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PubMed2002

Biological detoxification of tar-water.

Gasification is an important option for the swift implementation of biomass combined heat and power processes in the Danish energy supply system. Tar-water produced by the gas-cleaning system of gasifiers may contain substances toxic to nitrifying bacteria. As the gasification plants are small and often located in the catchment area of small wastewater treatment plants, discharge of the tar-water may be critical for wastewater treatment plants operated with nitrogen removal. Tar-water from a full-scale updraft gasifier has been thoroughly examined with respect to inhibition of nitrification and the toxicity for nitrifying bacteria has been evaluated for the dominating constituents in the tar-water. Simple organic substances make up the dominating part of the organic matter but phenol and phenolic compounds are also present in significant concentrations. The identified substances are biologically degradable and it has been demonstrated that most of the organic matter together with the toxicity can be eliminated in an aerobic activated sludge process.

Bacteria↗
PubMed2006

Assessment of the multi-compound non-equilibrium dissolution behaviour of a coal tar containing PAHs and phenols into water.

Herein, an experimental study coupled with a model in order to assess the non-equilibrium and multi-compound dissolution behaviour of a coal tar containing PAHs and phenols into water, is presented. For this aim, two experimental studies has been carried out: (1) coal tar-water partition equilibrium and (2) dissolution dynamics of coal tar under controlled hydrodynamic conditions in percolation columns packed with glass beads. The dissolution amount of the three target constituents (i.e. phenol, naphthalene and phenanthrene) was monitored by UV detection. The dissolution behaviour was modelled using a predictive fraction approach. The partition coefficients have been estimated from experimental data and the obtained results show that the partition coefficient of each constituent between the aqueous phase and the tar depends on the activities of the constituent in both phases and cannot be estimated only from the solubility of the pure compound in water. The non-equilibrium dissolution model was established, applied for the experimental conditions and validated for three target compounds adjusting the effective interfacial area between tar and water. This parameter is specific of the experimental set-up. The global behaviour of coal tar has been modelled taking into account four categories of compounds according to their water solubility and volatilities. The mass transfer parameters have been estimated using available correlations. The results of this paper indicate that a model based on component fractions can be used to assess the non-equilibrium dissolution behaviour of a coal tar.

Coal Tar↗
PubMed2003

PAH sorption mechanism and partitioning behavior in lampblack-impacted soils from former oil-gas plant sites.

This study assessed polycyclic aromatic hydrocarbon (PAH) association and aqueous partitioning in lampblack-impacted field soils from five sites in California that formerly housed oil-gas process operations. Lampblack is the solid residue resulting from the decomposition of crude oil at high temperatures in the gas-making operation and is coated or impregnated with oil gasification byproducts, among which PAHs are the compounds of the greatest regulatory concern. A suite of complementary measurements investigated the character of lampblack particles and PAH location and the associated effects on PAH partitioning between lampblack and water. PAH analyses on both whole samples and density-separated components demonstrated that 81-100% of PAHs in the lampblack-impacted soils was associated with lampblack particles. FTIR, 13C NMR, and SEM analyses showed that oil-gas lampblack solids comprise primarily aromatic carbon with soot-like structures. A free-phase aromatic oil may be present in some of the lampblack soils containing high PAH concentrations. Comparable long-term aqueous partitioning measurements were obtained with an air-bridge technique and with a centrifugation/alum flocculation procedure. Large solid/water partition coefficient (Kd) values were observed in samples exhibiting lower PAH and oil levels, whereas smaller Kd values were measured in lampblack samples containing high PAH levels. The former result is in agreement with an oil-soot partitioning model, and the latter is in agreement with a coal tar-water partitioning model. Lampblack containing high PAH levels appears to exhaust the sorption capacity of the soot-carbon, creating a free aromatic oil phase that exhibits partitioning behavior similar to PAHs in coal tar. This study improves mechanistic understanding of PAH sorption on aged lampblack residuals at former oil-gas sites and provides a framework for mechanistic assessment of PAH leaching potential and risk from such site materials.

Carbon↗
PubMed2006

Prediction of partitioning between complex organic mixtures and water: application of polyparameter linear free energy relationships.

Equilibrium partitioning between nonaqueous phase liquids (NAPLs) and water is a governing process for contaminants leaching from NAPLs. Conventional prediction methods, such as Raoult's law and single-parameter linear free energy relationship (SP-LFER), are inaccurate for compounds with polar functional groups. Therefore, this study introduces a polyparameter linear free energy relationship (PP-LFER) approach as a more general tool to predict NAPL-water partitioning coefficients. Our approach was evaluated using 441 experimental partitioning data from 30 references. Experimental fuel-water partitioning coefficients were generally well reproduced by existing PP-LFERs for pure solvents using either a volume-fraction weighted sum of partitioning coefficients K (linear model, R2 = 0.983, root-mean-squared error [rmse] = 0.23) or a volume-fraction weighted sum of log K (log linear model, R2 = 0.976, rmse = 0.28). Using the linear model, estimations were, in most cases, within a factor of 2 from the experimental values, regardless of the type of compounds and the presence of a fuel additive. In contrast, the log linear model considerably underestimated partitioning coefficients in the presence of strong solute-solvent hydrogen bonding. For coal tar-water partitioning coefficients (Kcoal tar/w), new PP-LFER equations were calculated based on experimental log Kcoal tar/w values of 35 compounds. The resulting regression equation was log Kcoal tar/w = 0.40(+/-0.33) + 0.34(+/-0.32)E+ 0.61(+/-0.57)S-0.55-(+/-0.61)A-5.07(+/-0.61)B + 3.22(+/-0.35)V with the rmse equal to 0.21, where E, S, A, B, and Vare Abraham's solute descriptors. Partitioning coefficients for phenol and alcohols, calculated by the above equation, were much closer to the experimental values than to those estimated by the SP-LFER approach with octanol-water partitioning coefficients. The values of the coefficients also provide insight into the properties of coal tar in terms of molecular interactions with solutes. Consequently, using the approaches presented in this study, complex organic mixture-water partitioning coefficients of a wide range of organic compounds with varying polarity can be reasonably estimated.

Organic Chemicals↗
PubMed2006

Role of weathered coal tar pitch in the partitioning of polycyclic aromatic hydrocarbons in manufactured gas plant site sediments.

Polycyclic aromatic hydrocarbons (PAHs) in manufactured gas plant (MGP) site sediments are often associated with carbonaceous particles that reduce contaminant bioavailability. Although black carbon inclusive partitioning models have been proposed to describe elevated PAH partitioning behavior, questions remain on the true loading and association of PAHs in different particle types in industrially impacted sediments. In the studied MGP sediments, the light density organic particles (coal, coke, wood, and coal tar pitch) comprised 10-20% of the total mass and 70-95% of the PAHs. The remainder of the PAHs in sediment was associated with the heavy density particles (i.e., sand, silt, and clays). Among the different particle types, coal tar pitch (quantified by a quinoline extraction method) contributed the most to the bulk sediment PAH concentration. Aqueous partition coefficients for PAHs measured using a weathered pitch sample from the field were generally an order of magnitude higher than reported for natural organic matter partitioning, and match well with theoretical predictions based on a coal tar-water partitioning model. A pitch-partitioning inclusive model is proposed that gives better estimates of the measured site-specific PAH aqueous equilibrium values than standard estimation based on natural organic matter partitioning only. Thus, for MGP impacted sediments containing weathered pitch particles, the partitioning behavior may be dominated by the sorption characteristics of pitch and not by natural organic matter or black carbon.

Coal Tar↗
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History, Modern 1601-↗