Comparative study of extraction methods for the determination of PAHs from contaminated soils and sediments

The following four methods were compared on the extraction efficiency of 16 EPA (US Environmental Protection Agency) polycyclic aromatic hydrocarbons (PAHs): German method of the Verband Deutscher Landwirtschaftlicher Untersuchungs und Forschungsanstalten (VDLUFA), two methods of the International Organization for Standardization using shaking (ISO A) and Soxhlet extraction (ISO B) and an ultrasonic method. Recovery rates of 16 PAHs were determined in two soils. Extraction efficiency was evaluated in five soils and three sediments. Effect of drying soils and sediments on extraction efficiency was tested using the VDLUFA and the ultrasonic methods. Our study shows that the number of aromatic rings, rather than extraction procedures, significantly influenced recovery rates of individual PAHs. No significant differences in extraction efficiency of the four methods were observed for less polluted samples. For highly polluted soils, extraction efficiency decreased in the following order: VDLUFA method > ISO A > ultrasonic method > ISO B. Influence of soil moisture on extraction efficiency depended to some extent on both solvent used and content of PAHs in samples. A mixture of dichloromethane/acetone (5:1) is recommended for PAH extraction from moist samples when the ultrasonic method is used.     

Changes in soil organic carbon storage under grassland as evidenced by changes in sulphur input-output budgets

Information about temporal changes in soil organic carbon (C) pools may be obtained indirectly from changes in input-output budgets of organically combined nutrients such as sulphur (S). Sulphur budgets were therefore evaluated for Northern Ireland (NI) for the period 1940-1990, inclusive. These budgets indicated that the land or soil had acted first as a sink but then as a source for S, and that reserves of soil S built up between 1940 and 1965 were totally depleted by the mid-1980s. Pooled data from six long-term soil-monitoring sites on undisturbed grassland suggested that negative S budgets from the late-1970s onwards had been due to the net mineralization of soil organic matter and thus were indicative of net losses of organic C from surface soil horizons. There was some evidence that the decline in rainfall and fertiliser S inputs from the mid-1960s may have precipitated the breakdown of soil organic matter.     

Municipal solid waste characteristics and management in China

The purpose of this investigation is to evaluate the current status and identify the problems of municipal solid waste (MSW) management in China in order to determine appropriate remedial strategies. This is the first of two papers, discussing primarily the general characteristics of MSW and its management in China. The second paper focuses on specific remedial strategies. MSW generation in China has increased rapidly in the past 20 years from 31.3 million tons in 1980 to 113.0 million tons in 1998. The annual rate of increase is 3-10%. The average generation per capita is 1.0 kg/day (0.38 t/year). Nearly one-half of the waste generated is dumped in the suburbs, where the accumulated quantity has reached 6 billion tons, which has caused heavy environmental pollution. This paper provides information on MSW management in China, such as MSW generation and its physical, chemical, and biological properties. Low calorific value and high moisture content characterize China's municipal waste. Other issues related to MSW management in China are also discussed, including the factors that influence MSW generation quantity and     

Incineration of paper sludge in a prototype vortexing fluidized bed combustor

All experiments were carried out in a prototype vortexing fluidized bed combustor (VFBC). The dimension of the combustion chamber is 0.7 x 1.4 x 2 m, and the freeboard section is 1 m i.d. and 4 m in height. Paper sludge was used as the feeding material. Two types of coal particles were employed as the supplementary fuel. In order to understand the characteristics of the VFBC system for paper sludge incineration, the effect of various operating parameters, such as the primary airflow, excess air ratio, and secondary airflow rates, on temperature distribution, ash elutriation, combustion efficiency, and pollutant emissions were investigated.     

Coupled production and transport of selenium vapor in unsaturated soil: evaluation by experiments and numerical simulation

