Biomedical subjects

Catherine N Mulligan

Publications and source records attributed to Catherine N Mulligan.

9 recordsLinked to original sources

PubMed2006

Natural attenuation processes for remediation of arsenic contaminated soils and groundwater.

Arsenic (As) contamination presents a hazard in many countries. Natural attenuation (NA) of As-contaminated soils and groundwater may be a cost-effective in situ remedial option. It relies on the site intrinsic assimilative capacity and allows in-place cleanup. Sorption to solid phases is the principal mechanism immobilizing As in soils and removing it from groundwater. Hydroxides of iron, aluminum and manganese, clay and sulfide minerals, and natural organic matter are commonly associated with soils and aquifer sediments, and have been shown to be significant As adsorbents. The extent of sorption is influenced by As speciation and the site geochemical conditions such as pH, redox potential, and the co-occurring ions. Microbial activity may catalyze the transformation of As species, or mediate redox reactions thus influencing As mobility. Plants that are capable of hyperaccumulating As may translocate As from contaminated soils and groundwater to their tissues, providing the basis for phytoremediation. However, NA is subject to hydrological changes and may take substantial periods of time, thus requiring long-term monitoring. The current understanding of As NA processes remains limited. Sufficient site characterization is critical to the success of NA. Further research is required to develop conceptual and mathematical models to predict the fate and transport of As and to evaluate the site NA capacity. Engineering enhanced NA using environmentally benign products may be an effective alternative.

Arsenic↗

PubMed2006

Effect of natural organic matter on arsenic release from soils and sediments into groundwater.

Arsenic (As) contamination in groundwater has received significant attention recently. Natural and anthropogenic sources contribute to the worldwide occurrence of As contamination. As speciation is an important factor related to its toxic and mobile behavior. The release of As from soils and sediments into groundwater is governed by several geophysicochemical processes, of which, As sorption behavior is of principle significance. This review paper summarizes existing information regarding the effects of natural organic matter (NOM) on the fate and mobility of As species in the environment. NOM may enhance the release of As from soils and sediments into the soil solution, thereby facilitating As leaching into the groundwater. The main influencing mechanisms include competition for available adsorption sites, formation of aqueous complexes, and/or changes in the redox potential of site surfaces and As redox speciation. NOM may also serve as binding agents, thereby reducing As mobility. However, comparably little research has been performed on this aspect. Since most investigations have been done on purified minerals under laboratory conditions, further research involving various geological materials under natural environmental conditions is required. Development of proper geochemical conceptual models may provide means of predicting the role of NOM in arsenic leaching and/or immobilization.

Adsorption↗

PubMed2005

Occurrence of arsenic contamination in Canada: sources, behavior and distribution.

Recently there has been increasing anxieties concerning arsenic related problems. Occurrence of arsenic contamination has been reported worldwide. In Canada, the main natural arsenic sources are weathering and erosion of arsenic-containing rocks and soil, while tailings from historic and recent gold mine operations and wood preservative facilities are the principal anthropogenic sources. Across Canada, the 24-h average concentration of arsenic in the atmosphere is generally less than 0.3 microg/m3. Arsenic concentrations in natural uncontaminated soil and sediments range from 4 to 150 mg/kg. In uncontaminated surface and ground waters, the arsenic concentration ranges from 0.001 to 0.005 mg/L. As a result of anthropogenic inputs, elevated arsenic levels, above ten to thousand times the Interim Maximum Acceptable Concentration (IMAC), have been reported in air, soil and sediment, surface water and groundwater, and biota in several regions. Most arsenic is of toxic inorganic forms. It is critical to recognize that such contamination imposes serious harmful effects on various aquatic and terrestrial organisms and human health ultimately. Serious incidences of acute and chronic arsenic poisonings have been revealed. Through examination of the available literature, screening and selecting existing data, this paper provides an analysis of the currently available information on recognized problem areas, and an overview of current knowledge of the principal hydrogeochemical processes of arsenic transportation and transformation. However, a more detailed understanding of local sources of arsenic and mechanisms of arsenic release is required. More extensive studies will be required for building practical guidance on avoiding and reducing arsenic contamination. Bioremediation and hyperaccumulation are emerging innovative technologies for the remediation of arsenic contaminated sites. Natural attenuation may be utilized as a potential in situ remedial option. Further investigations are needed to evaluate its applicability.

Arsenic↗

PubMed2005

Biosorption of lead(II), cadmium(II), copper(II) and nickel(II) by anaerobic granular biomass.

Biosorption is potentially an attractive technology for treatment of wastewater for retaining heavy metals from dilute solutions. This study investigated the feasibility of anaerobic granules as a novel type of biosorbent, for lead, copper, cadmium, and nickel removal from aqueous solutions. Anaerobic sludge supplied from a wastewater treatment plant in the province of Quebec was used. Anaerobic granules are microbial aggregates with a strong, compact and porous structure and excellent settling ability. After treatment of the biomass with Ca ions, the cation exchange capacity of the biomass was approximately 111 meq/100 g of biomass dry weight which is comparable to the metal binding capacities of commercial ion exchange resins. This work investigated the equilibrium, batch dynamics for the biosorption process. Binding capacity experiments using viable biomass revealed a higher value than those for nonviable biomass. Binding capacity experiments using non-viable biomass treated with Ca revealed a high value of metals uptake. The solution initial pH value affected metal sorption. Over the pH range of 4.0-5.5, pH-related effects were not significant. Meanwhile, at lower pH values the uptake capacity decreased. Time dependency experiments for the metal ions uptake showed that adsorption equilibrium was reached almost 30 min after metal addition. It was found that the q(max) for Pb2+, Cd2+, Cu2+, and Ni2+ ions, were 255, 60, 55, and 26 mg/g respectively (1.23, 0.53, 0.87, and 0.44 mmol/g respectively). The data pertaining to the sorption dependence upon metal ion concentration could be fitted to a Langmiur isotherm model. Based on the results, the anaerobic granules treated with Ca appear to be a promising biosorbent for removal of heavy metals from wastewater due to its optimal uptake of heavy metals, its particulate shape, compact porous structure, excellent settling ability, and its high mechanical strength.

