Larry E. Erickson

Beneficial effects of plants in the remediation of soil and groundwater contaminated with organic materials

Abstract The use of plants in remediation of soil and unconfined groundwater contaminated with organic materials is appealing for a variety of reasons: (1) plants provide a remediation strategy that utilizes solar energy; (2) vegetation is aesthetically pleasing; (3) plant samples can be harvested and tested as indicators of the level of remediation; (4) plants help contain the region of contamination by removing water from soil; (5) rhizosphere microbial communities are able to biodegrade a wide variety of organic contaminants; and (6) many plants have mechanisms for transporting oxygen to the rhizosphere. However, before effective plant remediation strategies can be developed, an understanding is needed of the physical, biological, and chemical relationships that determine the fate of each organic contaminant in the rhizosphere. This review presents an overview of some factors required to understand and model the complex processes that determine the fate of the organic contaminants in plant remediation ...

Degradation of atrazine and related s‐triazines

Atrazine, simazine, and propazine are closely related herbicides that can be used for weed control. The degradation of s‐triazines in soil, water, and sediments has received considerable attention. In this review, the literature related to degradation of atrazine and related s‐triazines is reviewed. Particular emphasis is directed toward those substances formed along the degradative pathways and to the biodegradation aspects of mineralization. The s‐triazines are unusual in that the carbon and nitrogen ring contains no available electrons for aerobic biodegradation. The only sources of energy for aerobic biodegradation of atrazine are found on the ethyl and isopropy I groups. There is some evidence to support the concept that dealkylation of s‐triazines occurs to support the bioenergetic needs of microorganisms. Biodegradation studies with simazine or atrazine as the carbon and energy source have generally shown biodegradation of the alkyl side chains with evolution of radioactive carbon dioxide from chai...

BUBBLE BREAKUP AND COALESCENCE IN TURBULENT GAS-LIQUID DISPERSIONS

Theoretical models are proposed to describe bubble breakup and coalescence in a turbulent gas-liquid dispersion. The first model, which is mainly based on probablistic theory, gives reasonable prediction of bubble breakage frequency in terms of the liquid density, interfacial tension, bubble diameter, and the turbulent energy dissipation rate. The second model predicts the binary bubble coalescence frequency as a function of the liquid viscosity, interfacial tension, bubble diameter, turbulent energy dissipation rate, and the surface immobility parameter. Favorable agreement between the breakage and coalescence models and the experimental evidence indicates that these models could be used to predict dispersion properties such as bubble size distributions and interfacial areas.

A Review of the Effects of Shear and Interfacial Phenomena on Cell Viability

The shear sensitivity of animal and plant cells is a problem often encountered in large-scale cell culture. Such sensitivity varies with different cell lines and the severity of cellular damage may depend on both the magnitude and the duration of the shear stress. In a bioreactor, the shear susceptibility of cells depends on their response to hydrodynamic forces arising from fluid motions of particular scale. Cell damage may be induced by forces in the bulk liquid phase, but fluid motions associated with the gas-liquid interface are especially energetic. The detrimental effects of hydrodynamic forces are abated by the addition of some polymers, such as Pluronic F-68, methylcellulose, or serum; the exact mechanisms of protection are the subject of current research.

Biodegradation of 2,4-D and related xenobiotic compounds

Abstract Organisms capable of degrading 2,4-D and related compounds have been studied in pure and mixed cultures. Most studies have been conducted under aerobic conditions. Some of the environmental factors identified to be significant in determining biodegradation rates include pH, temperature, aeration, supplemental nutrient supplies, culture enrichment and substrate concentration range. The Monod model appears to be most applicable to xenobiotic degradation in low substrate concentration ranges, where inhibition effects are not significant. The Haldane model provides a more complete description over a broad range of substrate concentrations because it takes substrate inhibition into account. Inhibitory effects caused by biodegradation products need to be modelled in some applications. Modelling of cometabolism is necessary to describe microbial degradation at very low concentrations. Several models are examined to determine their applicability in correlating physicochemical properties to biodegradation rate constants that can be applied to either cometabolic or growth associated substrate utilization.

