Pilot-scale Membrane Bioreactor Research Articles

Evaluation of the shear stability of aerobic granular sludge from a pilot-scale membrane bioreactor: Establishment of a quantitative method

This work established a quantitative method to access the shear stability of aerobic granular sludge (AGS) and validated its feasibility by using the mature AGS from a pilot-scale (50 tons/day) membrane bioreactor (MBR) for treating real municipal wastewater. The results showed that the changing rate (ΔS) of the peak area (S) of granule size distribution (GSD) exhibited an exponential relationship (R2≥0.76) with the shear time (y=a−b·cx), which was a suitable indicative index to reflect the shear stability of different AGS samples. The limiting granule size (LGS) was defined and proposed to characterize the equilibrium size for AGS after being sheared for a period of time, whose value in terms of Dv50 showed high correlation (R2=0.92) with the parameter a. The free Ca2+ (28.44–34.21 mg/L) in the influent specifically interacted with polysaccharides (PS) in the granule's extracellular polymeric substance (EPS) as a nucleation site, thereby inducing the formation of Ca precipitation to enhance its Young's modulus, while Ca2+ primarily interacted with PS in soluble metabolic product (SMP) during the initial granulation process. Furthermore, the Young's modulus significantly affected the parameter a related to shear stability (R2=0.99). Since the parameter a was more closely related (R2=1.00) to ΔS than that of the parameter b or c, the excellent correlation (R2=0.99) between the parameter a and the wet density further verified the feasibility of this method.

Evaluating the performance and membrane fouling of a submerged membrane bioreactor (MBR) treating plywood industry wastewater.

This study evaluates the performance of a membrane bioreactor (MBR) for treating wastewater from the laminated plywood industry. To this end, a pilot-scale MBR was operated for 60 days with a hydraulic retention time of 20 h and a solid retention time of 20 days. The reactor's performance was assessed based on the removal of chemical oxygen demand (COD), phenol, turbidity, and apparent color. Furthermore, we monitored the solids content, dissolved oxygen concentration, and pH of the mixed liquor, as well as the progression of the transmembrane pressure (TMP). The wastewater exhibited a COD/biochemical oxygen demand (BOD) ratio of 5.5, suggesting low biodegradability, usually when this ratio is higher than 4.0. Nevertheless, it was observed that the MBR's performance was stable and satisfactory, with average removal efficiencies of 98% for COD, 70% for phenol, 99% for turbidity, and 93% for true color. The evolution of TMP indicated gradual membrane fouling; however, the operational limit of 0.6 bar was not reached during the study period. In conclusion, the utilization of MBR presents a promising approach to mitigate the environmental impacts associated with wastewater from the laminated plywood industry.

Integration of Membrane Bioreactor and Reverse Osmosis for Textile Wastewater Treatment and Reclamation: A Pilot-Scale Study

Membrane bioreactor (MBR) technology, a combination of traditional activated sludge and membrane filtration, has been widely used for industrial wastewater treatment and reclamation. This paper highlights a pilot-scale MBR system treating textile wastewater from a textile factory in Taiwan. Over 7 months of continuous operation, the average MBR influent chemical oxygen demand (COD) is 332 mg/L, and the average effluent COD is 38 mg/L, which results in approximately 88% COD removal. A reverse osmosis (RO) module is installed after 2 months of MBR operation and uses the MBR permeate as its influent. The RO produces pure water with average COD, conductivity, and color of 7 mg/L, 16 μS/cm, and 7 Pt-Co, respectively. The RO permeate is suitable for reuse in manufacturing processes, and the RO membrane shows stable performance with TMP, which is less than or equal to 0.5 kg/cm2 during the test. The study demonstrates the great feasibility of MBR combined with RO for treating and reclaiming textile wastewater.

