Isotope fractionation of benzene during partitioning - Revisited.

Isotope fractionation between benzene-D0 and benzene-D6 caused by multi-step partitioning of the benzenes between water and two organic solvents, n-octane and 1-octanol, as well as between water and the gas phase, was measured. The obtained fractionation factors αH = KH/KD are αH = 1.080 ± 0.015 and αH = 1.074 ± 0.015 for extraction into n-octane and 1-octanol, respectively, and αH = 1.049 ± 0.010 for evaporation from aqueous solution. The comparison of solvent- and gas-phase partitioning reveals that about 2/3 of the driving force of fractionation is due to different interactions in the aqueous phase, whereas 1/3 is due to different interactions in the organic phase. The heavy benzene isotopologue behaves more 'hydrophilically' and the light one more 'hydrophobically'. This synergistic alignment gives rise to relatively large fractionation effects in partitioning between water and non-polar organic matter. In contrast to a previous study, there is no indication of strong fractionation by specific interactions between benzene and octanol. Partitioning under non-equilibrium conditions yields smaller apparent fractionation effects due to opposite trends of thermodynamic and kinetic fractionation parameters, i.e. partition and diffusion coefficients of the isotopologues. This may have consequences which should be taken into account when considering isotope fractionation due to sorption in environmental compartments.

Characterization of biochars and dissolved organic matter phases obtained upon hydrothermal carbonization of Elodea nuttallii.

The invasive aquatic plant Elodea nuttallii was subjected to hydrothermal carbonization at 200 °C and 240 °C to produce biochar. About 58% w/w of the organic carbon of the pristine plant was translocated into the solid biochar irrespectively of the operating temperature. The process water rich in dissolved organic matter proved a good substrate for biogas production. The E. nuttallii plants showed a high capability of incorporating metals into the biomass. This large inorganic fraction which was mainly transferred into the biochar (except sodium and potassium) may hamper the prospective application of biochar as soil amendment. The high ash content in biochar (∼ 40% w/w) along with its relatively low content of organic carbon (∼ 36% w/w) is associated with low higher heating values. Fatty acids were completely hydrolyzed from lipids due to hydrothermal treatment. Low molecular-weight carboxylic acids (acetic and lactic acid), phenols and phenolic acids turned out major organic breakdown products.

Organic breakdown products resulting from hydrothermal carbonization of brewer's spent grain.

Hydrothermal carbonization of brewer's spent grain resulted in a solid hydrochar and an aqueous phase rich in macromolecular dissolved organic matter. Both phases were analyzed with regard to low molecular weight organic compounds (MW<500 Da) in lyophilized form by exhaustive solvent extraction followed by pre-chromatographic derivatization and GC/MS-analysis. Low molecular weight acids, O-functionalized phenols, cyclopentenone derivatives, and benzenediols accounted for the majority of organic analytes in both hydrothermal carbonization product streams while being absent in solvent extracts of the pristine biomass. The pattern of short chain functionalized acids in the pristine biomass and in the hydrothermally produced matrices turned out very different. Acylglycerines as the most abundant lipids in pristine brewer's spent grain were quantitatively hydrolyzed under hydrothermal conditions. The recovery of total fatty acids present in the pristine biomass amounted to 19%. The major fraction of hydrophobic breakdown products including fatty acids, fatty alcohols, and sterols was sorbed onto the hydrochar.

Hydrothermal carbonization of poly(vinyl chloride).

