Reconsidering the quantitative analysis of organic carbon concentrations in size exclusion chromatography

The evaluation of the molecular size distribution of natural organic matter (NOM) in aquatic environments via size exclusion chromatography (SEC) is important for the understanding of environmental processes such as nutrient cycling and pollutant transport as well as of technical water treatment processes. The use of organic carbon (OC) detectors has become popular in recent studies due to improved availability and quantification possibilities, which supposedly are superior to those of ultraviolet (UV) detectors. A set of 12 NOM samples was used to demonstrate the limitations of online OC detection (OCD) when analyzing complex aquatic organic matter. A novel evaluation approach for SEC data is introduced by combining the information from UV absorbance (UVA) and OCD chromatograms as well as offline total OC (t-OC) and dissolved OC-specific UVA (SUVA) measurements. It could be shown that about 70% of certain OC components were not detected with the OCD system used in this study. For the investigated samples, these types of carbon accounted for up to 72% of the t-OC, i.e. for such NOM samples quantification by OCD is not possible or at least highly questionable. The addition of an oxidant improved the overall oxidation efficiency only slightly. Most likely NOM that predominantly consists of polysaccharides and features a nominal molecular weight of 150kg/mol or more was responsible for low OCD yields. For future applications, a further improvement of the OCD system would be worthwhile so that quantitative analytical data on the molecular size distribution of NOM and its structural characteristics such as the SUVA distribution can be obtained.

Assessing contaminant mobilization from waste materials: application of Bayesian parameter estimation to batch extraction tests at varying liquid-to-solid ratios

We investigated the release of chloride, sulfate, sodium, copper, chromium, and dissolved organic carbon from a demolition waste material and a municipal waste incineration product Batch leaching tests at the liquid-to-solid ratios (L/S ratios) 1, 2, 5, 10, and 50 L kg(-1) were carried out and the parameters of a mass balance-partitioning model were estimated from measured concentrations in the extracts by applying a Bayesian approach using a Markov Chain Monte Carlo sampler. We assessed the uncertainty of the model parameters, the desorption isotherms, and the model-predicted concentrations, respectively. Both the excellent fit to the experimental data and a comparison between the model-predicted and independently measured concentrations at the L/S ratios of 0.25 and 0.5 L kg(-1) showed the applicability of the model for almost all studied substances and both materials. Since experimental difficulties impede extraction tests at L/S ratios representative of field soil-water contents, the predictability of concentrations in this range is of great practical relevance for risk assessments. We conclude that batch extraction tests at varying L/S ratios provide, at moderate experimental cost, a powerful complement to established test designs like column leaching or single batch extraction tests.

Formation of brominated products in irradiated titanium dioxide suspensions containing bromide and dissolved organic carbon

We report the irradiation of TiO(2) suspensions containing Br(-) and dissolved organic carbon (DOC). In the absence of DOC, we found no evidence for the formation of BrO(3)(-) upon irradiation of 1gL(-1) P25 suspensions with UV light for initial Br(-) concentrations up to 10mgL(-1). In the presence of DOC (Lake Hohloh, Germany and salicylic acid), we found no evidence for the formation of either BrO(3)(-) or trihalomethanes (THMs). However, small amounts of adsorbable organic halogen (AOX) were formed at high bromide concentrations (3mgL(-1)). When irradiating P25 suspensions containing bromide and 2,4-dihydroxybenzoic acid (DHBA, high bromoform formation potential), we observed the formation of significant amounts of bromoform (up to 10microgL(-1)). Bromoform appeared only after the DHBA had been degraded.

The effect of nitrate, Fe(III) and bicarbonate on the degradation of bisphenol A by simulated solar UV-irradiation

The photoinitiated degradation of bisphenol A (BPA, 520 micromol/L) was investigated using a solar simulator in the absence/presence of NO(3)(-), Fe(III), and HCO(3)(-). The concentrations of NO(3)(-), Fe(III), and HCO(3)(-) were 0-160, 0-10, and 0-820 micromol/L, respectively, and were chosen to simulate a natural aquatic environment. The experimental region was explored using a Box-Behnken design for three factors, extended to experimentally include all eight possible combinations of presence/absence of the factors studied. The results show that, after 7h of irradiation, photolysis occurs only to a minimal degree (2%) in the absence of NO(3)(-) and HCO(3)(-). Increasing the concentration of NO(3)(-) and HCO(3)(-) gives rise to up to 24% degradation after 7h of irradiation. The concentration of Fe(III) was found to play no active role under the conditions studied. A simple linear model is given that very well describes the results obtained.