Greywater treatment performance of a pilot-scale membrane bioreactor and characteristics of bacterial biofilm signatures in permeate effluent

Treated greywater has a high potential for water reuse. However, the post-treatment processes of reclaimed greywater may face biofouling problems due to biofilm formation. In the present study, the greywater treatment performance of a pilot-scale membrane bioreactor (MBR) was evaluated, and the effect of a dominant bacterial biofilm growing on the Pall ring media placed in the permeate pipeline was investigated. The MBR was operated for 125 days with a constant hydraulic retention time of 2 days under complete sludge retention. The treatment performance in terms of the levels of organic compounds, ammonium nitrogen, suspended solids, total coliforms, and Escherichia coli was >90 %. During the operation, a high relative abundance (>70 %) of the following bacterial phyla was observed within the MBR and the bacterial biofilm: Proteobacteria, Chloroflexi, Actinobacteria, and Planctomycetes. Furthermore, the following bacterial orders were predominantly observed in the biofilm: Sphingomonadales, Burkholderiales, and Planctomycetes. Acidovorax, Methylibium, Blastomonas, and Planctomyces were the important genera identified in the biofilm. Interestingly, the present study revealed that these bacterial species were predominant and well adapted in treated greywater containing various surfactant and detergent components. Knowledge of the predominant bacterial species in the biofilm could enable to select the appropriate disinfection method and prevent the biofouling of the reverse osmosis (RO) membrane, which can facilitate further application of the MBR-RO process for water reuse.

Optimization of the operating parameters in a membrane bioreactor operated in direct-flow mode by assessing threshold flux for compressibility

Direct-flow filtration (i.e., without membrane aeration during the filtration phase) is a challenging operation strategy in membrane bioreactors (MBRs). This study aims to provide a comprehensive approach for assessing optimal values for the main operating parameters (filtration time between backwashes and permeate flux) through the determination of the threshold flux for compressibility (Jth,c). A pilot-scale tertiary MBR was used for conducting filtration tests. Flux-step trials revealed the crucial role of cake compressibility in fouling deposition and reversibility. Accordingly, the compressible cake model was used to investigate Jth,c under different operating conditions and suspension characteristics. Based on this approach, lower filtration times (5–7 min) are recommended so that sustainable process productivity can be maximized. Specifically, decreasing filtration times from 12 to 7 min results in net permeate flux increase of more than 50%. A significant effect of suspension properties (biopolymer cluster content, BPC) on Jth,c was also found which decreased from 41.9 to 13.0 L/h m2 when increasing BPC from 0.3 to 4.6 mg/L. Long-term tests, under temporized and variable filtration time modes, demonstrate the feasibility of using the Jth,c as a guideline for optimizing filtration performance.

Quantitative and qualitative variations of biopolymers in a pilot-scale membrane bioreactor treating municipal wastewater throughout 3 years of operation

In this study, the fouling potential of mixed liquor suspension samples collected from a pilot-scale membrane bioreactor (MBR) that treated municipal wastewater was monitored for more than 3 years. The fouling potential was assessed by batch filtration experiments using the same type of membrane as equipped in the MBR. The fouling potential increased when the temperature of the mixed liquor suspension in the MBR decreased. However, the polysaccharide and protein concentrations in the mixed liquor suspension, which have been focused on many previous studies, did not correlate with the fouling potential (R2 = 0.15 and 0.39, respectively). In contrast, the concentration of biopolymers, quantified by liquid chromatography–organic carbon detection (LC-OCD), exhibited a marked correlation with the fouling potential (R2 = 0.89). A high concentration of biopolymers with large molecular weight (>1 million Da) was likely responsible for the high fouling potential. Fourier transform infrared (FTIR) analysis of the dissolved organic matter in the mixed liquor suspension indicated that the chemical properties of the biopolymers considerably varied with the seasonal temperature variation, which has rarely been reported and gives insights into fouling in MBRs. The effect of temperature on the biopolymer concentration and molecular weight of biopolymers was also investigated in a separate bench-scale experiment in which temperature was controlled. It was clearly shown that a low temperature induced an increase in the biopolymer concentration and an associated increase in the fouling potential of the mixed liquor suspension.

