M. Katherine Banks

Effectiveness of Phytoremediation as a Secondary Treatment for Polycyclic Aromatic Hydrocarbons (PAHs) in Composted Soil

ABSTRACT A greenhouse study was conducted over a 12-month period to investigate the fate of polycyclic aromatic hydrocarbons (PAHs) in soil using phytoremediation as a secondary treatment. The soil was pretreated by composting for 12 weeks, then planted with tall fescue (Festuca arundinacea), annual ryegrass (Lolium multiflorum), and yellow sweet clover (Melilotus officinalis). Two sets of unvegetated controls also were evaluated, one fertilized and one unfertilized. Total PAH concentrations decreased in the tall fescue, annual ryegrass, and yellow sweet clover treatments by 23.9%, 15.3%, and 9.1%, respectively, whereas the control was reduced by less than 5%. The smaller two- and most of the three-ringed compounds—naphthalene, acenaphthylene, acenaphthene, fluorene, and anthracene—were not found in detectable concentrations in any of the treatments. The most probable number analysis for microbial PAH degraders did not show any statistically significant differences among treatments. There were significant differences among treatments (p < 0.05) for the residual concentrations of five of the target PAHs. Root surface area measurements indicated that tall fescue and annual ryegrass both had significantly higher root surface area than yellow sweet clover, although the two species were not significantly different from each other. The tall fescue treatment resulted in the highest root and shoot biomass, followed by annual ryegrass and yellow sweet clover, and also had the highest percent of contaminant removal after 12 months. These results imply a positive relationship between plant biomass development and PAH biodegradation.

EFFECT OF SIMULTANEOUS ESTABLISHMENT OF SEDUM ALFREDII AND ZEA MAYS ON HEAVY METAL ACCUMULATION IN PLANTS

Abstract Land application of biosolids to improve agricultural productivity is a cost-effective approach for resource recovery. Unfortunately, municipal biosolids often contain high concentrations of heavy metals, including zinc and copper. In this study, a co-cropping technique was investigated using a known zinc hyperaccumulator, Sedum alfredii, with a grain crop, Zea mays. After a 3-mo growth trial, the results indicate that when Z. mays is co-cropped with S. alfredii, heavy metals accumulated in the grains were significantly reduced when compared to monoculture cropping. Co-cropping improved the growth of both plant species. In addition, the biosolids maintained stable pH, N-P-K concentrations, germination potential, and water content after the plant treatment, regardless of the plant species used in the trial. In conclusion, co-cropping with hyperacumulators may be an effective approach to reducing the risk of contaminant uptake in edible crops.

Bacterial Community Evaluation During Establishment of Tall Fescue (Festuca arundinacea) in Soil Contaminated with Pyrene

ABSTRACT A greenhouse study was conducted to monitor microbial community dynamics related to contaminant concentration and plant growth during the phytoremediation of pyrene. Soil microbial communities in both bulk and rhizosphere soils were assessed using a polymerase chain reaction–denaturing gradient gel electrophoresis (PCR-DGGE). However, no correlation between pyrene concentration and bacterial community shifts was observed. Even though plants significantly enhanced pyrene degradation (undetectable after 91 d for planted treatments compared with 82 mg/kg for unplanted treatments after 147 d with initial concentration of 758 mg/kg), biodegradation may have been accomplished by the pre-existing microbial community. It is also possible that the method was unable to pick up subtle community shifts, considering that the carbon source from pyrene was only 3.7% of the existing soil organic matter. This research suggests that plants significantly enhance degradation and mineralization of pyrene in soil, although there was no conclusive evidence supporting any specific bacterial activity responsible for this enhancement.

Bacterial adsorption and transport in saturated soil columns.

Abstract Microbial activities directly affect the environmental quality of water, soil, and sediments. To improve our understanding of microbial attachment and transport in the subsurface, experimental studies were performed to evaluate bacterial adsorption and transport in two types of soil, Smolan (27% clay) and Haynie (5.5% clay) soils. Results indicate that bacterial breakthrough was slightly faster in columns with lower clay content and that the most rapid rate of bacterial adsorption occurred during the first 60 min of exposure.

Effect of soil depth on phytoremediation efficiency for petroleum contaminants

Biodegradation of organic contaminants in soil may be enhanced by the presence of vegetation. Evaluating the effect of soil depth on phytoremediation efficiency may provide researchers and regulators with a clearer understanding of contaminant clean-up. A column study with polycyclic aromatic hydrocarbons (PAHs) and diesel-contaminated soil was conducted over a 147-day period of switchgrass (Panicum virgatum) growth. Analysis of the contaminants and plant biomass was conducted along with microbial enumeration at three soil depths in 49-day intervals. Remediation proceeded rapidly near the surface of the soil (0–20 cm) for both vegetated and unvegetated columns, but the effect of vegetation relative to an unvegetated control only was significant in the lower soil depths. Contaminant dissipation in the 20–40 and 40–60 cm layers was not significantly different between vegetated and unvegetated soil.