Drowning in disinfection byproducts? Assessing swimming pool water

Disinfection is mandatory for swimming pools: public pools are usually disinfected by gaseous chlorine or sodium hypochlorite and cartridge filters; home pools typically use stabilized chlorine. These methods produce a variety of disinfection byproducts (DBPs), such as trihalomethanes (THMs), which are regulated carcinogenic DBPs in drinking water that have been detected in the blood and breath of swimmers and of nonswimmers at indoor pools. Also produced are halogenated acetic acids (HAAs) and haloketones, which irritate the eyes, skin, and mucous membranes; trichloramine, which is linked with swimming-pool-associated asthma; and halogenated derivatives of UV sun screens, some of which show endocrine effects. Precursors of DBPs include human body substances, chemicals used in cosmetics and sun screens, and natural organic matter. Analytical research has focused also on the identification of an additional portion of unknown DBPs using gas chromatography (GC)/mass spectrometry (MS) and liquid chromatography (LC)/MS/MS with derivatization. Children swimmers have an increased risk of developing asthma and infections of the respiratory tract and ear. A 1.6-2.0-fold increased risk for bladder cancer has been associated with swimming or showering/bathing with chlorinated water. Bladder cancer risk from THM exposure (all routes combined) was greatest among those with the GSTT1-1 gene. This suggests a mechanism involving distribution of THMs to the bladder by dermal/inhalation exposure and activation there by GSTT1-1 to mutagens. DBPs may be reduced by engineering and behavioral means, such as applying new oxidation and filtration methods, reducing bromide and iodide in the source water, increasing air circulation in indoor pools, and assuring the cleanliness of swimmers. The positive health effects gained by swimming can be increased by reducing the potential adverse health risks.

Comparison of leaching tests to determine and quantify the release of inorganic contaminants in demolition waste

The changes in waste management policy caused by the massive generation of waste materials (e.g. construction and demolition waste material, municipal waste incineration products) has led to an increase in the reuse and recycling of waste materials. For environmental risk assessment, test procedures are necessary to examine waste materials before they can be reused. In this article, results of column and lysimeter leaching tests having been applied to inorganic compounds in a reference demolition waste material are presented. The results show a good agreement between the leaching behaviour determined with the lysimeter unit and the column units used in the laboratory. In view of less time and system requirements compared to lysimeter systems, laboratory column units can be considered as a practicable instrument to assess the time-dependent release of inorganic compounds under conditions similar to those encountered in a natural environment. The high concentrations of elements in the seepage water at the initial stage of elution are reflected by the laboratory column leaching tests. In particular, authorities or laboratories might benefit and have an easy-to-use, but nevertheless reliable, method to serve as a basis for decision-making.

Degradation of endocrine disrupting bisphenol A by 254 nm irradiation in different water matrices and effect on yeast cells

The photodegradation of bisphenol A (BPA) in pure water, surface water and wastewater effluents was studied. The effect of different hydrogen peroxide concentrations on degradation was investigated. The rate of BPA photolysis in the presence of hydrogen peroxide was lower in wastewater effluent than in purified water. Phenol, 1,4-dihydroxylbenzene and 1,4-benzoquinone were identified by means of HPLC as intermediate products of the photodegradation of bisphenol A. In addition, the disappearance of the estrogenic activity of bisphenol A during irradiation was shown by the YES test. Based upon the YES test results, there was a strong decrease of estrogenic activity of parent compound after 120 min irradiation in the presence of hydrogen peroxide.

