Inhibition of Biofilm Formation
* Bacterial biofilm formation is the root cause of biofouling and blockages of wells and dam drains. Biofilm formation is a result of cell-to-cell quorum sensing communication.
* Can quorum sensing inhibitors be used to prevent or reduce biofilm formation, thereby extending the life of wells and dam drains?
Need and Benefit
Biofouling is a widespread problem on Reclamation structures. Reclamation manages the problem through conventional physical and chemical disinfection methods. The biofouling problem is commonly attributed to iron bacteria. Since ground water typically contain reduced iron/manganese species, Reclamation structures will continually be faced with this problem and rehabilitation efforts will lose their effectiveness as structures continue to age with time.
According to the Technical Service Center (TSC) Closed Circuit Television inspection program, 5-10 percent of all of all toe drains and outlet works conduits inspected were found to contain biofouling. In some areas, as many as 1/3 to 1/2 of drains contain evidence of biofilm formation. The extent of biofilm formation ranged from traces to complete plugging of the pipe. They are usually treated with high pressure jet cleaning, but there is a continued long term decline in performance. At Grassy Lake, a specially-designed toe drain with more open slot areas was installed with the hope that it will mitigate biofouling. Chemical biocide treatments have limited effect since biofilm confers antimicrobial resistance to the resident population. In addition, biocides may have unintended consequences when it is released in the environment and may be hazardous to nontarget species of plant and animal.
A similar situation exists with ground water wells. One example exist at the Closed Basin Project (Upper Colorado [UC] Region) where well biofouling issues take approximately 20 percent of labor time per year. The salvage wells begin to display a decrease in capacity after just a few years of operation. The biofouling closes pipes and clogs pumps and well screens. Some wells have been completely shut down. Another example is in the Pacific Northwest (PN) Region where there are 37 dewatering wells being used to stabilized the riverbank downstream of Grand Coulee Dam. These wells were constructed during the mid/late 1980s. By 1990, well yields have already declined and a mechanical/chemical well cleaning program was initiated. As the wells aged, the decline in yields has been more rapid in between cleaning. Most have the wells have already been cleaned 2-3 times. It has taken 3-1/2 to 4 weeks to complete a single well cleaning. At this rate, it will take 3 years to cycle the cleaning through all 37 wells. Recent studies indicated that well yields that are allowed to decline beyond 20-30 percent often permanently damage the wells and restoration efforts are less effective. A solution to prolong the optimum yields of these wells is needed for the critical purpose of stabilizing the riverbank. Similar well biofouling problems have been documented in other Reclamation regions.
Past treatments have included hot water scrubbing, high pressure jet, and numerous chemical treatments. Re-drilling the wells is the current remedy. Other treatments for biofouling include sonication and Zeta Rod. Sonication is a short term solution involving an aggressive method of physical removal. Zeta Rod is an electrode that is placed within a grounded conductive surface such as metal water pipes. It requires a high-voltage low-current power supply to maintain the capacitor, which only extends approximately 20 feet. It does not work within nonconductive polyvinyl chloride (PVC) pipes. Iron bacteria are sometimes managed by pre-oxidizing iron (and manganese). Abiotic iron oxidation is accelerated by adding oxidizing chemicals or oxygen releasing compounds, making iron/manganese unavailable to bacteria. The increased oxygen and pH levels in the water have the added advantage of suppressing the growth rates of some iron bacteria (e.g., _Gallionella_). However, there is chemical deposition of iron oxides, which may still lead to blockages.
What Reclamation need is a long-term solution to the biofouling problem to extend the production life of well fields and dam drains (toe drains and other internal drai
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