Characterization of marine dissolved organic matter and its effect on ozonation.

As the marine industry develops, the importance of seawater treatment process is increasing. To treat seawater, oxidation processes have primarily been used, such as ballast water treatment systems, aquaculture farm operations, aquarium management, and seawater desalination. However, dissolved organic matter in seawater, whose characteristics vary spatially and seasonally, affects the efficiency of oxidation processes. Therefore, in this study, seawater samples were acquired from various locations in the Republic of Korea to understand the spatio-temporal patterns of marine dissolved organic matter. It was reported that the characterization of marine dissolved organic matter using liquid chromatography-organic carbon detector and excitation-emission matrix-parallel factor modeling. Furthermore, the effects of marine dissolved organic matter were evaluated on ozonation, an oxidation process. The results demonstrate that marine dissolved organic matter varies in its aquagenic, pedogenic, and intermediate characteristics based on region and season. These variations affect ozonation by influencing the consumption of oxidants (e.g., bromine). As a result, it was concluded that characterizing marine dissolved organic matter can help improve the effectiveness of oxidation processes, particularly ozonation.

The Impact of Natural Variation of OH Radical Demand of Drinking Water Sources on the Optimum Operation of the UV/H2O2 Process.

Hydroxyl radical (•OH) water demand is a key parameter which impacts the design and operation of UV/H2O2 process for water treatment. Long-term monitoring of the •OH water demand in water sources used for drinking water production indicated significant seasonal variations of this parameter (1.59 × 104 to 4.98 × 104 s-1), which coincided with the occurrence of algal blooming events. Pilot-scale tests at a drinking water treatment plant confirmed that the UV/H2O2 process performance for contaminant removal is predictable when the •OH water demand is accurately determined through a validated experimental method. A predictive tool was developed to identify the optimum operating conditions of the UV system with the UV/H2O2 process and it was used to demonstrate the significant impact of seasonal variations of •OH water demand on the operating costs.

Evaluation of Moringa oleifera seed extract by extraction time: effect on coagulation efficiency and extract characteristic.

The seed of Moringa oleifera (MO) is a well-known coagulant used in water and wastewater treatment, especially in developing countries. The main mechanism of MO seed extract in coagulation is the positive protein component for charge neutralization. The method for efficient extraction of MO seed is very important for high coagulation activity. In this study, the effects of extraction mixing speed and extraction time of MO on coagulation activity were evaluated using a distilled water extraction method. Although the rotation per minute for extraction did not affect the coagulation efficiency, the extraction time strongly affected the coagulation efficiency of the extract. To evaluate the characteristic change of MO extract by extraction time, the charge of MO extract and protein characteristic in MO extract were analysed. As the extraction time was short, more positive charge and higher protein content were observed. For detailed protein analysis, the fluorescence spectroscopic study (EEM analysis) was performed. The tryptophan-like peak increased at longer extraction times. For efficient extraction of MO seed, a short extraction time is strongly recommended.

Characteristics of intracellular algogenic organic matter and its reactivity with hydroxyl radicals.

The aim of this study was to investigate the reactivity of intracellular algogenic organic matter (IOM) with hydroxyl radicals (·OH), a key reaction species in advanced oxidation processes. IOM was extracted from two green algae, Chlamydomonas reinhardtii and Scenedesmus sp., and two blue-green algae, Anabaena sp. and Microcystis aeruginosa using a freeze-thaw method. The second-order rate constants of the extracted IOM with ·OH were determined as 7.95 × 108 MC-1 s-1 (Chlamydomonas reinhardtii), 6.71 × 108 MC-1 s-1 (Scenedesmus sp.), 4.02 × 108 MC-1 s-1 (Anabaena sp.), and 4.45 × 108 MC-1 s-1 (Microcystis aeruginosa). These rate constants were significantly higher than values reported for dissolved organic matter in various water sources. This implies that IOM formation during algal bloom season could change the ·OH water matrix demand and adversely affect the performance of advanced oxidation processes. To investigate the physical and chemical composition characteristics of IOM and their relationship to the rate constants determined for the reaction between IOM and ·OH, liquid chromatography-organic carbon detection (LC-OCD) and fluorescence excitation-emission matrix & parallel factor analysis (FEEM-PARAFAC) were used. The IOM mainly consisted of low molecular weight (LMW) matter and protein-related compounds, as evidenced LMW neutrals (38-65%), biopolymers (7-19%), and tryptophan-like compounds (74-94%). Based on the composition characteristics of IOM, it was concluded that the molecular weight and the presence of nitrogen-containing compounds are influential parameters for determining the reactivity of IOM with ·OH.

