Biofouling of a well is a form of biochemical incrustation that involves the creation of continuous or discontinuous biofilms. A biofilm is defined as a “microbial growth occurring over a surface in which the individual cells are bound within a common extra-cellular matrix of polymeric molecules” (Dullimore, 1987). Biofouling is one of the five major causes for decreasing well yields and the development of poor well water quality, see Table 1.
Table1 | Bacteria in Groundwater and Their Influence on Water Quality.
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(Source: Method for Monitoring Fe and Mn, Biofouling in Water Wells, AWWA, 1992.)
With respect to well yield, the “biofouling” creates a reduction of well yield, well efficiency, and poorer system performance. Just like chemical incrustation, the biofouling creates a “thick” discontinuous irregular layer of slimes and biofilms along the wellbore, well screen, piping/equipment, bedrock fractures, gravel pack, and within the aquifer. These films consist of a combination of amorphous polymeric chains containing metal oxides of iron, manganese, aluminum, and other trace metals. These biofilms may also house or protect pathogenic bacteria, viruses, and protozoans.
1 | Decrease well yield and pump efficiency and ultimately pump failure.
2 | Sudden changes in water quality that adversely impact the taste, appearance, odor, and chemical composition of the water.
3 | Accelerated chemical and electrochemical corrosion that can result in increased metal content, aesthetic and taste problems, and failure of pumps and piping due to corrosion.
4 | Reduction in the strength of metal casings, well screens, and piping causing leaks and pipe failures.
Biofouling can influence the rate of chemical corrosion by producing organic/inorganic metabolites that can lower the pH, increase the concentration of hydrogen sulfide, and increase the ability of the fluid to carry a charge, enhancing corrosion by creating differential “aeration” cells. The formation of these cells provides the mechanism for electrochemical corrosion or microbiologically induced corrosion (MIC) to occur.
Two conditions are needed for electrochemical corrosion to occur. These conditions include a difference in the electrical potential of the metal surfaces and a fluid that connects the materials that have a capacity to carry a charge. Electrochemical corrosion is more commonly associated with galvanic corrosion associated with the use of dissimilar metals, such as the corrosion associated with the connection of a copper pipe to a cast iron pipe. At the connection between the copper and cast iron pipe, a galvanic or electrical cell is formed. The copper pipe acts like a cathode and the cast iron acts like the anode. The cathode area is identified by the buildup or gain of ions and the anode area or pitted area by the loss of ions.
Tuberculation is the most typical form of corrosion. Tuberculations are knob-like mounds of corrosion byproducts that are found scattered over the surface of a corroding material. Microbiologically Induced Corrosion (MIC) has been recognized to be responsible for 10 to 30% of pipe corrosion and a major cause of tuberculation.
With respect to the health effects associated with biofilms, these films are normally considered non-pathogenic (i.e., not disease causing). For individuals who are immunocompromised, these organisms may act as an “opportunistic pathogen”. In addition, these biofilms may accumulate trace metals (Fe, Mn, Al, Co, Ni, Cu, Zn, Cd, Sn) and provide a protected environment in which pathogenic organisms flourish. The slimy biofilms also provide a protective coating that limits the effectiveness of conventional disinfection practices.
If the odor associated with biofilms is stronger in the hot water, we recommend the following:
A | Turn off the hot-water system and drain it.
B | Allow the hot-water tank to refill, but raise the water temperature to a level above 140 °F.
C | Allow the tank to be set at this level for at least 6 hours.
D | Turn off the system and reduce the hot-water tank temperature to a normal operating temperature.
E | Drain the tank, allow the tank to refill, and turn the system back on.
First Step - Visual Inspection and Getting the Water Tested - It may be necessary to test for "Nuisance Bacteria and Standard Plate Count" or you can try a shock-chlorination of the well and a distribution system flush using Well Safe Sanitizer.
The KnowYourH2O Team has completed multiple evaluations and developed remediation systems for problems associated with sulfur, iron/manganese, slime-related bacteria, and other biofilm producers. Contact us for consultation on well rehabilitation related projects.
