Kwang-Ho Choo

Membrane fouling mechanisms in the membrane-coupled anaerobic bioreactor

Abstract This study focused on the membrane fouling mechanisms during the longtime operation of a membrane-coupled anaerobic bioreactor (MCAB) system designed for the treatment of alcohol-distillery wastewater. This system provided interesting information on anaerobic digestion and membrane performance associated with the fouling mechanisms in the membrane bioreactor. Enhanced COD removal was achieved with the complete retention of biomass either inside the anaerobic reactor or on the membrane surface. Membrane fouling was mainy attributed to external fouling, which was closely related to the movement of cell population to the membrane surface and inorganic precipitation at the membrane surface. The major composition of the inorganic foulant was identified as MgNH 4 PO 4 ·6H 2 O (struvite), whose deposition together with the microbial cells attached at the membrane surface played a significant role in the formation of the strongly attached cake layer limiting membrane permeability. The struvite precipitation/deposition mechanisms were examined thoroughly in relation to the chemical composition of the influent wastewater and the subsequent anaerobic decomposition in the membrane bioreactor. The conceptual resistance-in-series model was applied to assess the fouling characteristics.

Hydrophilic modification of polypropylene microfiltration membranes by ozone-induced graft polymerization

Abstract Hydrophilic modification of polypropylene microfiltration membranes was performed with the introduction of peroxide onto the membrane surface by ozone treatment followed by graft polymerization with hydroxyethyl methacrylate (HEMA). The grafting was initiated at a mild temperature by redox decomposition of the peroxide. The ozone treatment time was optimized in the range of 3–5xa0min to have a degree of grafting while keeping the mechanical strength. The HEMA grafting made the surface of the PP membrane hydrophilic and less adsorbable to BSA proteins, although its effects were dependent on the ozone treatment time. The grafted membrane with 5xa0min ozone treatment gave greater flux recoveries (up to approximately 95%) at the end of the MF of the BSA solution, suggesting that the protein fouling layer was reversible because of the hydrophilic nature of the modified membranes.

Flux Enhancement with Powdered Activated Carbon Addition in the Membrane Anaerobic Bioreactor

The effect of powdered activated carbon (PAC) addition on the performance of a membrane-coupled anaerobic bioreactor (MCAB) was investigated in terms of membrane filterability and treatabilty through a series of batch and continuous microfiltration (MF) experiments. In both batch and continuous MF of the digestion broth, a flux improvement with PAC addition was achieved, especially when a higher shear rate and/or a higher PAC dose were applied. Both the fouling and cake layer resistances decreased continuously with increasing the PAC dose up to 5 g/L. PAC played an important role in subtantially reducing the biomass cake resistance due to its incompressible nature and higher backtransport velocities. PAC might have a scouring effect for removing the deposited biomass cake from the membrane surface while sorbing and/or coagulating dissolved organics and colloidal particles in the broth. The chemical oxygen demand and color in the effluent were much removed with PAC addition, and the system was also more st...

Effect of the removal of DOMs on the performance of a coagulation-UF membrane system for drinking water production

Coagulation with only rapid mixing in a separate tank (ordinary coagulation) and coagulation with no mixing tank (in-line coagulation) were applied prior to ultrafiltration with an inside-out type hollow fiber membrane. In result the filterability at the former conditions was superior in both the crossflow and dead-end modes. Thus the relative importance of the removal rate of DOMs was investigated. Precoating the surface of the membranes with metal hydroxide particles of coagulants was also examined. This method of utilizing coagulants resulted in a smaller consumption of coagulant in the coagulation-UF system.

Activated carbons impregnated with iron oxide nanoparticles for enhanced removal of bisphenol A and natural organic matter.

The removal of bisphenol A (BPA) is important for the provision of safe drinking water, but its removal in the presence of natural organic matter (NOM) is challenging. Thus, the present study involved the fabrication and characterization of powdered activated carbons impregnated with iron oxide nanoparticles (IONPACs) with respect to the simultaneous removal of BPA and NOM. The number of Fe ions loaded into the PAC pores was optimized in terms of exposure time. Impregnation with iron oxide reduced the surface area and pore volume, but the pore size was maintained. IONPAC adsorbents had considerably greater sorption capabilities for BPA and NOM compared to native, bare PAC particles. The adsorption capacities of BPA and NOM were in the following sequence: bare PAC<hematite/PAC < magnetite/PAC < ferrihydrite/PAC. The enhanced removal by IONPACs was attributable to the surface coordination between the functional groups in the iron oxides (e.g., hydroxyl groups) and organics (e.g., phenolic/carboxyl groups). Iron oxide impregnation enabled the BPA uptake to be maintained in the presence of NOM, indicating that the hybrid adsorbent provided synergistic adsorption characteristics for BPA and NOM. Although the solution pH had a negligible impact on BPA uptake, the ionic strength showed a significant effect, particularly in the presence of divalent Ca ions.

