Self-forming Dynamic Membrane Research Articles

Recovery of organic matters in wastewater by self-forming dynamic membrane bioreactor: Performance and membrane fouling

Formation process and fouling characteristics of the dynamic membrane were studied in a modified self-forming dynamic membrane bioreactor (SF-DMBR) for recovering the organic matters in wastewater, and the performance of this SF-DMBR was investigated. Results indicated that 80% of the organic matters in wastewater could be quickly recovered under continuous operation. Furthermore, the evolutions of the fouling components were determined during the formation and development processes of dynamic membrane. After the long-term operation, the decreases of protein concentration, accompanying with the increases of polysaccharides and microorganisms contents due to special operating conditions, were interestingly observed in the sludge of membrane surface. This could explain why membrane fouling was much weak. Therefore, though high membrane fluxes at 50–150 L/(m2·h) were adopted in this study, the reactor can still obtain a long-term stable operation and the operating cycle reached as long as 8 days. Finally, membrane fouling process was described by combined models.

Biohydrogen production integrated with an external dynamic membrane: A novel approach

A dynamic membrane bioreactor integrating a self-forming dynamic membrane with a continuous fermenter was designed for biohydrogen production using mixed cultures under mesophilic conditions. The novel configuration used was designed to retain effective hydrogen producing bacterial consortia and was investigated at hydraulic retention times (HRTs) of 12–2 h at a constant glucose feed concentration of 15 g/L. A dynamic membrane was successfully formed on support material in an external module and this resulted in a maximum hydrogen production rate of 51.38 L/L-day and a peak hydrogen yield of 2.98 mol/mol glucoseadded at 3 h HRT. Acetate and butyrate were dominant metabolic by-products. Quantitative polymerase chain reaction (qPCR) analysis revealed that Clostridium butyricum was the dominant microbial consortium under all HRT conditions examined.

Novel application of high-density polyethylene mesh as self-forming dynamic membrane integrated into a bioreactor for wastewater treatment

ABSTRACTIn the present study, self-forming dynamic membrane (SFDM) on rigid high-density polyethylene (HDPE) mesh with a large pore size of 2 mm is reported for the first time. The system was investigated for utilisation in simulated wastewater treatment by integrating the mesh with an aerobic bioreactor. The SFDM was analysed using Fourier transform infra-red (FT-IR) spectroscopy and visualised by scanning electron microscopy (SEM). The effect of the operating parameter on the change in composition of SFDM was also investigated. The system was used as a single unit for treatment of wastewater and showed stability over long-term treatment. The system could achieve a chemical oxygen demand (COD) reduction of 82.16 ± 6.47% at an influent COD concentration of 613.93 ± 72.13 mg/l and ammonia removal efficiency of 97.21 ± 0.62% at an influent ammonia concentration of 55.54 ± 2.23 mg/l. The reactor generated high-quality effluent and the turbidity recorded was less than 2NTU. In addition, the operational parameters, namely hydraulic retention time and organic loading rate, were optimised.

Bioaugmentation of a continuous-flow self-forming dynamic membrane bioreactor for the treatment of wastewater containing high-strength pyridine.

For the treatment of high-strength pyridine containing wastewater, a bioaugmented continuous-flow self-forming dynamic membrane bioreactor (CSFDMBR), which was consisted of a continuous flow airlift reactor (CFAR) and a dynamic membrane bioreactor (DMBR), was developed in this study. The results indicated that through the bioaugmentation by Rhizobium sp. NJUST18, CSFDMBR could be successfully started, which was confirmed by complete removal of pyridine, efficient nitrification, and significant increase of biomass. Pyridine could be effectively degraded in the CSFDMBR even at influent pyridine loading rate as high as 9.0kgm-3day-1, probably due to the efficient biomass retention in the CSFDMBR, which could be attributed to the formation of aerobic granules and the key role of dynamic membrane. CSFDMBR presented good polishing performance in treating pyridine wastewater, with effluent total organic carbon (TOC) and turbidity as low as 22.5±6.8mgL-1 and 3.8±0.5 NTU, respectively. Membrane fouling could be effectively controlled, as indicated by backwash period as long as 60days. The observed efficient performance highlights the potential for the full-scale application of the bioaugmented CSFDMBR, particularly for highly recalcitrant pollutant removal.