Removal of sulfamethoxazole, ibuprofen and nitrobenzene by UV and UV/chlorine processes: A comparative evaluation of 275 nm LED-UV and 254 nm LP-UV.

The aim of this study is to evaluate the micropollutant removal capacity of a 275 nm light-emitting diode (LED)-UV/chlorine system. The sulfamethoxazole, ibuprofen, and nitrobenzene removal efficiencies of this system were compared with those of a conventional 254 nm low-pressure (LP)-UV system as a function of the UV dose. In a direct photolysis system, the photon reactivity of sulfamethoxazole is higher than that of nitrobenzene and ibuprofen at both wavelengths. The molar absorption coefficients and quantum yields of each micropollutant were as follows: sulfamethoxazole (εSMX, 275 nmprotonated = 17,527 M-1 cm-1, ΦSMX, 275 nmprotonated = 0.239, εSMX, 275 nmdeprotonated = 8430 M-1 cm-1, and ΦSMX, 275 nmdeprotonated = 0.026), nitrobenzene (εNB, 275 nm = 7176 M-1 cm-1 and ΦNB, 275 nm = 0.057), and ibuprofen (εNB, 275 nm = 200 M-1 cm-1 and ΦIBF, 275 nm = 0.067). The photon reactivity of chlorine species, i.e., HOCl and OCl-, were determined at 275 nm (εHOCl, 275 nm = 28 M-1 cm-1, ΦHOCl, 275 nm = 1.97, εOCl-, 275 nm = 245 M-1 cm-1, and ΦOCl-, 275 nm = 0.8), which indicate that the decomposition rate of OCl- is higher and that of HOCl is lower by 275 nm photolysis than that by 254 nm photolysis (εHOCl, 254 nm = 60 M-1 cm-1, ΦHOCl, 254 nm = 1.46, εOCl-, 254 nm = 58 M-1 cm-1, and ΦOCl-, 254 nm = 1.11). In the UV/chlorine system, the removal rates of ibuprofen and nitrobenzene were increased by the formation of OH and reactive chlorine species. The 275-nm LED-UV/chlorine system has higher radical yields at pH 7 and 8 than the 254 nm LP-UV/chlorine system.

Efficient removal of arsenic by strategically designed and layer-by-layer assembled PS@+rGO@GO@Fe3O4 composites.

The PS@+rGO@GO@Fe3O4 (PG-Fe3O4) hybrid composites for Arsenic removal were successfully fabricated and well dispersed using layer-by-layer assembly and a hydrothermal method. The PG-Fe3O4 hybrid composites were composed of uniformly coated Fe3O4 nanoparticles on graphene oxide layers with water flow space between 3D structures providing many contact area and adsorption sites for Arsenic adsorption. The PG-Fe3O4 hybrid composite has large surface adsorption sites and exhibits high adsorption capacities of 104 mg/g for As (III) and 68 mg/g for As (V) at 25 °C and pH 7 comparison with pure Fe3O4 and P-Fe3O4 samples.

Performance characterization and kinetic modeling of ozonation using a new method: ROH,O3 concept.

Ozonation is an effective treatment for removing various organic pollutants from aquatic systems. The Rct concept, which is defined as the ratio of OH exposure to O3 exposure, has been widely used to predict the removal efficiency of target compounds, but it has significant variations by water temperature and initial O3 dose which are crucial parameters in drinking water plant. The ROH,O3 concept, which is defined as the OH exposure by O3 consumption, was proposed as a kinetic parameter for characterization and kinetic modeling for ozonation. The ROH,O3 concept is independent of temperature and initial O3 dose. A higher ROH,O3 value indicates a higher OH formation when the same amount of O3 is consumed in different water samples; therefore, the OH yield from O3 decomposition of the water samples can be compared using the ROH,O3 values. The ROH,O3 concept can also be used to characterize and model the initial ozone demand phase, and it is more convenient method compared to Rct concept. Using the ROH,O3 concept, the dynamic O3 and OH kinetics and the removal efficiencies of iopromide and ibuprofen were well predicted (R2 = 0.98) over a wide range of experimental conditions (n = 124).

Characteristics and fate of natural organic matter during UV oxidation processes.