MEMBRANE BIOREACTOR APPLIED TO THE TREATMENT OF A FRUIT PROCESSING INDUSTRY WASTEWATER IN NORTHEAST BRAZIL

The market for Membrane Bioreactors (MBR) technology has recently grown due to increasingly strict standards for effluent discharge and the need for alternative water sources. The high quality of the effluent produced, enabling the possibility of reuse is one of the most attractive characteristics of this technology. The objective of this article was to evaluate the treatment efficiency of a pilot-scale MBR plant in a fruit processing industry, including an analysis of the possibilities for effluent reuse. The pilot plant comprised a MBR with approximately 5000L in capacity, with porous type ultrafiltration grade polyethersulfone membranes. Other details for the membranes were: submerged configuration, flat plate type geometry, pore diameter ranging from 0.035 to 0.1 μm and total area of 25m². The industrial effluent came from fruits processing, floors and machinery washing, and was characterized by physical, chemical and bacteriological parameters. Results showed that permeability decreased about 50% during the monitoring, indicating the need of membrane cleaning. The removal efficiency for COD, BOD 5 , total nitrogen and total phosphorus, was 97.1%, 98.7%; 95.7 % and 53.5%, respectively. There was an absence of both total coliform and E. Coli at the inlet and outlet of the system. The permeate fits into agricultural, urban, environmental, industrial and aquaculture reuse modalities.

The Pilot Study of the Influence of Free Ammonia on Membrane Fouling during the Partial Nitrosation of Pig Farm Anaerobic Digestion Liquid.

The problem of membrane fouling is a key factor restricting the application of the membrane bioreactor (MBR) in the partial nitrosation (PN) and anaerobic ammonia oxidation (anammox) processes. In this study, the pilot-scale continuous flow MBR was used to start up the partial nitrosation process in order to investigate the change trend of mid-transmembrane pressure (TMP) in the process of start-up, which was further explored to clarify the membrane fouling mechanism in the pilot-scale reactor. The results showed that the MBR system was in a stable operating condition during the partial nitrosation operation and that the online automatic backwash operation mode is beneficial in alleviating membrane fouling and reducing the cost of membrane washing. Particular attention was paid to the influence trend of free ammonia (FA)on membrane fouling, and it was found that the increase in FA concentration plays the most critical role in membrane fouling. The increase in FA concentration led to an increase in the extracellular polymer (EPS), dissolved microorganism product (SMP) and soluble chemical oxygen demand (SCOD) concentration. FA was extremely significantly correlated with EPS and SCOD, and the FA concentration was approximately 20.7 mg/L. The SCODeff (effluent SCOD concentration) concentration was approximately 147 mg/L higher than the SCODinf (influent SCOD concentration) concentration. FA mainly affects membrane fouling by affecting the concentration of EPS and SCOD.

Improving control of membrane fouling on membrane bioreactors: A data-driven approach

Despite the widespread application and plentiful benefits of membrane bioreactors (MBR), this technology is constrained by membrane fouling, which is regarded as the most serious drawback of process efficiency, especially for treating complex industrial wastewater. In order to control membrane fouling, a large set of variables that are often strongly correlated must be investigated and therefore data mining techniques can be used to extract relevant information from monitoring data sets. This work investigates the relations between different analytic and operating variables (mixed liquor volatile suspended solids, sludge filterability, pH, chemical oxygen demand of the feed, temperature, sequential days without cleaning (SDWC) and membrane permeability) of a pilot-scale MBR treating an oil refinery wastewater by applying Principal Components Analysis (PCA) and Multivariate Statistical Process Control (MSPC). The analyses were performed in R based on a five-year monitoring database. PCA identified sludge filterability, temperature and SDWC as the most influential variables on membrane permeability and it was effective in predicting MBR performance (R2 = 0.71 and Q2 = 0.78), enabling to detect atypical observations and thus identify operating faults. Besides, T2 and Q control charts were able to detect 100% and 96%, respectively, of the low membrane permeability operation (lower than 100 L h−1 m−2 bar−1) and also to alert preventively about permeability decrease. Therefore, the multivariate control charts could be applied as tools for supporting the decision-making regarding fouling control, e.g., guiding when to perform chemical cleanings and/or dose membrane permeability improvers.