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.

A hybridized photocatalysis-microfiltration system with iron oxide-coated membranes for the removal of natural organic matter in water treatment: effects of iron oxide layers and colloids.

A photocatalysis/microfiltration (MF) hybrid system, with the coating of a membrane using iron oxide particles (IOPs), was investigated with respect to natural organic matter (NOM) removal and membrane permeability during the treatment of various surface waters. A comparison of the performance between bare (uncoated) and IOP-coated membranes employed for the photocatalytic hybrid system was made. Due to the additional adsorption of NOM onto IOPs on the membrane surface, the IOP-coated membrane system always achieved greater DOC removal efficiencies during photocatalysis/MF. Particularly, the influence of colloidal particles that were present in different water sources with respect to membrane fouling was explored. Colloidal fouling occurred to both bare and IOP-coated membranes, but the interaction of colloids with IOP coating layers was in close association with the characteristics of colloids, such as size distribution, resulting in opposing fouling behaviors with varying water sources. The IOP-coated membrane was able to control fouling properly when a relatively large size of colloidal particles existed in raw water, but not for the case of small colloids. The IOP coat layer may become denser as small colloids penetrate into it, therefore leading to further fouling. The analysis of the hydraulic filtration resistances revealed that such fouling was virtually reversible in being removed by backwashing processes. Scanning electron microscopic observations, however, visualized the existence of several foulants remaining at the membrane surface after backwashing when feed water, containing a relatively large portion of small-sized colloids, was supplied.

Effect of precipitation and complexation on nanofiltration of strontium-containing nuclear wastewater

Abstract The performance of nanofiltration (NF) with the addition of poly (acrylic acid) (PAA) for treatment of strontium-bearing nuclear wastewater was investigated using different NF membranes at various pH levels and PAA/Sr ratios. Greater Sr removal at elevated pH was attributed to the formation of SrCO3(s) due to the dissolution of atmospheric CO2. A substantial improvement in Sr removal was achieved with the addition of PAA that can make complexes with strontium ions and then be rejected by NF membranes. However, a rapid decrease in feed solution pH aggravated the fouling of a NF membrane, possibly because of the formation and the sorption of associated forms of PAA at the membrane surface.

Hybridization of physical cleaning and quorum quenching to minimize membrane biofouling and energy consumption in a membrane bioreactor

Membrane fouling and energy consumption are interconnected and considered as a bottleneck in membrane bioreactor (MBR) applications. This study investigated synergistic combinations of quorum quenching (QQ) and physical cleaning under different cleaning conditions and aeration intensities with respect to fouling control and energy saving. The MBR operated with periodic air backpulsing had a lower fouling tendency compared with the reactor operated with relaxation. Frequent physical cleanings mitigated the membrane fouling, but irreversible fouling inevitably occurred over time. A significant improvement in fouling control was accomplished when QQ was coupled with physical cleanings, particularly in the filtration/relaxation mode. The submerged QQ vessel helped operate the MBRs stably even at the lowest end of aeration intensity (51 s(-1) in G value), without any significant loss of membrane permeability. The specific membrane filtration energy of the QQMBR remained low and independent of aeration intensities tested, whereas that of the normal MBR sharply increased with decreased aeration rates. The QQMBR with low aeration intensity (51 s(-1)) reduced approximately 27% of the specific aeration energy required for the MBR operated at high aeration intensity (103 s(-1)). QQ bacteria should hamper the formation of a biofilm on the membrane surface, but mixed liquor properties and treatment performances were not affected by the QQ activity.

Removal of residual organic matter from secondary effluent by iron oxides adsorption

Abstract Residual organic matter (ROM) removal is an important issue in wastewater reclamation and reuse processes. Use of iron oxide particles (IOPs) as adsorbents for further treatment of the secondary effluent was investigated to mainly remove non-biodegradable residual organic matter under various operating conditions. ROM removal by IOP adsorption was evaluated in terms of the changes of UV absorbance, COD, and DOC concentrations in feed (secondary effluent) and treated water. The respective relationship of UV removal with COD and DOC removal efficiencies exhibited somewhat different profiles, possibly due to the influence of ROM properties on adsorptive removal mechanisms by IOP, such as hydrophobicity and coordinative capability. The types of IOPs such as ferrihydrite, geothite, and hematite were compared, and it was found that amorphous ferrihydrite was most effective in ROM removal. Maximum ROM removal was occuring at a solution pH of approximately 6.0, which might be ascribed to the ability of ligand exchange related to the association and dissociation of ROM molecules and IOPs at differing pH levels. Substantial reduction in the oxidation state (OS) of the treated water at high ROM removal indicated the coordination of highly oxidized groups in ROM at the IOP surface, such as carboxylic groups.