Aleksandra Tubić

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.

Removal of arsenic and natural organic matter from groundwater using ferric and alum salts: A case study of central Banat region (Serbia)

This paper presents a comparison of the efficacy of three different coagulants (polyaluminium chloride (PACl), Aluminium sulphate (Al2(SO4)3) and ferrous chloride (FeCl3)) for natural organic matter and arsenic (As) removal from groundwater. Coagulation efficacy was evaluated for the coagulants alone and for combinations of them (PACl/FeCl3; Al2(SO4)3/FeCl3), on the basis of changes in dissolved organic matter (DOC) and arsenic content. For single coagulants, PACl (30 mg Al/L) showed optimal efficacy for DOC removal (57%, relative to raw water). The highest arsenic reduction (< 5 μ g As/L in coagulated water) was achieved when a very high 300 mg/L dose of FeCl3 was used. However, if PACl (30 mg Al/L) and FeCl3 (10 mg FeCl3/L) are combined, the efficacy of DOC removal increases compared to PACl and FeCl3 alone under similar doses (66% decrease in DOC relative to raw water). The DOC and As contents of the coagulated water after application of these doses were 2.26 mg C/L and 9.7 μ g/L, respectively, compared to 6.44 mg C/L and 60.5 μ g As/L measured in the raw groundwater. The combination of Al2(SO4)3 and FeCl3 did not show any improvement in DOC and As removal efficacy relative to using those coagulants alone.

Removal of Natural Organic Matter from Groundwater Using Advanced Oxidation Processes at a Pilot Scale Drinking Water Treatment Plant in the Central Banat Region (Serbia)

To improve water quality, a pilot-scale evaluation into upgrading the conventional treatment process was conducted. By following DOC content, UV254 absorbance, SUVA and by-products formation, three oxidative pre-treatments were evaluated: pre-ozonation (2.2 g O3/m3); O3/H2O2 process (2.2 g O3/m3; H2O2:O3 = 1:2) and O3/H2O2 process (2.2 g O3/m3; H2O2:O3 = 2:1). The second pre-treatment gave the best results, with a final average DOC content of 0.9 mg C/L, UV254 absorbance of 0.06 cm−1 and the lowest THMFP of 130 μg/L. UV254 absorbance can serve as a proper indicator for predicting THM and HAA formation, yielding a correlation coefficient ≥ 0.90.

Response surface methodology investigation into the interactions between arsenic and humic acid in water during the coagulation process.

Interactions between arsenic and natural organic matter (NOM) are key limiting factors during the optimisation of drinking water treatment when significant amounts of both must be removed. This work uses Response Surface Methodology (RSM) to investigate how they interact during their simultaneous removal by iron chloride coagulation, using humic acid (HA) as a model NOM substance. Using a three factor Box-Behnken experimental design, As and HA removals were modelled, as well as a combined removal response. ANOVA results showed the significance of the coagulant dose for all three responses. At high initial arsenic concentrations (200μg/l), As removal was significantly hindered by the presence of HA. In contrast, the HA removal response was found to be largely independent of the initial As concentration, with the optimum coagulant dose increasing at increasing HA concentrations. The combined response was similar to the HA removal response, and the interactions evident are most interesting in terms of optimising treatment processes during the preparation of drinking water, highlighting the importance of utilizing RSM for such investigations. The combined response model was successfully validated with two different groundwaters used for drinking water supply in the Republic of Serbia, showing excellent agreement under similar experimental conditions.

Oxidation of natural organic matter with processes involving O3, H2O2 and UV light: formation of oxidation and disinfection by-products

This study investigates the effects of UV photolysis, ozonation and different advanced oxidation processes (O3/UV, H2O2/UV and O3/H2O2/UV) on the oxidation of groundwater natural organic matter (NOM) and by-product formation. Although the investigated treatments only slightly reduce the total organic carbon content (4–15%), the NOM character was changed significantly. The fulvic acid fraction decreased and the content of the hydrophilic acid fraction increased in ozone treated water and even more noticeably in water treated by O3/H2O2/UV. All treatments led to significant increases in polar oxidation by-products such as aldehydes (up to 8 times) and carboxylic acids (up to 34 times), with no clear relationship between the changes in concentrations of these by-products and the addition of H2O2 and the UV dose. Statistical analysis showed a good correlation between carboxylic acids with ozone applications and carboxylic acids and UV254. Trihalomethane and haloacetic acid formation potentials were reduced best (43% for THMFP and 68% for HAAFP) during the O3/H2O2/UV process (0.5 mg O3 per mg DOC; 10 mg H2O2 per L: 600 mL cm−2) using the lower UV dose, and were also well correlated (R = 0.847) during all water treatments. Bromate formation was observed only in the processes involving ozone.

Toxicological and chemical investigation of untreated municipal wastewater: Fraction- and species-specific toxicity

Absence of a municipal wastewater (WW) treatment plant results in the untreated WW discharge into the recipient. The present study investigated toxic effects and chemical composition of water extracts and fractions from untreated WW and recipient Danube River (DR). Samples were prepared by solid-phase extraction and silica gel fractionation and screened for EROD activity and cytotoxicity using aquatic models, comprising of fish liver cells (PLHC-1) and a model of the early development of zebrafish embryos, while rat (H4IIE) and human (HepG2) hepatoma cells served as mammalian models. Polar fraction caused cytotoxicity and increased the EROD activity in PLHC-1 cells, and increased mortality and developmental abnormalities in developing zebrafish embryos. In H4IIE, polar fraction induced inhibition of cell growth and increased EROD activity, whereas HepG2 exerted low or no response to the exposure. Non-polar and medium-polar fractions were ineffective. Tentative identification by GC/MS showed that WW is characterized by the hydrocarbons, alkylphenols, plasticizers, and a certain number of benzene derivatives and organic acids. In DR, smaller number of organic compounds was identified and toxicity was less pronounced than in WW treatments. The present study revealed the potent toxic effect of polar fraction of untreated WW, with biological responses varying in sensitivity across organisms. Obtained results confirmed that fraction- and species-specific toxicity should be considered when assessing health risk of environmental pollution.