Cell-mediated deposition of porous silica on bacterial biofilms

Living hybrid materials that respond dynamically to their surrounding environment have important applications in bioreactors. Silica based sol-gels represent appealing matrix materials as they form a mesoporous biocompatible glass lattice that allows for nutrient diffusion while firmly encapsulating living cells. Despite progress in sol-gel cellular encapsulation technologies, current techniques typically form bulk materials and are unable to generate regular silica membranes over complex geometries for large-scale applications. We have developed a novel biomimetic encapsulation technique whereby endogenous extracellular matrix molecules facilitate formation of a cell surface specific biomineral layer. In this study, monoculture Pseudomonas aeruginosa and Nitrosomonas europaea biofilms are exposed to silica precursors under different acid conditions. Scanning electron microscopy (SEM) imaging and electron dispersive X-ray (EDX) elemental analysis revealed the presence of a thin silica layer covering the biofilm surface. Cell survival was confirmed 30 min, 30 days, and 90 days after encapsulation using confocal imaging with a membrane integrity assay and physiological flux measurements of oxygen, glucose, and NH 4⁺. No statistical difference in viability, oxygen flux, or substrate flux was observed after encapsulation in silica glass. Shear induced biofilm detachment was assessed using a particle counter. Encapsulation significantly reduced detachment rate of the biofilms for over 30 days. The results of this study indicate that the thin regular silica membrane permits the diffusion of nutrients and cellular products, supporting continued cellular viability after biomineralization. This technique offers a means of controllably encapsulating biofilms over large surfaces and complex geometries. The generic deposition mechanism employed to form the silica matrix can be translated to a wide range of biological material and represents a platform encapsulation technology.

Phytoremediation of polycyclic hydrocarbon contaminated soil: part II. Impact on ecotoxicity.

Several biological assays were used to evaluate the toxic effects of contaminants in soil after phytoremediation. During the treatment process, significant decreases in overall toxicity were observed. Specifically, earthworm survivability and lettuce germination increased over the study period. Microbial respiration improved, but only in planted treatments. Toxicity and total polycyclic aromatic hydrocarbon concentrations showed some correlation, but the relationships generally were not significant. Soil moisture was less of a predictor for biological responses. The presence of plants did not provide a clear advantage for improving toxicity compared to unplanted treatments.

A simple method for quantifying biomass cell and polymer distribution in biofilms.

Biofilms are ubiquitous and play an essential role in both environmental processes and hospital infections. Standard methods are not capable of quantifying biomass concentration in dilute suspensions. Furthermore, standard techniques cannot differentiate biomass composition. In this study, a user-friendly technique was developed for measuring biomass cell and polymer content in detached biofilms using a standard coulter counter. The method was demonstrated for an environmentally relevant strain of Pseudomonas aeruginosa (Schroeter) Migula grown in a bioreactor and also for a medically relevant strain of P. aeruginosa (PAO1) grown on standard growth pegs. Results were compared and validated by standard assays, including EPA method 1684 for measuring biomass, microscopic direct counts, and a crystal violet staining assay. The minimum detection limit for the coulter counter method (0.07 mg-biomass L(-1)) was significantly lower than the EPA method 1684 (1.9 ± 0.4 mg/L) and the crystal violet assay (1.1 ± 0.2 mg L(-1)). However, the coulter counter method is limited to dilute biomass samples (below 204 ± 16 mg L(-1)) due to clogging of the aperture tube. While biomass measurements are useful, the major advantage of the coulter counter method is the ability to directly determine EPS, cell, and aggregate fractions after mild chemical treatment. The rapid technique (4-5 min per sample) was used to measure biomass fractions in dispersed P. aeruginosa (Schroeter) and PAO1 biofilms. This technique will be critical for understanding biofilm formation/dispersal.

Characterization of Gaseous Ozone Decomposition in Soil

Laboratory scale batch experiments were performed to investigate the decomposition characteristics of gaseous ozone in porous media. The decomposition rates of gaseous ozone in several solid media were determined, and the relationship of moisture content with sorbed ozone molecules was evaluated. Ozone decomposition in control and glass beads packed columns followed second-order reaction kinetics, while ozone consumption in a sand-packed column demonstrated first-order kinetics with a rate constant of 0.0109 min−1 and half-life of 1.0 h. The presence of typical metal oxides in the soil resulted in ozone consumption rates in the following order: hematite (Fe2O3) > silica-alumina (SiO2Al2O3) > alumina (Al2O3) > silica (SiO2). Ozone decomposition was highly dependent upon soil moisture content. Over 90% of the total ozone mass decomposed in the field soil with moisture content at less than 1 wt%, whereas as low as 5–15% of the total ozone mass degraded with moisture content at more than 2 wt%. In conclusion, ozone decomposition in soils was primarily controlled not only by soil organic matter but also by reactive metal oxides on the soil surface. These two factors were shown to be highly dependent upon soil moisture content.

Adsorption of iron cyanide complexes onto clay minerals, manganese oxide, and soil.

The adsorption characteristics of an iron cyanide complex, soluble Prussian blue KFe(III)[Fe(II)(CN)6], were evaluated for representative soil minerals and soil at pH 3.7, 6.4 and 9.7. Three specimen clay minerals (kaolinite, montmorillonite, and illite), two synthesized manganese oxides (birnessite and cryptomelane), and a Drummer soil from Indiana were used as the adsorbents. Surface protonation of variable charge sites increased with decreasing pH yielding positively charged sites on crystal edges and enhancing the attractive force between minerals and iron cyanide complexes. Anion adsorption on clays often is correlated to the metal content of the adsorbent, and a positive relationship was observed between iron or aluminum content and Prussian blue adsorption. Illite had high extractable iron and adsorbed more ferro-ferricyande anion, while kaolinite and montmorillonite had lower extractable iron and adsorbed less. However, less pH effect was observed on the adsorption of iron cyanide to manganese oxides. This may due to the manganese oxide mediated oxidation of ferrocyanide [FeII(CN)6 4−], to ferricyanide [FeIII(CN)6 3−], which has a low affinity for manganese oxides.