Effect of mechanical cleaning with granular material on the permeability of submerged membranes in the MBR process

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

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

Comparative analysis of membrane fouling mechanisms induced by operation modes of membrane bioreactors with aerobic granular sludge

This experimental work investigated fouling characteristics induced by two different configurations of membrane bioreactor (MBR), which are submerged MBR and sidestream MBR with aerobic granular sludge. Submerged membrane bioreactor with granular sludge (Sub-MGSBR) ran the longest operation time 61 days with a steady overall TMP increase rate; Sidestream membrane bioreactor with granular sludge (SS-MGSBR) performed only 39 days, which exhibited Sub-MGSBR had more efficiently retarding membrane fouling. In both membrane bioreactors with flocculent sludge (MFSBRs) as a control, membrane foulants were compact, and cake resistance was the dominant fouling factor. In MGSBRs, however, pore blocking resistance turned out the key fouling factor. Especially in Sub-MGSBR, it went beyond 75%, and there was the most conglomeration of microorganisms of foulants with the highest porosity. Extracellular polymeric substances (EPS) content of foulants proved membrane fouling was hardly just for granules accumulation into cake but microorganisms' growth in MGSBRs.

The potential of microalgae Dunaliella salina to treat shrimp pond wastewater in a PAN/GO membrane bioreactor

Graphene has attracted a significant amount of attention because to its excellent mechanical, electrical, thermal, and optical characteristics. In this work, a membrane bioreactor with hollow fibre PAN/GO nanocomposite was studied for the treatment of Persian Gulf shrimp pond wastewater. Dunaliella salina microalgae have been used for better treatment and the formation of sludge mass in a shorter period of treatment in the MBR system. Additionally, GO nanoparticles were used in order to improve the hydrophilicity of the membranes. Various tests, such as Pure water permeate (PWP), X-ray diffraction spectroscopy (XRD), Atomic force microscopy (AFM), Dynamic light scattering (DLS), Contact angle (CA), Scanning electronic microscopy (SEM), Fourier transform infrared substances (FTIR) were used to characterize the synthesized membranes. To evaluate the treated wastewater, several factors were evaluated, including: TP, TN, TSS, NTU, BOD, COD, EC. The contact angle was reduced by the inclusion of GO nanoparticles from 53.8° for PAN-0 to 45.4° for PAN-3. The results of FTIR analysis confirmed the synthesis of GO and showed the formation of different deposits as fouling on the surface of the prepared membranes after MBR process. Also, the removal percentage of COD and BOD₅ was over 90% for membranes with graphene oxide nanoparticles. The turbidity for all fabricated membranes were removed ∼98%. Also, very little fouling occurred in the membranes constructed with GO membranes and the maximum concentration of GO let to maximum performance regarding to the high potential of fouling control. In addition, the growth of Microalgae Dunaliella salina with shrimp wastewater was observed successfully. In conclusion, the finding of this work not only proposed a promising solution for controlling fouling in an MBR but also resulted in a benefit product, i.e. microalgae Dunaliella salina.

Advanced water treatment process by simultaneous coupling granular activated carbon (GAC) and powdered carbon with ultrafiltration: Role of GAC particle shape and powdered carbon type

In current ultrafiltration systems, limited removal for small-sized contaminants and membrane fouling remain longstanding obstacles to overcome. Herein, a novel process by simultaneous coupling powered carbon (PC) and fluidized granular activated carbon (GAC) with ultrafiltration was proposed aiming to achieve high effluent quality and mitigated membrane fouling. This study conducted mechanistic explorations on the performances of different-shaped GAC particles on fouling control and PC release during fluidization, meanwhile comparing the utilizations of powdered activated carbon (PAC) and biochar in terms of their adsorption, deposition and interactions with aquatic contaminants during filtration. The results showed that the effluent COD of biochar-UF was slightly higher than PAC-UF attributed to lower specific surface area and pore volume present on biochar. Compared with PAC-UF, the biochar-UF without fluidized GAC exhibited higher fouling propensity due to more organics attached on membranes via bridging with Ca²⁺ released by the biochar. Concurrently, distinct morphologies were found for PAC and biochar depositions, where PAC uniformly dispersed on membranes but biochar tended to agglomerate. Interestingly, fluidized spherical GAC (RGAC) with highest particle momentum and least energy consumption appeared highly effective in reducing fouling associated with biochar, and the overall fouling rate of RGAC-biochar-UF was even lower than RGAC-PAC-UF system. More importantly, substantial amount of small-sized PC was released by two cylindrical-shaped GACs, which were determined to be around 12-16 mg/L in contrast to merely 3.4 mg/L produced from RGAC. Consequently, the RGAC-biochar-UF system achieved commensurate effluent quality but better permeability than RGAC-PAC-UF along with a 20% expenditure saved, which might be a promising water treatment system more suitable for large-scale applications.

