Thermal treatment of petroleum-contaminated marine sediment according to oxygen availability and temperature: Product quality as a potential plant-growth medium.

The sustainable management of dredged sediment from contaminated sites needs to consider the end-use of the treated sediment. In this regard, modifying conventional sediment treatment techniques to generate a product that is suitable for a range of terrestrial uses is necessary. In the present study, we evaluated the product quality of treated sediment as a potential plant-growth medium following the thermal treatment of marine sediment contaminated by petroleum. The contaminated sediment was subject to thermal treatment at temperatures of 300, 400, or 500 °C, and no, low, or moderate oxygen availability, and the resulting treated sediment was analyzed in terms of its bulk properties, spectroscopic properties, organic contaminants, water-soluble salts and organic matter, and the leachability and extractability of heavy metals. All operational combinations for the treatment process reduced the total petroleum hydrocarbon content of the sediment from 4922 mg kg-1 to lower than 50 mg kg-1. The thermal treatment process stabilized the heavy metals in the sediment, reducing the zinc and copper concentration by up to 58.9% and 89.6%, respectively, in the leachate from the toxicity characteristic leaching procedure. The hydrophilic organic and/or sulfate salt byproducts of the treatment were phytotoxic, but these can easily be removed by washing the sediment with water. By combining the sediment analysis results with experimental data from barley germination and early-growth tests, the end product was found to be of higher quality when higher temperatures and lower oxygen availability were employed in the treatment process. These findings demonstrate that it is possible to retain the natural organic resources of the original sediment by optimizing the thermal treatment, thus ensuring a suitably high product quality for use as a plant-growth medium.

Effects of treatment agents during acid washing and pH neutralization on the fertility of heavy metal-impacted dredged marine sediment as plant-growing soil.

The present study was aimed at investigating the effects of different acids and pH neutralizers applied to dredged marine sediment for the treatment of heavy metals, and the resulting influence on the sediment quality as a plant growth medium. The inspection of barley germination in the dredged marine sediment revealed that residual salts are critical plant stressors whose adverse effects exceed those exhibited by high-level heavy metals and petroleum hydrocarbons present in the sediment. Acid washing and pH neutralization reduced not only the heavy metal contents but also the sediment salinity (by factors of 6.1-9.5), resulting in 100% germination of barley. For acid-washed and calcium-oxide-neutralized sediment, the barley growth was comparable to that observed in untreated and water washed sediment despite factors of 5.2-8.0 greater sediment salinity in the former. This result represents the protective effect of residual calcium against sodium and chloride toxicity. Water washing of acid-washed and pH-neutralized sediments further enhanced barley growth owing to the reduction in osmotic pressure. This study showed the effect of different sediment-washing reagents on the product quality. It also indicated the significance of balancing the enhancement of product quality and economic cost of further treatment requirements.

Exploring reductive degradation of fluorinated pharmaceuticals using Al2O3-supported Pt-group metallic catalysts: Catalytic reactivity, reaction pathways, and toxicity assessment.

Recently, an increasing number of pharmaceutical compounds has become fluorinated. Owing to their pharmacological efficacy, the use of these fluorinated pharmaceuticals continues to grow, and they constitute 20% of the drugs on the current market. However, only a few studies have investigated the fate and transformation of these emerging contaminants in natural and engineered aquatic environments. In the present study, the H2-based reductive transformation of three fluorinated pharmaceutical compounds (levofloxacin, sitagliptin, and fluoxetine) were investigated using alumina-supported monometallic and bimetallic catalysts of the Pt-group noble metals (i.e., Ru, Rh, Pd, and Pt) under ambient temperature and pressure conditions. Degradation of all three compounds was observed with catalytic reactivity ranging from 4.0  ×  10-3 to 2.14  ×  102 L/(min·gcat), in which fluoxetine generally showed the highest reactivity, followed by sitagliptin and levofloxacin. The fluorination yields and transformation products were characterized for each fluorinated compound and three different degradation mechanisms were elucidated: 1) hydrodefluorination of C-F bond to CH bond, 2) hydrogenation of aromatic ring, and 3) reductive cleavage of CO bond from phenyl ether. Toxicity assessment using Aliivibrio fischeri showed there were no significant changes in toxicity over levofloxacin and sitagliptin degradation, suggesting the formation of no highly toxic by-products during catalytic reduction. For fluoxetine, an increased toxicity was observed during its degradation while ECOSAR-predicted toxicity values of all identified intermediates were lower than that of fluoxetine, suggesting the formation of unidentified secondary by-products that contribute to the overall toxicity. The study showed that catalytic reduction is a promising remediation process for treating and defluorinating the fluorinated pharmaceutical compounds.

Effect of basic oxygen furnace slag addition on enhanced alkaline sludge fermentation and simultaneous phosphate removal.

