Factors affecting Bioremediation

Microorganisms have limits of acceptance for particular environmental conditions, as well as optimal conditions for peak performance. Factors that affect efficiency of microbial biodegradation are nutrient availability, moisture content, pH, and temperature of the soil matrix.

-Nutrient availability

Inorganic nutrients such as nitrogen and phosphorus are necessary for microbial activity and cell growth. It has been shown that “treating petroleum-contaminated soil with nitrogen can increase cell growth rate, decrease the microbial lag phase, help to maintain microbial populations at high activity levels, and increase the rate of hydrocarbon degradation”. However, it has also been shown that excessive amounts of nitrogen in soil cause microbial inhibition.

-Moisture content

All soil microorganisms require moisture for cell growth and function. Availability of water affects circulation
of water and soluble nutrients into and out of microorganism cells. However, excess moisture, such as in saturated soil, is undesirable because it reduces the amount of available oxygen for aerobic respiration.

-pH

pH of the soil is important because survival of most microbial species are limited to a certain pH range. In addition, soil pH can affect availability of nutrients.

-Temperature

Temperature influences rate of biodegradation by controlling rate of enzymatic reactions within microorganisms. Generally, “speed of enzymatic reactions in the cell approximately doubles for each 10^oC rise in temperature” (Nester et al., 2001). There is an upper limit to the temperature that microorganisms can withstand. Most bacteria found in soil, including many bacteria that degrade petroleum hydrocarbons, are mesophiles which have an optimum temperature ranging from 25 degree C to 45 degree C .Thermophilic bacteria (those which survive and thrive at relatively high temperatures) which are normally found in hot springs and compost loads exist indigenously in cool soil environments and can be activated to degrade hydrocarbons with an increase in temperature to 60 degree C. 

Some contaminants can stick to soil particles and microorganisms are unable to use them for biodegradation. Therefore, under these circumstances, bioavailability of contaminants does not solely depend on the characteristics of the contaminant but also on soil type.