Marijana Kragulj Isakovski

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.

Sorption Behaviour of Trichlorobenzenes and Polycyclic Aromatic Hydrocarbons in the Absence or Presence of Carbon Nanotubes in the Aquatic Environment

This work investigates the sorption behaviour of six hydrophobic organic compounds (HOCs) from the trichlorobenzenes (TCBs) and polycyclic aromatic hydrocarbons (PAHs) on Danube sediment using batch and column experiments, either in the presence or absence of carbon nanotubes (CNTs). For all HOCs investigated, nonlinear isotherms were obtained. Based on logKoc, it can be concluded that the Danube sediment has a higher sorption affinity for PAHs than TCBs. A positive correlation between HOC molecular hydrophobicity and sorption affinity was obtained, meaning that hydrophobic interactions play a significant role. There was a negative correlation between molecular hydrophobicity and the percentage of eluted HOCs, indicating that more hydrophobic molecules show less mobility in the sediment column. In the presence of CNTs in the sediment column, HOC concentrations in the column eluate decreased by factors of 2–3. Metal oxides and hydroxides on the surface of the sediment under the given experimental conditions had positively charged centres that caused the deposition of CNTs, leading to simultaneous sorption of organic compounds on both sediment organic matter (SOM) and CNTs. The increased retention of HOCs in the presence of CNTs on the sediment column reduces their mobility, which might also suggest that CNTs may be used for remediation of contaminated soils and sediments.

Priority substances in sediments of the “Carska Bara” special nature reserve, a natural scientific research area on the UNESCO list

Surface sediments were subject to systematic long-term monitoring (2002-2014) in the Republic of Serbia (Province of Vojvodina). Eight heavy metals (Ni, Zn, Cd, Cr, Cu, Pb, As and Hg), mineral oils (total petroleum hydrocarbons), 16 EPA PAHs, selected pesticides and polychlorinated biphenyls (PCB) were monitored. As part of this research, this paper presents a sediment contamination spatial and temporal trend study of diverse pollution sources and the ecological risk status of the alluvial sediments of Carska Bara at three representative sampling sites (S1S3), in order to establish the status of contamination and recommend substances of interest for more widespread future monitoring. Multivariate statistical methods including factor analysis of principal component analysis (PCA/FA), Pearson correlation and several synthetic indicators were used to evaluate the extent and origin of contamination (anthropogenic or natural, geogenic sources) and potential ecological risks. Hg, Cd, As, mineral oils and PAHs (dominated by dibenzo(a,h)anthracene and benzo(a)pyrene, contributing 85.7% of the total) are derived from several anthropogenic sources, whereas Ni, Cu, Cr and Zn are convincingly of geogenic origin, and exhibit dual origins. Cd and Hg significantly raise the levels of potential ecological risk for all sampling locations, demonstrating the effect of long-term bioaccumulation and biomagnification. Pb is isolated from the other parameters, implying unique sources. This research suggests four heavy metals (Zn, Cr, Cu and As) and dibenzo(a,h)anthracene be added to the list of priority pollutants within the context of the application of the European Water Framework Directive (WFD), in accordance with significant national and similar environmental data from countries in the region.

Assessment of the retardation of selected herbicides onto Danube sediment based on small column tests

