Quick-release or soluble substrates have been used for Enhanced Reductive Dechlorination (ERD) since its first uses. Soluble substrates, such as lactate or simple carbohydrates, have been shown to be extremely effective at creating reductive conditions, complete solvent transformation, and successful bioremediation cleanups.
The three big advantages of using soluble, quick-release substrates are the ease of distribution, the rapid creation of reductive conditions, and the complete utilization of the applied food source.
- First, distribution away from wells or DPT points is greater than separate phase (soybean oil) and viscous substrates. This allows for better site wide coverage, ease of injection, and fewer application points. Re-application through wells is also possible.
- Second, since the substrates are simple and soluble, the bacteria can utilize them easily. This leads to fast bacteria growth, depletion of competing electron acceptors, and negative redox conditions in a very short timeframe.
- The last big reason for using soluble substrates, and the least discussed, is the utilization percentage of the substrate. Soluble substrates are very simple and are completely available upon injection for use by the microbial community. This allows for complete utilization of the applied substrate. Contrasting with long-term substrates, it may require years for the bacteria to use the slow-release substrate and then maybe only a portion of the applied mass. Clients have reported separate phase oil at ERD sites years after application. This represents incomplete use of the applied slow-release substrate mass, less than what is required for successful ERD, which can lead to remediation failure.
The argument against using soluble substrates is that they are transient and will not provide long-term remediation. The argument is flawed for a few reasons.
- First, the substrate will not “flow away” from the application area any faster than groundwater, which would be feet per year. It will not go to waste, and utilization will be higher.
- Second, and most importantly, the soluble substrate encourages the growth of a large amount of biomass which attaches to soil and becomes the long-term substrate for bacteria, supporting reductive conditions for months and years following application.
- Finally, what site-owner wants their remediation effort to be “long-lasting” in contrast to “fast-acting”?
Given the advantages of a quick-release substrate, we developed CarBstrate – a simple carbohydrate-based formula that also includes all the nutrients and B vitamins needed to achieve maximum distribution and support a large bacteria population for rapid and ongoing ERD. If you have a site you’d like us review and provide our analysis, please reach out!