Tae-Moon Tak

Fouling control in activated sludge submerged hollow fiber membrane bioreactors

The goal of this study is to determine the impact of various operating factors on membrane fouling in activated sludge membrane bioreactor (MBR) process, typically used for water reclamation. In this process, ultrafiltration (UF) and microfiltration (MF) hollow fiber membranes, submerged in the bioreactor, provided a solid-liquid separation by replacing gravity settling. Activated sludge from a food wastewater treatment plant was inoculated to purify synthetic wastewater consisting of glucose and (NH&SO, as a source of carbon and nitrogen, respectively. The results clearly showed that membrane fouling, defined as permeate flux decline due to accumulation of substances within membrane pores and/or onto membrane surface, was greatly influenced by membrane type and module configuration. It was also found that the rate and extent of permeate flux decline increased with increasing suction pressure (or initial operating flux) and with decreasing air-scouring rate. The mixed liquor suspended solids (MLSS) concentrations, however, exhibited very little influence on permeate flux for the range of 3600-8400 mgk. Another important finding of this investigation was that non-continuous membrane operation significantly improved membrane productivity. This observation can be explained by the enhanced back transport of foulants under pressure relaxation. During non-suction periods, the foulants not irreversibly attached to the membrane surface, diffused away from the membrane surface because of concentration gradient. Furthermore, the effectiveness of air scouring was greatly enhanced in the absence of transmembrane suction pressure, resulting in higher removal of foulants accumulated on the membrane surface. The use of intermittent suction operation may not be economically feasible at large-scale, but it may offer an effective fouling control means for small-scale MBR processes treating wastewaters with high fouling potential.

Sulfonated polyethersulfone by heterogeneous method and its membrane performances

Polyethersulfone was sulfonated by heterogeneous method with chlorosulfonic acid. Ion exchange capacity was controlled to 0.68 meq/g to reduce fouling. Sulfonation was confirmed by Fourier transform infrared spectroscopy and 1H-nuclear magnetic resonance. Polyethersulfone and sulfonated polyethersulfone ultrafiltration membranes were prepared successively by the typical phase inversion method. Membrane performance of sulfonated polyethersulfone was compared with that of polyethersulfone. In the preparation of ultrafiltration membranes, the effect of the addition of dichloromethane and poly(vinyl pyrrolidone) in a casting solution was investigated on the membrane performance. It was observed that the addition of dichloromethane increased the solute rejection rate. By changing the ratio between polymer and poly(vinyl pyrrolidone), membrane performance could be controlled. Negatively charged sulfonated polyethersulfone could reduce fouling at higher or lower pH than isoelectric point of protein bovine serum albumin.

The behavior of membrane fouling initiation on the crossflow membrane bioreactor system

Abstract A membrane bioreactor (MBR) system (i.e. an activated sludge system where the clarifier has been replaced with membrane filtration) has many advantages compared with the conventional activated sludge process. However a serious problems that has prevented this technology from reaching its potential is membrane fouling. In this study, the biomass was cultivated under three conditions: normal (high dissolved oxygen, DO); bulking; and normal conditions with low DO concentration. Membrane filtration tests were performed with cellulose acetate (CA), sulfonated polyethersulfone (SPES) and polyethersulfone (PES) membranes, respectively. Relatively hydrophobic PES membranes fouled more seriously than hydrophilic CA membranes. This phenomenon was especially significant under bulking conditions. Ultimate flux was almost equal for all three membrane types however, since the PES and SPES started with higher initial fluxes. Effluent quality was not affected by membrane fouling/flux but did deteriorate at low DOs.

Membrane sequencing batch reactor system for the treatment of dairy industry wastewater

Abstract A membrane separation process was coupled to a sequencing batch reactor (SBR) for biological nutrient removal (BNR) processes and a combined system was named a membrane sequencing batch reactor (MSBR). MSBR was used for the treatment of dairy industry wastewater and optimized to increase the treatment efficiency. Since a diffuser-attached module design, subcritical flux operation, and intermittent suction method were adapted to the system, long-term operation was possible, i.e. the system could be operated for more than 110 days with only one membrane washing. BOD removal was high (97–98%) and stable. SS (suspended solid)-free effluent was obtained by membrane separation. Since nitrogen was mainly consumed as nutrient for synthesis of new cells due to the low influent concentration, the removal rate reached 96%. Phosphorus removal was relatively low because of the limit of the biological process, i.e. removal efficiency ultimately depends on the amount of excess sludge wasting. A removal rate of 80% was reached after system optimization.

Phospholipids separation (degumming) from crude vegetable oil by polyimide ultrafiltration membrane

Abstract Soluble copolysulfoneimides were synthesized by a thermal two-step method. Bis[4-(3-aminophenoxy)phenyl] sulfone (BAPS-m) and 3,3′-diaminodiphenyl sulfone (3,3′-DDS) as diamines were used. PMDA, DSDA and ODPA were used as dianhydrides. In order to reduce the amount of BAPS-m, 3,3′-DDS was added, as much as possible. Ultrafiltration (UF) membrane with the polymer was prepared by the phase inversion method. Various solvent (water, alcohols, acetone and hexane) fluxes were measured. Phospholipid could be rejected above 90%. The soybean oil micelles could be concentrated to volume concentration ratio (VCR) of 10. Several effects like feed temperature, stirring speed and feed solid concentration on micelle flux were also investigated. Resistance values of membrane, concentration polarization and fouling were measured.