Volatilization of selenium (Se) from soil to the atmosphere involves several sequential chemical reactions that form volatile Se species, followed by transport of the gaseous Se through the soil. This paper describes a numerical model that simulates the chemical and physical processes governing the production and transport of Se vapor in unsaturated soil. The model couples the four Se species involved in the production of Se vapor through chemical reactions, and allows each to migrate through the soil by advection, liquid or vapor diffusion depending on its affinity for the dissolved or vapor phase. The coupled transformations and transport of the four Se species, i.e., selenate, selenite, elemental and organic Se, and Se vapor, were calculated based on the Crank-Nicolson finite difference method. The model was used to analyze fluxes of Se vapor measured from a soil amended with inorganic Se in the form of selenate and covered with unamended clean soil of various thicknesses. Evolution of Se vapor from the soil was very fast, with measurable amounts of Se detected within 24 h. The peak of Se volatilization, detected at the 6th day, reached 3.31 Se microgram/day for the uncovered soil, but was reduced to near the detection limit (0.05 microgram/day) in the presence of a 8- or 16-cm clean soil cover. With two reaction rate coefficients fitted to the data, the model described Se volatilization very well. The estimated rate coefficient of Se methylation was unexpectedly high, with a value of 0.167/day. The net volatilization of Se, however, was severely inhibited by the fast demethylation, i.e., the reverse reaction which converted volatile Se species back into nonvolatile forms. As a result, Se vapor only penetrated a few centimeters in the soil. The demethylation rate coefficient, assessed by independent transport experiments using dimethyl selenide, was estimated as 186.8/day, corresponding to a half-life of only 5.3 min for Se vapor. Results of this study indicated that rapid demethylation of Se vapor during its diffusive transport through a soil is probably an important limiting factor in the volatilization of Se under natural conditions.     

Performance evaluation of laser-induced breakdown spectrometry as a multimetal continuous emission monitor

Laser-induced breakdown spectroscopy (LIBS) has been evaluated as a multimetal continuous emissions monitor (CEM) at the U.S. Environmental Protection Agency (EPA) rotary kiln incinerator simulator (RKIS) facility in Raleigh, NC. Two detection systems with a bifurcated optical fiber bundle were used for simultaneously monitoring the concentrations of Be, Cd, Cr, and Hg in the test. Two calibration techniques were evaluated in the laboratory for the field measurements. On-line calibration of relative metal concentration was also performed in the simulated incinerator gas stream. Toxic metal concentrations measured with LIBS have been compared with the EPA reference method (RM) results.     

Mobilization of soil organic matter by complexing agents and implications for polycyclic aromatic hydrocarbon desorption

Complexing agents are frequently used in treatment technologies to remediate soils, sediments and wastes contaminated with toxic metals. The present study reports results that indicate that the rate and extent of soil organic matter (SOM) as represented by dissolved natural organic carbon (DNOC) and polycyclic aromatic hydrocarbon (PAH) desorption from a contaminated soil from a manufactured gas plant (MGP) site can be significantly enhanced with the aid of complexing agents. Desorption of DNOC and PAH compounds was pH dependent, with minimal release occurring at pH 2-3 and maximal release at pH 7-8. At pH-6, chelate solutions were shown to dissolve large amounts of humic substances from the soil compared to controls. The complexing agents mobilized polyvalent metal ions, particularly Fe and Al from the soil. Metal ion chelation may disrupt humic (metal ion)-mineral linkages, resulting in mobilization of SOM and accompanying PAH molecules into the aqueous phase; and/or reduce the degree of cross-linking in the soil organic matter phase, which could accelerate PAH diffusion.     

Mechanism of PCBs formation from the pyrolysis of chlorobenzenes

Polychlorinated biphenyls (PCBs) were formed by pyrolysis of chlorobenzenes in a HCl atmosphere. Varieties of substituted chlorobenzenes were used as model compounds to optimize the condensation reaction. Lower chlorinated benzenes produce more PCBs than that of higher ones. Up to 0.7 microg PCBs/mg 1,2,3-trichlorobenzene was produced through the condensation reaction.     

Photocatalytic activity of TiO2 films grown on different substrates

Titanium dioxide films were prepared on glass, indium-tin oxide (ITO) glass and p-type monocrystalline silicon and studied for the photocatalytic degradation of rhodamine B in an aqueous medium. Raman, AFM, and XPS spectroscopic investigations of these films indicated that microstructure of titanium oxide films were greatly affected by the substrate materials. Rutile was confirmed to be easily formed on the surface of ITO glass, and TiO2 tended to grow as closely packed particles that were elongated strips with an average size of 20 nm, and had lovely contrast with the perfectly round particles grown on p-type monocrystalline silicon. Charge transfer between the film and silicon substrate was verified by surface photovoltage spectra. This may be the real reason why the films grown on ITO glass and silicon substrates exhibit higher photocatalytic reactivity than the film on glass substrate. Moreover, the different surface properties also seem to be responsible for the different activity.