Effects of biofilm formation on membrane performance in submerged membrane bioreactors

The effects of biofilm formation on membrane performance were evaluated for a submerged membrane bioreactor (sMBR) system with six different types of micro- and ultrafiltration membranes (working volume = 19 l). After operation for 24 h the permeability of the membranes with a larger pore size (microfiltration) decreased to that of the membranes with a much smaller pore size (ultrafiltration). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) confirmed that biofilms could reduce the influence of the membrane surface properties. The chemical oxygen demand (COD) removal efficiency was 95% for the oily wastewater treatment in the sMBR where the filtration process made an important contribution (47% based on feed COD). Significant enhancement in COD removal occurred at the initial filtration stage because of biofilm formation and the dynamic member role of the biofilm layer. Membranes with various pore sizes had approximately the same permeate quality that was attributed to the biofilm on the membrane surfaces. Nevertheless, the ultrafiltration membranes had 43% more COD removal efficiency than the other applied membranes at the beginning of filtration (before biofilm formation) because of the smaller pore sizes and better sieving.     

The correlation between biofilm biopolymer composition and membrane fouling in submerged membrane bioreactors

Biofouling, the combined effect of microorganism and biopolymer accumulation, significantly reduces the process efficiency of membrane bioreactors (MBRs). Here, four biofilm components, alpha-polysaccharides, beta-polysaccharides, proteins and microorganisms, were quantified in MBRs. The biomass of each component was positively correlated with the transmembrane pressure increase in MBRs. Proteins were the most abundant biopolymer in biofilms and showed the fastest rate of increase. The spatial distribution and co-localization analysis of the biofouling components indicated at least 60% of the extracellular polysaccharide (EPS) components were associated with the microbial cells when the transmembrane pressure (TMP) entered the jump phase, suggesting that the EPS components were either secreted by the biofilm cells or that the deposition of these components facilitated biofilm formation. It is suggested that biofilm formation and the accumulation of EPS are intrinsically coupled, resulting in biofouling and loss of system performance. Therefore, strategies that control biofilm formation on membranes may result in a significant improvement of MBR performance.     

Strains of internal biofilm in aerobic granular membrane bioreactors

This study isolated strains in suspended liquor, the surface fouling layer, and biofilm inside hollow-fiber membranes of a membrane bioreactor (MBR); analyzed their distributions, sizes, surface charges, and growth behaviors; and determined the quantities of extracellular polymeric substances (EPS) secreted by these strains under different organic loadings. Three strains, which may penetrate the microfiltration membranes, were close relatives of the Ralstonia mannitolilytica strain SDV (GenBank Accession No. GU451066), Arthrobacter sp. BJQ-2 (GenBank Accession No. GU451067), and Actinobacterium DS3 (GenBank Accession No. GU451068). Among these three strains, only Arthrobacter sp. developed an internal biofilm. The relatively short length of Arthrobacter sp. minimizes resistance to cells moving through the membrane matrix, thereby enhancing its ability to build a biofilm in the interior surface of membranes.     

Effect of hydraulic retention time on membrane fouling and biomass characteristics in submerged membrane bioreactors

In this paper, three identical membrane bioreactors (MBRs) were operated in parallel in order to specify the influence mechanism of hydraulic retention time (HRT) on MBR. The results showed that the removal efficiency of chemical oxygen demand (COD) was stable though it decreased slightly as HRT decreased, but biomass activity and dissolved oxygen (DO) concentration in sludge suspension decreased as HRT decreased. The filamentous bacteria grew easily with decreasing HRT. The extracellular polymeric substances (EPS) concentration and sludge viscosity increased significantly as filamentous bacteria excessively grew. The over growth of filamentous bacteria, the increase of EPS and the decrease of shear stress led to the formation of large and irregular flocs. Furthermore, the mixed liquid suspended solids (MLSS) concentration and sludge viscosity increased significantly as HRT decreased. The results also indicated that sludge viscosity was the predominant factor that affecting hydrodynamic conditions of MBR systems.     

New insight into the effects of Ca(II) on cake layer structure in submerged membrane bioreactors

The effects of Ca(II) on the structure of the cake layer in submerged membrane bioreactors (SMBRs) were investigated in this study. Three parallel laboratory-scale SMBRs were operated with synthetic municipal wastewater with three Ca(II) levels (82, 208 and 410?mg?l^?1). As the Ca(II) concentration increased, the sludge floc size increased and the molecular weight of the soluble microbial products (SMP) in the bulk liquid decreased. These observations were attributed to the neutralization and bridging function of Ca(II). Furthermore, Ca(II) addition did not change the thickness of the cake layer, but inhibited the deposition of other elements, such as Al, Si, Mg, and Fe. As a result of Ca(II) addition, the cake layer became less compact and more porous. The interspaces among the flocs in the cake layer helped to reduce the membrane fouling potential.     

