is questionable to substitute polysaccharides in EPS with Alg for membrane fouling studies. Considering the substantial differences in the colloid properties, it would be better to modify Alg or find a more appropriate substitute for membrane fouling studies.

Ceramic membrane fouling by dissolved organic matter generated during on-line chemical cleaning with ozone in MBR

Ceramic membrane bioreactor (MBR) has attracted increasing interest due to its high flux, long membrane life-span and excellent resistance to hash operation conditions. Although ozone has been used for chemical cleaning of ceramic membranes, it is still unclear about the role of dissolved organic matter (DOM) generated during on-line chemical cleaning with ozone in the development of membrane fouling in ceramic MBR. This study clearly revealed that the released DOM could considerably induce irreversible membrane fouling, and humic acid like-substances (HAL) with molecular weight (MW) of about 500 Da were mainly responsible for the observed membrane fouling. A strong positive relationship existed between the membrane fouling rate of supernatant and the rejection level of HAL, evidenced by a high correlation coefficient (R2) of 0.99. Meanwhile, the results also showed that biopolymers with MW greater than 10 kDa were easily rejected by the ceramic membranes used, leading to the development of membrane fouling. However, the high ozone concentration helped to reduce the generation of biopolymers. The organic fractions with MW less than 500 Da in the DOM (e.g. building blocks, low-MW acid and low-MW neutrals) could pass through the ceramic membranes used, i.e. their contributions to the observed membrane fouling could be considered insignificant. Consequently, it appeared from this study that membrane fouling associated with the DOM generated by ozone during on-line chemical cleaning should not be ignored in the design and operation of ceramic MBR towards long-term process sustainability.

Fouling Development in A/O-MBR under Low Organic Loading Condition and Identification of Key Bacteria for Biofilm Formations

Membrane fouling in membrane bioreactors (MBR) remains a major issue and knowledge of microbes associated with biofilm formation might facilitate the control of this phenomenon, Thus, an anoxic/oxic membrane bioreactor (A/O-MBR) was operated under an extremely low organic loading rate (0.002 kg-COD·m−3·day−1) to induce membrane fouling and the major biofilm-forming bacteria were identified. After operation under extremely low organic loading condition, the reactor showed accumulation of total nitrogen and phosphorus along with biofilm development on the membrane surface. Thus, membrane fouling induced by microbial cell lysis was considered to have occurred. Although no major changes were observed in the microbial community structure of the activated sludge in the MBR before and after membrane fouling, uncultured bacteria were specifically increased in the biofilm. Therefore, bacteria belonging to candidate phyla including TM6, OD1 and Gammaproteobacteria could be important biofilm-forming bacteria.

Novel insights into membrane fouling in a membrane bioreactor: Elucidating interfacial interactions with real membrane surface

While governing adhesion/deposition of various foulants on membrane surface and membrane fouling in membrane bioreactors (MBRs), interfacial interactions with real membrane surface have not yet been fully quantified. In this study, theoretical deduction and experiments were carried out to numerically elucidate interfacial interactions in a MBR. A continuous real membrane morphology was reconstructed based on atomic force microscopy (AFM) characterization and triangulation technique. Thereafter, a method to calculate those interactions was established by incorporating the spatial relationship between a foulant and the reconstructed morphology into surface element integration (SEI) method. A case study of the proposed method was conducted. With surface characterization of the foulants and membrane, the interfacial interactions with real membrane morphology were approximated for the first time by computer programming according to composite Simpson’s rule. The results showed that rough morphology prolonged the interfacial interactions, indicating the profound role of morphology in the interfacial interactions related with membrane fouling. The new method would provide significant insights into membrane fouling in MBRs.

Microbial responses to transient shock loads of quaternary ammonium compounds with different length of alkyl chain in a membrane bioreactor

Extensive applications of quaternary ammonium compounds (QACs) in household and industrial products inevitably lead to their release into wastewaters; however, little attention has been paid to the acute effects on activated sludge. In this work, we investigated the responses of microorganisms in a membrane bioreactor (MBR) to transient shock loads of QACs with different alkyl chain length and their impacts on MBR performance. Results showed that QACs affected microbial viability and caused damage to key enzymes (e.g., ammonium monooxygenase and nitrite oxidoreductase), inhibiting organic matter degradation and nitrogen removal. The presence of QACs also caused negative influences on dehydrogenase activity, catalase and superoxide dismutase, thus increasing the production of reactive oxygen species. Moreover, QACs with longer alkyl chains and/or benzyl groups bonded to the nitrogen atom could induce a more severe damage to cell integrity and microbial viability. The interaction with QACs also induced the release of organic matters and the changes of adhesion properties of microbial products, resulting in aggravated membrane fouling in MBRs. Our results demonstrate the acute negative effects of QACs on activated sludge, and special attention should be paid to the performance of biological wastewater treatment processes subject to the shock loads of QAC-bearing industrial streams.

