Enhanced Dissolved Oxygen Technology -
(Patents #6,517,288; 6,719,904; 6,740,238; and 6,866,781)
The Enhance Dissolved Oxygen Technology (E-DOT) System is a bioremediation system. The system injects pure oxygen directly into the groundwater.
Bioremediation is a technique in which either naturally occurring bacteria or non-indigenous supplied bacteria are used to consume contamination in place. Bacteria are similar to humans in that they are living organisms which require basic conditions to live. These conditions are; 1) Food, they have to have something to eat; 2) Water, they have to have something to drink; 3) Nutrients, they need their vitamins and minerals; 4) Temperature, it can’t be too cold and it can’t be two hot; and 5) Oxygen, they have to have something to breath.
When trying to enhance biological activity, of the five conditions listed above, the addition of oxygen is the only condition which is practical and also provides substantial benefits.
One common question that is always asked regarding the E-DOT System™ is why compressed air is not used in place of oxygen. There are several reasons why oxygen is the preferred gas. When using ambient air injected into groundwater, the resulting dissolved oxygen concentration expected will be at best 10 to 12 parts per million (ppm). When using pure oxygen one can expect dissolved oxygen concentrations in the range of 35 to 40 parts per million (ppm). The reason for this increase in dissolved oxygen concentrations is based on the concentration of nitrogen in ambient air. The high concentration of nitrogen in ambient air essentially takes up available space in groundwater for dissolved gases. When using pure oxygen all available space can be occupied by the oxygen, resulting in a higher concentration of oxygen.
One benefit of this higher concentration is that fewer points are needed to affect the dissolved oxygen concentration over a given area. The higher concentration creates a concentration gradient and allows for a greater area of dispersion per point. The higher concentration allows it to affect a larger area, thus less points are needed, saving construction costs.
The other significant benefit of the E-DOT System™ is the lack of any pumps or electricity. With no pumps, no electricity and no mechanical moving parts, the system has virtually no maintenance. With nothing to break down that means there is nothing to fix. No unexpected change orders for repairs or replacements.
System Feasibility and Contamination Delineation
When evaluating a site for feasibility of an E-DOT System™ it is best to start by looking at soil gas in the vadose zone just above the ground water interface. Specifically, we’re looking at concentrations of carbon dioxide and oxygen. When we look at soil gas in an area of ground water contamination, what we will typically see is elevated levels of carbon dioxide and depleted or nearly depleted levels of oxygen. When we look at soil gas outside the area of contamination, we will see carbon dioxide lower than in the area of contamination and oxygen higher than in the area of contamination. One must be careful in this comparison to assure a comparison of similar soil types and conditions. However, when this situation is identified, it reasonable to assume that the reason for the elevated level of carbon dioxide and depleted levels of oxygen within the contaminated zone is based on the presence of bacteria consuming all available oxygen and producing carbon dioxide. Because of the lack of oxygen in the contaminated area, only a limited population of bacteria is possible, although all other conditions for a larger population exist. Any increase in the level of oxygen will increase the bacterial population and rate of contamination degradation (Refer to the illustration below).
The soil gas samples can be collected by capping the top of the monitoring well and pulling a vacuum on the monitoring well using a vacuum pump. Soil gas will be drawn up through the screen interval of the monitoring well located just above the ground water interface. The soil gas meter can then read the discharge of the vacuum pump and once the levels of soil gas have stabilized, this reading can be recorded as the levels of carbon dioxide and oxygen in the vadose zone. This technique assumes that the ground water monitoring well in question is installed to intersect the ground water interface.
Additional samplings of the soil and ground water to determine microbial population, species, and population size can also be conducted, however the soil gas analysis is believed to be the most cost effective and conclusive test to evaluate site conditions and current biological activity status. The same soil gas analysis will be used once the E-DOT System is in place to adjust oxygen flow rates for optimum system performance.
(Additional Point Installation Information Available in the Installation and Operation Manual)
There are four methods of point installation when installing the oxygen injection points at a site. The points are typically installed in a grid fashion in the area of the ground water impact. The purpose of the grid fashion is to increase the level of oxygen in the ground water and in the capillary fringe evenly across the area of ground water impact. Maintaining oxygen across the ground water impact assures that all areas of the impact will be treated and as impacted ground water migrates it will not move out of treatment zones prior to being treated to below desired target levels. It is understood that a grid my not always be possible because of surface features or access issues, however, it is considered the most desirable point layout. The grid system should also be positioned so each grid point is not directly up gradient from the next down gradient point. A staggered layout is considered the most desirable to assure the most even distribution of oxygen. When considering the grid spacing a general rule of thumb is a grid based on two months ground water flow as calculated for that particular site. For instance, if ground water has been calculated to travel 120’/ year at a particular site, the grid spacing recommended for that site would be a 20’ (e.g. 10’ / month; two months equals 20’). It is not recommended that a grid spacing of tighter than 10’ be used.
Points should be installed so that the depth of the injection point is such that the oxygen is leaving the injection point at the bottom of the impacted ground water. That is, if vertical profiling of the impacted ground water has determined that impact extends to 20’ below the ground water interface, the oxygen injection point should be installed so the oxygen leaves the injection point at 20’ below the ground water interface. If the impacted ground water zone is determined to be only 10’ in thickness, then the oxygen should leave the injection point at 10’ below the ground water interface. If no information is available on the vertical impact of ground water, it is recommended that the oxygen injection point extend 10’ below the ground water interface, as most petroleum plumes are not thicker than 10’. However, it is strongly recommended that vertical definition be determined prior to the design or installation of any system.
(Additional System Operation Information Available in the Installation and Operation Manual)
The object of injecting oxygen into the ground water is to increase the dissolved oxygen concentration. As stated earlier, oxygen is needed for bacteria to convert contamination into carbon dioxide. At most sites of contamination, oxygen is significantly limited reducing the rate at which bacteria can convert contamination into carbon dioxide. The purpose of the E-DOT System™ is to provide an ample amount of oxygen for the bacteria to survive and thrive. Like we humans, bacteria do not like oxygen deficient environments nor do they like oxygen rich environments. The system should be operated to maintain an oxygen concentration between 15% and 25%. As discussed previously soil gas should be collected and analyzed to determine the oxygen concentration in the area of oxygen injection. Should the oxygen concentration fall below 15% in the vadose zone, just above the area of the oxygen injection, the rate of oxygen injection should be increased slightly to achieve the desired concentration between 15% and 25%. Conversely, should the oxygen concentration exceed 25% in the vadose zone, just above the area of the oxygen injection, the rate of oxygen injection should be decreased slightly to achieve the desired concentration range. Dissolved oxygen concentrations in ground water should also be collected.
A baseline should be established prior to system start up and the injection of oxygen. It is recommended that samples be collected and the system monitored once per week for the first month. After the first month, the system can be sampled and monitored once per month for the next two months and then quarterly thereafter. An increase in carbon dioxide in the area of ground water impact can be anticipated within the first month. This increase in carbon dioxide is a result all of increased contaminant degradation because of the increase in the bacterial population. Additional sample parameters can also be collected (e.g. plate counts and bacterial species analysis); however, the results of the carbon dioxide analysis are telltale signs of bacterial activity and can be relied upon as good indicators of contaminant degradation and a bacteria population.
To learn more about the system, download the E-DOT System™ Installation and Operations and Maintenance Manual.
8666 E. Traverse Highway - Traverse City, Michigan 49684
Phone:(231) 933-7035 - Fax: (231) 933-7135 - Cell: (231) 218-7955