Photodegradation of endocrine disrupting chemical nonylphenol by simulated solar UV-irradiation

The photolysis of nonylphenol (NP) was investigated using a solar simulator in the absence/presence of dissolved organic matter (DOM), HCO3-, NO3- and Fe(III) ions. The effects of different parameters such as initial pH, initial concentration of substrate, temperature, and the effect of hydrogen peroxide concentration on photodegradation of nonylphenol in aqueous solution have been assessed. The results indicate that the oxidation rate increases in the presence of H2O2, Fe(III) and DOM with dissolved organic carbon concentrations not higher than 3 mg L(-1). Phenol, 1,4-dihydroxylbenzene and 1,4-benzoquinone were identified as intermediate products of photodegradation of nonylphenol, through an HPLC method. In addition, the disappearance of the estrogenic activity of nonylphenol during irradiation using YES test was investigated. Based upon the YES test results, there was a strong decrease of estrogenic activity of nonylphenol after 80 h irradiation in the presence of hydrogen peroxide.

Monitoring the formation of an Aureobasidium pullulans biofilm in a bead-packed reactor via flow-weighted magnetic resonance imaging

The biofilm-forming fungus, Aureobasidium pullulans DSM 2404, was grown in a bead-packed reactor. Alterations within the reactor were analysed in several cross-sectional slices by magnetic resonance imaging (MRI) with flow contrast. For the first time, biofilm accumulation could be continuously elucidated without using any contrast agents, and the non-stationary flow through the fixed-bed reactor could be visualized. The results indicate that the non-stationary flow through the biofilm reactor changes significantly due to the changing reactor morphology. Preferential flow lines arise during biofilm formation. The accumulation of the biomass was determined and compared to gravimetrical biomass data. The described technique can be used to monitor hydrodynamic transport, and to combine flow-field characteristics with morphological data for the prediction of undesirable reactor processes, e.g. clogging.

Swimming pool water--fractionation and genotoxicological characterization of organic constituents

Swimming pool water treatment in general includes flocculation, sand filtration, and subsequent disinfection with chlorine. The continuous chlorination and input of organic material by bathers in combination with recirculation of the pool water leads to an accumulation of disinfection by-products (DBPs) in the water. Several DBPs have been identified as human carcinogens and are thought to cause allergic asthma. Therefore, the elimination of DBPs is one major aim of pool water treatment. Using membrane filtration as an alternative treatment technology, DBPs can be removed more efficiently than with conventional treatment. In this study membrane filtration and genotoxicity testing were applied for the characterization of pool water constituents and for the identification of the necessary molecular weight cut off of the membrane for an efficient elimination. Two-step membrane filtration revealed that most of the DBPs (as adsorbable organically bound halogen, AOX) were present in the molecular weight fraction below 1000 g/mol. The fraction below 200 g/mol contained more than 30% of the AOX. The distribution of the dissolved organic carbon (DOC) across the fractions was similar to that of the AOX. The genotoxicity was found to be strongest in the low-molecular weight fraction. Thus, considerable DBP removal by membrane treatment requires membranes with low-molecular weight cut offs down to 200 g/mol. The comprehensive elimination of the genotoxic compounds requires further treatment steps.

Size exclusion chromatography to characterize DOC removal in drinking water treatment

A full-scale (110 ML/d) potable water treatment plant (WTP) based on the MIEX process, an innovative new process based on a strong base anion-exchange resin with magnetic properties, has been operating in Perth Western Australia since 2001. This plant has been configured so that a combined MIEX-coagulation (MIEX-C) process can be operated in parallel with a conventional enhanced coagulation (EC) process, allowing comparison of the performance of the two processes. Here, we report the use of size exclusion chromatography (SEC) to compare the removal of different apparent molecular weight (AMW) fractions of DOC by the two processes. Water was sampled from five key locations within the WTP, and SEC was carried out using three different on-line detector systems, DOC-specific detection, UV absorbance detection at lambda = 254 nm, and fluorescence detection (lambda(ex) = 282 nm; lambda(em) = 353 nm). This approach provided information on the chemical nature of the DOC comprising the various AMW fractions. The study showed that the MIEX-C process outperformed the EC process with greater removal of DOC in each of the eight separate AMW fractions identified. While EC preferentially removed the fractions of highest AMW, and those exhibiting the greatest aromatic (humic) character, MIEX-C removed DOC across all AMW fractions and did not appear to discriminate as strongly on the basis of differences in aromatic character or AMW. The results demonstrate the benefits of combining these complementary treatment processes. The study also demonstrates the utility of SEC coupled with multiple detection systems in determining the characteristics of various AMW components of DOC.

