Simon H. Davies

Efficacy of in-situ for the remediation of PAH contaminated soils

Abstract Polycyclic aromatic hydrocarbons (PAHs) are of environmental concern because many PAHs are either carcinogens or potential carcinogens. Petroleum products are a major source of PAHs. The occurrence of PAH contamination is widespread and novel treatment technologies for the remediation of contaminated soils are necessary. Ozone has been found to be extremely useful for the degradation of PAHs in soils. For these compounds, the reaction with molecular ozone appears to be the more important degradation pathway. Greater than 95% removal of phenanthrene was achieved with an ozonation time of 2.3 h at an ozone flux of 250 mg h −1 . After 4.0 h of treatment at an ozone flux of 600 mg h −1 , 91 % of the pyrene was removed. We have also found that the more hydrophobic PAHs (e.g. chrysene) react more slowly than would be expected on the basis of their reactivity with ozone, suggesting that partitioning of the contaminant into soil organic matter may reduce the reactivity of the compound. Even so, after 4 h of exposure to ozone, the chrysene concentration in a contaminated Metea soil was reduced from 100 to 50 mg kg −1 . Ozone has been found to be readily transported through columns packed with a number of geological materials, including Ottawa sand, Metea soil, Borden aquifer material and Wurtsmith aquifer material. All of these geological materials exerted a limited (finite) ozone demand, i.e. the rate of ozone degradation in soil columns is very slow after the ozone demand is met. Moisture content was found to increase the ozone demand, most likely owing to the dissolution of gaseous ozone into the pore water. As once the initial ozone demand is met, little degradation of ozone is observed, it should be possible to achieve ozone penetration to a considerable distance away from the injection well, suggesting that in-situ ozonation is a feasible means of treating uncontaminated unsaturated soils. This is substantiated by two field studies where in-situ ozonation was apparently successful at remediating the sites.

Mn oxide coated catalytic membranes for a hybrid ozonation-membrane filtration: Comparison of Ti, Fe and Mn oxide coated membranes for water quality

In this study the performance of catalytic membranes in a hybrid ozonation-ceramic membrane filtration system was investigated. The catalytic membranes were produced by coating commercial ceramic ultrafiltration membranes with manganese or iron oxide nanoparticles using a layer-by-layer self-assembly technique. A commercial membrane with a titanium oxide filtration layer was also evaluated. The performance of the coated and uncoated membranes was evaluated using water from a borderline eutrophic lake. The permeate flux and removal of the organic matter was found to depend on the type of the metal oxide present on the membrane surface. The performance of the manganese oxide coated membrane was superior to that of the other membranes tested, showing the fastest recovery in permeate flux when ozone was applied and the greatest reduction in the total organic carbon (TOC) in the permeate. The removal of trihalomethanes (THMs) and haloacetic acids (HAAs) precursors using the membrane coated 20 times with manganese oxide nanoparticles was significantly better than that for the membranes coated with 30 or 40 times with manganese oxide nanoparticles or 40 times with iron oxide nanoparticles.

Transport of iron, manganese, cadmium, copper and zinc by magela creek, Northern territory, Australia

Abstract Five major flood events occurring in Magela Creek during the 1978–1979 tropical wet season were sampled for conductivity, suspended solids and the trace metals iron, manganese, cadmium, copper and zinc. All concentrations were found to be very low, as were the denudation rates for trace metals and suspended materials. These results are as expected since the catchment is highly weathered, and is relatively undisturbed by man. The variations in conductivity, suspended solids and trace metal concentrations during individual flood events are also discussed.

Frozen soil subsurface barriers: formation and ice erosion

Abstract Before and during soil remediation, frozen soil barriers are used to provide containment of liquid contaminants so as to prevent their migration to adjacent areas. Questions concerning formation of frozen gravelly sand barriers in the vadose zone and barrier resistance to ice erosion by liquid contaminants provided the impetus for this study. Bench-scale barriers with full and partial ice saturation were studied. For comparison, one barrier was formed in gravelly sand using water injection via a bentonite-water slurry. The bentonite increased the slurry viscosity, thereby providing a water retention period suitable for freezing. Liquid contaminants included a sodium nitrate solution (freezing point of −5°C) and an antifreeze solution (freezing point of −33°C). Results showed that ice erosion in the bench-scale barriers occurred when the contaminant freezing point depression was lower than the temperature of the frozen soil. When liquid contaminants entered the voids of partially ice saturated frozen soil, the rate of ice erosion was significantly increased. Full ice saturation and barrier temperatures below the freezing point depression of the contaminant are needed to minimize ice erosion.