Effect of Operating Conditions on Membrane Fouling in Pilot-Scale MBRs; Filaments Growth, Diminishing Dissolved Oxygen and Recirculation Rate of the Activated Sludge.

This is the first study that examines the effect of operating conditions on fouling of Membrane Bio-Reactors (MBRs), which treat municipal wastewater in field conditions, with specific regard to the controlled development of filamentous microorganisms (or filaments). The novelty of the present work is extended to minimize the dissolved oxygen (DO) in recirculated activated sludge for improving the process of denitrification. For this purpose, two pilot-scale MBRs were constructed and operated in parallel: (i) Filament-MBR, where an attempt was made to regulate the growth of filaments by adjustment of DO, the Food-to-Microorganisms (F/M) ratio and temperature, and (ii) Control-MBR, where a gentle stirring tank was employed for the purpose of zeroing the DO in the recycled sludge. Results showed that low temperature (<15 °C) slightly increased the number of filaments in the Filament-MBR which, in turn, decreased the Trans-Membrane Pressure (TMP). As the Soluble Microbial Products (SMP) and the colloids are considered to be the basic foulants of membranes in MBR systems, specific attention was directed to keep their concentration at low values in the mixed liquor. The low F/M ratio in the aeration tanks which preceded the membrane tank was achieved to keep the SMP proteins and carbohydrates at very low values in the mixed liquor, i.e., less than 6 mg/L. Moreover, as a result of the low recirculation rate (2.6∙Qin), good aggregation of the produced excess sludge was achieved, and low concentration of colloids with a size ≤50 nm (nearly the membranes’ pore size used for filtration/separation) was measured, accounted for maximum 15% of the total colloids. Additionally, the increase in filamentous population at the Filament-MBR contributed to the further reduction of colloids in the mixed liquor at 7.9%, contributing beneficially to the reduction of TMP and of membrane fouling. The diminishing of DO in the recirculated sludge improved denitrification, and resulted in lower concentrations of Ν-NO3− and TN in the effluent of the Control-MBR. Furthermore, the recirculation rate of Qr = 2.6∙Qin, in comparison with Qr = 4.3∙Qin, resulted in improved performance regarding the removal of N-NH4+. Finally, high organics removal and ammonium nitrification was observed in the effluent of both pilots, since COD and Ν-ΝH4+ concentrations were generally in the range of 10–25 mg/L and <0.1 mg/L, respectively.

Effect of prolonged sludge retention times on the performance of membrane bioreactor and microbial community for leachate treatment under restricted aeration

Leachate treatment is challenging owing to the complex composition of pollutants. This study investigated the treatment performance of a membrane bioreactor (MBR) and the microbial community structure corresponding to the effect of prolonged sludge retention times (SRTs) under restricted aeration. In the present study, a pilot-scale MBR was designed to treat leachate after being pretreated with an anaerobic filter for continuous operation for 240 days. The experimental results showed that removal performance of over 90% was achieved for biochemical oxygen demand, total Kjeldahl nitrogen, ammonia-nitrogen, and suspended solids when the MBR was operated at SRTs of 150–300 days. The results on microbial communities revealed that Proteobacteria, Bacteroidetes, Firmicutes, Planctomycetes, Chloroflexi, and Actinobacteria were the major phyla. Furthermore, ammonia-oxidizing bacteria belonging to Nitrosomonadaceae were considered to play a vital role in the ammonia-nitrogen removal. A high abundance of Rhizobiales was detected on the biofilm of the membrane, which could be the key driver of bio-fouling. The dynamic changes in the microbial community indicate steady performance of MBR and can act as an indicator of membrane bio-fouling. The results of our study highlight that MBR can be viably operated in long SRTs under restricted aeration for leachate treatment with technical, economic, and environmental feasibility for resource recovery.

