Biodegradation and transport of benzene,toluene, and xylenes in a simulated aquifer: comparison of modelled and experimental results

Both laboratory experiments and numerical modelling were conducted to study the biodegradation and transport of benzene–toluene–xylenes (BTX) in a simulated semi‐confined aquifer. The factors incorporated into the numerical model include advection, hydrodynamic dispersion, adsorption, and biodegradation. The various physico‐chemical parameters required by the numerical model were measured experimentally. In the experimental portion of the study, BTX compounds were introduced into the aquifer sand. After the contaminants had been transported through the system, BTX concentrations were measured at 12 equally spaced wells. Subsequently, microorganisms obtained from the activated sludge of a sewage treatment plant and cultured in BTX mixtures were introduced into the aquifer through the 12 sampling wells. The distribution data for BTX adsorption by the aquifer sand form a nonlinear isotherm. The degree of adsorption by the sand varies, depending on the composition of the solute. The degradation time, measured from the time since the bacteria were added to the aquifer until a specific contaminant was no longer detectable, was 35–42 h for BTX. The dissolved oxygen, after degradation by BTX compounds and bacteria, was consumed by about 40–60% in the entire simulated aquifer; thus the aerobic conditions were maintained. This study provides insights for the biodegradation and transport of BTX in aquifers by numerical modelling and laboratory experiments. Experimental and numerical comparisons indicate that the results by Monod degradation kinetics are more accurate than those by the first‐order degradation kinetics. Copyright © 2002 John Wiley & Sons, Ltd.     

Biodegradation of Petroleum Hydrocarbons by Pseudomonas putida Strain MHF 7109

Pseudomonas putida MHF 7109 has been isolated and identified from cow dung microbial consortium for biodegradation of selected petroleum hydrocarbon compounds – benzene, toluene, and o‐xylene (BTX). Each compound was applied separately at concentrations of 50, 100, 250, and 500 mg L^?1 in minimal salt medium to evaluate degradation activity of the identified microbial strain. The results indicated that the strain used has high potential to degrade BTX at a concentration of 50 mg L^?1 within a period of 48, 96, and 168 h, respectively; whereas the concentration of 100 mg L^?1 of benzene and toluene was found to be completely degraded within 120 and 168 h, respectively. Sixty‐two percent of o‐xylene were degraded within 168 h at the 100 mg L^?1 concentration level. The maximum degradation rates for BTX were 1.35, 1.04, and 0.51 mg L^?1 h^?1, respectively. At higher concentrations (250 and 500 mg L^?1) BTX inhibited the activity of microorganisms. The mass spectrometry analysis identified the intermediates as catechol, 2‐hydroxymuconic semialdehyde, 3‐methylcatechol, cis‐2‐hydroxypenta‐2,4‐dienoate, 2‐methylbenzyl alcohol, and 1,2‐dihydroxy‐6‐methylcyclohexa‐3,5‐dienecarboxylate, for BTX, respectively. P. putida MHF 7109 has been found to have high potential for biodegradation of volatile petroleum hydrocarbons.     

A multi-methodological approach to determine CO2 and CH4 fluxes and concentrations in solid waste disposal

The municipal solid waste （MSW） landfills are the significant sources of atmospheric contamination, due to biogas production by anaerobic decomposition of organic matter via bacterial activity. Biogas released from landfills is commonly composed of a mixture of methane （55%-60%） and carbon dioxide （40%-45%）, with minor contents of N2, H2, CO and traces of toxic and bad smelling inorganic and organic compounds. Particular attention has to be paid to CH4 and CO2 because of their liability for the greenhouse effect. Presently, the U.S. methane emission from landfills is considered to be about 25% of the total methane released to the atmosphere. Accordingly, field measurements should be planned in order to verify and, eventually, optimize the amount of gases released from waste disposals to the atmosphere. Simultaneous measurements of methane and carbon dioxide fluxes are an effective tool to better evaluate： （1） the amount of biogas released, （2） the real efficiency of the impervious cover, and （3） the presence of anomalous degassing zones or of newly formed fractures. Static closed-chamber methods for CH4 and CO2 flux measurements have been developed and used in both natural and artificial systems. Furthermore, portable gas-chromatographers equipped with flame ionization detector （FID） and accumulation chamber connected to infrared detectors （IR） .have been utilized for measuring CH4 and CO2 fluxes, respectively. This paper deals with a detailed investigation that combines （1） CH4 and CO2 flux measurements from solid waste disposal and surrounding areas （determined by an accumulation chamber equipped with two IR detectors, respectively）, （2） chemical composition of soil and piezometer gases （collected in pre-evacuated glass tubes and analyzed by gas-chromatography）, and （3） CO2 linear concentration measurements on optical air paths with IR laser devices. This multi-methodological approach was successfully applied to an active MSW in Tuscany （Central Italy）. The analytical results have shown that the CO2/CH4 ratios of the piezometer gases have large variations, likely related to the different stage of decomposition processes affecting the heterogeneous solid material of the waste landfill. Significant contents of light hydrocarbons and BTX were also detected.