Advanced oxidation processes (AOPs) are widely used in water treatments. During oxidation processes, natural organic matter (NOM) is modified and broken down into smaller compounds that affect the characteristics of the oxidized NOM by AOPs. In this study, NOM was characterized and monitored in the UV/hydrogen peroxide (H2O2) and UV/persulfate (PS) processes using a liquid chromatography-organic carbon detector (LC-OCD) technique, and a combination of excitation-emission matrices (EEM) and parallel factor analysis (PARAFAC). The percentages of mineralization of NOM in the UV/H2O2 and UV/PS processes were 20.5 and 83.3%, respectively, with a 10 mM oxidant dose and a contact time of 174 s (UV dose: approximately 30,000 mJ). Low-pressure, Hg UV lamp (254 nm) was applied in this experiment. The steady-state concentration of SO4- was 38-fold higher than that of OH at an oxidant dose of 10 mM. With para-chlorobenzoic acid (pCBA) as a radical probe compound, we experimentally determined the rate constants of Suwannee River NOM (SRNOM) with OH (kOH/NOM = 3.3 × 108 M-1s-1) and SO4- (kSO4-/NOM = 4.55 × 106 M-1s-1). The hydroxyl radical and sulfate radical showed different mineralization pathways of NOM, which have been verified by the use of LC-OCD and EEM/PARAFAC. Consequently, higher steady-state concentrations of SO4-, and different reaction preferences of OH and SO4- with the NOM constituent had an effect on the mineralization efficiency.

Comparative evaluation of magnetite-graphene oxide and magnetite-reduced graphene oxide composite for As(III) and As(V) removal.

Arsenic removal using Fe3O4-graphene oxide composite (M-GO) and Fe3O4-reduced graphene oxide composite (M-rGO) was investigated. The M-GO was more effective to adsorb both As(III) and As(V) than M-rGO, because the more functional groups existing on the M-GO could lead to synthesize more Fe3O4 with M-GO. As(III) was more favorable to be adsorbed than As(V) onto both M-GO and M-rGO. According to the effect of pH on arsenic removal, the electrostatic interaction between the positively charged surface of Fe3O4-graphene based adsorbents and anionic As(V) species was a major factor to adsorb As(V). The adsorption mechanism of As(III), on the other hand, was strongly affected by a surface complexation, rather than electrostatic interactions. Consequently, in terms of the process energy consumption, energy saving could be achieved via omitting the reduction process to fabricate M-rGO from M-GO and the pre-oxidation process to convert As(III) to As(V).

Evaluation of the formation of oxidants and by-products using Pt/Ti, RuO2/Ti, and IrO2/Ti electrodes in the electrochemical process.

The aim of this study was to evaluate the formation of oxidants and by-products by using different electrode materials, such as Pt/Ti, RuO2/Ti, and IrO2/Ti, in the electrochemical process. The harmful by-products ClO3- and ClO4- were formed during the electrolysis of a Cl- electrolyte solution, as well as active chlorine, which is the most common water disinfectant. With regard to drinking water treatment, the most efficient electrode was defined as that leading to a higher formation of active chlorine and a lower formation of hazardous by-products. Overall, it was found that the Pt/Ti electrode should not be used for drinking water treatment applications, while the IrO2/Ti and RuO2/Ti electrodes are ideal for use.

Inactivation characteristics of ozone and electrolysis process for ballast water treatment using B. subtilis spores as a probe.

Since ballast water affects the ocean ecosystem, the International Maritime Organization (IMO) sets a standard for ballast water management and might impose much tighter regulations in the future. The aim of this study is to evaluate the inactivation efficiency of ozonation, electrolysis, and an ozonation-electrolysis combined process, using B. subtilis spores. In seawater ozonation, HOBr is the key active substance for inactivation, because of rapid reactivity of ozone with Br(-) in seawater. In seawater electrolysis, it is also HOBr, but not HOCl, because of the rapid reaction of HOCl with Br(-), which has not been recognized carefully, even though many electrolysis technologies have been approved by the IMO. Inactivation pattern was different in ozonation and electrolysis, which has some limitations with the tailing or lag-phase, respectively. However, each deficiency can be overcome with a combined process, which is most effective as a sequential application of ozonation followed by electrolysis.

Alternative Electrode Materials and Ceramic Filter Minimize Disinfection Byproducts in Point-of-Use Electrochemical Water Treatment.

Effects of various electrodes and prefiltration to minimize disinfection byproducts (DBPs) in electrochemical water disinfection was evaluated. The target microorganism, Escherichia coli O157:H7, was effectively inactivated even applying a solar-charged storage battery for the electrolysis process. Extent of microbial inactivation decreased with lower water temperature and higher pH in the free chlorine disinfection system. The RuO2/Ti electrode was most efficient because it produced the lowest concentration of chlorate and the highest generation of free chlorine. Prefiltration using a ceramic filter inhibited formation of halogenated DBPs because it removed precursors of DBPs. For safe point-of-use water treatment, the use of a hybrid prefiltration stage with the electrolysis system is strongly recommended to reduce risks from DBPs. The system is particularly suited to use in developing regions.

