Iron-Related Bacteria & Biofouling in Water Bores

Iron-related bacteria activity in a bore influences the pattern and amount of biofouling. Research has shown that there is a decrease in the bacterial population with depth. There can also be significant differences in water quality bacteriologically with time in an aquifer. The changes in bacterial populations reflect changes in the hydrochemistry eg. Dissolved oxygen, iron and nutrients. Find out how our product Clearbore can help to keep your bore water running clean.

Gallionella, Sphaeotilus, Leptothrix and Siderocapsa spp. will form a biofilm by precipitating iron and manganese. Thiobacillus sp. is a sulphur-reducing bacterium, which can cause a ‘rotten egg’ smell in the water. There are also various forms of fermentative and fungi matter which can form into organic acids.

IRON-RELATED BACTERIA (continued)

occur naturally in groundwater and are increasing rapidly throughout the world

The interaction of dissolved iron and iron-related bacteria forms a solid, resulting in an encrustation. With age, bores and wells can develop a build-up of encrustation and a biofilm that causes a decrease in the bore yield and water quality.

Bacteria that live underground, feed on iron-rich water and create an orange/rust-coloured slime, this is iron bacteria. Ground water is low in oxygen, and this limits the growth of bacteria underground, however when groundwater rises into the bore column, the oxygen introduced from the environment and by pumping the water can act like a “fertiliser” for the bacteria and it can grow quickly (oxidisation) leaving a rust-coloured slime and ultimately encrustation on the bore screens, column and pumping infrastructure.

All bacteria produce an exopolymer product known as a polysaccharide. These are long-chain polymers used by the bacteria to provide adhesion to surfaces, as a means of entrapping nutrients, and as a method of protection. Free-swimming bacteria have a biological need to attach themselves to a surface to grow and reproduce. As soon as they land on the surface, they begin to produce the polysaccharide material to attach themselves. Later as the cells divide more exopolymer is produced until many cells live in the formation covered with this protective layer. The formation made up of the slimy polysaccharide and living bacteria is known as biofilm. This is normal habitat for bacteria and is present wherever there is water and a surface to attach to. Biological encrustations or biofilms are the primary reason for most blockages as a result of bacterial growth. This sticky, slimy surface is an ideal place for particulates to attach and multiply.

Biofilms respond to conditions in the bore. Increases in oxygen content from aeration due to cascading water often result in excessive growth of certain bacterial populations. Food sources coming into the bore flow may encourage growth and increase biofilms thus blocking more flow pathways. Velocity increases due to higher pumping rates often result in thicker biofilm as the bacteria produce more exopolymer in an attempt to protect themselves from being pulled into the flow. Each bacterium is capable of producing at least 30 to 100 times its own weight in exopolymer. Flow pathways are then blocked by the growth of this biofilm.

The exponential growth rates of bacteria cause rapid changes in the bore environment. Odour and colour problems can appear overnight and often a good-yielding bore loses capacity rapidly as a direct result of the growth of bacteria. In less than three hours, the bacteria will multiply 1,000 times. The average growth rate of bacteria varies considerably, however, the average is between 20 minutes and three hours. If all factors were perfect such as food and by-product removal, and 50 percent of the flow pathways were already plugged, it would only take one generation to fill the remaining pathways. While we will not see 20-minute transition periods, we often see bores that deteriorate over a few weeks explained by the fact that doubling the bio growth quickly produces excessive populations. This excess population often results in taste and odour problems or a measurable slowdown in bore production due to pore space and pump blockage.

Since most bores are more than capable of sustaining production with only 50 percent of the flow pathways open, the capacity being pumped is not limited until the blockage begins to close off the remaining 50 percent. It may take many years for the first 50 percent to become plugged, but the remaining 50 percent or a major part of it can become closed in considerably less time.

While most groundwater contains a certain concentration of dissolved iron, iron-related bacteria does not affect all bores. When iron bacteria infect a bore with iron in the groundwater, their interaction results in bacterial growth that may either be suspended in the bore water, or cause encrustation on the bore casing, screens, pumping equipment, or in extreme cases in the gravel pack around the bore. This is termed “biofouling”.   The occurrence of biofouling in groundwater systems will result in:

• Decreased flow through the screen, pump and pipelines causing increased pumping costs and unnecessary load on pumps

• Plugging of the voids in the gravel pack surrounding the bore, leading to a decreased yield

• Increased resistance to heat flow across the submersible pump motor causing operating problems such as overheating and potential burn-out

• Possible metal corrosion – the bacteria are thought to secrete an acidic by-product substance

• Decreased water quality (taste, colour, odour) due to a biofilm build-up as well as undesirable staining, usually red, brown or rust coloured

• Plugging of drip irrigation systems due to the small nozzle orifice.

One or more of the following symptoms can indicate the presence of iron-related bacteria in a bore:

• Reduction in the capacity of the bore
• Deterioration of water quality – colour, odour, taste and staining
• Increase in power consumption
• Motor burn-out in the submersible pump
• Encrustation on the pump, column, bore casing, screens and reticulation system.

Iron bacteria is not dangerous and poses no health risk to humans, wildlife or the community. In surface water, it can be very slippery so care should be taken when walking in and around bodies of water that contain iron bacteria. Iron bacteria in the surface water is aesthetically unappealing and often mistaken for an oil spill. Iron Bacteria is naturally occurring and is difficult to both prevent and remediate.

In still or stagnant water, the bacteria can create a film on the surface of the water that has a rainbow sheen, that is almost identical to oil. The easiest way to tell the difference between them is by using a stick to break the surface sheen. Iron bacteria will crack and separate whereas oil will clump and stick.