Poly(vinyl chloride) (PVC) was subjected to hydrothermal carbonization in subcritical water at 180-260 °C. Dehydrochlorination increased with increasing reaction temperature. The release of chlorine was almost quantitative above ∼235 °C. The fraction of organic carbon (OC) recovered in the hydrochar decreased with increasing operating temperature from 93% at 180 °C to 75% at 250 °C. A wide array of polycyclic aromatic hydrocarbons (PAHs) could be detected in the aqueous phase, but their combined concentration amounted to only ∼140 µg g(-1) PVC-substrate at 240 °C. A pathway for the formation of cyclic hydrocarbons and O-functionalized organics was proposed. Chlorinated hydrocarbons including chlorophenols could only be identified at trace levels (low ppb). Polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) could not be detected. The sorption potential of the hydrochar turned out to be very low, in particular for polar organic pollutants. Our results provide strong evidence that hydrothermal carbonization of household organic wastes which can be tied to co-discarded PVC-plastic residues is environmentally sound regarding the formation of toxic organic products. Following these findings, hydrothermal treatment of PVC-waste beyond operating temperatures of ∼235 °C to allow complete release of organic chlorine should be further pursued.

Characterization of biocoals and dissolved organic matter phases obtained upon hydrothermal carbonization of brewer's spent grain.

The wet biomass brewer's spent grain was subjected to hydrothermal carbonization to produce biocoal. Mass balance considerations indicate for about two thirds of the organic carbon of the input biomass to be transferred into the biocoal. The van Krevelen plot refers to a high degree of defunctionalization with decarboxylation prevailing over dehydration. Calorific data revealed a significant energy densification of biocoals as compared to the input substrate. Sorption coefficients of organic analytes covering a wide range of hydrophobicities and polarities on biocoal were similar to those for dissolved humic acids. Data from GC/MS analysis indicated that phenols and benzenediols along with fatty acids released from bound lipids during the hydrothermal process constituted abundant products. Our findings demonstrate that the brewer's spent grain by-product is a good feedstock for hydrothermal carbonization to produce biocoal, the latter offering good prospects for energetic and soil-improving application fields.

Carbon and hydrogen isotope fractionation of benzene and toluene during hydrophobic sorption in multistep batch experiments.

The application of compound-specific stable isotope analysis (CSIA) for evaluating degradation of organic pollutants in the field implies that other processes affecting pollutant concentration are minor with respect to isotope fractionation. Sorption is associated with minor isotope fractionation and pollutants may undergo successive sorption-desorption steps during their migration in aquifers. However, little is known about isotope fractionation of BTEX compounds after consecutive sorption steps. Here, we show that partitioning of benzene and toluene between water and organic sorbents (i.e. 1-octanol, dichloromethane, cyclohexane, hexanoic acid and Amberlite XAD-2) generally exhibits very small carbon and hydrogen isotope effects in multistep batch experiments. However, carbon and hydrogen isotope fractionation was observed for the benzene-octanol pair after several sorption steps (Δδ(13)C=1.6 ± 0.3‰ and Δδ(2)H=88 ± 3‰), yielding isotope fractionation factors of αC=1.0030 ± 0.0005 and αH=1.195 ± 0.026. Our results indicate that the cumulative effect of successive hydrophobic partitioning steps in an aquifer generally results in insignificant isotope fractionation for benzene and toluene. However, significant carbon and hydrogen isotope fractionation cannot be excluded for specific sorbate-sorbent pairs, such as sorbates with π-electrons and sorbents with OH-groups. Consequently, functional groups of sedimentary organic matter (SOM) may specifically interact with BTEX compounds migrating in an aquifer, thereby resulting in potentially relevant isotope fractionation.

Hydrothermal carbonization of olive mill wastewater.

Hydrothermal carbonization (HTC) is an emerging technology to treat wet biomasses aimed at producing a biochar material. Herein, olive mill wastewater (OMW) was subjected to HTC. Mass balance considerations provide evidence that the yield of biochar is low (~30%, w/w), which is associated with a low fraction of carbohydrates in OMW. The combination of different preparation schemes, pre-chromatographic derivatization reactions and GC/MS analysis for the analysis of organic compounds in aqueous HTC-solutions allowed to identify and quantify a wide array of analytes which belong either to intrinsic constituents of OMW or to characteristic HTC-breakdown products. Biophenols, such as hydroxyl-tyrosol (OH-Tyr), tyrosol (Tyr) account for the most abundant members of the first group. Most abundant breakdown products include phenol and benzenediols as well as short-chain organic acids. Secoiridoids, such as decarbomethoxy ligostride aglycon and decarbomethoxy oleuropein aglycon, all of them being typical components of OMW, are less abundant in HTC-solutions.

