Seockheon Lee

Influence of membrane surface properties on the behavior of initial bacterial adhesion and biofilm development onto nanofiltration membranes.

In order to investigate biofouling problems, the fundamental behaviors of initial bacterial adhesion and biofilm development on four different nanofiltration (NF) membranes were evaluated using Pseudomonas aeruginosa PAO1 as a model bacterial strain. Initial cell adhesion was considerably higher on an aromatic polyamide-based NF membrane with a hydrophobic and rough surface, whereas cell aggregation on a polypiperazine-based NF membrane with a relatively hydrophilic and smooth surface was lower. Moreover, significant differences in the structural heterogeneity of the biofilms were observed among the four NF membranes. This study shows that the surface roughness and hydrophobicity of a membrane play an important role in determining initial cell adhesion, aggregation and favorable localization sites for colony formation. In addition, it was found that biofilm development was strongly influenced by the surface morphology of a membrane.

Effect of anions and humic acid on the performance of nanoscale zero-valent iron particles coated with polyacrylic acid

Effects of anions (NO3(-), HCO3(-), Cl(-), SO4(2-)) and humic acid on the reactivity and core/shell chemistries of polyacrylic acid-coated nanoscale zero-valent iron (PAA-NZVI) and inorganically modified NZVI (INORG-NZVI) particles were investigated. The reactivity tests under various ion concentrations (0.2-30mN) revealed the existence of a favorable molar ratio of anion/NZVI that increased the reactivity of NZVI particles. The presence of a relatively small amount of humic acid (0.5mgL(-1)) substantially decreased the INORG-NZVI reactivity by 76%, whereas the reactivity of PAA-NZVI decreased only by 12%. The XRD and TEM results supported the role of the PAA coating of PAA-NZVI in impeding the oxidation of the Fe(0) core by groundwater solutes. This protective role provided by the organic coating also resulted in a 2.3-fold increase in the trichloroethylene (TCE) reduction capacity of PAA-NZVI compared to that of INORG-NZVI in the presence of anions/humic acid. Ethylene and ethane were simultaneously produced as the major reduction products of TCE in both NZVI systems, suggesting that a hydrodechlorination occurred without the aid of metallic catalysts. The PAA coating, originally designed to improve the mobility of NZVI, enhanced TCE degradation performances of NZVI in the presence of anions and humic acid.

Effects of washing solution and drying condition on reactivity of nano-scale zero valent irons (nZVIs) synthesized by borohydride reduction.

Washing and drying processes are essential when synthesizing nano-scale zero valent irons (nZVIs) by borohydride reduction of iron salts in aqueous phase. However, effects of these processes on nZVI reactivity have not been investigated in detail, although different washing and drying conditions might alter surface characteristics of nZVIs and thus vary their reactivity towards reducible contaminants. In this study, effects of three washing solutions and drying conditions on the reactivity of nZVIs for nitrate were investigated. Washing with volatile solvents and drying under anaerobic condition decreased thickness of Fe-oxide layer on nZVIs and increased content of Fe(2+)-containing oxides in the layer, which enhanced nZVI reactivity toward nitrate. Volatile solvent washing could minimize the decrease in nZVI reactivity according to changing anaerobic drying condition to aerobic. Findings from this study suggest that application of washing with volatile solvents and drying under aerobic condition should be recommended as effective processes to obtain nZVIs with maximum reactivity at reasonable costs and efforts.

Oxidation of bisphenol A by UV/S2O : Comparison with UV/H2O2

The UV/S2O process was applied to decompose bisphenol A (BPA), which is a representative endocrine-disrupting chemical (EDC), and was comared with the UV/H2O2 process. The BPA degradation efficiency by UV/S2O was increased by increasing S2O concentration or decreasing BPA concentration. The presence of humic acid caused an inhibitory effect. The BPA oxidation rate by UV/S2O was increased in the following order: neutral pH (pH i=7)<acidic pH (pH i=4)<basic pH (pH i=10). The main oxidizing species in the UV/S2O system was sulphate radical (SO ), whereas the main oxidizing species in the UV/H2O2 system was OH radical (OHċ). Compared with UV/H2O2, the UV/S2O process showed higher performance for not only BPA degradation but also its mineralization, which means that SO is a more effective oxidant for BPA than the OH ċ. The results shown in this study imply that the SO -based UV/S2O process can be an excellent alternative process for the widely used UV/H2O2 process, with higher remediation performance.

Chemometrics in assessment of seasonal variation of water quality in fresh water systems

The chemometric techniques were applied for evaluation of the seasonal variation of water qualities at 17 stations along a stretch of the Bagmati river of Nepal for 23 water quality parameters measured during 1999–2003. The application of discriminant analysis confirmed the classification of the water quality measurements into three seasons: pre-monsoon, monsoon, and post-monsoon affording 93.8% correct classification. Factor analysis and box–whisker plots facilitated to investigate the seasonal variation of water quality and the pattern of pollution sources. Application of FA revealed that the influence of water quality parameters changes from season to season. A parameter that is most important in contributing to water quality variation for one season may not be important for another season. Comparison of the discriminant analysis and factor analysis helped to identify the most important water quality parameters, as water temperature, DO, EC, COD, CL, Ca, alkalinity, PO4P, and TP, that are most important for seasonal variation and play a significant role in establishment of water quality control strategy.

Targeted removal of trichlorophenol in water by oleic acid-coated nanoscale palladium/zero-valent iron alginate beads.