Evaluation of disinfection efficacy and chemical formation using MPUV ballast water treatment system (GloEn-Patrol).

This study was undertaken to evaluate the efficacy of inactivation of several indigenous marine species and the formation of oxidants and other by-products using medium-pressure ultraviolet (MPUV) ballast water treatment. The ballast water treatment system (BWTS) used in this study was composed of filtration modules as a pretreatment process, followed by a UV irradiation process equipped with a polychromatic MPUV lamp. The experiments were performed on seawater (Busan, >32 PSU) and brackish water (Nakdong River, 20-22 PSU) with flow rates of 50 and 250 m(3)/h. The disinfection efficacy of the system was evaluated using indigenous species (>50 microm and 10-50 microm) and surrogate microorganisms (E. coli and Enterococci group). The test results successfully met the D-2 regulation of the IMO (International Marine Organization). In addition, oxidants, such as H202, total residual oxidants (TRO) and OH radicals, and potential halogenated by-products, such as haloacetic acids, trihalomethanes and total organic halides, that had potentially formed after MPUV treatment, were measured. In conclusion, the ballast water treatment system employing the MPUV physical process not only effectively eliminated indigenous species in ballast water but also generated no harmful by-products.

Removal of iopromide and degradation characteristics in electron beam irradiation process.

The aim of this study is to evaluate the removal efficiency of iopromide using electron beam (E-beam) irradiation technology, and its degradation characteristics with hydroxyl radical (OH) and hydrated electron (e(aq)(-)). Studies are conducted with different initial concentrations of iopromide in pure water and in the presence of hydrogen peroxide, bicarbonate ion, or sulfite ion. E-beam absorbed dose of 19.6 kGy was required to achieve 90% degradation of 100 µM iopromide and the E-beam/H(2)O(2) system increased the removal efficiency by an amount of OH· generation. In the presence of OH scavengers (10 mM sulfite ion), the required dose for 90% removal of 100 µM iopromide was only 0.9 kGy. This greatly enhanced removal was achieved in the presence of OH· scavengers, which was rather unexpected and unlike the results obtained from most advanced oxidation process (AOP) experiments. The reasons for this enhancement can be explained by a kinetic study using the bimolecular rate constants of each reaction species. To explore the reaction scheme of iopromide with OH· or e(aq)(-) and the percent of mineralization for the two reaction paths, the total organic carbon (TOC), released iodide, and intermediates were analyzed.

Removal of amoxicillin by UV and UV/H2O2 processes.

The degradation of the ß-lactam antibiotic amoxicillin (AM) treated with direct UV-C and UV/H(2)O(2) photolytic processes was investigated in the present study. In addition, the antibacterial activity of the solution treated by UV/H(2)O(2) advanced oxidation was compared with AM solution treated with ozone. The degradation rate of amoxicillin in both processes fitted pseudo first-order kinetics, and the rates increased up to six fold with increasing H(2)O(2) addition at 10mM H(2)O(2) compared to direct photolysis. However, low mineralization was achieved in both processes, showing a maximum of 50% TOC removal with UV/H(2)O(2) after a reaction time of 80min (UV dose: 3.8×10(-3)EinsteinL(-1)) with the addition of 10mM H(2)O(2). The transformation products formed during the degradation of amoxicillin in the UV and UV/H(2)O(2) processes were identified by LC-IT-TOF analysis. In addition, microbial growth inhibition bioassays were performed to determine any residual antibacterial activity from potential photoproducts remaining in the treated solutions. An increase of the antibacterial activity in the UV/H(2)O(2) treated samples was observed compared to the untreated sample in a time-based comparison. However, the UV/H(2)O(2) process effectively eliminated any antibacterial activity from AM and its intermediate photoproducts at 20min of contact time with a 10mM H(2)O(2) dose after the complete elimination of AM, even though the UV/H(2)O(2) advanced oxidation process led to bioactive photoproducts.

Evidence of singlet oxygen and hydroxyl radical formation in aqueous goethite suspension using spin-trapping electron paramagnetic resonance (EPR).