Intensive monitoring of sludge filterability of a pilot-scale membrane bioreactor treating municipal wastewater for better interpretation of fouling

In this study, a pilot-scale membrane bioreactor (MBR) treating municipal wastewater was operated over 600 d. Intensive monitoring of sludge filterability with high frequency, which is rarely reported in previous studies, was performed. Detailed information on sludge filterability obtained in this study makes the advanced interpretation of membrane fouling possible and allows to take effective countermeasures. Two methods (batch membrane filtration and measurement of capillary suction time (CST)) were used to assess sludge filterability, which significantly varies during the long-term operation. Although these two methods generated similar data, the CST measurement is easier than batch-filtration and is therefore recommended for intensive monitoring of sludge filterability in MBRs. Using the data obtained in this study, the evolution of reversible and irreversible fouling was distinguished. The importance of separately assessing the impact of colloidal matter on sludge filterability was also demonstrated: colloidal matter caused the deterioration of sludge filterability. To detect such impacts, the frequency of the assessment should be sufficiently high. A new method (modification of CST measurement) proposed in this study could be used for such frequent assessments. Temperature in the reactor and ion balance in raw wastewater were identified as key factors in the deterioration of sludge filterability. A specific fraction of polysaccharides (lipopolysaccharides) exhibited a significant correlation with the deterioration of sludge filterability. This study can provide important information for the operation and maintenance of large-scale MBRs treating municipal wastewater.

Long-Term Operation of a Pilot-Scale Membrane Bioreactor Treating Brewery Wastewater: Relaxation as a Method for Detection of Membrane Fouling

AbstractFouling control and operation below critical fluxes are relevant for operating membrane bioreactors (MBRs). Within this study, the long-term performance of a pilot-scale MBR was characteriz...

Study and Treatment of Medical Liquid Waste, Raipur Chhattisgarh, India

Hospitals discharge considerable amounts of chemicals and microbial agents in their wastewaters. Problem chemicals present in hospital wastewater belong to different groups, such as antibiotics, X-ray contrast agents, disinfectants and pharmaceuticals. Many of these chemical compounds resist normal wastewater treatment. They end up in surface waters where they can influence the aquatic ecosystem and interfere with the food chain. Humans are particularly exposed by the drinking water, produced from surface water. Microbial agents of special concern are multiresistant microbial strains. The latter are suspected to contribute to the spread of antibiotic resistance. In this paper, we will discuss the different approaches towards hospital wastewater treatment. The principle of uncoupling hospitals from public sewers warrants in depth evaluation by technologists and ecotoxicologists as well as public health specialists. A pilot-scale membrane bioreactor (MBR) was installed and operated for 75 days at laboratory. It was fed an influent directly from the hospital drainage collection system. To study pharmaceutics compounds toxicity with micro pollutant concentrations ranging from low ng /L to mg/L, toward activated sludge. Lab scale experiments were conducted and microscopic techniques as confocal laser scanning microscopy (CLSM). Samples were observed using confocal scanning laser microscopy to characterize the extracellular polymeric substances of sludge (EPS content). The study was focused on efficacy the membrane bioreactor in treatment the hospital effluent and the extra cellular polymeric substances (EPS) as indicator of bacteria sensitivity to toxic agents. Results suggested that after 20 days of exposure the pharmaceuticals compounds induced a significant increase of concentration soluble EPS in flocs, the pharmaceuticals compounds not inhibited COD removal and the nitrification during the experiments. These findings are in agreement with the microscopic studies, which showed a significant increase of concentration EPS. The presence of the pharmaceuticals compounds and its main metabolites stimulates mechanisms of protection and production of EPS with a slightly higher production of proteins. The removal of PPCPs by biological treatment processes including membrane bioreactor (MBR) was studied during the experience. The performance of MBR was demonstrated to be stable after 20 days of the experience. Although presence the fouling, the membrane look as technique very important for elimination the organics micro pollutants from the hospital wastewater.

