Aerobic Bioremediation using the DO-IT™ System

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.

Mass Balance

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: C6H6 + 12 H2O → 6 CO2 + 30 H+ + 30 e-

Reduction Reaction: 7.5 O2 + 30 H+ + 30 e- → 15 H2O

Overall Reaction: C6H6 + 7.5 O2 → 6 CO2 + 3 H2O

The O2 requirement for this reaction is that 1 mole of C6H6 requires 7.5 moles of O2. Converting to the appropriate mass ratio results in the following:

1 unit C6H6 : 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 45 mg/L of dissolved oxygen, a Super-Ox™ unit will deliver approximately 6 pounds of dissolved oxygen to the subsurface per day, or close to 200 lbs. of dissolved oxygen per month!! On an annual basis, this would support aerobic biological degradation of over 750 lbs. of benzene.

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 secondary electron acceptors (nitrate, sulfate) to support facultative degradation of TPH constituents. By combining dissolved oxygen and secondary electron acceptor delivery, we can stimulate plume-wide degradation of TPH constituents and reach cleanup levels within a reasonable timeframe, usually within 1-2 years for typical UST sites.

Hydraulic Influence

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 timeframes.

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

O2bacteria diagram

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.