In-Soung Chang

Membrane filtration characteristics in membrane-coupled activated sludge system -- the effect of physiological states of activated sludge on membrane fouling

The effect of sludge physiology on membrane fouling was investigated in a membrane-coupled activated sludge (MCAS) system. A series of ultrafiltrations were performed to assess the flux behaviors according to foaming potential, solids retention time (SRT), growth phase and nutrient condition of the activated sludge. The foaming sludge showed greater flux decline than the non-foaming sludge. The extraordinary increase, that is, more than 100 times in membrane fouling for the foaming sludge, was attributed to the hydrophobic and waxy nature of the foaming sludge surface, which was confirmed by a comparison with relative hydrophobicity. Membrane fouling tendency was increased as SRT decreased. A greater flux decline was observed at the endogenous phase than at the log growth phase. The activated sludge acclimated to the nitrogen deficient substrates produced less extracellular polymeric substances (EPS) and exhibited higher flux than the control activated sludge. The quantitative measurements of EPS content in order to estimate the extent of membrane fouling in various activated sludges showed that, in any physiological states of activated sludge, the higher the content of EPS the activated sludge had, the greater the membrane fouling proceeded. The EPS content of activated sludge is suggested as a probable index for the membrane fouling in a MCAS system.

Effects of membrane fouling on solute rejection during membrane filtration of activated sludge

To assess the relationship between solute rejection and membrane fouling in a MBR system, membrane filtrations of activated sludge in different physiological states were carried out with ultrafiltration membranes. Regardless of the physiological states of the activated sludge (foaming, bulking, pin-point floc, exponential growth, endogenous phase, normal state sludge), the hydrophobic membrane (PM30) always showed greater solute rejection than the hydrophilic membrane (YM30). To investigate the key factors affecting solute rejection, the cake layer resistances (Rc) and the fouling resistances (Rf) were measured. The Rc and Rf values for the PM30 were always higher than for the YM30 and the Rc prevailed over the Rf in all cases. The solutes rejection by the adsorption onto/into the membrane was relatively small. This suggests that the cake layer deposited on the membrane surfaces played an important role in the solute rejection, i.e. dominant solute removals were attributed to the adsorption and/or sieving onto the cakes. Consequently, the difference in solute rejection efficiency between hydrophilic and hydrophobic membranes was mainly due to the degree of sieving and/or adsorption onto the cakes deposited on the membrane, and partly due to adsorption into membrane pores and the surfaces.

Treatment of oily wastewater by ultrafiltration and ozone

Abstract An experimental study to treat and reuse oily wastewater generated from the automobile-components manufacturing industry was performed. The feasibility of using an ultrafiltration (UF) membrane and ozone treatment to reuse oily wastewater was investigated. The UF membrane system (capacity, 5 t/d) was employed to treat two kinds of degreasing wastewater and cutting oil wastewater. Flux behavior and organic removal strongly depended on the type of oily wastewater. The UF permeates from the degreasing wastewater could be reused as make-up water. However, the cutting oil formulated with the UF permeates had very different characteristics such as emulsion size and foaming ratio because surfactant existed excessively in the UF permeates. Partial oxidation of surfactants in UF permeates using ozone makes it unable to change the emulsion size, foaming ratio and refratory index, and thus, possible to reuse the UF permeates as process water.

Application of ceramic membrane as a pretreatment in anaerobic digestion of alcohol-distillery wastes☆

Abstract Pretreatment of alcohol-distillery wastes with ceramic membranes was performed prior to anaerobic digestion. Ceramic membranes with 0.05 μm pore size were chosen based on the particle size distribution in raw wastes. In this pretreatment, chemical oxygen demand (COD) was reduced from 36,000 to 18,000 mg/l and suspended solids were almost completely removed. The permeates from the ceramic membrane were further separated by ultrafiltration, but further COD reduction by using the PM30 and PM10 membranes was not achieved. Mixed stillages exhibited higher fouling tendency than pure naked barley stillage. Several cleaning methods were attempted to recover water flux. Although lumen flushing was effective, hydrogen peroxide proved to be the most effective cleaning agent. The negative flux recovery after nitric acid cleaning could be explained by the ligand exchange theory. The performance of digester was greatly improved with membrane pretreatment, specially in the ease of naked barley based stillage.

Pollution prevention for manufacturing of ammonium chloride - an ecperimental study of wastewater recycling

Abstract An experimental study was performed to assess the feasibility of recovering valuable chemical from waste streams. The ammonia in the wastewater generated from the NH 4 Cl manufacturing could be recovered using an ion-exchange technique. After the ammonia-rich wastewater passed through cation exchange resin, regeneration with HCl was performed. The resultant regenerant solution was composed of NH 4 Cl. This spent solution could be recycled into the upstream, i.e., drying process for the NH 4 Cl production. However, NH 4 Cl concentration in the regenerant solution was so little for drying that the direct recycling of the regenerant solution could not be valid. Therefore, pre-concentration of the regenerant was strongly proposed to increase the NH 4 Cl concentration. Typical concentration methods such as reverse osmosis, evaporation and electrodialysis were attempted to select an appropriate method for the pre-concentration. It was found that the electrodialysis was the most effective method to concentrate the regenerant NH 4 Cl solution. Since the ammonia concentration in the effluent of ion exchange was negligible, the effluent was able to be reused as process water or discharged directly. This new process makes it possible to recover the valuable material from the wastewater and to improve the effluent water quality. Consequently, it provides an environmentally sound alternative for manufacturing NH 4 Cl.