Improving volatile fatty acid yield from sludge anaerobic fermentation through self-forming dynamic membrane separation

Self-forming dynamic membrane (SFDM) separation was applied to the conventional sludge fermenter for improving VFA yields. Results indicated SFDM presented good performance in transferring products, retaining substrates, and enriching useful bacteria. The retention ratios of suspended solids, soluble COD, proteins, and polysaccharides reached 99%, 30%, 70%, and 40%, respectively, and more than 90% of the VFAs and ammonia could be transferred in a timely manner. The structure of the microbial community was optimized, which led to enhanced releases of hydrolytic enzymes and accelerated enrichments of functional bacteria. Protease and β-glucosidase activities increased from 1.0 to 5.0U/mL and 15.0 to 23.0μmol/L·h, respectively. VFA yield and sludge conversion ratio increased by 233.3% and 227.9%, respectively. Moreover, SFDM had good operation stability, including a short formation time, a long operation period, and a low transmembrane pressure. These results show VFA yield from sludge fermentation can be greatly improved by SFDM separation.

Hydrophilic Fe2O3 dynamic membrane mitigating fouling of support ceramic membrane in ultrafiltration of oil/water emulsion

Abstract Oil/water (O/W) emulsion is daily produced and difficult to be treated effectively. Ceramic membrane ultrafiltration is one of reliable processes for the treatment of O/W emulsion, yet still hindered by membrane fouling. In this study, two types of Fe 2 O 3 dynamic membranes (i.e., pre-coated dynamic membrane and self-forming dynamic membrane) were prepared to mitigate the fouling of support ceramic membrane in O/W emulsion treatment. Pre-coated dynamic membrane (DM) significantly reduced the fouling of ceramic membrane (i.e., 10% increase of flux recovery rate), while self-forming dynamic membrane aggravated ceramic membrane fouling (i.e., 8.6% decrease of flux recovery rate) after four filtration cycles. A possible fouling mechanism was proposed to explain this phenomenon, which was then confirmed by optical images of fouled membranes and the analysis of COD rejection. In addition, the cleaning efficiency of composite membranes (i.e., Fe 2 O 3 dynamic membrane and support ceramic membrane) was enhanced by substitution of alkalescent water backwash for deionized water backwash. The possible reason for this enhancement was also explained. Our result suggests that pre-coated Fe 2 O 3 dynamic membrane with alkalescent water backwash can be a promising technology to reduce the fouling of ceramic membrane and enhance membrane cleaning efficiency in the treatment of oily wastewater.

Optimal operating strategies of SFDM formation for MBR application

This study develops process of self-forming dynamic membrane (SFDM) formation on mesh filter and investigates the capability of such process in treating municipal waste water. The formation process is mainly divided into two stages, i.e., the agitation and the aeration. At the agitation stage, the dynamic membrane is built up by deposition of suspended sludge particles on the mesh surface. The just-complete suspension of sludge flocs is performed using mechanical axial-flow agitator. Four imposed fluxes are applied to obtain the optimal flux for SFDM. Three parameters, i.e., effluent chemical oxygen demand (COD), filtrate turbidity, and trans-membrane pressure (TMP) are simultaneously measured to determine the time required for SFDM formation at agitation stage. The optimal aeration rate is also determined to steady operate the self-forming dynamic membrane bioreactor (SFDMBR). At the aeration stage, the rest of dynamic membrane is gradually formed during continuous operation. The compressibility index of dynamic membrane is also measured at the aeration stage. The results indicate that variations of the trans-membrane pressure correspond to the variations of compressibility index. Scanning electronic microscopy is also utilized to observe the development of SFDM. The performance of SFDMBR is evaluated in terms of total dissolved solids (TDS) and COD removal. The results reveal that the SFDMBR can be substituted for conventional membrane bioreactors. A clean surface of mesh filter is restored by using two cleaning methods, i.e., air scouring and water backwash. Based on Fourier transform infrared analysis, proteins and carbohydrates are the dominant substances comprising the SFDM.