Impacts of morphology on fouling propensity in a membrane bioreactor based on thermodynamic analyses

Impacts of morphologies of both membrane and foulant on interaction energies related with adhesive fouling in a membrane bioreactor (MBR) were explored by thermodynamic analyses. Interaction energies in three possible interaction scenarios regarding different membrane and foulant morphologies under conditions in this study were quantified according to the thermodynamic methods. It was interestingly found that, strength of total interaction between soluble microbial products (SMPs) and rough membrane was over 20,000 times of that between sludge flocs and rough membrane under same conditions, indicating the extremely higher adhesion ability of SMPs than the large particulate foulants. This result plausibly explained the high fouling propensity of SMPs over sludge flocs. As compared with smooth surfaces, rough surfaces of both membrane and sludge flocs significantly reduced total interaction strength, alleviating adhesive fouling caused by the sludge flocs. Reduce in fractal dimension (Df) of membrane increased adhesive fouling caused by the SMPs, but alleviated adhesive fouling caused by the sludge flocs. These findings gave important implications to better understand and control membrane fouling in MBRs.

Effect of nitrifiers community on fouling mitigation and nitrification efficiency in a membrane bioreactor

Membrane fouling in membrane bioreactors (MBR) normally depends on the microbial cell density and microbial population structure. A nitrifying-enriched activated sludge (NAS) was obtained in this study through particular ammonium feeding of conventional activated sludge (CAS). Next, the dominance of autotrophic nitrifier population in NAS system was checked and compared with CAS system by its high nitrification efficiency (100% vs. 43%) and low COD removal (9% vs. 65%). Furthermore, the maximum amount of N-NO3− produced from similar concentrations of ammonium in CAS and NAS systems were 6.6 mg/L and 37.5 mg/L, respectively. A filterability test also was done in the cross-flow and simple dead-end filtration systems proportionally employing different amount of NAS and CAS with a constant MLSS concentration of 2000 mg/L. NAS was twice as filterable compared to CAS. Soluble microbial products (SMP) and extracellular polymeric substance (EPS) in CAS were significantly higher than NAS system (2 and 6 mg/L for NAS vs.100 and 36 mg/L for CAS). By increasing the proportion of nitrifying bacteria, the permeation was enhanced remarkably about 2.5 folds and the operation time of MBR was approximately doubled (6–11.5 h). The results indicated that an appropriate C/N ratio can control the microbial population and help the nitrifier significantly mitigate fouling in MBR.

Fouling control mechanisms in filtrating natural organic matters by electro-enhanced carbon nanotubes hollow fiber membranes

Membrane fouling is a ubiquitous and costly problem for membrane bioreactor (MBR) that usually deteriorated membrane performance. Applied voltage on membrane is an important strategies mitigating the fouling. To evaluate antifouling mechanisms of electro-enhanced carbon nanotubes hollow-fiber membranes (CNTs-HFMs), the removal of bovine serum albumin (BSA), sodium alginate (SA) and supernatant of anaerobic bioreactor (SAB) were performed. The results showed that the optimal applied voltage (− 1.2 V) could effectively reduce membrane fouling from excluding the negative pollutants far away from the membrane surface, offering an impediment on forming gel layer and controlling the formation of high-molecular-weight pollutants. The effluent COD removal efficiencies by filtrating BSA (92.1%), SA (87.3%) and SAB (56.8%) at − 1.2 V were 3.3, 1.4 and 1.5 times higher than that of membrane filtration alone. Then, a short-term experiment (30 days) was performed, where CNTs-HFMs served dual function as the cathode and filtration function in an electro-enhanced anaerobic bioreactor (AnEMBR). The results presented that a low transmembrane pressure of 0.35 bar was obtained compared to the control reactor (0.60 bar), implying that applied voltage on CNTs-HFMs contributed to alleviate membrane fouling. This work implied that electrochemical control might provide a promising avenue to mitigate membrane fouling in MBR.