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5 - Temperature effects on biodegradation of petroleum contaminants in cold soils
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- By Anne Gunn Rike, Dept. of Environmental Technology, Norwegian Geotechnical Institute, PO Box 3930, Ullevaal Stadion, N-0806 Oslo, Norway, Silke Schiewer, Dept. of Civil and Environmental Engineering, University of Alaska Fairbanks, PO Box 755900, Fairbanks AK 99775, USA, Dennis M. Filler, Dept. of Civil and Environmental Engineering, University of Alaska Fairbanks, PO Box 755900, Fairbanks AK 99775, USA
- Edited by Dennis M. Filler, University of Alaska, Fairbanks, Ian Snape, David L. Barnes, University of Alaska, Fairbanks
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- Book:
- Bioremediation of Petroleum Hydrocarbons in Cold Regions
- Published online:
- 22 August 2009
- Print publication:
- 21 February 2008, pp 84-108
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Summary
Introduction
Bioremediation in cold climates is frequently regarded with skepticism. Owners of polluted sites and regulatory agencies may doubt the effectiveness of biological degradation at near freezing temperatures. While it is true that biodegradation rates decrease with decreasing temperatures, this does not mean that bioremediation is inappropriate for cold regions. Microbial degradation of hydrocarbons occurs even around 0 °C (Chapter 4). In remote alpine, Arctic, and Antarctic locations, excavation and shipping of contaminated soil may be prohibitively expensive. Bioremediation may be the most cost-effective alternative. This chapter discusses microbial adaptation to cold temperatures as well as results of laboratory and field studies of bioremediation at low temperatures.
Microorganisms can grow at temperatures ranging from subzero to more than 100 °C. Microbes are divided into four groups based on the range of temperature at which they can grow. The psychrophiles grows at temperatures below 20 °C, the mesophiles between 20 °C and 44 °C, the thermophiles between 45 °C and 70 °C, and the hyperthermophiles require growth temperatures above 70 °C to over 110 °C. The term “cold-adapted microorganisms” (CAMs) is frequently used for describing bacteria growing at or close to zero degrees Celsius. Depending on the cardinal temperatures (the minimal, the optimal, and the maximum growth temperature), CAMs can be classified as psychrophiles or psychrotrophs. Morita's (1975) definition, which holds that psychrophiles have a maximum growth temperature of less than 20 °C and an optimal growth temperature of less than 15 °C, while psychrotrophs have a maximum temperature of 40 °C and an optimal growth temperature higher than 15 °C, is widely accepted.
Soil heating and optimized nutrient addition for accelerating bioremediation in cold climates
- Silke Schiewer, Thomas Niemeyer
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- Journal:
- Polar Record / Volume 42 / Issue 1 / January 2006
- Published online by Cambridge University Press:
- 18 January 2006, pp. 23-31
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Low temperatures severely limit the rate of bioremediation in cold climates. The goal of this study was to investigate the effect of temperature on bioremediation rates and to optimize the nutrient supply in order to accelerate bioremediation. Samples of diesel-contaminated soil from two Alaskan sites were incubated in the laboratory at different temperatures (1, 6, or 20°C) with varying nutrient levels (0, 100, 300, or 800 mg nitrogen per kg dry soil). As expected, biodegradation was fastest at higher temperatures. However, after approximately two months of treatment, the cumulative amount of CO2 produced at a temperature of 6°C could reach 75% of the amount produced at 20°C. Based on this data, researchers concluded that a temperature of 6°C was sufficient to achieve efficient treatment if all other potentially limiting factors — such as oxygen, water content, and nutrient supply — were addressed. A cost-effective process based on passive solar soil heating is proposed to raise the soil temperature and thereby improve the bioremediation rate. Furthermore, in field applications, an even distribution of nutrients cannot be taken for granted, especially when granulized fertilizer is applied; this method often results in suboptimal local concentrations (too high or too low). Particularly in cold climates with a short growth season, it is important to utilize this short time-window efficiently. The second part of the study explored improving the method of fertilizer application (granular versus liquid application, with and without irrigation) to achieve a homogeneous nutrient distribution. It was found that irrigation can substantially improve the distribution of nitrogen, thereby increasing bioremediation rates and shortening treatment times by as much as 50%.