Effect of sludge properties on the filtration characteristics of self-forming dynamic membranes (SFDMs) in aerobic bioreactors: Formation time, filtration resistance, and fouling propensity

This study attempts to elucidate the effect of sludge properties on the formation time, filtration resistance, and fouling propensity of self-forming dynamic membranes (SFDMs), developed on coarse-pore filters in aerobic wastewater treatment bioreactors. Short-term filtration experiments were performed with twenty aerobic sludge samples having twelve sludge properties characterized. Statistical analysis showed that mean particle diameter (Dvm) associated with particle size distribution strongly affected both formation time (rp=−0.803, p=0.000) and filtration resistance (rp=−0.733, p=0.000) of SFDMs, whereas relative hydrophobicity (RH) exhibited a moderate correlation with SFDM formation time (rp=−0.487, p=0.029). In contrast, four other different sludge properties, i.e. viscosity (rp=0.811, p=0.000), extractable extracellular polymeric substances (eEPS) (rp=0.723, p=0.000), the carbohydrate content of eEPS (rp=0.766, p=0.000), and specific oxygen uptake rate (SOUR) (rp=−0.610, p=0.004), were identified as having significant impact on the fouling propensity of fresh SFDMs. Besides statistical analysis, more detailed experimental evidences were obtained by directly examining the identified important properties of fresh and initially fouled SFDMs. Sludge deposition during SFDM formation appears to be dominated by permeate drag force and hydrophobic interaction, whereas the subsequent fouling rate turns out to be controlled by the content of eEPS, particularly carbohydrates, which significantly correlated with viscosity and SOUR.

Stable aerobic granules in continuous-flow bioreactor with self-forming dynamic membrane

A novel continuous-flow bioreactor with aerobic granular sludge and self-forming dynamic membrane (CGSFDMBR) was developed for efficient wastewater treatment. Under continuous-flow operation, aerobic granular sludge was successfully cultivated and characterized with small particle size of about 0.1–1.0mm, low settling velocity of about 15–25m/h, loose structure and high water content of about 96–98%. To maintain the stability of aerobic granular sludge, strategies based on the differences of settling velocity and particle-size between granular and flocculent sludge were implemented. Moreover, in CGSFDMBR, membrane fouling was greatly relieved. Dynamic membrane was just cleaned once in more than 45days’ operation. CGSFDMBR presented good performance in treating septic tank wastewater, obtaining average COD, NH4+−N, TN and TP removal rates of 83.3%, 73.3%, 67.3% and 60%, respectively, which was more efficient than conventional bioreactors since that carbon, nitrogen and phosphorus were simultaneously removed in a single aerobic reactor.

Determination of fouling-related critical flux in self-forming dynamic membrane bioreactors: Interference of membrane compressibility

A new measurement protocol was proposed for appropriate determination of the fouling-related critical flux of highly compressible self-forming dynamic membranes (SFDMs) developed on coarse-pore supporting materials. Intermittent relaxation periods and parallel clean water filtration tests were incorporated into the common transmembrane pressure (TMP) step method to minimize the interference of SFDM compressibility on fouling-related critical flux determination and to better understand the filtration characteristic of SFDMs. The average fouling-related critical flux of SFDMs determined by the new measurement protocol turned out to be significantly higher than that obtained with the common measurement protocol. This is attributed partly to the exclusion of the flux reduction associated with SFDM compression by conducting the parallel clean water filtration tests, and partly to the minimization of the effect of “continuous” compression on the structure and fouling propensity of SFDMs by integrating the intermittent relaxation periods. The intermittent relaxation periods also prevented the occurrence of irreversible fouling and steady compression of SFDMs, embodied by the relatively smaller and faster disappeared hysteresis observed in the new measurement protocol. As one way to control SFDM compression, intermittent effluent production mode appears to be a potentially promising strategy for further optimization of SFDMBR operation. Stepwise increment of relaxation time and proper selection of higher initial TMP turned out to be the options recommended for reducing the time consumption of the new measurement protocol.

Effect of sludge retention time on characteristics of dynamic membrane in sequencing bioreactors

The characteristics of self-forming dynamic membrane (DM) in sequencing bioreactors under different sludge retention times (SRT) (SRT = 5, 10, 20, 40, 60 days) were studied using a scanning electron microscope, particle sizing distribution and others. The results indicated that the SRT has an evident effect on the characteristics of DM. The content of extracellular polymeric substances and protein decreased with the increase of SRT. The change of polysaccharide was small regardless of SRT. The filtration resistance of the DM was divided into two stages: an initial slowly-rising stage and a fast-rising later stage which were both irrespective of SRT. With the increase of SRT, the filtration resistance increase extent reduced and the running cycle became longer. Compared to the lower SRT, the particle size distribution of mixed liquor and DM has a decreasing trend at higher SRT. The average particle size of DM was larger than that of the mixed liquor irrespective of SRT. The amounts and types of microorganisms on the surface of DM were more abundant as SRT increased. Low SRT produced the DM surface with some Cocci while the high SRT gave the DM dominated with Cocci, Filamentous and Bacillus.

