AEROBIC - OXIDATIVE
Dissolved Oxygen In Situ Treatment
ETEC offers the most effective aerobic bioremediation system on the market today.
The key to our Dissolved Oxygen In Situ Treatment (DO-IT™) Process is its application as a closed loop groundwater re-circulation system. Extracted groundwater is oxygenated (with 40-ppm levels of dissolved oxygen) and amended with nutrients and other acceptors by our Super-Ox™ equipment, which then injects this treatment water back into the subsurface.
This consistent recirculation of oxygen-rich, nutrient-rich treatment water satisfies several critical requirements of all in situ bioremediation systems, including:
Constant and appropriate delivery of bioremediation products to support accelerated biological degradation of contaminants.
Continuous movement of the injected treatment water through the contaminated soil and groundwater for optimum contact with dissolved and adsorbed contaminants.
Control the distribution amended groundwater to specific zones throughout the target area and establish hydraulic control while inducing localized groundwater gradients.
Complete biological degradation of:
THE DO-IT™ PROCESS
The Dissolved Oxygen In situ (DO-IT™) System process addresses the critical governing principles that control the success or failure of any in situ bioremediation effort. These principles can be used to better understand any bioremediation treatment.
All remediation processes come down to mass balance. How many pounds or kilograms of a contaminant exists in the subsurface, and how much of this mass can be removed by the proposed remediation system? With aerobic bioremediation, the mass balance is a function of the stoichiometry of the oxidation-reduction reactions that govern the biological utilization of a particular compound.
For example, oxidation-reduction reactions for the aerobic utilization of benzene are as follows:
Oxidation Reaction: C6 H6 + 12 H2O → 6 CO2 + 30 H+ + 30 e-
Reduction Reaction: 7.5 O2 + 30 H+ + 30 e- → 15 H2O
Overall Reaction: C6 H6 + 7.5 O2 → 6 CO2 + 3 H2O
The O2 requirement for this reaction is that 1 mole of C6 H6 requires 7.5 moles of O2.
Converting to the appropriate mass ratio results in the following:
1 unit C6 H6 : 7.5 x (32/78) units of O2 , or 1 unit C6H6 requires 3 units of O2
Therefore, aerobic biological degradation requires 3 pounds of dissolved oxygen to degrade 1 pound of benzene in the subsurface. Our Super-Ox™ systems fully address this need for large masses of dissolved oxygen. For example, by oxygenating a 10-gpm flow of water with 40 mg/L of dissolved oxygen, a Super-Ox™ unit will deliver approximately 5 pounds of dissolved oxygen to the subsurface per day, and over 150 lbs. of dissolved oxygen per month! On an annual basis, this would support over 600 lbs. of benzene with just the oxygenation portion of our process.
Because many UST sites have thousands of pounds of contamination in the subsurface, dissolved oxygen alone often cannot provide the necessary mass of electron acceptor. To address this, ETEC utilizes a nutrient amendment that also provides and promotes the use of additional electron acceptors to support facultative degradation of TPH constituents. By combining dissolved oxygen and other electron acceptor delivery, we can stimulate plume-wide degradation of TPH constituents and reach cleanup levels within a reasonable time-frame, usually within 1-2 years for typical UST sites.
Additional Details on ETEC's DO-IT™ Process
Oxygenation is only one part of ETEC’s bioremediation technology (Our DO-IT™ Process). Regardless of the oxygenation method, a complete system including the right biological enhancements (bacteria, nutrients, other electron acceptors, rhamnolipids) is critical to ensure a highly successful bioremediation system. In the absence of oxygen, for example further from injection points or on the fringe of the treatment area, ETEC relies on electron acceptors (nitrates) for microbial respiration.
The goal of ETEC’s DO-IT™ Process in combination with our CBN™ and Petrobac™ products is to create geochemical conditions in groundwater, favorable for the degradation of petroleum constituents, by providing dissolved oxygen, nitrate, macro/micro nutrients, rhamnolipids and a pre-acclimated microbial consortium into the subsurface.
The existing and enhanced microbial community in the subsurface uses the petroleum hydrocarbons as a food source; the added oxygen/nitrate (plus naturally occurring secondary electron acceptors) as a respiration source, and the nitrogen, phosphorous (N&P) and other beneficial nutrients to build proteins and multiply. ETEC’s process creates the optimal geochemical conditions to facilitate the necessary mass balance by adding enough bioamendments to degrade the contamination present (mass balance).
ETEC’s bacterial consortium contains various strains of facultative petroleum degraders (able to use oxygen as well as nitrates and other secondary electron acceptors), allowing ETEC to take a multiple electron acceptor approach to degrade the contamination.
To achieve mass balance, our bioamendments are added over time, maintaining optimal conditions.