The comparison between two methods of membrane cleaning to control membrane fouling in a hybrid membrane photobioreactor (HMPBR)

In this study, the effect of two membrane cleaning methods, such as aeration and addition of granular particles in a hybrid membrane photobioreactor (HMPBR) including Spirulina sp. with the concentration of 1.5 g·L^-1 was investigated. Three different spargers [i.e., different diameters of orifice (d_o): 0.5, 1, and 1.5 mm] and granular particles (i.e., three packing ratios of 0.5, 1, and 1.5%) were used. The results showed that with the increase in granular packing ratio, R_c/R_t decreased significantly. The best result was achieved by combining aeration with an orifice diameter of 1.5 mm and a granular packing ratio of 1.5%, which led to the lowest R_c/R_t value (0.38), while R_c/R_t value with a d_o of 1.5 mm was 0.68 without particles. In contrast, the ratio of pore blocking resistance to total resistance (R_p/R_t) increased by 4.2% under the combined application of 1.5 mm of orifice diameter and 1.5% of granular packing ratio. The results from protein concentrations in the cake layer showed that as the d_o became larger, cake protein concentration decreased by 40%, whereas increasing the granular packing ratio from 0.5 to 1.5% increased protein concentration by 60% in the cake layer.

Effects of microplastic accumulation on floc characteristics and fouling behavior in a membrane bioreactor

Issues associated with accumulating microplastic (MP) in sewage sludge during wastewater treatment in a membrane bioreactor (MBR) system have not been studied in detail. Here, we investigated the microplastic's effects on floc characteristics, microbial community compositions, and fouling behavior inside sequencing-batch MBRs. MBRs were operated with 0, 7, 15, and 75 MPs/L of feed for 124-days. Results indicated that MP presence decreased sludge floc size, floc hydrophobicity, and extracellular polymeric substance (EPS) molecular size, and increased EPS concentration and the floc's negative zeta potential. These results were attributed to the facilitation of divalent cation (Ca²⁺ and Mg²⁺) uptake by MPs that weakened ion-bridging interactions within the sludge flocs. MPs accumulation slightly affected microbial structure and diversity. Relative abundances of dominant phyla, Actinobacteria, also decreased substantially. MPs also acted like a scouring material on membrane surfaces, inducing transformation of matured biofilm structures where protein content was substantially lower than nucleic acid content, in contrast to the control. Overall, MPs' negative effects on sludge flocs were counteracted by their scouring effect; consequently, SB-MBRs operated up to 4 months did not suffer from severe cake fouling, compared to control.

Combined Effect of Activated Carbon Particles and Non-Adsorptive Spherical Beads as Fluidized Media on Fouling, Organic Removal and Microbial Communities in Anaerobic Membrane Bioreactor