Comparison of the performance of submerged membrane bioreactor (SMBR) and submerged membrane adsorption bioreactor (SMABR)

This study focuses on comparing the performance of submerged membrane bioreactor (SMBR) and submerged membrane adsorption bioreactor (SMABR) over a period of 20 days at a hydraulic retention time (HRT) of 3.1h. The effects of PAC on critical flux and membrane fouling were also investigated. The SMABR exhibited better results in terms of mixed liquor suspended solids (MLSS) growth, DOC removal (over 96%), COD removal (over 95%), transmembrane pressure (TMP) and oxygen uptake rate. Nearly 100% of bacteria and 100% of total coliforms were removed in both systems. The addition of PAC could maintain the critical flux at a lower TMP value (7.5 kPa), while irreversible fouling caused by PAC occurred when the filtration flux exceeded critical flux.     

Effects of ginseng on Pseudomonas aeruginosa motility and biofilm formation

Biofilm-associated chronic Pseudomonas aeruginosa lung infections in patients with cystic fibrosis are virtually impossible to eradicate with antibiotics because biofilm-growing bacteria are highly tolerant to antibiotics and host defense mechanisms. Previously, we found that ginseng treatments protected animal models from developing chronic lung infection by P. aeruginosa. In the present study, the effects of ginseng on the formation of P. aeruginosa biofilms were further investigated in vitro and in vivo. Ginseng aqueous extract at concentrations of 0.5-2.0% did not inhibit the growth of P. aeruginosa, but significantly prevented P. aeruginosa from forming biofilm. Exposure to 0.5% ginseng aqueous extract for 24 h destroyed most 7-day-old mature biofilms formed by both mucoid and nonmucoid P. aeruginosa strains. Ginseng treatment enhanced swimming and twitching motility, but reduced swarming of P. aeruginosa at concentrations as low as 0.25%. Oral administration of ginseng extracts in mice promoted phagocytosis of P. aeruginosa PAO1 by airway phagocytes, but did not affect phagocytosis of a PAO1-filM mutant. Our study suggests that ginseng treatment may help to eradicate the biofilm-associated chronic infections caused by P. aeruginosa.     

Effects of temperature and temperature shock on the performance and microbial community structure of a submerged anaerobic membrane bioreactor

Effects of temperature and temperature shock on the performance and microbial community structure of a submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping pressate were studied for 416 days. The results showed that the SAnMBR system were highly resilient to temperature variations in terms of chemical oxygen demand (COD) removal. The residual COD in treated effluent was slightly higher at 55 °C than that at 37 and 45 °C. There were no significant changes in biogas production rate and biogas composition. However, temperature shocks resulted in an increase in biogas production temporarily. The SAnMBR could tolerate the 5 and 10 °C temperature shocks at 37 °C and the temperature variations from 37 to 45 °C. The temperature shock of 5 and 10 °C at 45 °C led to slight and significant disturbance of the performance, respectively. Temperature affected the richness and diversity of microbial populations.     

Effects of nitrogen limitation on biofilm formation in a hydrocarbon-degrading trickle-bed filter

The effect of nitrogen limitation on young and mature steady-state biofilm in a trickle-bed filter was studied. Toluene and n-heptane were the sole carbon source. Biomass concentration, respiration, substrate-induced respiration, metabolic quotient, and total hydrocarbon degradation efficiency were measured. The aim of the experiment was to control excess biomass production in the trickle-bed filter by limiting the mineral nutrients and to achieve increased mineralization of the carbon source. Biofilm growth responded strongly to the amount of available nitrogen, whereas hydrocarbon degradation efficiency reached a maximum of 60% and could not be increased even by further addition of nitrogen. The experiments showed that 95% of the adsorbed carbon was mineralized completely and only 5% was used for biofilm formation. This complete mineralization can also be concluded from the metabolic quotient. The value of the latter was about 6–10 mg CO₂-C g⁻¹C_mic h⁻¹, indicating an expanded energy demand due to stress effects in the presence of nutrient deficiency. It was postulated that determination of the metabolic quotient could be an simple instrument to measure the rate of mineralization of carbon sources and also the rate of biomass formation in trickle-bed filters or biofilters. Received: 11 November 1998 / Accepted: 5 December 1998     

Effects of low-concentration Cr(VI) on the performance and the membrane fouling of a submerged membrane bioreactor in the treatment of municipal wastewater

The effects of low-concentration Cr(VI) (0.4 mg?l^?1) on the performance of a submerged membrane bioreactor (SMBR) in the treatment of municipal wastewater, as well as membrane fouling were investigated. Compared with the SMBR for control municipal wastewater, the SMBR for Cr(VI)-containing municipal wastewater had a higher concentration of soluble microbial products (SMP) with lower molecular weights, and smaller sludge particle sizes. Furthermore, low-concentration Cr(VI) induced membrane fouling, especially irreversible membrane pore blocking, which markedly shortened the service life of the membrane.     