A new material was developed and evaluated for the targeted removal of trichlorophenol (TCP) from among potential interferents which are known to degrade removal activity. To achieve TCP-targeted activity, an alginate bead containing nanoscale palladium/zero-valent iron (Pd/nZVI) was coated with a highly hydrophobic oleic acid layer. The new material (Pd/nZVI-A-O) preferentially sorbed TCP from a mixture of chlorinated phenols into the oleic acid cover layer and subsequently dechlorinated it to phenol. The removal efficacy of TCP by Pd/nZVI-A-O was not affected by co-existing organic substances such as Suwannee River humic acid (SRHA), whereas the material without the oleic acid layer (Pd/nZVI-A) became less effective with increasing SRHA concentration. The inorganic substances nitrate and phosphate significantly reduced the reactivity of Pd/nZVI-A, however, Pd/nZVI-A-O showed similar TCP removal efficacies regardless of the initial inorganic ion concentrations. The influence of bicarbonate on the TCP removal efficacies of both Pd/nZVI-A and Pd/nZVI-A-O was not significant. The findings from this study suggest that Pd/nZVI-A-O, with its targeted, constant reactivity for TCP, would be effective for treating this contaminant in surface water or groundwater containing various competitive substrates.

Modification of polyamide membrane surface with chlorine dioxide solutions of differing pH

Abstract Free chlorine is the common biocide used in the membrane desalination industry. However, it is incompatible with polyamide membranes. Chlorine dioxide (ClO2) is an effective biocide and is more compatible with polyamide membranes. The effects of ClO2 on polyamide membrane hydrophillicity and surface charge were studied under static soaking conditions. Membrane coupons were soaked in acidic, neutral, and alkaline pHs of ClO2. The membrane’s hydrophilicity and surface charge were assessed by dynamic contact angle and streaming potential analyzer respectively, while performance was analyzed on a bench scale desalination system. The result of the experiment showed that ClO2 influenced membrane hydrophilicity and surface charge. Hydrophilicity improved irrespective of ClO2 pH, whereas surface charge was either suppressed or improved depending on ClO2 pH. Permeate flux increased for acidic, neutral, and alkaline conditions by 34%, 34%, and 77%, respectively. A slight trade-off in salt leakage for acidi...

A Detailed Investigation of Phosphorus Removal in Soil and Slag Media

Kinetic studies on phosphorus (P as orthophosphate) sorption onto a sandy loam soil from North Sydney, Australia, and a slag (waste products from the BHP steel industry, Australia) revealed that more than 90% of the P was adsorbed within 70 and 12 hours for the soil and slag respectively. The pH of the P solution played a critical role in the rate of P removal. Removal was at a minimum at pH 2. Dominant removal mechanism of P at pH less than 8 was physical sorption, while it was chemical precipitation at pH greater than 10. Adsorptive capacity of the slag was 225 and 53 times of that of the soil for the static and dynamic systems respectively. Breakthrough curves obtained from the column experiments are S-shaped and more spreaded with the decrease of influent P concentration. Simulated results from an equilibrium sorption model (ESM) and Freundlich isotherm constants did not always match the corresponding experimental breakthrough data. Mobility of P is restricted by the adsorbent due to its high sorption...

Optimization of the mechanical strength of PVA/alginate gel beads and their effects on the ammonia-oxidizing activity

AbstractPoly (vinyl alcohol) (PVA)/alginate gel beads were fabricated to entrap ammonia-oxidizing bacteria. The PVA/alginate gel beads were prepared in different conditions to investigate the effects of the fabrication procedures on the mechanical strength and the initial ammonia-oxidizing activity. For the mechanical strength, the optimal conditions were analyzed using response surface analysis (RSA) considering the inter-correlated effects of the reaction times of cross-linking and phosphorylation. For RSA, nine trials resulted in a partial cubic polynomial equation, which best predicted the amount of residual debris after homogenization. In the model, the optimum conditions of 3.5 h of cross-linking and 5.6 h of phosphorylation were estimated to ensure the maximum mechanical strength. The initial ammonia-oxidizing activity was significantly affected by the cross-linking due to the highly acidic environment of pH 3.3, but it was not affected by the phosphorylation in pH 4.2. Batch experiments to measure...

Effect of engineered environment on microbial community structure in biofilter and biofilm on reverse osmosis membrane

Four dual media filters (DMFs) were operated in a biofiltration mode with different engineered environments (DMF I and II: coagulation with/without acidification and DMF III and IV: without/with chlorination). Designed biofilm enrichment reactors (BERs) containing the removable reverse osmosis (RO) coupons, were connected at the end of the DMFs in parallel to analyze the biofilm on the RO membrane by DMF effluents. Filtration performances were evaluated in terms of dissolved organic carbon (DOC) and assimilable organic carbon (AOC). Organic foulants on the RO membrane were also quantified and fractionized. The bacterial community structures in liquid (seawater and effluent) and biofilm (DMF and RO) samples were analyzed using 454-pyrosequencing. The DMF IV fed with the chlorinated seawater demonstrated the highest reductions of DOC including LMW-N as well as AOC among the other DMFs. The DMF IV was also effective in reducing organic foulants on the RO membrane surface. The bacterial community structure was grouped according to the sample phase (i.e., liquid and biofilm samples), sampling location (i.e., DMF and RO samples), and chlorination (chlorinated and non-chlorinated samples). In particular, the biofilm community in the DMF IV differed from the other DMF treatments, suggesting that chlorination exerted as stronger selective pressure than pH adjustment or coagulation on the biofilm community. In the DMF IV, several chemoorganotrophic chlorine-resistant biofilm-forming bacteria such as Hyphomonas, Erythrobacter, and Sphingomonas were predominant, and they may enhance organic carbon degradation efficiency. Diverse halophilic or halotolerant organic degraders were also found in other DMFs (i.e., DMF I, II, and III). Various kinds of dominant biofilm-forming bacteria were also investigated in RO membrane samples; the results provided possible candidates that cause biofouling when DMF process is applied as the pretreatment option for the RO process.