The combined effect of acrylonitrile butadiene styrene (ABS) spherical beads and granular activated carbon (GAC) particles as fluidized media on the performance of anaerobic fluidized bed membrane bioreactor (AFMBR) was investigated. GAC particles and ABS beads were fluidized together in a single AFMBR to investigate membrane fouling and organic removal efficiency as well as energy consumption. The density difference between these two similarly sized media caused the stratified bed layer where ABS beads are fluidized above the GAC along the membrane. Membrane relaxation was effective to reduce the fouling and trans-membrane pressure (TMP) below 0.25 bar could be achieved at 6 h of hydraulic retention time (HRT). More than 90% of soluble chemical oxygen demand (SCOD) was removed after 80 d operation. Biogas consisting of 65% of methane was produced by AFMBR, suggesting that combined use of GAC and ABS beads did not have any adverse effect on methane production during the operational period. Scanning Electron Microscope (SEM) examinations showed the adherence of microbes to both media. However, 16S rRNA results revealed that fewer microbes attached to ABS beads than GAC. There were also compositional differences between the ABS and GAC microbial communities. The abundance of the syntrophs and exoelectrogens population on ABS beads was relatively low compared to that of GAC. Our result implied that syntrophic synergy and possible occurrence of direct interspecies electron transfer (DIET) might be facilitated in AFMBR by GAC, while traditional methanogenic pathways were dominant in ABS beads. The electrical energy required was 0.02 kWh/m3, and it was only about 13% of that produced by AFMBR.

Impact of static biocarriers on the microbial community, nitrogen removal and membrane fouling in submerged membrane bioreactor at different COD:N ratios

The polyvinyl formal (PVFM) biocarrier addition in a membrane bioreactor (MBR) was evaluated at high and low carbon/nitrogen (C/N) ratio of 20.0 and 6.7. Results indicated that static biocarrier addition could enrich nitrification and denitrification bacteria, dominating by Tauera, Amaricoccus and Nitrosospira at the genus level and slightly improved the total nitrogen removal even at a low C/N ratio. The bulk sludge characteristics (such as bigger particle size, lower SMP, lower SMP P/C) were also significantly changed in the hybrid MBR (HMBR), leading to a more sustainable membrane operation. The biocarrier addition also reduced the relative abundance of Sphingobacterials_unclassified, Ohtaekwangia and Rhodocyclaceae_unclassified at the genus level, indicating less membrane fouling in the HMBR. Consequently, HMBR with static PVFM addition could partially overcome the drawback of low C/N ratio for total nitrogen removal and membrane fouling control, providing a more resilient MBR to the undesirable environment such as low C/N ratio.

Feasibility of isolated novel facultative quorum quenching consortiums for fouling control in an AnMBR

Anaerobic membrane bioreactor (AnMBR) technology is being recognized as an appealing strategy for wastewater treatment, however, severity of membrane fouling inhibits its widespread implementations. This study engineered novel facultative quorum quenching consortiums (FQQs) coping with membrane fouling in AnMBRs with preliminary analysis for their quorum quenching (QQ) performances. Herein, Acyl-homoserine lactones (AHLs)-based quorum sensing (QS) in a lab-scale AnMBR initially revealed that N-Hexanoyl-dl-homoserine lactone (C6-HSL), N-Octanoyl-dl-homoserine lactone (C8-HSL) and N-Decanoyl-dl-homoserine lactone (C10-HSL) were the dominant AHLs in AnMBRs in this study. Three FQQs, namely, FQQ-C6, FQQ-C8 and FQQ-C10, were harvested after anaerobic screening of aerobic QQ consortiums (AeQQs) which were isolated by enrichment culture, aiming to degrade C6-HSL, C8-HSL and C10-HSL, respectively. Growth of FQQ-C6 and FQQ-C10 using AHLs as carbon source under anaerobic condition was significantly faster than those using acetate, congruously suggesting that their QQ performance will not be compromised in AnMBRs. All FQQs degraded a wide range of AHLs pinpointing their extensive QQ ability. FQQ-C6, FQQ-C8 and FQQ-C10 remarkably alleviated extracellular polymeric substances (EPS) production in a lab-scale AnMBR by 72.46%, 35.89% and 65.88%, respectively, and FQQ-C6 retarded membrane fouling of the AnMBR by 2 times. Bioinformatics analysis indicated that there was a major shift in dominant species from AeQQs to FQQs where Comamonas sp., Klebsiella sp., Stenotrophomonas sp. and Ochrobactrum sp. survived after anaerobic screening and were the majority in FQQs. High growth rate utilizing AHLs under anaerobic condition and enormous EPS retardation efficiency in FQQ-C6 and FQQ-C10 could be attributed to Comamonas sp.. These findings demonstrated that FQQs could be leveraged for QQ under anaerobic systems. We believe that this was the first work proposing a bacterial pool of facultative QQ candidates holding biotechnological promises for membrane fouling control in AnMBRs.