Development of clean technology in wafer drying processes

Abstract In the aqueous processing of silicon wafers, drying of wafers must take place after each processing step. However, the drying processes currently used are not environmentally sound, i.e., great amounts of solvents and energy are consumed. To fulfill environmental and economic requirements, a new wafer drying system based on concepts of clean technology was investigated. To reduce isopropyl alcohol (IPA) and energy consumption and to improve drying performance, a new dryer consisting of two separate chambers (IPA-chamber and drying-chamber) was developed. On-site operation with this new configuration was performed to compare its characteristics with those of other widely used dryers. It showed that IPA and energy consumption were smaller than those of the conventional dryers. Drying performance of the new dryer was also better than that of the conventional dryer. Consequently, the new dryer provides an environmentally friendly alternative to wafer drying.

Effect of PAC Addition on the Physicochemical Characteristics of Bio-Cake in a Membrane Bioreactor

The effect of powdered activated carbon (PAC) addition on the architecture and cohesion strength of bio-cake in a membrane bioreactor (MBR) was investigated. Two reactors, a conventional MBR and a membrane-coupled biological activated carbon reactor (MBR ac ), were run in parallel. The addition of PAC led to a substantial increase in membrane permeability. Based on the conventional filtration theory, microbial floc size (d), bio-cake porosity (ε), and total attached biomass (TAB) were determined to find the key mechanism for the enhanced permeability. Unexpectedly the addition of PAC did not significantly change either the microbial floc size (d) or the porosity (ε) of the bio-cake. It decreased, however, not only the concentration of extra-cellular polymeric substances (EPS) in the bulk phase but also the TAB on the membrane. Using a separate batch cohesion test, it was revealed that the cohesion strength between microorganisms in the bio-cake in the MBR ac was weaker than that in the MBR. The addition of PAC led to the reduction of EPS, which act as glue-like materials, which in turn weakened the cohesion strength of the microorganisms. This resulted in a lower amount of TAB, i.e., a smaller amount of the bio-cake on the membrane, which ultimately gave rise to the enhanced permeability in the MBR ac .

Study on the Treatment of Contaminated Lake Water Using Micro Air Bubbles

Many lakes or irrigative reservoirs in Korea are rapidly contaminated due to the ever increasing pollutants. Although lots of treatment processes have been recommended and practiced, economical and technical improvement is currently needed. In this study, contaminated irrigation reservoir was treated using the proposed process which is consisted of fine air bubbles, coagulation and flotation. Fine bubbles, approximate diameter of 3 to , were generated using cavitation in the pressurized tank and polyaluminum chloride was used as coagulants. This fine bubbles, coagulation and flotation effectively controlled the low density algae, for example, Chlorophyll-a was removed more than 97 %. Removal efficiency of COD, SS, T-N and T-P were 80.7%, 94.3%, 64.1 % and 92.4%, respectively. Pollutants released from the sediments was removed more than 80% of organics and 60-70 % of nutrients. Consequently, fine bubbles coagulation and flotation process could be effectively used as an alternative treatment method for the purpose of control of lake water quality.

Comparison of the Cake Layer Removal Options during Determination of Cake Layer Resistance (Rc) in the Resistance-In-Series Model

The resistance-in-series (RIS) model should be used cautiously, particularly in the experimental determination of the cake layer resistance (Rc) which is determined by calculation of a series of flux data that are obtained empirically before and after removing the cake layer on the membrane surface. However, the calculated Rc values are very dependent upon the cleaning methods used for removing the cake layer. Therefore, this study investigated how the various cleaning methods influence the determination of Rc. Four different cleaning methods were used: water rinsing in a shaker, manual water rinsing, ultrasonication, and sponge scrubbing. For the hydrophilic membrane, sponge scrubbing removed the cake layer completely, whereas the other methods showed removal efficiencies ranging from 79% to 99%. For the hydrophobic membrane, none of the options achieved complete cake layer removal. In addition, sponge scrubbing was not the best option for cake removal, indicating that even a method with the potential to completely remove the cake layer on a specific membrane is not universal for every kind of membrane. Consequently, a standardized method for cake layer removal to determine cake resistance (Rc) is needed for correct interpretation of the fouling phenomena with the RIS model.

A Study on the Biofouling Control in Membrane Processes Using High Voltage Impulse

Although membrane technologies are widely applied to the water and wastewater treatment processes, strategy for the control of membrane biofouling is strongly required. In this study, a possibility of control of membrane biofouling using HVI(High Voltage Impulse) was verified based on the inactivation of microorganisms by the HVI. The HVI system was consisted of power supply, voltage amplifier, impulse generator and disinfection chamber and the model microorganism was E. coli. When 15[kV/cm] of electric fields was applied to the E. coli solution, inactivation of the microorganism was found. A possibility of the control of membrane biofouling using HVI was verified with experiments of membrane filtration with and without exposure of the HVI to biomass solution. Another membrane filtration experiments with the contaminated membranes by E. coli solution were carried out and indicate that the HVI could be used as an alternative method for membrane biofouling control. A series of simulation of the electric fields between electrodes and microorganisms was carried out for the visualization of the disinfection that showed where the electric fields are formed.