Soil heating and optimized nutrient addition for accelerating bioremediation in cold climates

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 degrees 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 degrees C could reach 75% of the amount produced at 20 degrees C. Based on this data, researchers concluded that a temperature of 6 degrees 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%.