Impact of sludge recirculation ratios on the performance of anaerobic membrane bioreactor for wastewater treatment

The performance of a lab scale anaerobic membrane bioreactor (AnMBR) was evaluated for wastewater treatment. The efficacy of the system was determined at different operating conditions in terms of fluxes and recirculation ratios (R); 10.28 L/m² h (R = 1, Phase I), 8.8 L/m² h (R = 2, Phase II and R = 3, Phase III) and 6 L/m² h (R = 2, Phase IV and R = 3, Phase V), respectively. In comparison with all the operating conditions tested, optimum efficacy of the system was found at flux of 6 L/m² h and R of 3 in terms of highest COD removal (96.7%), and maximum biogas yield (0.44 L/g COD_removed). The MLSS and MLVSS concentrations under optimum phase were 6.23 and 4.83 g/L, respectively at OLR of 0.46 kg COD/m³ day. The system also exhibited significant reduction of foulants i.e. extracellular polymeric substances (EPS) and soluble microbial products (SMP) resulting in longer membrane runs in optimized phase.

Intensive membrane cleaning for MBRs equipped with flat-sheet ceramic membranes: Controlling negative effects of chemical reagents used for membrane cleaning

Intensive membrane cleaning can be used with ceramic membranes since they are physically/chemically robust. It might therefore be possible for membrane bioreactors (MBRs) to be operated under the condition of a high membrane flux when ceramic membranes are used with such intensive membrane cleaning. In this study, bench-scale MBRs equipped with flat-sheet ceramic membranes were operated for long periods. Circulation of granular materials (cylindrical polyurethane) in the tank and frequent chemically enhanced backwash (CEB) were used as intensive physical cleaning and chemical cleaning in this study, respectively. Experiments were carried out with synthetic wastewater. The use of granular materials, which can cause significant damage to polymeric membranes (Kurita et al., 2015), was effective for controlling the formation of cake (deposition of microbial flocs) on the surface of the ceramic membranes. When both mechanical cleaning using the granular materials and CEB with 1000 ppm of sodium hypochlorite (NaClO) were applied, contrary to an expectation, evolution of reversible fouling (formation of a transparent gel layer on the membrane surface) became uncontrollable, whereas irreversible fouling was effectively controlled. The use of NaClO induced release of organic macromolecules via biomass decay, leading to the evolution of reversible fouling. When the intensity of CEB with NaClO was adequately lowered, with the aid of the mechanical cleaning using the granules, the bench-scale MBR could be operated stably under an elevated membrane flux for a long period (>70 days). It was postulated that the adjustment of CEB intensity preferably altered properties of organic macromolecules released from biomass: the structure of the gel layer was porous when the CEB intensity was lowered. When CEB is used in MBRs, it is thus important to balance cleaning efficiency and its harmful effect on biomass. When adequate CEB is used with intensive mechanical cleaning, MBRs with ceramic membranes can be operated under high flux conditions.

A Brief Review on the Resistance-in-Series Model in Membrane Bioreactors (MBRs)

The cake layer deposited on the membrane modules of membrane bioreactors (MBRs), especially under a submerged configuration, represents a relevant and fundamental mechanism deeply influencing the development of membrane fouling. It negatively affects the total resistance to filtration, while exerting a positive effect as a "pre-filter" promoting the "dynamic membrane" that protects the physical membrane from internal fouling. These two opposite phenomena should be properly managed, where the submerged membranes are usually subjected to a periodical cake layer removal through ordinary (permeate backwashing and air scouring) and/or irregular cleaning actions (manual physical cleaning). In this context, the physical removal of the cake layer is needed to maintain the design filtration characteristics. Nevertheless, the proper evaluation of the effect of physical cleaning operations is still contradictory and under discussion, referring in particular to the correct evaluation of fouling mechanisms. The aim of the present work was to summarize the different aspects that influence the fouling investigations, based on simple models for the evaluation of the resistance to filtration due to the cake layer, through physical cleaning operations.

