Understanding Bioremediation: A Rough Guide
‘Bioremediation’ is a term that often confuses even the well-informed reader. It is, simply put, the process of removing hazardous hydrocarbon pollutants from soil or water via bacterial digestion. Importantly, this is a natural process (hence the ‘bio’); however human beings do possess the capacity to accelerate it, shortening its duration from decades and years to months and weeks. This ‘Rough Guide’ will go through some of the tools and methods currently at our disposal.
Part I: Agents
Microbes or bacteria are the agents that carry out bioremediation. Increasing the size or vitality of their population at a particular site is one very obvious way of accelerating the natural decontamination process.
How can the rate at which hydrocarbons are removed from the soil be accelerated?
Soil microbes often lay dormant underground for years because they are deprived of the key micronutrients and trace elements they require to sustain their metabolic processes. Hence, one way to accelerate the remediation process is to deliver these compounds to these largely inactive colonies in order to kick-start them into life and recommence their natural digestion of hydrocarbon chains. This process is called ‘biostimulation.’ Our Sea Power 101 is a good example of a biostimulant, containing as it does a potent mix of amino acids, carbohydrates and vitamins present within natural seaweed.
This approach produces excellent results; however there are two key problems:
1. Microbe populations are fixed, which means that the speed at which they can bring about extensive bioremediation is capped at an optimum level. If the soil has a particularly low microbial level, this might present a real problem.
2. Native microbes are often unsuitable for tackling the most stubborn chains within the soil, meaning that the worst pollutants, such as PAH (Polyaromatic Hydrocarbons), are not removed. When these compounds are present, extensive bioremediation via biostimulation is not possible.
How can we negate these problems?
‘Bioaugmentation’ is the practice of introducing billions of new microbes into a contaminated site with a view to reducing the overall time required for bioremediation. Our BioBoost – a dried mixture of bacterial spores – is one such example of a bioaugmentation product. Bioaugmentation, if carried out properly, can be highly effective at accelerating the decontamination of soil. It can also overcome the second great problem presented by using only a biostimulant: bioaugmentation products can be configured to contain certain species of bacteria that are not ordinarily present within soil, such as pseudomonas, which are able to break down PAHs more easily.
Is bioaugmentation the way to go then?
Advocates of bioaugmentation have often been bullish regarding the power of what has sometimes been termed ‘Magic Dust.’ Indeed, when their rhetoric was actually tested on contaminated sites, contractors were often left disappointed.
There were two main problems:
1. Many of the new microbes they introduced were in fact dead upon entry into the site because the conditions required for their survival could not be met.
2. It was very difficult to apply a dry powder to a site, which meant the new spores often did not reach the contaminated areas deep within the soil.
It seems then that successful acceleration of the bioremediation process is best affected when the principles of biostimulation and bioaugmentation are combined. Only then can you be sure that the billions of new microbes that are entering the site will survive, thrive and begin digesting hydrocarbon pollutants immediately. Mixing a biostimulant, such as Sea Power 101, with a bioaugmentation product, such as BioBoost, prior to application is therefore recommended for best results. Such a system also provides the new bacteria with a vehicle in which to travel through the soil to the most contaminated areas, thus solving the other great problem posed by bioaugmentation alone. See Our Synergistic System for more details.
Part II: Conditions
Bacteria require the same fundamental conditions for their survival as human beings. If these are not adequately met, the process of bioremediation will be slowed down or stop altogether. Contractors therefore try to optimize these conditions in order to accelerate the decontamination of polluted soil.
How is the supply of water and oxygen regulated?
Microbes are not able to function effectively without a regular supply of water and oxygen, and hence several techniques exist in order to ensure these demands are met. Water is perhaps easiest to regulate as soils already hold vast amounts of it. However, if the site is particularly sandy, water retention still presents a serious problem, and regular watering is often necessary. One way of increasing retention capacity in such cases is to apply a solution to the soil that is high in wetting agents (surfactants), such as Sea Power 101.
Oxygen supply presents a bigger problem altogether. Various elaborate methods exist for aerating contaminated soil; the one that is eventually chosen depends chiefly upon the dimensions of the site and the nature of the contamination. Typical approaches include: pumping air into the ground (in-situ remediation); constructing biopiles over vented oxygen tubes; turning windrows to circulate air; or introducing an oxidizing agent, such as Hydrogen Peroxide (although the environmental value of this last approach is often very questionable).
Besides ensuring a regular supply of water and oxygen, what other conditions need to be fulfilled for a successful bioremediation?
Native soil microbes are extremely sensitive to both the temperature and pH value of their environment, operating best in ambient and neutral conditions. Typically, when the temperature drops below 9 degrees centigrade or the pH value falls outside the range 6-9, their metabolic processes will be severely curtailed or stop altogether.
Can we do anything to optimize these conditions?
Of course, it is incredibly difficult to try to control temperatures on a large bioremediation site, but there are methods available, such as the construction of large ‘greenhouse’ tents around the contaminated area. With regards to the pH level, no quick fix exists, although increasing the water retention capacity of the soil by introducing wetting agents will help to neutralize the site. However, that is not to say that contractors are powerless. Bioaugmentation of bacterial spores that are more resistant to low temperatures or inhospitable pH levels offers one way of getting around this problem. Our BioBoost, for example, contains species which operate at temperatures as low as 5 degrees centigrade and in pH environments between 5 and 10.
Part III: Bioavailability
Bioavailability refers to the availability of pollutant hydrocarbons within soil for digestion by the microbial population. Increasing this property can also help accelerate the natural bioremediation process.
How can bioavailability be increased at a site?
Contractors usually try to increase bioavailability at a site by mechanically breaking down the soil to a finer consistency, which increases its surface area and makes it easier for bacteria to reach the hydrocarbon chains and begin their digestion.
Are there any other methods for increasing the availability of hydrocarbons for bacteria?
Yes, there are other approaches, one of which has been shown to be incredibly efficacious and low maintenance. This involves adding a wetting agent to the soil, which will help to emulsify the long hydrocarbon chains, and make it easier for bacteria to bind to them and begin their digestion. Sea Power 101 is one particularly good source of these compounds (surfactants), which further contributes to the success it has had in accelerating the bioremediation process to date.