VertaseFLI Limited
Number One
Middle Bridge Business Park
Bristol Road, Portishead
Bristol
BS20 6PN
Registered England & Wales No: 3944198
Ex-situ bioremediation is a biological process in which excavated soil is placed in a lined above-ground treatment area and aerated following processing to enhance the degradation of organic contaminants by the indigenous microbial population. Under aerobic conditions, specific micro-organisms can utilise organic contaminants such as petroleum hydrocarbon mixtures, polycyclic aromatic hydrocarbons (PAH), phenols, cresols, and some pesticides as a source of carbon and energy, ultimately degrading them to carbon dioxide and water.
The native microbial populations are usually sufficient to break down the contamination, but it is common to assess the nutrient requirements and amend the basic nutrients and organic substrate of the soil if any of these elements are deficient or absent. Oxygen (i.e. air) is essential to allow the microbial population to develop cultures capable of sustaining degradation. Therefore, frequent aeration of the soil is an important element in maintaining the population.
Ex-situ bioremediation can remediate a wide range of hydrocarbon contaminants, including but not limited to:
Non-chlorinated hydrocarbons within the carbon chain lengths C6 to C14 are readily treatable. Non-chlorinated hydrocarbons with carbon chain lengths C15-C32 are treatable but require longer time periods to degrade. Chlorinated hydrocarbons and other more complex chains can be degraded but require detailed assessment and analysis to determine suitability.
The excavated soil is placed into a shaped pile between 1.5 and 2 meters in height and up to 6 meters wide in a lined area. The pile is aerated by periodically turning the windrows with specialised machinery, which can be excavator-mounted or self-propelled. Soil organic amendments and nutrients can be easily added to the windrows during turning to improve aeration and soil characteristics as required. This is often the most cost-effective method of ex-situ biological treatment.
Where more complex contaminants are present in the soils or treatment timescales are short, additional measures can be adopted to optimise the treatment process via forced ventilation.
The excavated soil is placed into a shaped pile up to 3 meters in height and 6 meters wide in a lined area. The pile is aerated either via a vacuum pump or air injection blower system to force oxygen into the biopile. The vapours generated in the biopile can be collected and treated onsite by granular activated carbon (GAC) or an air bio-filter to reduce emissions to the atmosphere. Biopiles can be constructed taller than windrows, requiring less space on-site. Additionally, the injection of air can be used to control bed temperature during winter if overwintering is required. It is also the preferred choice if particularly odorous or volatile contaminants are an issue.
Environmental Considerations for Ex-Situ Bioremediation
For all bioremediation techniques, an Environmental Permit is required from the Environment Agency (or for a limited number of smaller projects working in accordance with a Regulatory Position Statement). Any vapours and runoff (or “leachate”) from the soil need to be collected and treated appropriately during the works.
Treatment times range from 6 to 16 weeks depending on contamination, target concentrations, contaminant type, concentration, soil properties, and the time of year. Ambient temperature has a significant effect on bioremediation, with the best degradation rates occurring during the warmer summer months; cold winter weather can significantly slow and even halt biodegradation.
Lee Howard – GradIOSH & AIEMA
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Talk to usNumber One
Middle Bridge Business Park
Bristol Road, Portishead
Bristol
BS20 6PN