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

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

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

Gas sparging is used as a traditional way to control membrane fouling in submerged membrane bioreactors (MBRs) in wastewater treatment. However, the gas sparging accounts for the largest fraction in operational cost to run the MBR systems. In this study, membrane fouling was controlled by integrating scouring media with gas sparging to reduce fouling rate at relatively low operational energy. Comparative study was performed using a fluidized membrane reactor treating synthetic feed solutions between polyethylene terephthalate (PET) scouring media (SM) fluidized by gas sparging (GS), liquid recirculation (LR), and combination of them to control membrane fouling. Addition of PET scouring media reduced the gas flow rate by 67% more with 30% less in fouling rate than gas sparing only. Combined usage of gas sparging and liquid recirculation to fluidize the PET scouring media (LR + GS + SM) showed 37% lower in fouling rate than that obtained by the scouring media fluidized by liquid recirculation (LR + SM) only through the reactor. The LR + GS + SM configuration reduced energy consumption by 90% more than that required by gas sparging alone. Mechanical cleaning driven by fluidizing PET scouring media could reduce membrane fouling due to removing deposit of inorganic particles from membrane surface effectively. However, the PET scouring media was not very effective to reduce membrane fouling caused by organic colloids which are expected to contribute pore fouling significantly.

Development of a new method for measuring the abrasive potential of water: risk of membrane failure in water treatment plants

The objectives of this study were to develop an analytical method to distinguish feed water used to produce drinking water, with varying concentrations of suspended solids, in terms of abrasiveness and to define an index that can assess the abrasive potential of the feed water coming in contact with a polymeric membrane. For such process configurations, membrane abrasion has been identified as one of the most recurring and major concerns in operation because the polymeric materials used in treatment plants are relatively sensitive to abrasion. Five different types of apparatus were benchmarked and were evaluated on their ability to be adapted to particles commonly found in most drinking water treatment plants at low concentrations. After comparing 10 criteria, the MCR302 with a tribological cell of Anton Paar was identified as the most relevant device. For the selected tool (MCR302), a statistical approach was used to provide a safe and robust ranking of the abrasive potential of the different types of water. An analysis of variance allowed the origin of the result variability to be explained. The newly developed methodology enables quantification of the abrasive potential of natural waters used for membrane filtration with a relevance of ranking higher than 90%.

Critical review of fouling mitigation strategies in membrane bioreactors treating water and wastewater

The current research was an effort to critically review all approaches used for membrane fouling control in the membrane bioreactors treating water and wastewater. The first generation of antifouling methods tried to optimize operational conditions, or used chemical agents to control membrane fouling. Despite their positive impacts on the fouling mitigation, these methods did not provide a sustainable solution for the problem. Moreover, chemical agents may affect microorganisms in bioreactors and has some environmental drawbacks. The improved knowledge of membrane fouling mechanism and effective factors has directed the attention of researchers to novel methods that focus on disrupting fouling mechanism through affecting fouling causing bacteria. Employing nanomaterials, cell entrapment, biologically- and electrically-based methods are the latest efforts. The results of this review indicate that sustainable control of membrane fouling requires employing more than one single approach. Large scale application of fouling mitigation strategies should be the focus of future studies.

Membrane fouling control in membrane bioreactors (MBRs) using granular materials

Membrane fouling is considered the major limitation of membrane bioreactors (MBRs). This paper provides an overview on fouling mitigation in MBRs using granular materials. Adsorbents addition extends filtration period, improves critical flux as well as sludge properties (increased flocs size, reduced soluble EPS, improved dewaterability). However, determination of optimal dosages of adsorbents is needed to balance cost savings from fouling mitigation versus cost of adsorbents and sludge handling. The abrasion from granular media reduces cake layer formation, extends membrane filtration period, increases flux (∼20-30%), and reduces aeration intensity by 50%. Finding appropriate aeration intensity and optimum dose for different media is critical for full-scale application. Granular sludge substantially reduces fouling in MBRs; but, optimal operational conditions for long-term granule stability are required. Quorum quenching (QQ) mitigates biofouling (energy savings ∼27-40%). Cost savings from QQ need assessment against the production and application of QQ approaches.