Oxidation of 1,3,5- trichlorobenzene using advanced oxidation processes

Abstract The oxidation of 1,3,5‐trichlorobenzene (TCB) by ozone, ozone/UV, ozone/H2O2 and ozone/UV/H2O2 was studied. All studies were conducted in a continuously‐flowing completely mixed reactor (CFCMR), operated at steady‐state conditions using a hydraulic retention time of 10 minutes. The greatest removal of TCB using ozone/H2O2 treatment was achieved using a H2O2 concentration of 60 μM. At low pH values (approx. 2) ozone/UV performed significantly better than either ozone alone or ozone/H2O2. However, at circumneutral pH, the removal efficiencies of TCB by ozone/UV and ozone/H2O2 and ozone/UV/H2O2 were essentially equal (∼ 97% for TCB). The removal efficiency of ozone alone was ∼93% for TCB. At high pH (> 9) there was no advantage in supplementing ozone with either UV or H2O2 as the removal efficiencies for all processes studied were essentially equal. The effect of humic acid and bicarbonate on the removal of TCB was studied. At 1.6 mg/L humic acid, 92–95% of the TCB was oxidized by the processes stud...

Movement of liquid contaminants in partially saturated frozen granular soils

Abstract Understanding the migration of nonaqueous phase liquids in frozen subsurface soils is becoming increasingly important in permafrost regions and in temperate zones where frozen subsurface barriers have been proposed to confine contaminants. Tests were performed on 32 specimens of gravelly sands from the Hanford, Washington reservation to determine the relationship between degree of ice saturation and intrinsic permeability. Decane, a representative nonaqueous phase liquid, was employed as the permeant, and was infiltrated through the frozen specimens at −10°C. In addition to pure water, a NaCl brine and a mixture of water and decane were utilized as the pore liquids. For all specimens the intrinsic permeability correlated linearly with the ice saturation, varying from approximately 2.7× 10−7 cm2 at 0% saturation to negligible values at nearly 100% saturation. The different pore liquids did not affect the correlation significantly. Bentonite was added to some of the specimens prior to freezing, reducing the intrinsic permeability to negligible levels.

Bromate formation in a hybrid ozonation-ceramic membrane filtration system

The effect of pH, ozone mass injection rate, initial bromide concentration, and membrane molecular weight cut off (MWCO) on bromate formation in a hybrid membrane filtration-ozonation reactor was studied. Decreasing the pH, significantly reduced bromate formation. Bromate formation increased with increasing gaseous ozone mass injection rate, due to increase in dissolved ozone concentrations. Greater initial bromide concentrations resulted in higher bromate concentrations. An increase in the bromate concentration was observed by reducing MWCO, which resulted in a concomitant increase in the retention time in the system. A model to estimate the rate of bromate formation was developed. Good correlation between the model simulation and the experimental data was achieved.

EFFECT OF OZONATION ON ODOR AND THE CONCENTRATION OF ODOROUS ORGANIC COMPOUNDS IN AIR IN A SWINE HOUSING FACILITY

This study reports the effect of ozone on odor thresholds and the concentration of selected odorous organic compounds in a swine housing facility. This study was conducted in four rooms that each housed 24 pigs. Ozone was injected at different rates into the each of the rooms to give a final concentration of gaseous ozone in the rooms of approximately 0 (control), 0.01, 0.05, or 0.1 ppm. The concentrations of phenolic and indolic compounds and volatile fatty acids (VFAs) were measured in the air in the rooms using solid-phase microextraction (SPME). The results showed that ozonation reduced the levels of indolic compounds in the swine building air significantly (at the 95% confidence level). However, the reduction in the levels of volatile fatty acids and phenolic compounds in the air was small and generally not statistically significant. Sensory measurements showed that there was a small increase (less than 0.5 log units) in the odor detection thresholds for air in the ozonated rooms. At the ozone levels used in this experiment, the reduction in odor levels achieved is small. It is not likely to be practicable to achieve significantly higher reductions in odor levels, as the ozone concentration needed would exceed the OSHA permissible exposure limit for ozone.

Removal of Escherichia coli after Treatment Using Ozonation-Ultrafiltration with Iron Oxide-Coated Membranes

The effect of membrane filtration, ozonation, and combined ozonation-membrane filtration on the removal of Escherichia coli was studied. Commercially available ceramic membranes with a molecular weight cutoff (MWCO) of 5kDa were used as is, and also coated with iron oxide nanoparticles and sintered at 900°C. With membrane filtration and ozonation-membrane filtration using the uncoated membrane, 7 log removal of E. coli was achieved, as compared to 7.5 log removal with ozonation-membrane filtration with the coated membrane. A Live-Dead assay indicated that the mortality of E. coli in the product water was 15%, ∼50%, ∼86%, and >99% with membrane filtration, ozonation, combined ozonation-membrane filtration with the uncoated membrane and the coated membrane, respectively. With the coated membrane, the concentration of assimilated organic carbon (AOC) was reduced by up to 50% more than with the uncoated membrane filtration (with both systems operated using ozone). This indicates that there is a reduced potential for regrowth after treatment using the coated membranes and ozone. Scanning electron micrographs (SEM) of the membrane surface suggest that after filtration there is less detritus on the surface of the coated membrane than on the uncoated membrane. As a result of the inactivation of the E. coli and the lower AOC concentrations observed using combined catalytic ozonation-membrane filtration this process is likely to be very effective to both disinfect the water and control bacterial regrowth in the distribution system.

Flint Water Crisis: What Happened and Why?

The Flint River is a variable water source and thus a challenge to treat; oversights and missteps combined with inherent chemical conditions set the stage for the historic water crisis in Flint, Mich.