Jelena Molnar

A comparative study of the effects of ozonation and TiO2-catalyzed ozonation on the selected chlorine disinfection by-product precursor content and structure

This study compares the effects of ozonation (0.4-3.0 mg O(3)/mg DOC) and TiO(2)-catalyzed ozonation - TiO(2)-O(3) (0.4-3.0 mgO(3)/mg DOC; 1.0 mgTiO(2)/L) at pH 6 on the content and structure of natural organic matter (NOM) and trihalometane (THM) and haloacetonitrile (HAN) precursors in groundwater. The investigated groundwater from Northern Serbia is rich in NOM (9.85 mg/L DOC) which is mostly of hydrophobic character (65% fulvic acid and 14% humic acid fraction). It was found that the TiO(2)-catalyzed process, by favoring the radical mechanism of NOM oxidation, resulted in a more effective reduction in the content of total NOM (up to 18% DOC) compared to ozonation alone (up to 6% DOC). The use of TiO(2) also resulted in an improvement of ozonation in terms of THM precursor content removal (up to 80%). On the other hand, the application of both oxidation treatments resulted in an increase in the HANFP compared to the raw water. NOM oxidation during ozonation and TiO(2)-O(3) caused changes in their structure in the direction of an increased proportion of the hydrophilic fraction (up to 70%), which has the most reactive THM and HAN precursors, as well as the fraction with the highest content of their brominated species.

Insight into changes during coagulation in NOM reactivity for trihalomethanes and haloacetic acids formation

Natural organic matter (NOM) in raw water can contribute in many ways to the poor quality of drinking water, including the formation of disinfection byproducts such as trihalomethanes (THM) and haloacetic acids (HAA) during disinfection. This paper investigates the role of individual NOM fractions on changes in THM and HAA formation during coagulation with iron chloride (FeCl3) and a combination of polyaluminium chloride and iron chloride (FeCl3/PACl). The dissolved organic carbon (DOC) in the raw water and after coagulation was fractionated into four fractions, based on their hydrophobicity. Fractionation showed that most of the DOC (68%) in the raw water comes from the fulvic acid fraction, yielding 41% of the total THM precursors and 21% of the total HAA precursors. Both coagulants remove the humic acid fraction, but result in different changes to the reactivity of the remaining NOM fractions towards THM and HAA formation, indicating that coagulation occurs by different pathways, depending upon the type of coagulant used. In particular, significant changes in the reactivities of the hydrophilic acidic and non-acidic fractions were observed.

Adsorption of chlorinated phenols on multiwalled carbon nanotubes

This work studies the adsorption of four chlorinated phenols (2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,5-tetrachlorophenol and pentachlorophenol) in aqueous solutions on multiwalled carbon nanotubes (MWCNT). To investigate the influence of oxygen containing functional groups, adsorption parameters for the phenols were determined for original MWCNT (OMWCNT) and functionally modified MWCNT (FMWCNT) by acid treatment for 3 h and 6 h. The correlation between phenol adsorption affinity and specific surface area (SSA) indicates that OMWCNT have higher adsorption affinities for larger molecules such as tetrachlorophenol and pentachlorophenol, which suggests that mesopore filling is not the dominant mechanism controlling their adsorption. Electrostatic repulsion between disassociated chlorinated phenols and disassociated functional groups on the surface of both FMWCNT lead to adsorption decreasing with increasing functionalisation under neutral pH conditions. On OMWCNT, a positive correlation between molecular hydrophobicity and adsorption affinity was obtained, indicating hydrophobic interactions control the adsorption of chlorinated phenols. To investigate the role of π–π interactions, Kd values (at 0.01 and 0.5 SW) were normalized by hydrophobicity. The Kd/KOW values for all MWCNT decreased from 2,4-dichlorophenol to pentachlorophenol and were negatively correlated with the electron-acceptor property of the molecules. The most pronounced π–π interactions were observed for 2,6-dichlorophenol on all MWCNT.

Hydrodynamic chronoamperometric method for the determination of H2O2 using MnO2-based carbon paste electrodes in groundwater treated by Fenton and Fenton-like reagents for natural organic matter removal

A simple hydrodynamic chronoamperometric method based on the application of an unmodified carbon paste electrode (CPE) and bulk-modified with different contents of MnO2 was investigated for the determination of H2O2. The optimized method involving the CPE with 5% of MnO2 was applied for the determination of the H2O2 consumption in samples of groundwater from the Central Banat region (Province of Vojvodina, Serbia) treated by the Fenton (Fe(2+) and H2O2) and Fenton-like (Fe(3+) and H2O2) reagents to remove natural organic matter at different initial concentrations of iron species, and of their ratios to the initial concentration of H2O2. Under optimized conditions, with a working potential of 0.40V vs. the saturated calomel electrode and a phosphate buffer solution (pH 7.5) as supporting electrolyte, the method enabled the quantitation of H2O2 in the concentration interval from 1.4 to 65 μg mL(-1) with a relative standard deviation of less than 10%. The results obtained for the H2O2 consumption are in good agreement with those obtained by parallel measurements related to the efficiency of organic matter removal.