The following points outline what we typically add:
(DO-IT™) Provides dissolved oxygen to the subsurface at 30-40 mg/L to support aerobic degradation (the half-life of dissolved oxygen is greater than 19 days using our process). Dissolved oxygen as a respiration source can degrade petroleum at a 3:1 ratio (i.e. 3 pounds of D.O. to degrade 1 pound of contamination).
(CBN™) - Provides nitrate to support nitrate-reducing degradation and micro/macro nutrients. Nitrate as a respiration source degrades petroleum at a 5:1 ratio and is very soluble, so large masses can be added to the subsurface to promote nitrate reducing conditions. The microbial community will degrade contamination at a Carbon:Nitrogen:Phosporus ratio of ~100:20:5. ETEC’s CBN is blended to provide nutrients to satisfy these ratios.
Nitrate has a very low retardation factor increasing the likelihood of distribution, and dispersion which ultimately leads to contact with areas of contamination.
(PetroBac™) - Provides a known petroleum degrading microbial community and rhamnolipids to jump start the microbial community. PetroBac™ helps maintain an optimal microbial community throughout and reduces lag phase as the geochemical conditions in the aquifer shift during the various phases of remediation.
ETEC’s products are pH neutral and contain a buffer) - Aquifer pH is another important factor and can be adjusted further if needed.
With these elements we create and maintain the optimal geochemical conditions to degrade the contamination. ETEC supports the project throughout its entirety and works with the client to modify the dosing scheme, as we clean up the target treatment area.
In order to create these optimal geochemical conditions, pore volume “turn-over” in the treatment area via groundwater recirculation is important for creating hydraulic gradients promoting the distribution of amendments. The faster we are able to do so, the quicker we will create the correct geochemical conditions to be successful.
Utilizing infrastructure that allows us the highest possible recirculation flow rate, coupled with the addition of ETEC amendments to create the optimal geochemical conditions, we will see rapid reductions in onsite contaminant levels and have the ability to make real time changes to system operation as the clean-up progresses. Once the infrastructure/system is installed we can sequence the use of our products depending on the specific site conditions at that time. Coupled with a monitoring program that includes COC data, field parameters, and a suite of nutrient indicator parameters we can monitor our progress and make real time adjustments to the system as necessary.
Exchanging / displacing many pore volumes of groundwater, allows for efficient and effective distribution of all the components necessary to contact, desorb and degrade the contaminant mass, and most importantly achieve mass balance.
Conceptual site models and contaminant distribution understanding are only as good as the data currently available. The resolution of understanding will become greater with the additional well installations and even greater with system operation. The flexibility with ETEC’s system will allow real-time adjustments to be made, based on ongoing data collected; ultimately achieving site remedial goals.
By utilizing our Super-Ox™ equipment in combination with localized injection and extraction wells, artificial groundwater gradients can be produced within the plume area to induce circulation of biologically-active treatment water through the groundwater and smear-zone soil. By placing injection and extraction wells at specific locations, individual “circulation cells” can be created throughout a plume zone (i.e. source area, sidegradient, downgradient, etc.), resulting in:
Optimized dissolved oxygen transfer
Hydraulic plume control
Induced groundwater gradients via GW mounding/drawdown
The importance of hydraulic influence as part of a groundwater remediation process cannot be overstated…groundwater management results in long-term flexibility, accelerated cleanup, and shorter remediation time-frames.
Dissolution & Desorption
Contaminants in the subsurface partition into various phases depending upon their specific physical/chemical characteristics. However, contaminants in the adsorbed phase (i.e. the constituents that are bound to the organic soil fraction) usually represents over 70% of the total subsurface mass. Successful in situ bioremediation must address the adsorbed-phase mass in conjunction with the dissolved-phase constituents to achieve site closure.
By constantly replacing and recirculating groundwater within the soil matrix, the DO-IT™ process accelerates dissolution of adsorbed constituents via:
Maximized and continuous smear-zone soil contact
Enhanced delivery of biological products
By forcing adsorbed constituents into solution, they are rendered bio-available and susceptible to subsequent biological degradation. This hydraulically-assisted dissolution process ensures treatment of both sorbed- and dissolved-phase contaminant mass.
Complete Biological Process
At a minimum, successful bioremediation requires:
Availability of specific nutrients (N, P, K, etc.) to support growth of these bacterial species
Abundance of electron acceptors (i.e. dissolved oxygen and secondary electron acceptors)
Contact with the dissolved and adsorbed contaminants
If any one of these requirements is not fulfilled, bioremediation will be inhibited, either partially or completely. The DO-IT™ process addresses each of these governing principles by providing effective bioremediation products, large masses of dissolved oxygen (using the Super-Ox™ equipment), and ongoing contact with soil and groundwater contaminants via consistent groundwater recirculation.