A hybrid system combining self-forming dynamic membrane bioreactor with coagulation process for advanced treatment of bleaching effl uent from straw pulping process

An innovative hybrid system combining self-forming dynamic membrane bioreactor (SFDMBR) with coagulation process was developed to treat bleaching wastewater from pulping process. Pilot-scale experimental results showed that the average removal effi ciencies of chemical oxygen (COD) demand and lignin by the SFDMBR were over 80% and 51%, respectively. The fairly good treatment performances can be attributed partly to the high biomass concentration (i.e. -10 g/L) maintained in the SFDMBR, and partly to the more efficient solid-liquid separation achieved by the self-forming dynamic membranes. It was found that the self-forming dynamic membranes can be quickly created, normally less than 60 min, during the initial stage of SFDMBR operation. Effluent turbidity was lower than 5 NTU in most cases. Membrane fouling can be effectively controlled via 5 min online air backwashing at an intensity of 3.2m3·m−2·h−1, and the separation capacity can be restored within 30 min. The effluent of SFDMBR was subsequently treate...

Fouling control of a pilot scale self-forming dynamic membrane bioreactor for municipal wastewater treatment

A pilot scale self-forming dynamic membrane bioreactor (SFDMBR) was used for municipal wastewater treatment and its fouling control was investigated. Two methods, on-line bottom aeration flushing and off-line high-pressure water flushing, were applied to control the self-forming dynamic membrane (SFDM) fouling. Aeration intensity of 22 m 3 /(m 2 ·h) and aeration time of 2 min were the optimized operational conditions. Fouling of SFDM could be on-line controlled by bottom aeration flushing to keep the bioreactor continuously working for about 50 days. However, the intervals of bottom aeration flushing were gradually shortened which suggested that fouling could be controlled to some extent but gel layer could not be removed effectively. High-pressure water flushing could remove cake layer and most gel layer, and the membrane flux could be almost 100% recovered. Through the convenient fouling control by combination of bottom aeration and high-pressure water flushing, the present SFDMBR has been normally operated for more than one year and the effluent was suitable for urban miscellaneous water consumption if disinfection was added.

Anaerobic membrane bioreactors: are membranes really necessary?

Membranes themselves represent a significant cost for the full scale application of anaerobic membrane bioreactors (AnMBR). The possibility of operating an AnMBR with a self-forming dynamic membrane generated by the substances present in the reactor liquor would translate into an important saving. A self-forming dynamic membrane only requires a support material over which a cake layer is formed, which determines the rejection properties of the system. The present research studies the application of self-forming dynamic membranes in AnMBRs. An AnMBR was operated under thermophilic and mesophilic conditions, using woven and non woven materials as support for the dynamic membranes. Results showed that the formation of a cake layer over the support materials enables the retention of more than 99% of the solids present in the reactor. However, only low levels of flux were achieved, up to 3 L/m2 x h, and reactor operation was unstable, with sudden increases in filtration resistance, due to excessive cake layer formation. Further fine-tuning of the proposed technology involves looking for conditions that can control effectively cake layer formation

Function of self-forming dynamic membrane and biokinetic parameters’ determination by microelectrode

The self-forming dynamic membrane coupled bioreactor (SFDMBR), which uses coarse pore-sized material to separate solids and liquids in a bioreactor, has some advantages compared with membrane bioreactor (MBR) using micro-/ultra-filtration membranes such as low module cost and high flux. In this study, we investigate the microbial activity change of a self-forming dynamic membrane (DM) during its bio-fouling process by a microelectrode for O2. At a high flux of 40L/m2h, the dissolved oxygen was determined to be depleted at the depth of 1.5–2.0mm in the self-forming DM. Based on the dissolved oxygen concentration profiles in the self-forming DM, a reliable and simple model and computational procedure were developed to estimate the biokinetic parameters in the self-forming DM. Sensitivity analysis of the model revealed that the dissolved oxygen profiles are sufficiently sensitive to the maximum specific rates of oxygen uptake (q⌢max,20), which were computed to be within the range of 3.8–11.1mg O2/gSSh. q⌢max,20 decreased sharply in the first 5 days with the development of the bio-fouling process in the surface cake layer of the self-forming DM and then reached a relatively steady state afterwards. The Monod half-saturation coefficient for oxygen (Ko) was computed to be in the range of 0.16–0.75mgO2/L. In summary, the results gave new experimental evidence on the change of microbial activity in the self-forming DM during its bio-fouling process.