Investigation of the impact of ozone pretreatment and powdered activated carbon addition on the removal of natural organic matter by coagulation

AbstractThe main goal of this study was to investigate the effects of ozone oxidation pretreatment and powdered activated carbon (PAC) addition on the efficacy of natural organic matter (NOM) removal by coagulation. Relatively high iron chloride doses from 100 to 200 mg FeCl3/L were applied, due to the high dissolved organic carbon (DOC) content (10.27 ± 0.49 mg C/L) of the raw water investigated, with PAC used in doses of 5–30 mg/L. Preozonation was carried out at doses of 0.2–1.3 mg O3/mg DOC. Jar test results indicate that baseline coagulation with the optimal coagulant dose (200 mg FeCl3/L) achieved was 39% DOC and 54% UV254 removals. PAC addition improves coagulation efficacy in NOM removal by up to 9% DOC and 25% UV254. The best results were obtained in combination with 0.6 mg O3/mg DOC, 5 mg/L PAC and 200 mg FeCl3/L (removals of 58% DOC and 72% UV254), and were a significant improvement compared to coagulation alone.

A Study on the Removal of Natural Organic Matter and Disinfection Byproducts Formation Potential from Groundwater Using Fenton’s Process

Abstract This work investigates the efficiency of the Fenton process in removing natural organic matter (NOM) from groundwater. Previous studies focused mostly on the use of Fenton’s process to remove total organic matter, but this research also studies the conditions leading to the formation of hazardous disinfection by-product precursors, and their removal. Solutions of a commercial humic acid as a model of NOM and natural groundwater as a real matrix rich in NOM (dissolved organic carbon, DOC=9.92±0.87 mg/L) were studied. Under optimum reaction conditions, the respective removal efficiencies (expressed as DOC) were 95% from commercial humic acid solution and 82% from groundwater. The decrease in DOC resulted in 99% decrease of the content of precursors of trihalomethanes (THMs) and 98% of haloacetic acids (HAAs) for the investigated matrixes. Precursors of haloacetonitriles, haloketones and chloropicrin were detected at much lower concentrations than the THMs and HAAs precursors.

Correlation of selected molecular properties and recovery values in volatile organic compounds analysis: comparison of two water matrices

This study investigates if certain molecular properties can influence the recovery of 18 volatile organic compounds (VOCs) in water under the applied analytical conditions, a purge and trap gas chromatographic method with mass spectrometric detection (P&T GC MS). Statistical and quantitative structure property relationship (QSPR) analyses were applied to find correlations between molecular parameters and analytical recoveries in two different water matrices (clean water (CW) produced in the laboratory and natural groundwater (GW)) at two different concentration levels. At 1 μg L−1, most compounds had higher recoveries in CW than in GW, whereas at 15 μg L−1, the recoveries were higher in the GW matrix. Polarity number and hydrophilic factor were correlated with the recovery differences at both concentration levels in GW. Polarity was significant in the distinction of recovery differences for CW and GW matrices at low concentration, while air diffusivity had an acceptable correlation with recovery differences for both matrices at the higher concentration. Further correlation of the recoveries themselves with the molecular properties was made by multivariate linear regression (MLR) resulting in a QSPR model. This was only possible for GW at the low 1 μg L−1 concentration. Partial least square analysis indicated that hydrophilic factor, polarity, and molecular weight were the most important properties investigated. No significant correlation was found in CW matrix or in the higher concentration level in GW matrix, which implies that the most significant properties might only be relevant for the VOCs recovery at low concentrations and only if the matrix contains other water constituents (DOC, salt).

Application of the pyrite ash in the microwave Fenton process of decolorization of the synthetic color solution

The aim of this study is to investigate the possibility of fly ash and pyrite ash applications as a Fenton catalysts in the advancement of the microwave/hydrogen peroxide (MW/H2O2) treatment in the Rhodamine B decolorization process. At the same time, a comparison of the influence of these heterogenous catalysts with the homogenous Fenton catalyst on the decolorization process was conducted. The influence of the catalyst was tracked in previously optimized conditions MW/H2O2: [Rhodamine B] = 0.2 mM; pH 3.2; temperature 85oC; [H2O2] = 80 mM; power = 300 W. Under such conditions, the efficiency of 99.5% was achieved after 30 minutes of reaction time. The same efficiency was achieved through the application of MW/Fe2+/H2O2 and MW/pyrite ash/H2O2 after only 10 minutes of reaction time. The order of the tested integrated processes according to the initial reaction rate is as follows: MW/Fe2+/H2O2>MW/fly ash/H2O2>MW/H2O2. The results of this study present a basis for further research and optimization of water solution decolorization process through pyrite ash with MW and hydrogen peroxide application.