Seok-Oh Ko

MODIFICATION OF COAGULATION AND FENTON OXIDATION PROCESSES FOR COST-EFFECTIVE LEACHATE TREATMENT

Physicochemical processes have been used to remove nonbiodegradable organic compounds in leachate generated from sanitary landfills. In this study, a coagulation process combined with Fenton oxidation was evaluated for the removal of refractory organics in leachate. Recycling of sludge generated from Fenton oxidation to a coagulation process was attempted to reduce operation cost and to improve organic removal rate. The addition mode of Fenton reagent was also modified to obtain a better organic removal rate and more cost-effective operation. With Fenton sludge recycling, 9% higher COD removal was obtained, and the sludge to be disposed could be reduced up to 50%. Also, the coagulant could be reduced by 50%. For Fenton oxidation process, stepwise addition of reagents gave a 5% higher COD removal, and a 25% reduction in chemical consumption.

Effects of ozonation and coagulation on effluent organic matter characteristics and ultrafiltration membrane fouling.

Effluent organic matter (EfOM) is the major cause of fouling in the low pressure membranes process for wastewater reuse. Coagulation and oxidation of biological wastewater treatment effluent have been applied for the fouling control of microfiltration membranes. However, the change in EfOM structure by pre-treatments has not been clearly identified. The changes of EfOM characteristics induced by coagulation and ozonation were investigated through size exclusion chromatography, UV/Vis spectrophotometry, fluorescence spectrophotometry and titrimetric analysis to identify the mechanisms in the reduction of ultrafiltration (UF) membrane fouling. The results indicated that reduction of flux decline by coagulation was due to modified characteristics of dissolved organic carbon (DOC) content. Total concentration of DOC was not reduced by ozonation. However, the mass fraction of the molecules with molecular weight larger than 5 kDa, fluorescence intensity, aromaticity, highly condensed chromophores, average molecular weight and soluble microbial byproducts decreased greatly after ozonation. These results indicated that EfOM was partially oxidized by ozonation to low molecular weight, highly charged compounds with abundant electron-withdrawing functional groups, which are favourable for alleviating UF membrane flux decline.

Reductive dechlorination of chlorinated biphenyls by palladized zero-valent metals.

Abstract Laboratory-scale reductive dechlorination studies using bimetals were conducted to detoxify chlorinated biphenyls, which are known as one of the most recalcitrant organic compounds. Palladized iron and palladized zinc readily dechlorinated mono- and di-chlorinated biphenyls while plain metals were not active. Biphenyl and less chlorinated biphenyls were detected as the major products and calculated mass balance was around 100%, indicating that predominant degradation reaction was dechlorination. For Pd/Fe, degradation rates of mono-chlorobiphenyls were higher than those of di-chlorobiphenyls. Pd/Zn showed higher reactivity than Pd/Fe for the degradation of chlorobiphenyls. Degradation rates of three mono-chlorobiphenyls were in order of 4-CBP > 3-CBP > 2-CBP and this order was matched with the selectivity and dechlorination rate of dichlorobiphenyls. Based on the detected daughter products, it was considered that degradation reaction of dichlorobiphenyls was mainly governed by stepwise dechlorination. However, sequential reaction model fittings indicated that concerted dechlorination was also partly involved in the dichlorobiphenyl degradation. This study demonstrated that catalytically modified ZVM could be successfully applied for the detoxification of chlorinated aromatic compounds including PCBs.

Kinetic Studies of Reductive Dechlorination of Chlorophenols with NI/FE Bimetallic Particles

The catalytic dechlorination of five chlorophenols, by Ni/Fe bimetal was investigated through batch experiments. The results showed that the destruction of chlorophenols by hydrodechlorination over Ni/Fe was very effective and followed the pseudo-first-order kinetics under aqueous conditions. The order of reaction rate was 2-chlorophenol > 4-chlorophenol > 2,4-dichlorophenol > 2,4,6-trichlorophenol > 2,6-dichlorophenol (2,6-DCP). The dechlorination rate of chlorophenol increased linearly with increasing nickel coating on iron. In general, increasing the degree of chlorine substitution on the phenol ring decreased the rate of dechlorination except for 2,6-DCP. Chlorophenols were dechlorinated to phenol via both stepwise as the major pathway and concerted mechanisms with minor contribution. The relative contribution of each reaction pathway is discussed through a model fitting.

Stabilization of hydrogen peroxide using phthalic acids in the Fenton and Fenton-like oxidation.

The stabilization of hydrogen peroxide was evaluated in Fenton reaction with phthalic acid as a stabilizer. The stabilization effect was high at a low pH<pK(a1) and the effect was negligible at a high pH above pK(a2) in both Fenton and Fenton-like reactions. While the lifetime of hydrogen peroxide was prolonged by phthalic acid, the stabilization could not contribute on the increase of the reaction rate in the current Fenton and Fenton-like experimental systems because the systems were all well mixed systems. The interaction between dissolved iron and phthalic acid was spectroscopic monitored in variable pH over pK(a1) and pK(a2) of phthalic acid. Ferrous iron was well stabilized and the initial concentration was kept after mixing with phthalate while ferric iron was removed from the aqueous phase by the phthalic acid. It could be concluded that the stabilization by phthalic acid is due to inhibition of catalytic activity of dissolved iron and minimizes the self-decomposition of hydrogen peroxide. The stabilization is affected by ionization state of the organic acid.

