Reactive transport of uranium with bacteria in fractured rock: model development and sensitivity analysis.

A numerical model for the reactive transport of uranium and bacteria in fractured rock was newly developed. The conceptual model consists of four phases (fracture, fracture surface, matrix pore, and matrix solid) and eight constituents (solutes in the fracture, on the fracture surface, on mobile bacteria, on immobile bacteria, in the rock matrix pores and on the rock matrix solids, and bacteria in the fracture and on the fracture surface). In addition to the kinetic sorption/desorption of uranium and bacteria, uranium reduction reaction accompanying with bacteria growth was considered in the reactive transport. The non-linear reactive transport equations were numerically solved using the symmetric sequential iterative scheme of the operator-splitting method. The transport and kinetic reaction modules in the developed model were separately verified, and the results were reasonably acceptable. From the sensitivity analysis, the uranium transport was generally more sensitive to the sorption rate rather than desorption rate of U(VI). Considering a uranium reduction reaction, bacteria could considerably retard the uranium transport no matter the uranium sorption/desorption rates. As the affinity of U(VI) onto the bacteria becomes higher than that onto a rock fracture surface, a biofilm effect, rather than a colloidal effect, of the bacteria becomes more influential on the uranium transport.

Effect of soil organic matter (SOM) and soil texture on the fatality of indigenous microorganisms in intergrated ozonation and biodegradation.

In situ ozonation has been proposed as a method to remediate soils contaminated with organic pollutants. Soil column experiments were performed on eight different soils in order to investigate the effects of soil properties, such as soil organic matter (SOM) and soil texture on the survival and regrowth of indigenous microorganisms after in situ ozonation. Indigenous microorganisms were found to be very sensitive to ozone in the soil column experiments. The microbial fatality revealed a linear relationship with the SOM content in the range of 1.72-2.42% of SOM content, whereas water content was poorly correlated. Four weeks of incubation of ozone-treated soil samples allowed for the regrowth of indigenous microorganisms with inverse relation to ozonation time. The regrowth was also significantly influenced by the SOM content in the same soil texture. Oxidation and removal rate of hexadecane was affected by particle size distribution. Especially, sand exhibited the highest oxidation rate of hexadecane, which resulted from having the lowest SOM content, water content, and surface area with respect to the other samples. The soil samples ozonated for 90-180 min were determined to exhibit the lowest concentration of hexadecane, with the exception of sand, after 4 weeks of incubation. This study provided insight into the influence of SOM and soil texture on indigenous microbial potential to degrade hexadecane in integrated ozonation and biodegradation.

Preparation of biotic and abiotic iron oxide nanoparticles (IOnPs) and their properties and applications in heterogeneous catalytic oxidation.

Iron oxide nanoparticles (IOnPs) as solid catalyst were prepared using a biotic method, i.e., biomineralization, and abiotic methods, i.e., thermal decomposition and electrochemical methods, for use as solid catalysts in the heterogeneous catalytic ozonation of para-Chlorobenzoic acid (pCBA). It was determined that characteristics of IOnPs, including particle size, morphology, surface area, electrokinetic mobility, basic group content, and chemical composition were significantly influenced by the preparation methods. TEM and FE-SEM analyses showed that the thermal decomposition method produced monodispersed and regularly spherical particles. The smallest iron oxide was also prepared by the thermal decomposition method, whereas the electrochemical method produced the largest iron oxide in terms of mean particle size. The specific surface area was found to be inversely proportional to the mean particle size. In catalytic ozonation at acidic pH levels, it was clearly observed that IOnPs enhanced the degradation of pCBA by the production of *OH radicals resulting from the catalytic decomposition of ozone. Additionally, functional groups and surface area were found to play an important role in the catalytic activity of IOnPs. To this extend, in a comparison of particle types, IOnPs prepared by the thermal decomposition method (IO(TD)) showed the greatest catalytic activity in terms of R(ct) value representing the ratio of hydroxyl radicals and ozone. This result may be due to the relatively higher surface area and basic group content of IO(TD) than other IOnPs.

Laboratory-scale application of fiber optic transflection dip probe (FOTDP) for in situ monitoring of gas phase ozone in unsaturated porous media.

A fiber optic transflection dip probe (FOTDP) system was developed for in situ and real-time monitoring of the transport of gas phase ozone in unsaturated porous media. A unique property of this system is the employment of a dip probe, which is inserted within the porous media. At the probe's tip, incoming light interacts with gas phase ozone and is partially reflected back into the probe by a mirror attached to the tip. Calibration of the FOTDP system was successfully carried out with various ozone concentrations using a column packed with glass beads. The ozone breakthrough curves (BTCs) were obtained by converting normalized UV intensities into gas phase ozone concentrations. The FOTDP system worked well for in situ monitoring of gas phase ozone using a column packed with sand under various water saturations in the presence of SOM and reflected the ideal transport phenomena of gas phase ozone for various flow rates.

Effects of in-situ ozonation on indigenous microorganisms in diesel contaminated soil: survival and regrowth.