Quantifying the Effect of COD to TN Ratio, DO Concentration and Temperature on Filamentous Microorganisms’ Population and Trans-Membrane Pressure (TMP) in Membrane Bio-Reactors (MBR)

Using moderate populations of filaments in the biomass of Membrane Bio-Reactors (MBRs) is a biological anti-fouling method which has been increasingly applied over the last few years. This study aims to quantify the effect of COD to TN ratio, Dissolved Oxygen (DO) concentration and temperature on filaments’ population and Trans-Membrane Pressure (TMP) in a pilot-scale MBR, with a view to reducing membrane fouling. The novelty of the present work concerns the development of a mathematical equation that correlates fouling rate (dTMP/dt) with the population of filamentous microorganisms, assessed by the Filament Index (FI), and with the concentration of the carbohydrate fraction of Soluble Microbial Products (SMPc). Apart from TMP and SMPc, other fouling-related biomass characteristics, such as sludge filterability and settleability, were also examined. It was shown that at high COD to TN ratio (10:1), low DO concentration in the filaments’ tank (0.5 ± 0.3 mg/L) and high temperature (24–30 °C), a moderate population of filaments is developed (FI = 1–2), which delays the TMP rise. Under these conditions, sludge filterability and settleability were also enhanced. Finally, TMP data analysis showed that the fouling rate is affected by FI and SMPc concentration mainly in the long-term fouling stage and increases exponentially with their increase.

Fouling Mitigation by Cationic Polymer Addition into a Pilot-Scale Anaerobic Membrane Bioreactor Fed with Blackwater.

Cationic polymers have proven to be suitable flux enhancers (FEs) in large-scale aerobic membrane bioreactors (MBRs), whereas in anaerobic membrane bioreactors (AnMBRs) research is scarce, and so far, only done at lab-scale. Results from MBRs cannot be directly translated to AnMBRs because the extent and nature of membrane fouling under anaerobic and aerobic conditions are different. Our research focused on the long-term effect of dosing the cationic polymer Adifloc KD451 to a pilot AnMBR, fed with source-separated domestic blackwater. A single dosage of Adifloc KD451 at 50 mg L−1 significantly enhanced the filtration performance in the AnMBR, revealed by a decrease in both fouling rate and total filtration resistance. Nevertheless, FE addition had an immediate negative effect on the specific methanogenic activity (SMA), but this was a reversible process that had no adverse effect on permeate quality or chemical oxygen demand (COD) removal in the AnMBR. Moreover, the FE had a long-term positive effect on AnMBR filtration performance and sludge filterability. These findings indicate that dosing Adifloc KD451 is a suitable strategy for fouling mitigation in AnMBRs because it led to a long-term improvement in filtration performance, while having no significant adverse effects on permeate quality or COD removal.

Energy efficiency and biofouling control in a pilot-scale membrane bioreactor using low-frequency reciprocating motion and the succession of biofilm communities resistant to mechanical shear

We evaluated the energy consumption and permeability performance of a novel membrane bioreactor (MBR) that employs reciprocating motion to generate mechanically imposed shear on a hollow-fiber membrane. This pilot-scale reciprocation MBR was operated for eight months in a local wastewater treatment plant. The inertial forces generated by the reciprocating motion of membrane modules and the looseness of the fiber successfully mitigated membrane fouling without air scouring. The specific energy demand (SED) for the reciprocation MBR ranged from 0.003 to 0.015 kWh/m3 at 25 LMH, resulting in up to an 85% reduction of energy consumption as compared to conventional air scouring MBRs. The MLSS concentrations were correlated to the SED because of the drag forces acting on the mixed liquor in the reciprocation MBR. Also, the relative abundance of bacterial phylotypes in biofilm indicated that specific bacteria could become dominant in the succession of biofilm communities during the operational period.

Membrane Bioreactor-Treated Domestic Wastewater for Sustainable Reuse in the Lake Victoria Region.