Effects of medium carbon-to-nitrogen ratio on biofilm formation and plasmid stability

Biofilm formation and plasmid segregational instability in biofilm cultures of Escherichia coli DH5alpha (pMJR1750) were investigated under different medium-carbon-to-nitrogen (C/N) ratios. At C/N ratios of 0.07 and 1, net accumulation of both biofilm plasmid-bearing and plasmid-free cells continued through the entire experiment without attaining any apparent steady state. At C/N ratios of 5 and 10, net biofilm cell accumulation for the two populations reached apparent steady states after 84 and 72 h, respectively. At C/N ratios of 0.07 and 1, polysaccharide production increased slowly and reached about 2g alginate equivalent/cm(2) by the end of both experiments. At a C/N ratio of 5, polysaccharide increase significantly after 84 h, reaching about 7mug alginate equivalent/cm(2) prior to termination. At a C/N ratio of 10, polysaccharide increased significantly after 72 h and reached 21 mug alginate equivalent/cm(2) at 108 h. At C/N ratios of 0.07 and 1, protein production reached 6.5 and 4 mug/cm(2), respectively. At C/N ratios of 5 and 10, protein production increased slightly for the first 84 h and reached a maximum at 108 h, at 3 and 2 mug/cm(2), respectively, then decreased over the last 12 h of the experiment. Ratios of polysaccharide to protein increased with increasing C/N ratios. At C/N ratios of 0.07 and 1, the ratios between extracellular polysaccharide (EP) and protein were no more than 205 mug polysaccharide/mug protein, whereas those at C/N ratios of 5 and 10 increased to about 7 and 12 mug polysaccharide/mug protein, respectively.Probabilities of plasmid loss in the biofilm cultures increased with increasing C/N ratios. At C/N ratios of 0.07, 1, and 5, the probabilities of plasmid loss were 0.0013 +/- 0.011, 0.020 +/- 0.006 and 0.122 +/- 0.021, respectively. At a C/N ratio of 10, the probability of plasmid loss was significantly higher, reaching 0.38 +/- 0.125. The increase of probability of plasmid loss at higher C/N ratios results from competition between cell replication and extracellular polysaccharide production. (c) 1994 John Wiley & Sons, Inc.     

Influence of elevated pH shocks on the performance of a submerged anaerobic membrane bioreactor

The effects of elevated pH shocks on the performance and membrane fouling of a submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping (TMP) whitewater was studied over a 120-day period. Changes in chemical oxygen demand (COD) removal, biogas production, sludge and cake layer properties, and their correlations to membrane fouling – before and after pH shocks – were systematically studied using various analytical tools. The results showed that a pH 8.0 shock had a minor impact, while pH 9.1 and 10.0 shocks exerted significant long-lasting negative impacts on COD removal, biogas production and membrane filtration performance of the SAnMBR. When the normal pH (7.0) was resumed, it took approximately 1, 6, and 30 days for the performance to recover for pH 8.0, 9.1 and 10.0 shocks, respectively. The elevated pH shocks induced the dispersion of sludge flocs and resulted in the accumulation of colloids and solutes or biopolymers in the sludge suspension, and thus deteriorated membrane performance. Statistical analysis showed that the ratio of proteins (PN) to polysaccharides (PS) in extracellular polymeric substances (EPS) had a strongly negative effect on the membrane fouling rate. There were smaller size particles deposited on the membrane surface and a more compact and denser cake layer was formed after being exposed to an alkaline shock at pH 10, resulting in higher membrane fouling rates.     

Analysis of microbial community structure in a biofilm on membrane surface in the submerged membrane bioreactor treating domestic wastewater on the basis of respiratory quinone profiles

The objective of this study was to investigate the microbial community structure of the biofouling film formed on hollow-fiber membrane surfaces in the submerged membrane bioreactor (SMBR) with a nitrification-denitrification process. In this experiment, aeration was conducted intermittently (60 min off, 90 min on) cyclic anoxic and oxic conditions in the SMBR. The dominant quinone types of biofilm on the membrane surface in an intermittently aerated SMBR were ubiquinone (UQs)-8, -10, followed by menaquinones (MKs)-8(H4), -8(H2) and -7, but those of suspended microorganisms were UQ-8, UQ-10 followed by MKs-8, -9(H4) and -6. The change in quinone profiles of biofilm on the membrane surface suggested that UQ-9, MK-7, MK-8(H2) and MK-8(H4) contributed to microbiological fouling in the intermittently aerated SMBR treating domestic wastewater. The microbial diversities of suspended microorganisms and biofilm, calculated based on the composition of all quinones, were 9.5 and 10.9, respectively.     