Soil column experiments were conducted to investigate the effects of chemical oxidation on the survival of indigenous microbes (i.e., heterotrophic microbes, phenanthrene-degrading microbes, and alkane-degrading microbes) for field soil contaminated with diesel fuel. Rapid decreases of total petroleum hydrocarbons (TPH) and aromatics of diesel fuel were observed within the first 60 min of ozone injection; after 60 min, TPH and aromatics decreased asymptotically with ozonation time. The three types of indigenous microbes treated were very sensitive to ozone in the soil column experiment, hence the microbial population decreased exponentially with ozonation time. The numbers of heterotrophic, alkane-degrading, and phenanthrene-degrading bacteria were reduced from 10(8) to 10(4), 10(7) to 10(3), and 10(6) CFU g soil(-1) to below detection limit after 900 min of ozonation, respectively. Except for the soil sample ozonated for 900 min, incubation of ozone-treated soil samples that were not limited by oxygen diffusion showed further removal of TPH. The soil samples that were ozonated for 180 min exhibited the lowest concentration of TPH and the highest regrowth rate of the heterotrophic and alkane-degrading populations after the 9 weeks of incubation.

Earthworm toxicity during chemical oxidation of diesel-contaminated sand.

An ecotoxicity test with Eisenia fetida was performed to monitor the removal of diesel and toxicity variation during the ozonation process. The three-dimensional (3-D) cell test was introduced for the monitoring of the ozonation process, and the removal rate based on total petroleum hydrocarbons (TPHs) mass was about 95% near the ozone inlet ports. This high removal rate might be caused by the low soil organic matter (SOM) content and low water content of sand. The use of a fiber-optic transflection dip probe (FOTDP) demonstrated that more than half of the injected ozone was consumed by reactions with diesel or natural ozone-consuming materials. The earthworm toxicity test using Eisenia fetida demonstrated that diesel concentrations in soil exceeding 10,000 mg/kg caused a dose-dependent weight loss in earthworms and increased mortality. Toxic effects were reduced greatly or eliminated after ozonation, and the degradation products of the ozonation were not toxic to the earthworms at the concentrations tested. One specific result was that the sublethal test on the earthworm might be more sensitive for the evaluation of the quality of contaminated soil, for some samples, which did not result in mortality and produced an adverse effect on weight.

Monitoring of petroleum hydrocarbon degradative potential of indigenous microorganisms in ozonated soil.

This study was performed to investigate the petroleum hydrocarbon (PH) degradative potential of indigenous microorganisms in ozonated soil to better develop combined pre-ozonation/bioremediation technology. Diesel-contaminated soils were ozonated for 0-900 min. PH and microbial concentrations in the soils decreased with increased ozonation time. The greatest reduction of total PH (TPH, 47.6%) and aromatics (11.3%) was observed in 900-min ozonated soil. The number of total viable heterotrophic bacteria decreased by three orders of magnitude in the soil. Ozonated soils were incubated for 9 weeks for bioremediation. The number of microorganisms in the soils increased during the incubation period, as monitored by culture- and nonculture-based methods. The soils showed additional PH-removal during incubation, supporting the presence of PH-degraders in the soils. The highest removal (25.4%) of TPH was observed during the incubation of 180-min ozonated soil during the incubation while a negligible removal was shown in 900-min ozonated soil. This negligible removal could be explained by the existence of relatively few or undetected PH-degraders in 900-min ozonated soil. After a 9-week incubation of the ozonated soils, 180-min ozonated soil showed the lowest TPH concentration, suggesting that appropriate ozonation and indigenous microorganisms survived ozonation could enhance remediation of PH-contaminated soil. Microbial community composition in 9-week incubated soils revealed a slight difference between 900-min ozonated and unozonated soils, as analyzed by whole cell hybridization. Taken together, this study provided insight into indigenous microbial potential to degrade PH in ozonated soils.

Sonolytic degradation of methyl tert-butyl ether: the role of coupled Fenton process and persulphate ion.

The sonolytic degradation of methyl tert-butyl ether (MTBE) has been investigated at ultrasonic frequency of 20 kHz. The observed pseudo-first-order rate constant decreased from 1.25 x 10(-4) to 5.32 x 10(-5) s(-1) as the concentration of MTBE increased from 2.84 x 10(-2) to 2.84 x 10(-1) mM. The rate of degradation of MTBE increased with the increase of the power density of ultrasonicator and also with the rise in reactor system temperature. In the presence of oxidising agent, potassium persulphate, the sonolytic rate of degradation of MTBE was accelerated substantially. Tert-butyl formate (TBF) and acetone were found to be the major intermediates of the degradation of MTBE. It is found that the ultrasound/Fe2+/H2O2 method is promising process for the degradation of MTBE. More than 95% degradation of MTBE (2.84 x 10(-2) mM) along with its intermediate products has been achieved during the coupled ultrasound/Fe2+/ H2O2 method. Hence, the coupled ultrasound/Fe2+/H2O2 may be a viable method for the degradation MTBE within a short period of time than the ultrasound irradiation process only. A kinetic model, based on the initial rates of degradation of MTBE and TBF, provides a good agreement with the experimental results.