Benefits of vegetation for soils with organic contaminants

Referee: Dr. Paul E. Olson, Colorado State University, Department of Biology, E414 Anatomy/Zoology Building, Fort Collins, CO 80523-1878 Plants have many beneficial effects on contaminated soils, including direct metabolism of some organic compounds, stimulation of microbial activity in the root zone, extraction of water, reduction of infiltration, improved aeration of the soil and stabilization against wind and water erosion. Some of these benefits have been explored and exploited in the newly named field of phytoremediation, whereas others remain largely in the domain of agronomy and ecology. This review attempts an assessment of the major environmental impacts of plants in general, recently termed phytotechnology, while including some case studies where particular species have been shown to have impacts on certain contaminants, more specifically termed phytoremediation. There is growing evidence that plants can have significant benefits in phytoremediating a range of complex organic molecules, including pesticides, solvents, explosives, and industrial byproducts.

Potential for Plant-Based Remediation of Pesticide-Contaminated Soil and Water using Nontarget Plants such as Trees, Shrubs, and Grasses

Appropriate environmental management of pesticides includes their proper application, use of filter strips and riparian buffers to contain pesticides in runoff from fields, prompt cleanup of spills, and treatment processes for wastewater associated with manufacturing and equipment usage. Plants have beneficial effects in the management of pesticide-contaminated soil and water, including direct metabolism of many pesticides, stimulation of microbial activity in the root zone, extraction of contaminated water, and reduction of infiltrating contaminated water. In this work, we review the literature on nontarget plants that can grow in pesticide-contaminated soil and water, and the fate of pesticides in filter strips, riparian buffers, and vegetated remediation environments. Past research indicates that there are significant differences in the tolerance of plants to pesticides present in soil and water, and that some plants are more effective than others in the remediation of pesticide-contaminated soil and water. Thus, there is value in the identification of tolerant plants and favorable plant-based remediation technologies for management of pesticides and contaminated sites.

Fate of volatile chlorinated organic compounds in a laboratory chamber with alfalfa plants.

The fate of two volatile organo chlorinated compounds, 1,1,1-trichloroethane (TCA) and trichloroethylene (TCE), was studied in rhizosphere soil. Laboratory experiments were performed with alfalfa (Medicago sativa) growing in sandy silt soil fed continuously with groundwater contaminated with TCA and TCE at 50 and 200 μL/L, respectively. Methane generated in the groundwater provided evidence for anaerobic biodegradation. Groundwater samples indicated that the concentration of TCE decreased with axial position during the steady-state period. The flow rate of the effluent was significantly less than the inlet flow because of active evapotranspiration. Thus, a significant fraction of TCA and TCE disappeared. Headspace analysis of the gas in the enclosed chamber using a FT-IR spectrophotometer showed that small quantities of TCA and TCE migrated into the gas phase above the alfalfa plants ; no chlorinated intermediates or methane were found in this gas phase.

Miscanthus as a Productive Biofuel Crop for Phytoremediation

There are many locations where soil quality improvements would be beneficial because of contamination, erosion, flooding, or past human activities. Miscanthus, a C-4 grass related to sugarcane, grows well in mildly contaminated soil and on sites where soil quality is poor, particularly with respect to nitrogen. Because of its high biomass yield, it is of interest as an energy crop, and as a plant to use for simultaneous crop production and phytoremediation. Here we review recent literature on using miscanthus for combined biomass production and phytoremediation of contaminated and marginal lands. We analyze both advantages and disadvantages for production of this crop along with phytoremediation of sites contaminated with metals and petroleum hydrocarbon. Reports of laboratory and field investigations, which use Miscanthus spp. for stabilizing and removing metals are considered. The potential for growing miscanthus commercially at contaminated and marginal sites in the regions of Central and Eastern Europe as well as the United States appears to be good because large quantities of biomass can be produced and effective phyto-stabilization can be achieved with very slow metal removal over time. In addition, soil quality is improved in many cases.

DYNAMICS OF BUBBLE SIZE DISTRIBUTION IN TURBULENT GAS-LIQUID DISPERSIONS

The population balance equation coupled with the proposed breakage kernel and the previously developed breakage model is applied to the analysts of bubble size distribution for non-coalescing systems in a bench-scale airlift column. Good agreement obtained between the theoretical results and the experimental data is encouraging and indicates that the model is suitable for predicting dispersion properties such as bubble size and interfacial area in turbulent gas-liquid dispersions.