A Laboratory and Pilot Study of Thermally Enhanced Soil Vapor Extraction Method for the Removal of Semi-Volatile Organic Contaminants

Abstract Laboratory and field pilot study was conducted to evaluate the effectiveness of thermally enhanced soil vapor extraction (SVE) system for the removal of semi-volatile organic contaminants (SVOCs) from soils. Several parametric studies were conducted to evaluate the effect of temperature and air flow rate on the removal of SVOCs. Column studies near ambient temperature show very little efficiency for SVOCs removal. The removal rates of SVOCs are highly dependent on temperature. Moving fronts in the effluent concentrations of contaminants are observed, according to the order of volatility of contaminant. This result is attributed to continuous changes in the liquid composition toward less volatile fractions, thus increasing the mole fraction of the less volatile fractions remaining in the liquid mixture. It is also found that increased air flow rate results in high removal rate of contaminants. However, too high air flow rate brings about the mass transfer limitation on the volatilization of the contaminants. Results from steady-state column studies show that mass transfer limitation is reduced at high temperature, possibly due to the increase in the diffusivity of contaminant in the liquid and gas phase. A field pilot study of a hot air injection method for the remediation of diesel-contaminated soil has shown advantages over the conventional SVE. Within 30 days of test operation, TPH concentrations at unsaturated soils were dramatically reduced, corresponding to more than 95% removal. However, temperature profiles and the removal rates of SVOCs near groundwater level indicate that moisture content would be a limiting factor in the real application of hot air injection.

Humic acid characteristics and effects on the reactivity of nano-scale zero-valent iron particles during nitrate reduction

ABSTRACT Humic acid (HA) comprises a significant fraction of natural organic matter (NOM), greatly influencing the performance of water and wastewater treatment processes. HA is expected to significantly affect the reactivity of nano-scale zero-valent iron (NZVI), which is receiving increasing attention due to its high reactivity. The effects of HA on nitrate reduction by NZVI were investigated to evaluate the potential of NZVI in practical applications. HA was characterized to identify the mechanism whereby HA affects. Nitrate reduction was enhanced at low HA concentration, but inhibited as HA concentration increased. HA decreased to reach a plateau and considerable amount of Fe3+ was detected when HA was present in dissolved phase. The increase in the degree of condensation of HA was verified by UV–vis spectroscopy, fluorescence spectroscopy, and size exclusion chromatography. Fourier transform infrared spectra confirmed that the Fe3+–HA complexes were formed in both the dissolved and solid fractions, w...

Characterization of sludge generated by electrocoagulation for the removal of heavy metals

AbstractIn this work, heavy metal removal by electrocoagulation (EC) was evaluated, and the characteristics of the EC sludge were investigated to understand the behavior of heavy metals during EC. It was found that iron electrodes are superior to aluminum due to the negatively charged surface. Using iron electrodes, the removal rate of heavy metals increased as the current density increased and as the total initial heavy metal amount, either single or multiple heavy metals, decreased, suggesting that the efficiency is closely related to the floc amount. The X-ray diffraction (XRD) patterns showed that the chemical species in the EC sludge are different from those obtained by chemical equilibrium analysis, indicating that many electrochemical and chemical reactions occur during EC. The pH variation during EC and the XRD patterns of the sludge indicate that precipitation, adsorption, and chemical oxidation/reduction in the vicinity of the electrodes contribute much to Pb(II), Cd(II), and Cu(II) removal, res...

Deactivation of nanoscale zero-valent iron by humic acid and by retention in water

The effects of the deactivation of nanoscale zero-valent iron (NZVI), induced by humic acid (HA) and by the retention of NZVI in water, on nitrate reduction were investigated using a kinetic study. Both the nitrate removal and generation of ammonia were significantly inhibited as the HA adsorption amount and retention time were increased. However, HA removal was greatly enhanced when the NZVI was used after 1 d or 25 d of retention in water. The results are caused by the formation of iron oxides/hydroxides, which increased the specific surface area and the degree of NZVI aggregation which was observed by transmission electron microscopy (TEM). However, the nitrate reduction was greater at the beginning of reaction in the presence of HA when fresh NZVI was used, because of the enhanced electron transfer by the HA in bulk phase and on NZVI surface as train sequences. The pseudo second order adsorption kinetic equation incorporating deactivation and a Langmuir-Hinshelwood (LH) type kinetic equation provided accurate descriptions of the nitrate removal and ammonia generation, respectively. The deactivation constant and the reaction rate constant of the LH type kinetic equation were strongly correlated with the HA amount accumulated on NZVI. These results suggest that the HA accumulation on the NZVI surface reactive sites plays the dominant role in the inhibition and the inhibition can be described successfully using the deactivation model. The HA accumulation on NZVI was verified using TEM.

Transformation of dissolved organic matter by oxidative polymerization with horseradish peroxidase

Dissolved organic matter (DOM) has significant influence on the transport and fate of contaminants in multiple phases and it has potential hazard by acting as a precursor of disinfection by-products in water supply. The changes in DOM characteristics, especially by oxidative polymerization might result in different behaviour in the interaction with many contaminants. The aim of this work was to verify the catalytic effects of peroxidase on oxidative polymerization of humic and fulvic substances by examination of the structural characteristics. Transformation of humic acid (HA) and fulvic acid (FA) by oxidative polymerization catalyzed by horseradish peroxidase and hydrogen peroxide were investigated. Size exclusion chromatography, excitation-emission matrices spectra (EEMs), synchronous fluorescence spectra, and infrared spectroscopy was used to evaluate the structural transformation of HA and FA. Molecular weight of HA and FA was continuously changed and their weight-average molecular weight (MWw) reached maximum after 8 h. The MWw of HA and FA were proportionally increased with a dosage of horseradish peroxidase and hydrogen peroxide, indicating that HA and FA was transformed into larger and complex molecules. Spectroscopic results indicated that HA and FA structure contains strong polycyclic aromatic structures with more aromatic rings and a higher degree of conjugation.