Analysis of outer membrane vesicle protein involved in biofilm formation of Helicobacter pylori

Helicobacter pylori is one of the most common causes of bacterial infection in humans. Infection with H. pylori is closely associated with gastritis and peptic ulcers and is a risk factor for gastric cancer and mucosa-associated lymphoid tissue lymphoma. H. pylori forms biofilms on glass surfaces at the air–liquid interface in in-vitro batch cultures. We previously reported that strain TK1402 showed a strong biofilm-forming ability in vitro. We also suggested the outer membrane vesicles (OMV) produced by strain TK1402 might be related to its biofilm forming ability. In the present study, we analyzed the protein profile of the OMV produced by strain TK1402 and found a unique 22-kDa protein in TK1402 OMV cultured for 2–3 days. In addition, this protein could not be detected in the OMVs produced by other H. pylori strains. These results suggest that the 22-kDa protein is involved in effective biofilm formation by strain TK1402.     

Effect of operating variables on biofilm formation and performance of an anaerobic fluidized-bed bioreactor

The effect of various operating variables such as initial inoculum circulation, dilution rate, chemical oxygen demand (COD) loading rate, and quantity and quality of inoculum on the process of film formation on sand surface and reactor performance were studied using synthetic glucose based wastewater. It was found that the film formation process is favored by a high dilution rate, a large quantity of inoculum, and an inoculum having high methane producing capacity. Experimental observations indicate that the biofilm formation process is initiated by methanogenic bacteria.     

Effects of chronic sub-lethal oxidative stress on biofilm formation by Azotobacter vinelandii

This work showed that perturbations of the physiological steady-state level of reactive oxygen species (ROS) affected biofilm genesis and the characteristics of the model bacterium Azotobacter vinelandii. To get a continuous endogenous source of ROS, a strain exposed to chronic sub-lethal oxidative stress was deprived of the gene coding for the antioxidant rhodanese-like protein RhdA (MV474). In this study MV474 biofilm showed (i) a seven-fold higher growth rate, (ii) induction of catalase and alkyl-hydroxyl-peroxidase enzymes, (iii) higher average thicknesses due to increased production of a polysaccharide-rich extracellular matrix and (iv) less susceptibility to hydrogen peroxide than the wild-type strain (UW136). MV474 showed increased swimming and swarming activity and the swarming colonies experienced a higher level of oxidative stress compared to UW136. A continuous exogenous source of ROS increased biofilm formation in UW136. Overall, chronic sub-lethal oxidative events promoted sessile behavior in A. vinelandii.     

Phenol biodegradation in hybrid hollow-fiber membrane bioreactors

Hollow-fiber membrane bioreactors were developed with granular activated carbon (GAC) for the biodegradation of phenol using Pseudomonas putida. Hollow fibers showed similar structure with/without GAC incorporated; while GAC hollow fiber had a stronger phenol adsorption capacity. In batch biotransformation experiments, complete depletion of 1000 mg phenol l⁻¹ (at which concentration free cells cannot grow) was accomplished in the reactor within 18 h in the hybrid bioreactor, comparing with 23 h in the GAC free bioreactor. Desorption and bioregeneration of the hollow-fiber membrane were believed to be the key for the enhancement of bioreactor performance. At continuous running, the GAC bioreactor showed its superiority over the GAC free bioreactor during start-up and elevated loading phase. More than 90% of the phenol was transformed in the GAC bioreactor when the phenol loading was <24 mg h⁻¹. The better bioreactor performance may be due to the enhanced mass transportation and adsorption capacity with the incorporation of GAC.     

Effects of quorum sensing on cell viability in Streptococcus mutans biofilm formation

Streptococcus mutans (S. mutans) uses a quorum sensing (QS) signaling system, which is dependent on competence stimulating peptide (CSP), to regulate diverse physiological activities including bacteriocin production, genetic transformation, and biofilm formation. However, the mechanism of the QS system-induced biofilm formation remains unclear. Here, we demonstrated that the late-stage biofilm formation was increased by the addition of exogenous CSP in S. mutans. The numbers of dead cells in biofilms formed in presence of CSP was 64.5% higher than that without CSP after 12 h (p < 0.05) and 76.3% higher after 24 h (p < 0.05), the numbers of live cells in biofilms formed in presence of CSP were 89.3% higher than that without CSP after 24 h (p < 0.01). The expression of QS-associated genes was increased 3.4-5.3-fold by CSP in biofilms. Our results revealed that cell viability of S. mutans grown in biofilms is affected by the CSP-dependent QS system.