Lake Victoria is a shared water resource between Kenya, Uganda, and Tanzania, which is the second largest freshwater lake in the world. It has long since suffered from the consequences of overexploitation of its resources, mainly fish stocks, and increasingly high pollution. The closure of 58% of the fish processing plants (FPPs) is attributed to the declining fish stocks due to overfishing and pollution in particular. The installation and operation of a pilot membrane bioreactor (MBR) in Kisumu, Kenya, adopts an integrated approach by providing an integral, sustainable, cost-effective, and robust solution for water sanitation, which also meets the demand for clean water in the fish processing industry, aquaculture, and irrigation. The innovative system comprises a pilot MBR coupled with a recirculation aquaculture system (RAS). The RAS is able to recirculate 90% to 95% of its water volume; only the water loss through evaporation and drum filter back flushing has to be replaced. To compensate for this water deficit, the MBR treats domestic wastewater for further reuse. Additionally, excess purified water is used for irrigating a variety of local vegetables and could also be used in FPPs. The pilot-scale MBR plant with around 6 m2 submerged commercial polyethersulfone (PES) membranes provides treated water in basic agreement with Food and Agriculture Organization (FAO) standards for irrigation and aquaculture, showing no adverse effects on tilapia fingerlings production. A novel membrane module with a low-fouling coating is operating stably but has not yet shown improved performance compared to the commercial one. Integr Environ Assess Manag 2020;16:942-954. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

The Use of Natural Minerals in a Pilot-Scale MBR for Membrane Fouling Mitigation

This study examines the effect of bentonite and zeolite concentration (0.25–5 g/L) on the membrane fouling of a fully automated, pilot-scale membrane bioreactor (MBR) treating high-strength synthetic municipal wastewater. Reversible fouling was estimated by sludge filterability measurements and irreversible fouling was estimated by the reduction of the carbohydrate fraction of soluble microbial products (SMPc), which are considered to be significant MBR foulants. Both minerals were added to biomass samples (during batch-mode experiments) which were obtained from the system’s aeration tank. Results showed that the optimal bentonite and zeolite concentrations were 3.5–4 g/L and 2.5–3.5 g/L, respectively. Interestingly, above these values, the addition of both minerals increased the examined fouling indices, i.e., the measured filterability times and the SMPc concentration, implying that they might act as foulants at high concentrations. Optical microscopy images of the biomass samples showed that the addition of minerals at the optimal concentrations did not affect significantly filamentous microorganisms, since filament index (FI) was practically unaffected (~2). Finally, regarding the system’s treating performance, it was found that the pilot-scale MBR can operate successfully with high-strength synthetic municipal wastewater, since remarkable behaviour was exhibited in terms of organics (BOD5, COD) and ammonium (NH4+-N) removal (&gt;98%).

Fouling potential of lipopolysaccharides released at low temperatures in MBRs.

Sludge filterability in membrane bioreactors (MBRs) fluctuates and affects membrane fouling. Therefore, understanding the reasons for the fluctuations of sludge filterability is important for the efficient operation of MBRs. In this study, a pilot-scale MBR treating municipal wastewater was operated for about 600 days and the variations in sludge filterability were continuously monitored by batch-filtration experiments using the same membranes as in the MBR. To investigate the reasons for the deterioration of sludge filterability, constituents in sludge supernatant were intensively monitored, and the correlations with sludge filterability were determined. The concentration of lipopolysaccharides (LPS) in sludge supernatant exhibited significantly higher correlation with sludge filterability than did conventional indexes (i.e. polysaccharides and proteins). Size fractions affecting MBR sludge filterability were also investigated, and it was suggested that colloidal LPS deteriorated MBR sludge filterability. Based on the long-term operation of the MBR, increase in colloidal LPS under low temperatures of the mixed liquor suspension was a key factor in the deterioration of sludge filterability. The impact of LPS increasing under low temperatures should be investigated by operating bench-scale MBRs fed with synthetic wastewater in controlled conditions.