Effects of casting solution composition on performance of poly(ether sulfone) membrane

Flat-type poly(ether sulfone) (PES) membranes for ultrafiltration were prepared by the traditional phase-inversion technique. The effects of the concentration of PES and the combination of two solvents, dichloromethane (DCM) and N-methyl-2-pyrrolidone (NMP), with differences in volatility and solvating power on membrane performance were examined in terms of pure water flux (PWF) and solute rejection (SR) against poly(ethylene glycol) (PEG, MW 20,000). Changing the thermodynamic quality of PES/NMP casting solution by combining DCM, a volatile and weak solvent, affected the PWF of the resulting membrane. The SR of PES/DCM–NMP membrane, however, was more likely dependent upon the effect of evaporating the volatile solvent from the casting solution/air interface rather than the effect of changing the thermodynamic quality of the casting solution. Combining DCM in PES/NMP casting solution transformed the fingerlike macrovoids of PES/NMP membrane prepared without DCM into the isolated macrovoids. PES/DCM–NMP membrane prepared with PVP, a water soluble poreforming agent, showed an increased PWF while maintaining SR of over 90%, even under the reduced feeding pressure of 1 kg/cm2. It is necessary to measure molecular weight cutoff of membrane for demonstrating the potential of PVP for improving the membrane permeability without losing the selectivity.© 1996 John Wiley & Sons, Inc.

Synthesis and characterization of block copoly(urethane–imide)

A newly synthetic method has been developed for the preparation of block copoly(urethaneimide) (PUI). The copolymer was yielded from the direct reaction of the prepolyurethane terminated with isocyanate and the prepolyimide terminated with anhydride. The latter is prepared by reacting an excess amount of pyromellic dianhydride (PMDA) with bis [4-(3-aminophenoxy)phenyl] sulfone (BAPS) in one-step polymerization. The structure was confirmed by infrared (IR) spectra. Other characterizations were evaluated. Among them were solubility, viscosity, mechanical properties, and thermal properties.

Preparation of soluble polyimides and ultrafiltration membrane performances

Various soluble polyimides with bis[4-(3-aminophenoxy)phenyl]sulfone and three kinds of dianhydrides were prepared in a polar N-methyl-2-pyrrolidone solvent by the traditional chemical two-step method. All the polymers synthesized had good solubilities in polar solvents and excellent thermal properties. Wide-angle X-ray diffraction studies showed that all polyimides were amorphous. Polyimide ultrafiltration asymmetric membranes were successfully prepared by the traditional phase-inversion method. The cross sections of the polyimide ultrafiltration membranes showed a very thin surface layer and a porous sublayer. The pure water flux was very high and the solute rejection rate at poly(ethylene glycol) of MW 20,000 was above 90%.

Synthesis and characterization of soluble random copolyimides

Random copolyimides with different proportions of a diamine component were prepared by polymerizing different compositions of diamines with various dianhydrides and imidized thermally to 260°C. The imidization percent of poly(amic acid) was characterized at various temperatures by infrared spectroscopy. The homopolyimide based on bis[4-(3-aminophenoxy)phenyl]sulfone and pyromellitic dianhydride was the only one soluble. By changing the compositions of bis[4-(3-aminophenoxy)phenyl]sulfone and other diamines with pyromellitic dianhydride in N-methyl-2-pyrrolidone, soluble random copolyimides could be prepared. By random copolymerization, the thermal properties and viscosities of homopolyimide could be controlled. All the soluble polyimides prepared in this work were amorphous because of the lack of stereoregularity.

Synthesis and characterization of homo- and copolyimides prepared from two-step polymerization

Homopolyamic acids and copolyamic acids were prepared from four dianhydrides and three diamines. Copolyimides could be arranged in sequence through different reaction processes, such as alternating, block, and random. Polyamic acids were subsequently converted into corresponding polyimides by the solid-phase imidization. Polyimide derivatives were characterized by viscosity, thermal stability, mechanical properties, and solubility. The extent of polymerization might be influenced by the nucleophilicity of a diamine and the electrophilicity of a dianhydride. In gel permeation chromatography, molecular weight distribution of polymers was 2.5-3.0. The thermal stability of polymers decreased with increasing the ratio of a more flexible component, and alternating copolyimides showed slightly better than corresponding random and block ones. The melting temperatures of all polyimide derivatives did not exist on the differential scanning calorimetry curves, and the results were proof that the X-ray diffraction curves. Polymers derived from bis[4-(3-amino phenoxy)phenyl]sulfone dissolved well in some polar solvents. Alternating copolymers represented a better solubility than the corresponding random and block ones. All polymers had good mechanical properties, both tensile and elongation. The kinetics of imide formation could be also dependent on the structure and reactivity of reagents. The kinetics of cyclodehydration was described by the first-order kinetics up to relatively high conversion but deviated from the first-order kinetics at high conversion followed by the second-order kinetics.