Membrane Bioreactor (MBR) Technology for Wastewater Treatment and Reclamation: Membrane Fouling

The membrane bioreactor (MBR) has emerged as an efficient compact technology for municipal and industrial wastewater treatment. The major drawback impeding wider application of MBRs is membrane fouling, which significantly reduces membrane performance and lifespan, resulting in a significant increase in maintenance and operating costs. Finding sustainable membrane fouling mitigation strategies in MBRs has been one of the main concerns over the last two decades. This paper provides an overview of membrane fouling and studies conducted to identify mitigating strategies for fouling in MBRs. Classes of foulants, including biofoulants, organic foulants and inorganic foulants, as well as factors influencing membrane fouling are outlined. Recent research attempts on fouling control, including addition of coagulants and adsorbents, combination of aerobic granulation with MBRs, introduction of granular materials with air scouring in the MBR tank, and quorum quenching are presented. The addition of coagulants and adsorbents shows a significant membrane fouling reduction, but further research is needed to establish optimum dosages of the various coagulants/adsorbents. Similarly, the integration of aerobic granulation with MBRs, which targets biofoulants and organic foulants, shows outstanding filtration performance and a significant reduction in fouling rate, as well as excellent nutrients removal. However, further research is needed on the enhancement of long-term granule integrity. Quorum quenching also offers a strong potential for fouling control, but pilot-scale testing is required to explore the feasibility of full-scale application.

Crossing the Border between Laboratory and Field: Bacterial Quorum Quenching for Anti-Biofouling Strategy in an MBR

Quorum quenching (QQ) has recently been acknowledged to be a sustainable antifouling strategy and has been investigated widely using lab-scale membrane bioreactor (MBR) systems. This study attempted to bring this QQ-MBR closer to potential practical application. Two types of pilot-scale QQ-MBRs with QQ bacteria entrapping beads (QQ-beads) were installed and run at a wastewater treatment plant, feeding real municipal wastewater to test the systems' effectiveness for membrane fouling control and thus the amount of energy savings, even under harsh environmental conditions. The rate of transmembrane pressure (TMP) build-up was significantly mitigated in QQ-MBR compared to that in a conventional-MBR. Consequently, QQ-MBR can substantially reduce energy consumption by reducing coarse bubble aeration without compromising the effluent water quality. The addition of QQ-beads to a conventional MBR substantially affected the EPS concentrations, as well as microbial floc size in the mixed liquor. Furthermore, the QQ activity and mechanical stability of QQ-beads were well maintained for at least four months, indicating QQ-MBR has good potential for practical applications.

Application of glyco-blotting for identification of structures of polysaccharides causing membrane fouling in a pilot-scale membrane bioreactor treating municipal wastewater

A new approach for the analysis of polysaccharides in membrane bioreactor (MBR) is proposed in this study. Enrichment of polysaccharides by glyco-blotting, in which polysaccharides are specifically collected via interactions between the aldehydes in the polysaccharides and aminooxy groups on glycoblotting beads, enabled MALDI-TOF/MS analysis at a high resolution. Structures of polysaccharides extracted from fouled membranes used in a pilot-scale MBR treating municipal wastewater and those in the supernatant of the mixed liquor suspension in the MBR were investigated. It was found that the overlap between polysaccharides found in the supernatants and those extracted from the fouled membrane was rather limited, suggesting that polysaccharides that dominate in supernatants may not be important in membrane fouling in MBRs. Analysis using a bacterial carbohydrate database suggested that capsular polysaccharides (CPS) and/or lipo-polysaccharides (LPS) produced by gram-negative bacteria are key players in the evolution of membrane fouling in MBRs.

Direct membrane filtration of municipal wastewater with chemically enhanced backwash for recovery of organic matter

Direct membrane filtration (DMF) of municipal wastewater using a microfiltration membrane was investigated to capture organic matter. In contrast to the expectation that membrane fouling cannot be controlled in DMF of domestic wastewater, it was possible to stably continue membrane filtration with relatively high membrane fluxes (∼20 LMH) for >200 h by applying chemically enhanced backwash (CEB), whereas approximately 75% of the organic matter in wastewater could be recovered. Off-line chemical membrane cleaning could completely restore membrane permeability, indicating the possibility of a much longer operation of DMF. Selection of chemical reagents used for CEB was found to influence the amount of organic matter recovered by DMF. Based on the experimental results, feasibility of DMF was discussed by a comparison with a conventional wastewater treatment plant treating the same wastewater as studied in this study.