Toxicological profiles assessment of the water and sediments from the Krivaja and Jegrička Rivers, Serbia

This study utilizes a combinatorial bio/chemical approach to assess the toxicological profiles of organic pollutants in water and sediment samples from two watercourses that are under significant anthropogenic pressure—the Krivaja and Jegrička rivers in Serbia. Sample preparation by solid-phase extraction and silica-gel fractionation followed by GC/MS analysis, allowed the tentative identification of a variety of non-target contaminants, divided into non-polar, medium-polar and polar fractions. The instrumental analysis revealed slightly different toxicological profiles for the water and sediment from both rivers, and confirmed the presence of various classes of organic contaminants, from non-polar hydrocarbons, to more polar compounds such as aldehydes, ketones and phenols. Polycyclic aromatic hydrocarbons and pesticides were identified, but below toxicologically relevant concentrations. The results of bioanalyses on H4IIE and PLHC-1 cells indicated that cytotoxic potential was pronounced in Jegrička water and sediment samples, and CYP1A inducing potential was observed in both Krivaja and Jegrička sediment samples, although they did not reflect high levels of contamination. Based on the overall data, the sediments of the Krivaja and Jegrička rivers are a more toxicologically relevant matrix than the water.

Effects of O3, O3/H2O2 and Coagulation on Natural Organic Matter and Arsenic Removal from Typical Northern Serbia Source Water

The objectives of this study were to investigate the effects of ozone and the O3/H2O2 process on FeCl3 coagulation efficiency for the removal of the high content of natural organic matter (NOM) and arsenic (As) from groundwater (DOC = 9.27 ± 0.92 mg/L; 51.7 ± 16.4 µg As/L). Arsenic and NOM removal mechanisms during coagulation/flocculation are well investigated. However, data concerning arsenic removal in the presence of NOM, which is the subject of this article, are still insufficient. Laboratory and pilot plant test results have shown that the competition of NOM and As for adsorption sites on the coagulant surface have great influence on coagulation/flocculation efficiency for their removal. With both oxidation pre-treatments, arsenic content after the coagulation process was less than 2.0 µg/L in treated water. Application of ozone has a lower influence on coagulation efficacy in terms of DOC reduction, compared to the O3/H2O2 process with the same ozone dose.

Tracking disinfection by-products and arsenic removal during various drinking water treatment trains

In the central Banat region (Northern Serbia), groundwater is used as a drinking water source. Raw water originates from a 40-80 m and 100-150 m deep layer. It contains a high amount of natural organic matter (DOC = 9.17+/-0.87 mg C/L) with a trihalomethanes formation potential of 448+/-88.2 microg/L and a haloacetic acid formation potential of 174+/-68.9 microg/L. A high amount of arsenic (86.0+/-3.4 microg/L) is also found in this water. This study used a pilot-scale system to investigate the possibilities of combining polyaluminium chloride and ferrous-chloride to remove disinfection by-products precursors and arsenic by coagulation. Two treatment trains with different pre-treatment steps were investigated (ozone vs. H2O2/O3). For the final water polishing, filtration with granulated activated carbon (GAC) was applied. Both investigated treatment lines achieved a satisfactory chemical water quality. Simulation of disinfection conditions was performed and the contents of trihalomethanes and haloacetic acids measured, to investigate whether the chemical quality of the water remained satisfactory over a 48 hour period.

Some arguments in favor of a Myriophyllum aquaticum growth inhibition test in a water–sediment system as an additional test in risk assessment of herbicides

The present study compares the practicability, reproducibility, power, and sensitivity of a Myriophyllum aquaticum growth inhibition test in a water-sediment system with the recently accepted Myriophyllum spicatum test in an equivalent testing system and the standard Lemna sp. test. Special consideration was given to endpoints based on M. aquaticum control plant growth and variability of relative growth rate and yield: shoot length, fresh weight, dry weight, and root weight. Sensitivity analysis was based on tests performed with 3,5-dichlorophenol, atrazine, isoproturon, trifluralin, 2,4-dichlorophenoloxyacetic acid, and dicamba. Growth rates for average M. aquaticum control plants were 0.119 d(-1) and 0.112 d(-1), with average estimated doubling time 6.33 d and 6.74 d for relative growth rate fresh weight and shoot length, respectively. Intrinsic variability of M. aquaticum endpoints was low: 12.9%, 12.5%, and 17.8% for relative growth rate shoot length, relative growth rate fresh weight and yield fresh weight, respectively. The power of the test was fairly high. When the most sensitive endpoints were used for comparison, the 2 Myriophyllum species were similarly sensitive, more sensitive (in the case of auxin simulators), or at least equally sensitive as Lemna minor to other tested herbicides. The M. aquaticum 10-d test with a 7-d exposure period in a water-sediment system has acceptable sensitivity and can provide repeatable, reliable, and reproducible results; therefore, it should not be disregarded as a good and representative additional test in environmental risk assessment.