This study presents a promising approach that enhances the sludge fermentation by using basic oxygen furnace (BOF) slag as an alkaline source for the first time. BOF slag added to the reactors could maintain a stable alkaline condition due to continuous release of Ca(OH)2 from slag. The reactor pH could be adjusted to a target value by the choice of the BOF slag dose. Concentrations of soluble chemical oxygen demand (sCOD) and short-chain carboxylates (SCCs) were substantially increased in the presence of BOF slag. At a BOF slag mass to sludge volume ratio of 1/10 g slag/L sludge, the reactor pH was maintained at 10 and the concentration of SCCs produced was the highest (i.e., 3510 mg COD L-1 from 14,000 mg VS L-1 of sludge mixture), followed by B/S ratios of 1/20, 1.50, 1/5, and 1/2.5 g slag L-1 sludge with reactor pH of 9.4, 8.9, 10.5, and 11, respectively. Our data suggest that the pH value that best facilitates the degradation of sludge into SCCs and inhibit the conversion of SCCs into biogas is around 10. Interestingly, compositions of the accumulated SCCs varied greatly depending on the BOF slag dose. BOF slag showed phosphorus removal ability due to enhanced precipitation of Ca-PO43--P complexes, which significantly lowered PO43- concentration of the reactor effluent.

In situ sequestration of hydrophobic organic contaminants in sediments under stagnant contact with activated carbon. 2. Mass transfer modeling.

The validity of a hydrophobic organic contaminant mass transfer model to predict the effectiveness of in situ activated carbon (AC) treatment under stagnant sediment-AC contact is studied for different contaminants and sediments. The modeling results and data from a previous 24-month column experiment of uptake in polyethylene samplers are within a factor of 2 for parent- and alkylated-polycyclic aromatic hydrocarbons in petroleum-impacted sediment and factors of 3-10 for polychlorinated biphenyls. The model successfully reproduces the relative effects of AC-sediment contact time, contaminant properties, AC particle size, AC mixing regime, AC distribution, and hydraulic conditions observed in the sediment column experiments. The model tracks contaminant concentrations in different sediment compartments over time, which provides useful information on the contaminant sequestration by the added AC. Long-term projection of the effectiveness of AC amendment using the model shows that the effects of AC particle size and particle-scale heterogeneity in AC distribution are pronounced within a year or so. However, the effect of those factors becomes less significant after a much longer contact period (on the order of a decade or two), resulting in substantial reduction in pore-water concentrations, for example, greater than 99% for benz[a]anthracene, under various scenarios.

In situ sequestration of hydrophobic organic contaminants in sediments under stagnant contact with activated carbon. 1. Column studies.

The effectiveness of activated carbon (AC) treatment to sequester hydrophobic organic contaminants in sediments under stagnant contact was comprehensively studied for the first time. Two years of column experiments were conducted to simulate field conditions with two study sediments contaminated with petroleum and polychlorinated biphenyls, respectively, and variations in AC-sediment contact times, initial AC mixing regimes and distribution, AC particle sizes, and pore-water flow. The benefit of AC treatment was gradually enhanced with time toward the end point of the treatment, where sorption equilibrium is established between sediment and AC. After two years of stagnant contact, the contaminant uptake in polyethylene passive samplers embedded in the columns was reduced by 95-99% for polycyclic aromatic hydrocarbons and 93-97% for polychlorinated biphenyls with 5 and 4 wt % AC dose, respectively, when AC was initially applied by mechanical mixing. These results verify that AC treatment can effectively control the availability of hydrophobic organic contaminants under stagnant conditions within a reasonable time frame following an initial distribution of AC into the sediment. The effectiveness of AC treatment was strongly dependent on AC particle size and AC distribution, while the effect of AC initial mixing regimes and pore-water flow was not pronounced.

Measurement and modeling of activated carbon performance for the sequestration of parent- and alkylated-polycyclic aromatic hydrocarbons in petroleum-impacted sediments.

We present a first comprehensive set of experiments that demonstrate the performance of activated carbon (AC) to reduce the availability of polycyclic aromatic hydrocarbons (PAHs) including alkylated-PAHs in petroleum-impacted sediments. The uptake in polyethylene samplers for total PAHs in a well-mixed sediment slurry was reduced up to 99% and 98% for petroleum-impacted sediments with oil contents of 1% and 2%, respectively, by treatment with 5% AC. The AC showed similar efficiency for parent-PAHs and a suite of alkylated-PAHs, which predominate over parent-PAHs in petroleum-impacted sediments. A mass transfer model was used to simulate the AC performance in a slurry phase with site-specific mass transfer parameters determined in this study. Comparison between the experimental data and simulation results suggested that dissolved organic matter and/or oil phase may have attenuated the AC performance by a factor of 5-6 for 75-300 µm AC with 5% dose at one month. The attenuation in AC performance became negligible with increase in AC-sediment slurry contact time to 12 months and with decrease in AC particle size. The results show the potential for AC amendment to sequester PAHs in petroleum-impacted sediments and the effect of contact time and AC particle size on the efficiency of the treatment.