Function of dynamic membrane in self-forming dynamic membrane coupled bioreactor

The Self-Forming Dynamic Membrane Coupled Bioreactor (SFDMBR), which uses coarse pore-sized material to separate solid and liquid in bioreactors, has some advantages compared with MBR using micro-/ultra-filtration membranes, for example, low module cost and high flux. The cake layer and gel layer formed on the surface and in the pores of the material during filtration played an important role, called self-forming dynamic membrane (DM), which mainly consisted of activated sludge. In this study, the function of DM in pollutant removal was investigated. It was found that DM could remove some organic matter (12.6 mg L(-1) on average) and total nitrogen (3.01 mg L(-1) on average) in the supernatant. Colloids and organic nitrogen were partly removed by DM while DOC, ammonia nitrogen and nitrate nitrogen removal by DM varied from negative to positive, which resulted from the combination of various biological activities, e.g. nitrification, biological utilization and so on. DO concentration in DM decreased with the depth and reached zero at about 1.5-2.5 mm depth. The organic degradation activity and nitrification activity of the biomass suspended in the bioreactor were higher than those of the biomass in the cake layer, which might be caused by the low DO concentration and low organic pollutant content in DM.

Characteristics of a self-forming dynamic membrane coupled with a bioreactor for municipal wastewater treatment.

A self-forming dynamic membrane (SFDM) method that used the biomass layer formed on a coarse mesh to effect solid-liquid separation was proposed. A 100-microm Dacron mesh material was used to make the SFDM modules. A SFDM coupled bioreactor (SFDMBR) was tested to treat actual municipal wastewater, and the performance and mechanisms of the SFDM were investigated. The SFDMBR worked by gravity filtration, and the water head drop was generally <5 cm. The effluent suspended solid concentrations were undetectable in most cases, and the COD and NH3 N removal efficiencies averaged 84.2% and 98.03%, respectively. An aeration in situ was adequate for cleaning the clogged modules, and the SFDM was readily and quickly re-formed. The biomass layer of the SFDM consisted of a cake layer and a gel layer. The gel layer had structures like conventional membranes and acted the key role in the SFDM. The permeability of the used mesh attached to the gel layer could be improved because the gel layer made the filtration surface more hydrophilic.

Self-forming dynamic membrane for ultrafiltration of pineapple juice

The formation of self-forming dynamic membrane on a porous ceramic support was studied. Pineapple juice of 12° Brix concentration was used in the experiments which were carried out at 25°C by circulating the pineapple juice at the applied pressure of 100, 200, and 300 kPa and at cross-flow velocities of 1.30–2.95 m s −1 through the ceramic membrane module for 1 h. The experimental data of flux and rejections showed that the dynamic membrane was well-formed after 30 min of circulation under the applied pressure of 300 kPa and at a cross-flow velocity of 2.0 m s −1 in which the steady values of flux and rejections of macromolecules and sugars obtained from the filtration mode were 6.0×10 −3 m 3/m 2 h, 84–87% and 6%, respectively. The corresponding values for ultrafiltration by alumina membrane of MW cut-off 50,000, using equivalent conditions, were 15.8×10 −3 m 3/m 2 h, 91% and 10.5%. Ultrafiltration was found to be more promising. The stability of the self-forming dynamic membrane was acceptable when subjected to change of filtration conditions. The permeation flux increased with cross-flow velocity and decreased when the applied pressure was reduced. The resistances for filtration by dynamic membrane and by ultrafiltration were calculated. For a porous support of large pore sizes, an in-pore blockage of solutes which were smaller than the membrane pores reduced the pore volume and induced fouling. Internal fouling resistance ( R f) was, therefore significant and responsible for the values of flux and rejection and was approximately 70% of total resistance. While in ultrafiltration, in which membrane with a smaller pore diameter was used, R f was only 20% but R p, the polarized layer resistance, was as high as 60% of total resistance.