Absorption↗

PubMed2005

Environmental applications for biosurfactants.

Biosurfactants are surfactants that are produced extracellularly or as part of the cell membrane by bacteria, yeasts and fungi. Examples include Pseudomonas aeruginosa which produces rhamnolipids, Candida (formerly Torulopsis) bombicola, one of the few yeasts to produce biosurfactants, which produces high yields of sophorolipids from vegetable oils and sugars and Bacillus subtilis which produces a lipopeptide called surfactin. This review includes environmental applications of these biosurfactants for soil and water treatment. Biosurfactant applications in the environmental industries are promising due to their biodegradability, low toxicity and effectiveness in enhancing biodegradation and solubilization of low solubility compounds. However, more information is needed to be able to predict and model their behaviour. Full scale tests will be required. The role of biosurfactants in natural attenuation processes has not been determined. Very little information is available concerning the influence of soil components on the remediation process with biosurfactants. As most of the research until now has been performed with rhamnolipids, other biosurfactants need to be investigated as they may have more promising properties.

Biodegradation, Environmental↗

PubMed2004

Bioleaching of heavy metals from a low-grade mining ore using Aspergillus niger.

The main concern of this study is to develop a feasible and economical technique to microbially recover metals from oxide low-grade ores. Owing to the significant quantities of metals that are embodied in low-grade ores and mining residues, these are potential viable sources of metals. In addition, they potentially endanger the environment, as the metals they contain may be released to the environment in hazardous form. Hence, mining industries are seeking an efficient, economic technique to handle these ores. Pyrometallurgical and hydrometallurgical techniques are either very expensive, energy intensive or have a negative impact on the environment. For these reasons, biohydrometallurgical techniques are coming into perspective. In this study, by employing Aspergillus niger, the feasibility of recovery of metals from a mining residue is shown. A. niger exhibits good potential in generating a variety of organic acids effective for metal solubilization. Organic acid effectiveness was enhanced when sulfuric acid was added to the medium. Different agricultural wastes such as potato peels were tested. In addition, different auxiliary processes were evaluated in order to either elevate the efficiency or reduce costs. Finally, maximum solubilization of 68%, 46% and 34% were achieved for copper, zinc and nickel, respectively. Also iron co-dissolution was minimized as only 7% removal occurred.

Aspergillus niger↗

PubMed2004

An evaluation of surfactant foam technology in remediation of contaminated soil.

Soil contamination is notoriously difficult to treat because the contaminants are often tightly bound to the soil particles. Conventional remediation technologies are becoming less popular due to the high treatment costs. This paper gives a comprehensive overview and evaluation of an emerging promising alternative, surfactant foam technology. Different from other approaches, surfactant foam technology may be designed either to remove contaminants or/and simultaneously act as an augmentation for the existing technologies such as pump-and-treat systems and bioremediation processes to improve the contaminant removal efficiency and cost effectiveness. Encouraging results were achieved from laboratory and field demonstrations. However, as an innovative technology, there are many factors to be investigated with the future development. Special attention is paid to the selection of the most appropriate foaming surfactant and surfactant concentration, which are critical to the success of the implementation of the remediation process and have significant effects on the treatment costs. Moreover, development of predictive mathematical models in for future research is helpful to optimize the remediation process.

Bacteria↗

PubMed2004

Natural attenuation of contaminated soils.

Natural attenuation is increasing in use as a low cost means of remediating contaminated soil and groundwater. Modelling of contaminant migration plays a key role in evaluating natural attenuation as a remediation option and in ensuring that there will be no adverse impact on humans and the environment. During natural attenuation, the contamination must be characterized thoroughly and monitored through the process. In this paper, attenuation mechanisms for both organic and inorganic contaminants, use of models and protocols, role of monitoring and field case studies will be reviewed.

Adsorption↗

PubMed2003

Bioremediation of metal contamination.

A study was initiated to evaluate the use of the fungus Aspergillus niger for bioleaching and then to determine the effect of process steps, the tailings concentration and type of substrate. An oxidized mining tailing containing mainly copper (7240 mg kg(-1) tailings) was studied. A sucrose and mineral salts medium was initially used to produce citric and gluconic acids by A. niger at various concentrations of tailings ( 1, 5, 7, 10 and 15% w/v). Maximal removal of up to 60% of the copper was obtained for the 5% tailings when the organic acid supernatant was added to the tailings. In a single step process, A. niger was then grown in the presence of mining tailings at various concentrations. Maximum copper solubilization (63%) occurred with 10% mining tailings using sucrose as the substrate. Other substrates were then evaluated including molasses, corn cobs and brewery waste (10% mining tailings). Sucrose gave the best results for copper removal, followed by molasses, corn cobs and brewery waste. Other experiments using ultrasound as a pretreatment showed that 80% removal of the copper could be obtained for a 5% tailings concentration. In conclusion, leaching of copper from mining tailings is technically feasible using A. niger but further research will be required to increase the economic feasibility of the process.

Aspergillus niger↗