The generation of reactive species in an aqueous goethite suspension, under room light and aeration conditions, was investigated using the electron paramagnetic resonance (EPR) technique employing spin trap agents. The trap reagents, including 5,5-dimethylpyrroline N-oxide (DMPO) and 2,2,6,6-tetramethylpiperidine (TEMP), were used for the detection of OH radicals (OH·) and singlet oxygen (1O2), respectively. On the addition of DMPO to the goethite suspended solution, a DMPO-OH adduct was formed, which was not decreased, even in the presence of the OH· scavenger, mannitol. This result implied a false positive interpretation from the DMPO-OH EPR signal. In the presence of TEMP reagent, a TEMP-O signal was detected, which was completely inhibited in the presence of the singlet oxygen scavenger, sodium azide. With both DMPO-OH and TEMP-O radicals in the presence and absence of radical scavengers, singlet oxygen was observed to be the key species formed in the room-light sensitized goethite suspension. In the goethite/H2O2 system; however, both OH· and singlet oxygen were generated, with significant portions of DMPO-OH resulting from both OH· and singlet oxygen. In fact, the DMPO-OH resulting from OH· should be carefully calculated by correcting for the amount of DMPO-OH due to singlet oxygen. This study reports, for the first time, that the goethite suspensions may also act as a natural sensitizer, such as fulvic acids, to form singlet oxygen.

Formation of hazardous inorganic by-products during electrolysis of seawater as a disinfection process for desalination.

From our previous study, an electrochemical process was determined to be a promising tool for disinfection in a seawater desalination system, but an investigation on the production of several hazardous by-products is still required. In this study, a more intensive exploration of the formation patterns of perchlorate and bromate during the electrolysis of seawater was conducted. In addition, the rejection efficiencies of the targeted by-products by membrane processes (microfiltration and seawater reverse osmosis) were investigated to uncover the concentrations remaining in the final product from a membrane-based seawater desalination system for the production of drinking water. On the electrolysis of seawater, perchlorate did not provoke any problem due to the low concentrations formed, but bromate was produced at a much higher level, resulting in critical limitation in the application of the electrochemical process to the desalination of seawater. Even though the formed bromate was rejected via microfiltration and reverse osmosis during the 1st and 2nd passes, the residual concentration was a few orders of magnitude higher than the USEPA regulation. Consequently, it was concluded that the application of the electrochemical process to seawater desalination cannot be recommended without the control of bromate.

An investigation of the formation of chlorate and perchlorate during electrolysis using Pt/Ti electrodes: the effects of pH and reactive oxygen species and the results of kinetic studies.

The characteristics of chlorate (ClO(3)(-)) and perchlorate (ClO(4)(-)) formation were studied during the electrolysis of water containing chloride ions (Cl(-)). The experiments were performed using an undivided Pt/Ti plate electrode under different pH conditions (pH 3.6, 5.5, 7.2, 8.0 and 9.0). ClO(3)(-) and ClO(4)(-) were formed during electrolysis in proportion to the Cl(-) concentration. The generation rates of ClO(3)(-) and ClO(4)(-) under acidic conditions (pH 3.6 and 5.5) were lower than in basic pH conditions (pH 7.2, 8.0 and 9.0). However, the pH of the solution did not influence the conversion of ClO(3)(-) to ClO(4)(-). The effects of intermediately formed oxidants on the production of ClO(3)(-) and ClO(4)(-) were observed using sodium thiosulfate (Na(2)S(2)O(3)) as the active chlorine scavenger and tertiary butyl alcohol (t-BuOH) as the hydroxyl radical (OH) scavenger. The results revealed that electrolysis reactions that involved active chlorine contributed dominantly to ClO(3)(-) production. The direct oxidation reaction rate of Cl(-) to ClO(3)(-) was 13%. The OH species that were intermediately formed during electrolysis were also found to significantly affect ClO(3)(-) and ClO(4)(-) production. The key formation pathways of ClO(3)(-) and ClO(4)(-) were studied using kinetic model development.

The degradation of diethyl phthalate (DEP) during ozonation: oxidation by-products study.

The degradation of diethyl phthalate (DEP) in an aqueous solution during ozonation was investigated by identifying the oxidation intermediates using GC-MS. The experiments were carried out in semi-batch mode with a 1.5 mg l(-1)-min ozone dose. The proposed degradation pathways were divided into hydrolysis of the aliphatic chain (pathway (A)) and hydroxylation resulting from OH attack in the aromatic ring (pathway (B)). With increasing ozone dose, the aromatic ring of DEP was opened and acidic compounds, such as malonic acid, succinic acid and glutaric acid were formed. In addition, the ozonation of DEP for 18 min induced hydrogen peroxide (H(2)O(2)) generation at levels six times higher than pure water. Of the intermediates indentified, phthalic acid (PA) and phthalic anhydride (PAH) enhanced the degradation of DEP by promoting ozone decomposition.