Composting
Why implement composting in hydrocarbon bioremediation techniques?
The high temperatures prevalent during composting, combined with the high nutrient contents of decomposing organic matter such as manure, and the heavy microbial load of the compost system efficiently stimulate the biodegradation of hydrocarbon contamination.
How does composting help degrade hydrocarbons in contaminated soil?
Organic matter found in compost systems is rich in carbon and mineral nutrients, such as nitrogen, that are necessary for supporting microbial life. The microorganisms digest the hydrocarbon contamination in addition to the carbon rich compost material by producing enzymes that are required to metabolize hydrocarbons.
How is composting implemented?
Current research is focused on ex situ composting methods- meaning that the contaminated soil is taken from the site of contamination and is added to compost material in a reactor at a different location. This is the preferred method because it is more easily controlled and monitored without the risk of leaching contaminants into surrounding areas. Composting can be optimized has a bioremediation technique by insuring adequate oxygen supply, sufficient nutrients, and suitable pH, temperature, and moisture for the microbial activity.
Composting is usually divided into three categories:
Windrow: The solid waste mixtures are composted in long rows and aerated. They are also turned periodically to expose decomposing matter to oxygen. There is no effective control of either oxygen or temperature within the compost. It is easy to implement and relatively inexpensive, but can take a long time if oxygen or temperature becomes limiting to the microbial community.
Static pile: Piles of solid waste mixture, often mixed with bulking agents, are force-aerated to maintain the oxygen level necessary for microbial life.
In-vessel: Composting takes place in an enclosed container allowing for control of environmental conditions. In-vessel systems are limited in application because of their high implementation costs, so they are often used as pretreatments for up to five days prior to the usage of other forms of composting.
For more on aeration, see Nitrogen and Halogenated Organic Compounds
For more on composting, see Halogenated Organic Solvents
SOURCES: Antizar-Ladislao, Atagana