On this page (10 sections)
Biostimulation feeds and conditions the microbes already in the soil. Bioaugmentation adds microbes that are missing or too few. Which one a project uses, or whether it uses both, comes down to whether the right degraders are already present and what is holding them back. EPA notes that bioaugmentation may be needed for contaminants native organisms don’t degrade, and that it is almost always paired with biostimulation [1]. Four published studies below show each approach working in different settings.
The two terms
| Biostimulation | Bioaugmentation | |
|---|---|---|
| What gets added | Air or oxygen, nutrients, and carbon sources such as vegetable oil, molasses, or lactate [1][2] | Cultures of microbes, native or non-native [2] |
| Working assumption | The right microbes are present but limited by conditions | The right microbes are absent, too few, or cannot finish the job |
| Typical use | Fuels and other compounds common soil microbes can eat | A specialized step, such as complete dechlorination of solvents |
| Usually combined with | Nothing else, or later bioaugmentation | Biostimulation, to create conditions the added microbes need [1][2] |
EPA’s technical paper uses “enhanced bioremediation” for the general idea and keeps “biostimulation” for the case where only amendments go in [1]. Its examples include bioventing, land farming, biopiles and composting [1].
How a project decides
The first question is whether the right degraders are already there, which is what bench-scale treatability tests are for. EPA lists what they establish: the mass of contaminant and breakdown products on site, the existing microbial populations, and which mechanisms and amendments work [2].
The next question is what is limiting them, and at many fuel sites, EPA’s technical paper says, oxygen limits how much treatment happens, and adding air lets degradation continue [1]. Elsewhere the limit may be nutrients, moisture, pH or temperature. When conditions are wrong, EPA’s public guide says, microbes grow too slowly or die and the contaminant stays [3].
Some compounds need a specialist, since anaerobic dechlorination of solvents can stall at an intermediate compound even with plenty of food available, EPA notes, and adding microbes may then speed it up [1].
What four studies found
| Study | Setting | What was tested | What was reported |
|---|---|---|---|
| Bragg et al., 1994 [4] | Oiled shorelines after the Exxon Valdez spill, field | Fertilizer applied to stimulate native oil degraders | Fertilizer significantly increased biodegradation rates. Rates depended mainly on nitrogen concentration, oil loading, and how much natural biodegradation had already occurred. |
| Lendvay et al., 2003 [5] | Chlorinated solvent plots, groundwater | Lactate and nutrients vs. adding a Dehalococcoides-containing culture | Biostimulation dechlorinated after a 3-month lag. Bioaugmentation produced near-complete dechlorination to ethene within 6 weeks. |
| Major et al., 2002 [6] | Kelly Air Force Base, lab microcosms and a field pilot | Lactate or methanol, then a dechlorinating culture (KB-1) | Amended microcosms stopped at partial dechlorination. After KB-1, chlorinated ethenes converted fully to ethene. In the pilot, concentrations fell below 5 µg/L within 200 days. |
| Szulc et al., 2014 [7] | Diesel-contaminated soil, 365-day field study | Natural attenuation, a biosurfactant, bioaugmentation, and bioaugmentation plus biosurfactant | Bioaugmentation gave the highest diesel biodegradation. The biosurfactant did not notably change the outcome. |
Two of these are groundwater studies, included because they are the cleanest side-by-side comparisons published. Their logic applies to soil, though their numbers don’t.
No single approach wins across the four. Shoreline oil responded to nitrogen because oil degraders were already there. The solvent sites needed a specific organism to finish the chemistry. The diesel soil did better with an added consortium, and stacking a biosurfactant on top added nothing measurable.
What the amendments are
The materials are often ordinary ones, and EPA’s green remediation fact sheet lists carbon sources for soil treatment such as wood chips, sawdust, straw and cottonseed hulls, manure compost from farms, municipal biosolids, and pesticide-free mushroom compost, which brings beneficial fungi along with nitrogen, phosphorus and potassium [2]. It lists chitin from seafood waste as a nitrogen source for petroleum-contaminated soil [2]. Liquid amendments include lactate, food-grade molasses and anhydrous ammonia [2].
The diesel study offers a caution, because a biosurfactant, a soap-like additive meant to free oil from soil particles, was tested at a lab-selected dose and made no notable difference in the field [7]. Each added input should prove itself in a treatability test.
Adding microbes has costs too
Added microbes need food and the right conditions. EPA’s public guide says organisms added for bioaugmentation typically die off once the contamination and the supporting conditions are gone [3]. That is reassuring for safety, and it also means a culture added without support won’t persist.
Regulators may ask about it as well. EPA’s green remediation fact sheet notes that permits for underground injection vary by state [2], so anyone proposing to introduce non-native microbes should be able to name the agency that approved it.
And a species name on a label guarantees nothing. The solvent studies worked because of one organism group and one specific culture. Whether another strain of a similar-sounding species carries the same ability has to be tested.
When you see first data
In the solvent comparison, the bioaugmented plot was producing ethene within 6 weeks, while the biostimulated plot didn’t start dechlorinating until after a 3-month lag [5]. A lag isn’t necessarily failure, so monitoring has to run long enough to catch the change, and the proposal should say up front how long the project will wait before changing course.
Reading a proposal
- Ask which approach is proposed and why the proposer thinks the native microbes are or aren’t enough.
- Ask for the control, as the diesel study kept a natural-attenuation arm, and the solvent study ran separate plots. A project that adds food and microbes together with no comparison can’t say which did the work. Our guide to evaluating a bioremediation proposal has the full list of questions.
- Ask for a treatability study on your soil before any full-scale spending [2].
Where Elm Dirt fits
Elm Dirt’s liquid biologicals carry living microbial communities together with natural nutrient sources. A project built on them has to separate those two effects, so we recommend a treatability study with a nutrient-only comparison arm. An independent lab, Biome Makers, found 291 microbial species in our Plant Juice. That tells us what we are adding, not which part of the product does the work on a particular site, and Elm Dirt has not published product-level degradation data.
Your site
The right approach depends on the contaminant, the soil, the climate and what the native microbes can already do. The four studies differ on all of those, so they can shape a design but can’t stand in for testing it. Tell us what’s in your soil.
Sources
- U.S. EPA. Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites. EPA/625/R-06/015, October 2006. Link. Accessed 2026-10-01.
- U.S. EPA. Green Remediation Best Management Practices: Bioremediation. EPA 542-F-21-028, December 2021. Link. Accessed 2026-10-01.
- U.S. EPA. A Citizen’s Guide to Bioremediation. EPA 542-F-12-003, September 2012. Link. Accessed 2026-10-01.
- Bragg JR, Prince RC, Harner EJ, Atlas RM. Effectiveness of bioremediation for the Exxon Valdez oil spill. Nature 368:413-418, 1994. doi:10.1038/368413a0.
- Lendvay JM, Löffler FE, Dollhopf M, et al. Bioreactive barriers: a comparison of bioaugmentation and biostimulation for chlorinated solvent remediation. Environmental Science & Technology 37(7):1422-1431, 2003. doi:10.1021/es025985u.
- Major DW, McMaster ML, Cox EE, et al. Field demonstration of successful bioaugmentation to achieve dechlorination of tetrachloroethene to ethene. Environmental Science & Technology 36(23):5106-5116, 2002. doi:10.1021/es0255711.
- Szulc A, Ambrożewicz D, Sydow M, et al. The influence of bioaugmentation and biosurfactant addition on bioremediation efficiency of diesel-oil contaminated soil: feasibility during field studies. Journal of Environmental Management 132:121-128, 2014. doi:10.1016/j.jenvman.2013.11.006.