The Challenge of Site Remediation

Remediation methods, such as soil vapour extraction and in situ chemical oxidation are challenging in cold, low-permeability conditions, highlighting the need for alternative approaches. Using naturally occurring microorganisms to deplete hydrocarbons is attractive. However, it is challenging to repeatably execute this remediation technique successfully across multiple sites due to nuanced site mineralogies.

Biostimulant INNOVATION

LiORA offers an alternative; a proprietary all-natural nutrient mix, BioLodestone, that  biostimulates hydrocarbon depletion (Figure 1). A biostimulant is a chemical mixture that enhances the hydrocarbon degradation activity of microorganisms already in the soil. Biostimulation can target pollutants that are at very low concentrations relative to other microbial food sources in the soil and groundwater. A good biostimulant, such as BioLodestone, enables the small but mighty fraction, typically less than 5% of a natural soil microbial community that degrades pollutants, to multiply and focus on degrading compounds. LiORA will recommend a specific nutrient combination that provides the target microbes with what they need to thrive and avoid feeding the other 95% of the microbial community that do not degrade hydrocarbons.

BioLodestone’s name originates from when one of LiORA’s scientists noticed that when the solution was added to degrading microbial cultures, those cultures became magnetic. Magnetic ores are called lodestones, and the creation of magnetic ores, typically iron oxide, is a result of LiORA’s BioLodestone adding key electron acceptors to promote hydrocarbon degradation. BioLodestone allows these microbes to overcome subsurface oxygen depletion and increases the bioavailability of nutrients that are essential for the hydrocarbon-degrading microbes to thrive.

Figure 1. BioLodestone stimulates microbial hydrocarbon degradation by maximizing phosphorus bioavailability through a mixed community of syntrophic and hydrocarbon degrading bacteria. Syntrophic means cross-feeding and comes from Greek syn (together) and trophe (nourishment). Basically, some microbes will feed on the nutrients and substrates provided by the others.

BioLodestone Reduces Costs and Accelerates Closure

Over the last 4 years, LiORA evaluated hydrocarbon depletion across 23 sites. All sites had historic diesel and/or gasoline releases that were at least 20 years old. Several of these sites had mobile Light Non-Aqueous Phase Liquids (LNAPL) and all had residual LNAPL. The issue with LNAPL is that it is not soluble in water and is less dense than water so will float on the surface, meaning mobile LNAPL can more easily travel offsite presenting a higher risk to receptors.

BioLodestone was applied to 5 sites over a three-month period each year, then monitored using LiORA Sensors.

LiORA’s BioLodestone is applied using a unique method that involves slowly and continuously adds biostimulant solution to the upper soil regions. The infiltration rate mimics fractured flow to avoid short-circuiting injection fluid to the surface.

RESULTS

On Average, BioLodestone Increases Hydrocarbon Depletion by 270%.

LiORA analyzed 23 sites over 4 years and estimated depletion rates throughout the calendar year using LiORA Soil Sensors. The comparison was made among the 5 sites biostimulated using BioLodestone and 18 where simple baseline natural depletion was occurring.

However, these biological processes require stimulant and time. Some sites indicate target depletion (i.e., doubling of depletion rates) was met within 1 year of application. Other sites required 2 to 4 years of application for target depletion to occur.

The timeline to closure for sites with BioLodestone application was reduced by 50-80% versus the control sites. Factors for differences in the range include the contaminant type and volume, and soil composition.

The result was a near tripling of hydrocarbon depletion rates with low-footprint BioLodestone, with the BioLodestone sites performing at a mean of 0.659 L m^-2 month^-1 and the Control sites performing at a mean of 0.245 L m^-2 month^-1 (Figure 2).

Figure 2. A comparison of BioLodestone stimulated and non-stimulated hydrocarbon depletion. Bars represent the estimate of the mean, and error bars represent the standard error of the depletion estimate.

CONCLUSION

Biostimulation is an effective solution to reduce soil and groundwater hydrocarbon concentrations. BioLodestone offers:

• Reduced remediation timelines of 1 to 4 years, a vast reduction from other remedial methods with marginal returns; and
• Low carbon footprint solution that allows for reduced costs versus other expensive remediation excavations and/or high resource intensive vapour extraction systems.