Tracing biofouling to the structure of the microbial community and its metabolic products: a study of the three-stage MBR process

The biofouling characteristics of a sequential anoxic/aerobic-membrane bioreactor (A/O MBR) were analyzed during the three-stage process (fast-slow-fast transmembrane pressure (TMP) increasing). The results indicated: during the stage 1 (before day 1), the microbial communities in the activated sludge (AS), cake sludge (CS) and biofilm (BF) were similar to each other, and the adsorption of microbes and the metabolic products was the main factor that led to TMP increase; during the stage 2 (between day 1 and day 7), the cake layer begun to form and the TMP continued to rise gradually at a reduced rate compared to stage 1, at this point a characteristic microbial community colonized the CS with microorganisms such as Saprospiraceae and Comamonadaceae thriving on the membrane surface (BF) probably due to greater nutrient availability, and the predominance of these species in the microbial population led to the accumulation of biofouling metabolic products in the CS, which resulted in membrane fouling and the associated rise in TMP; during the final stage (after day 7), the biofilm had matured, and the activity of anaerobes stimulated cake compaction. The statistical analysis showed a correlation between the TMP changing rate and the carbonhydrates of soluble microbial products (SMPc) content in the CS. When the SMPc concentration rose slowly there was a low level of biofouling. However, when the SMPc accumulating rate was greater, it resulted in the more severe biofouling associated with the TMP jump. Furthermore, the correlation coefficient for the TMP increase and protein concentrations of extracellular polymeric substances (EPSp) in the CS was highly significant. The cluster analysis suggested that the AS microbial community remained stable during the three TMP change stages, while the CS and BF community were changed accompanied with the TMP change. The interaction between the microbial communities and the metabolic products lead to the significant correlation between them. The EPSp in conjunction with the SMPc were the main factors that accelerate the membrane fouling. The rapid rise of SMPc triggered a sudden increase in the TMP, while the accumulation of EPSp caused the sustained rise in TMP.

Performance of submerged membrane bioreactor (SMBR) with and without the addition of the different particle sizes of GAC as suspended medium

In this study the effect of different particle sizes of granular activated carbon (GAC) on the performance of a submerged membrane bioreactor (SMBR) was investigated. The sizes of GAC used were 150-300, 300-600 and 600-1200 μm. The SMBR was operated at a filtration flux of 20 L/m(2)h. The removal of dissolved organic carbon (DOC) and chemical oxygen demand (COD) with the addition of GAC was 95%. The concentration of biopolymers, humic, building block and low molecular weight neutral and acids in the SMBR effluent was reduced by 20%, 66-76%, 20-50%, 30-56%, respectively. It helped to reduce the sludge volume index (SVI) and transmembrane pressure (TMP) development by 30-40% and 58%, respectively. However, the removal of NH₄(+) and PO₄(3-) was relatively low of 35-45% and 34-43%, respectively. The SMBR effluent was rich in PO₄(3-) and was removed/recovered using hydrated ferric oxide (HFO). The removal of PO₄(3-) was almost 90%.

The membrane fouling characteristics of MBRs with different aerobic granular sludges at high flux

This experimental work investigated the property of membrane fouling for different sludges at high flux 20 L/(m(2)h). The MBR with good aerobic granular sludge performed the longest operation time 61 days, and TMP rose up in a steady overall rate, while only 10, 14 and 19 days for bulking, flocculent and small granular sludge, respectively, which clearly demonstrated the good and complete aerobic granules greatly retarded the membrane fouling. The pore blocking resistance 76.21% was the key fouling factor for aerobic granules, but the cake resistance 61.23% or 79.02% was the main factor for flocculent or bulking sludge. The difference in EPS composition of membrane foulants between granules MBR and flocculent sludge MBR led to the different behaviour of fouling. Aerobic granules were quite stable during operation. These results suggested MBR with aerobic granules might be operated at high flux, which was very valuable for practical application.