Engineering aspects of radio-wave heating for soil remediation and compatibility with biodegradation.

Dielectric heating of soil using radio waves (RW) can be applied to support various remediation techniques, namely biodegradation and soil vapor extraction, under in situ, on site or ex situ conditions. To improve the spatial resolution of energy dissipation, the design of rod electrodes was modified with an air gap around the electrode allowing thermal treatment focused to the desired soil volume. A combination of low- and high-frequency electrical energy was successfully applied to homogeneously heat the capillary fringe, the boundary region of saturated and unsaturated zones. The energetic efficiency of the method was evaluated showing that an efficient transformation of RW energy to heat in the target volume can be achieved. By comparing biodegradation and soil respiration under conventional and electric (low-frequency resistive and dielectric RW) heating, the compatibility of the electric heating methods with bioremediation processes could be proven. Therefore, RW-supported microbial degradation of pollutants is a real option for accelerated soil remediation.

Results of field tests on radio-wave heating for soil remediation.

After developing the radio-wave technique for various conditions in laboratory-scale and technical plant-scale experiments, field tests in combination with biodegradation and soil vapor extraction were carried out at three sites: (i) a bioremediation facility for ex situ cleaning of soil, (ii) in situ remediation of contamination at a former storage facility for organic solvents, and (iii) a polluted soil under a former petrol station. Various electrode arrangements such as parallel plates, rod arrays, and coaxial antenna were applied in order to meet the site-specific requirements optimally. Soil temperatures between 35 and 100 degrees C were established. The successful tests gave much insight into the engineering, physical, biological, and chemical aspects of radio-wave application. General conclusions on the appropriateness and competitiveness of the radio-wave method as well as on preferred application fields are drawn.

Sorption of pyrene to dissolved humic substances and related model polymers. 1. Structure--property correlation.

Solid-phase microextraction (SPME) was employed to determine sorption coefficients for pyrene on dissolved humic substances (DHS) of various origins and also on model polymers to gain a better understanding of the relationships between sorption potential and sorbent structures. The sorption potential of DHS from very different sources is described by an empirical two-parameter correlation involving the polarity (O/H atomic ratio) and the aromaticity (epsilon 280 nm) as descriptors. On the other hand, sorption experiments with well-defined model polymers, poly(acrylic acid) esters, led to the conclusion that aliphatic chains may be more effective than aromatic moieties in binding PAHs. The molecular weight of the model sorbents was found to have a significant influence on the sorption potential.

Sorption of very hydrophobic organic compounds (VHOCs) on dissolved humic organic matter (DOM). 2. Measurement of sorption and application of a Flory-Huggins concept to interpret the data.

Sorption phenomena of very hydrophobic compounds (VHOCs, log K(OW) > 5) on dissolved humic organic matter (DOM) are overwhelmingly based on partitioning processes. In this respect, DOM is very similar to "rubbery" soil/sediment OM. To exclude system adsorption effects, the DOM sorption coefficients (K(DOM)) of VHOCs were determined using a dynamic approach based on the VHOCs' aqueous solubility enhancement in the presence of DOM. Partition coefficients are strongly correlated to the analytes' Kow across the alkane, PAH, and PCB groups under study. These three "families" are regarded to be good models of hydrophobic partitioning. On the basis of a uniform one-parameter concept characterizing sorption on amorphous polymers, Hildebrand solubility parameters of amorphous polymeric sorbents, including DOM, and of sorbates can be calculated on the basis of partition coefficients. Likewise, partition coefficients can be estimated using Hildebrand solubility parameters. Literature-based partition coefficients on DOM fit very well in this universal one-parameter concept. On using our own sorption data of PAHs, PCBs, and alkanes on DOM, an almost identical solubility parameter for the DOM polymer under study is obtained. The concept is also very useful in understanding both waterborne and airborne bioconcentration processes, which are considered to be partitioning phenomena.