Cross-flow microfiltration with periodical back-washing for photocatalytic degradation of pharmaceutical and diagnostic residues-evaluation of the long-term stability of the photocatalytic activity of TiO2

The combination of semiconductor photocatalysis with cross-flow microfiltration accompanied by periodical back-washing was investigated in a pilot plant. The investigation included the testing of membrane materials because the membrane must resist the abrasion and the periodical back-washing. Another objective of this investigation was to assess the potential of two different TiO(2) materials (Hombikat UV100 and P25) for continuous photocatalytic degradation of persistent organic pollutants. The study focused on the long-term stability of the photocatalytic activity of TiO(2) during its continuous application. The combination of photocatalysis and cross-flow microfiltration allowed the separation and reuse of TiO(2) after the photocatalytic degradation of clofibric acid, carbamazepine and iomeprol. The investigations showed that the photocatalytic activity of P25 and Hombikat UV100 was constant during continuous usage over several days. This study indicates the high potential of the combination of heterogeneous photocatalytic oxidation processes with cross-flow microfiltration accompanied by periodical back-washing of the membrane. Thus environmentally relevant pharmaceuticals and X-ray contrast media can be transformed and mineralized in a continuous water treatment process.

Photocatalytic degradation of carbamazepine, clofibric acid and iomeprol with P25 and Hombikat UV100 in the presence of natural organic matter (NOM) and other organic water constituents

The photocatalytic degradation of natural organic matter (NOM) and organic substance mixtures under simulated solar UV light has been investigated with suspended TiO(2). It could be shown by size-exclusion chromatography that photocatalysis of NOM led to a reduction of the average hydrodynamic radii and presumably of the nominal molecular weight, too. The decrease of the UV/Vis absorption of NOM was faster than the NOM mineralization. This study also focuses on the different abilities of photocatalytic materials (P25 and Hombikat UV100) to decrease persistent substances influenced by the presence of NOM and mixtures of pharmaceuticals or diagnostic agents. In general, the presence of NOM and other organic substances retarded the photocatalysis of a specific persistent substance by the combination of radiation attenuation, competition for active sites and surface deactivation of the catalyst by adsorption. The results of this work prove that photocatalysis is a promising technology to reduce persistent substances like NOM, carbamazepine, clofibric acid, iomeprol and iopromide even if they are present in a complex matrix.

Ultrafiltration of nonionic surfactants and dissolved organic matter

A brownwater sample with a high content of humic substances (HS) was fractionated by multistage ultrafiltration (mst-UF) into five fractions with nominal molecular weights ranging from >30 to <1 kDa. Fractions were characterized with respect to molecular size distribution and structure. Size exclusion chromatography with online DOC detection revealed that mst-UF yielded fractions with decreasing Mp (molecular weight at peak maximum) and polydispersities from nominally large to small mst-UF fractions. 13C MAS NMR analysis showed that the content of carbohydrate structures decreased from the original sample toward smaller molecular weight (MW) fractions, which in turn contained more carboxylic groups and branched aliphatic structures. Specific UV absorbances (SUVA254) were highest in the >30 kDa fraction and decreased with decreasing MW. To evaluate whether separation mechanisms other than size exclusion were of importance during the fractionation, the behavior of low molecular weight model compounds (MC) with a range of polarities was studied. Recoveries decreased with increasing hydrophobicity of the MC. For selected nonylphenol ethoxylates and 4-nonylphenol the recovery correlated well with the hydrophile-lipophile balance value. The presence of dissolved organic matter (DOM) caused an additional loss of hydrophobic MC, possibly because of sorption of the compounds onto DOM fouling layers. The hydrophilic MC caffeine was recovered almost completely (85-86%) regardless of the DOM content of the model solution. It was concluded that size exclusion was the dominant fractionation mechanism for caffeine, whereas hydrophobic interactions played a major role during the mst-UF fractionation of nonpolar contaminants. For a better understanding of the behavior of polyfunctional molecules such as HS, the effect of other physicochemical properties needs to be investigated in further studies.