PurposeThis study utilizes column tests to investigate the retardation of certain herbicides with different hydrophobicities (atrazine, alachlor and trifluralin) during transport through surface Danube sediment. The influence of water matrix on the retardation factor Rd and Freundlich constant Kf is investigated. The results are compared with batch tests to establish whether different methodologies result in similar or different conclusions.Materials and methodsA stainless steel column was filled with natural Danube sediment. Three water matrices were investigated: synthetic, Danube surface, and deep groundwater rich in natural organic matter (NOM). The goal was to examine whether different water matrices would result in changes in the Rd and corresponding Kf values. After a tracer experiment, single herbicide solutions were tested in the three water matrices. Herbicides were analyzed by gas chromatography coupled with electron capture detector (GC/ECD). Retardation factors obtained in the column experiments were calculated using Transmod software (version 2.2). The Kf values calculated were compared with the values obtained in previous batch experiments.Results and discussionA breakthrough curve (BTC) for trifluralin could not be obtained during the experiment. Atrazine Rd values were almost the same in the natural matrices (54 and 55 for the ground and surface waters, respectively), and lower in the synthetic water (40). Alachlor Rd values in the three water matrices were very similar (30–35). The corresponding Kf values for alachlor (8.47–17.4) were lower than those of atrazine (13.5–27.9). These results differ from those obtained by earlier batch tests, which showed similar Kf values for both atrazine (4.4–9.2) and alachlor (4.43–10.35) in all three matrices. In contrast to the results observed during the batch tests, the column tests exhibited higher Kf values in the natural water matrices than the synthetic water, possibly due to the influence of dissolved organic carbon on herbicide sorption.ConclusionsOf the three herbicides investigated, the smallest retardation was observed for alachlor. This was unexpected given the relative hydrophobicities of alachlor and atrazine. The potential risk of transport through the sediment may therefore be greater for alachlor than the other two herbicides. This was indicated neither by the batch tests nor from the Koc–Kow estimations. Both herbicides exhibited similar Kd and Kf values in the batch tests, and lower values in the natural water matrices. In comparison, the column tests showed higher Kf values, with higher values in the natural matrices than in the synthetic water matrix.

Potential for anaerobic treatment of polluted sediment

Due to the anaerobic nature of aquatic sediments, the anaerobic treatment of sediments utilizing already present microflora represents an interesting treatment option. Contaminated sediment can contain a variety of organic contaminants, with easily degradable organics usually present in the higher amounts, along with traces of specific organic pollutants (total petroleum hydrocarbons and polycyclic aromatic hydrocarbons). This study applies a comprehensive approach to contaminated sediment treatment which covers all the organic contaminants present in the sediment. The aim of this study was to (1) evaluate the anaerobic treatment of aquatic sediment highly loaded with easily degradable organics via determination of potential biogas and methane production, and (2) assess possibilities of using anaerobic treatment for the degradation of specific organic pollutants in order to reduce the risks posed by the sediment. In order to promote the methanogenic conditions of the indigenous microflora in the sediment, the addition of co-substrates acetate and glucose was investigated. The results, expressed as mL biogas produced per volatile solids content in sediment (VSadded) indicate that the addition of the co-substrate has a significant impact on biogas production potential (58.7 and 55.1 mL/g VSadded for acetate and glucose co-substrate addition respectively, and 14.6 mL/g VSadded for the treatment without co-substrate addition). Theoretical biochemical methane potential was assessed by Gompertz model and Chemical oxygen demand model. The Gompertz model fit better for all the applied treatments, and was capable of predicting the final productivity of biogas and methane in the first 30 days with a relative error of less than 14%. From the aspects of specific organic pollutants, total petroleum hydrocarbon degradation was promoted by co-substrate addition (degradations of 75% and 60% achieved by acetate and glucose co-substrate addition, compared to 45% for the treatment without co-substrate addition). Polycyclic aromatic hydrocarbons were reduced by significant amounts (84-87%) in all the applied treatments, but the addition of co-substrate did not further improve their degradation.

Photochemical degradation of alachlor in water

This study investigates the photochemical degradation of alachlor, a chloroacetanilide herbicide. All experiments were conducted in ultra-pure deionized water (ASTM Type I quality) using direct ultraviolet (UV) photolysis and the UV/H2O2 advanced oxidation process. The direct UV photolysis and UV/H2O2 experiments were conducted in a commercial photochemical reactor with a quartz reaction vessel equipped with a 253.7 nm UV low pressure mercury lamp (Philips TUV 16 W). The experimental results demonstrate that UV photolysis was very effective for alachlor degradation (up to 97% removal using a high UV fluence of 4200 mJ/cm 2 ). The UV/H2O2 process promoted alachlor degradation compared to UV photolysis alone, with a high degree of decomposition (97%) achieved at a significantly lower UV fluence of 600 mJ/cm 2 when combined with 1 mg H2O2/L. The application of UV photolysis alone with a UV fluence of 600 mJ/cm 2 gave a negligible 4% alachlor degradation. The photo degradation of alachlor, in both direct UV photolysis and the UV/H2O2 process, followed pseudo first-order kinetics. The degradation rate constant was about 6 times higher for the UV/H2O2 process than for UV photolysis alone.