Successful implementation of bioremediation:  interview with Hydrogeologist, Casey O’Farrell

Casey O'Farrell (5)

The 2022 Bioremediation symposium hosted by Australian Land and Groundwater Association (ALGA) in Mudgee, New South Wales explored the myths and benefits of bioremediation.

Tetra Tech Principal Hydrogeologist Casey O’Farrell was invited to speak at the symposium on demonstrating the efficacy of bioremediation, a topic which she is passionate about.  Here she breaks down the approach to bioremediation and why supporting nature to work well is often the best option.

What is bioremediation?

In simple terms, bioremediation is the use of biological processes to degrade or change contaminants to reduce the risk posed to receptors. Typically, this involves enhancing or optimising the environmental conditions so that they suit or facilitate the degradation of contamination.

What are some of the approaches in bioremediation?

An example of this might be the addition of electron acceptors for petroleum hydrocarbon impact so that the hydrocarbons are used by microorganisms as food.

The addition might be as simple as adding oxygen by aerating the subsurface by bubbling oxygen through groundwater or blowing air through a stockpile.

For other contaminants which are only degraded or modified where oxygen isn’t present, degradation might be enhanced through the addition of a carbon source, and that might be, believe it or not, injecting vegetable oil or molasses or some simple organics into the ground. The addition of this material creates the reducing conditions whereby the contaminants are then used by the microorganisms as an electron acceptor, so they effectively breathe the contamination.

What other elements make up this process?

For some man-made compounds it actually helps to add specific microorganisms to the environment to get degradation happening. For most sites it just optimises the conditions for the microorganisms that are there and working with the existing environments is actually the best option. So, you are really facilitating, as opposed to changing conditions to get remediation pumping.

Why is it sometimes important for people to have a bioremediation strategy?

It’s not just sometimes important.  It’s always important.

If you don’t have a strategy in place, with clear baseline and monitoring plans and triggers, then you can’t demonstrate the efficacy of the remediation. What’s also really important with bioremediation is that you need to show that the effect of remediation hasn’t just been temporary, and that the results really do represent future conditions.

So the approach should always be to establish a baseline, and continuously monitor to either tweak or assess the success of the overall activities that we’re supporting.

Basically, nature is often already fixing a problem, we are just trying to give a helping hand to speed up the process.

What are some of the challenges to this approach?

You need data to get started so that you can understand the extent of the problem and the existing conditions. Collecting this data, and setting up a monitoring network and plan, is an upfront cost that can be daunting.  The actual cost of doing bioremediation, and making the additions to overcome limiting factors, is relatively small.

Perception of both the client and the public can also be a challenge. During bioremediation there is no large equipment onsite, or big holes in the ground or workers with high-VIS, so it looks like nothing is happening. Of course, this can also be an advantage as bioremediation can work away in the background at a busy site without interfering with operation, or needlessly alarming the public.

Do extreme weather conditions impact strategies?

Whatever strategy is adopted, you can’t just ‘set and forget’. Remediation goals can be set, but you need to take into account what’s happening in the environment, or due to an extreme event, as this can really affect your assessment of how well bioremediation is working.

A good example of this is where a change in groundwater levels may affect petroleum hydrocarbon observations. When the groundwater level comes up, it can hide the extent of petroleum hydrocarbon contamination, which then increases again when the groundwater level drops. If you have a monitoring strategy that doesn’t consider groundwater levels the results might not truly reflect performance, and you think you have failed when you haven’t, and vice versa.

What motivates clients to look at a bioremediation approach?

Well, it’s all driven by the risk and timing.

Sometimes bioremediation isn’t quick enough to manage the risk or future plans for the site, and alternative approaches are more appropriate.

But there is a focus on sustainable remediation. We work with associations like Australian Land and Ground Water Association to put the focus on sustainable remediation, and most of us would prefer to use sustainable rather than high energy remediation where it makes sense. And that’s where bioremediation comes in, using a simple biologically driven system to have a big impact, often in hard to reach environments.

Can you share an example with us?

An obvious one is the use of oxygen in the air to enhance degradation in an oxygen-limited environment. Although oxygen makes up 20% of air, it isn’t very soluble in groundwater, and can be quickly exhausted in soil piles. Just like in the centre of a compost bin where it goes stinky because all the oxygen is gone. So, getting some fresh air into soil piles by turning them over, or sparging air into the ground can really enhance the degradation.

Another more left field one is where contamination is near a marine environment, if conditions are right, seawater can be injected to provide sulphate as an electron acceptor to enhance the hydrocarbon degradation.

Yes, there are some energy costs to get the oxygen into the soil or ground, or to pump and inject the seawater, but the great thing is you’re not using or adding any more chemicals into the environment.

A good example of this is where a change in groundwater levels may affect petroleum hydrocarbon observations. When the groundwater level comes up, it can hide the extent of petroleum hydrocarbon contamination, which then increases again when the groundwater level drops. If you have a monitoring strategy that doesn’t consider groundwater levels the results might not truly reflect performance, and you think you have failed when you haven’t, and vice versa.

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