What is ground water iron?
Ground water usage for all purposes is increasing. Domestic garden bores are now common place and more ground water is being accessed by municipal water providers than ever before. The issues of ground water chemistry and more particularly dissolved iron and its effects continues to create confusion for many users of groundwater. During irrigation dissolved iron can be instrumental in causing various problems, such as brown – red stains on contact buildings, paths, roadways and plants. Additionally, under certain circumstances dissolved iron can cause blockages on the inside of the distribution pipes and down in the bore hole itself.
Cascading bores that contain appreciable amounts of iron are most noted for iron problems within the bore. Bores of this type are where water enters the bore hole outside the normal water column, or more simply the water tumbles down from the top of the bore hole and is exposed to air during its decent. These types of bores emit a ‘water fall’ sound when filling soon after the bore pump is stopped. As well as cascading bore types, water levels that vary during pumping can also contribute to iron problems both in and out of the bore hole.
Other problems with dissolved iron may be caused by the construction of the bore hole itself and can relate to the way the water enters the bore from the aquifer during pumping. Now more commonly iron impacts on pumping and irrigation systems when the water chemistry is altered by groups of colony forming micro-organisms called iron and/or sulphate reducing bacteria. These bacteria can cause large amounts of insoluble iron to be produced in the bore hole, pump and distribution lines.
Dissolved iron does not exist in all water bores at levels that cause problems. Most ground water contain some iron, but it is usually to small an amount to cause a problem. Iron concentrations are measured in milligrams per litre (mg/l). For example an iron concentration of greater than 1mg/l will usually become apparent during use. Iron concentrations of 5 – 6mg/l will leave no uncertainty about the existence of iron within your bore water.
Iron in ground water continues to represent serious problem for many irrigation systems, in particular micro-irrigation. The problems of premature wear and fouling of distribution systems by iron is just the beginning of the problem. High concentrations of iron in irrigation water can lead to illthrift with plants that come in contact with this water. Illthrift is caused by the red/black material (iron) accumulating on plant leaves and reducing the plant’s ability to perform the functions of photosynthesis, transpiration, and respiration.
Determining how iron will affect your water system can require a laboratory analysis and a qualified evaluation of the results. In many situations where iron exists alone in the bore hole water, the answers are not simple and solutions may not be within the bore hole itself, but may need the removal of iron by aeration and settling in a tank or other means.
Where bacteria are proven to be part of the problem then remedial work on the bore hole can be completed and equipment installed to give long term control. If the bore hole water contains even moderate levels of iron in the presence of bacteria, then simply controlling the bacteria in many cases will not control iron staining.
Biostat engineering can provide answers and solutions for iron related problems. Our new analytical department, comprised of a full time microbiologist, chemist and technical staff, will provide you with sample testing results. The Biostat Engineering team based in all Australian states can then provide you with the equipment you need to solve your iron bacterial problems.
Could you explain the basic process of Iron Oxidation to me?
The formation of iron rust is thought to begin with the oxidation of iron to ferrous. This is the point at which iron enters the water and is described as a substance in solution. While iron remains in solution it rarely represents any serious problem.
2 e– (electrons)
When water containing iron contacts oxygen the reaction further oxidises soluble ferrous iron (+2) to form ferric (iron +3) ions.
1 e– (electrons)
The electrons provided from both oxidation steps are used to reduce oxygen in the following manner.
4 OH –
Insoluble iron (iron oxide) over time will usually settle from the water it is contained within. It normally appears as a brown sediment on or near the base of the container.
Iron reducing bacteria through the action of their metabolism can reduce iron from soluble to insoluble. The electrons that are liberated during this process is used by the iron reducing bacteria as a source of energy. The resultant chemistry is somewhat different to the normal iron oxygen process. Typically IRB are responsible for the biomass usually seen in pumping and distribution systems. The red/brown slime seen is chemically described as hydrated ferric hydroxide (FeOH3) .
With the addition of extracellular bipolymer or slime produced by the bacteria (which is already combined with the altered iron chemistry). Biofouling becomes a serious problem. Other than the obvious hazards this material represents to irrigation, attempts to remove the iron through aeration and precipitation are foiled or made more difficult as the added buoyancy created by the additional chemistry prevents the material from settling out of the water column.
Tell me more about Iron Reducing & Oxidising Bacteria...
Where do bacteria come from?
In many situations bacteria (Micro-organisms) are not native to the aquifers they are found within. These additional micro-organisms have in part entered the ground water bores through maintenance activities and other accidental ways through the top of the bore hole. It is now more common to find the bacteria already present in the aquifer before any excavation or drilling is done. In recent times we have found evidence that deep underground aquifers are not devoid of bacteria but harbour vast colonies of micro-organisms, even at great depths.
Bacteria in the ground water .
Bacteria have many ways of getting into the ground water. For example they can hitch a lift on water or mud going into the bore hole. Alternately we know from mining rocks that contained no microbes to begin with, were contaminated with a wide range of potential colonists when excavation of underground structures took place. With plenty of time and a pathway bacteria will migrate and set-up house in any aquifer. In fact so long as they have water, micro-organism will adapt to almost any environment on Earth. Bacteria have been found around volcanic vents at temperatures of up to 200oC. They were also found in the coolant off the Three Mile Island nuclear reactor, after narrowly escaping melt down in 1979.
Bacterial Iron Build-Up.
What causes bacterial iron build-up? The basic cause is the presence of the bacteria themselves, dissolved or complex iron, manganese or sulphur species and an environment suited to survival and growth of these bacteria. Other factors which may cause iron to be a greater problem than it might otherwise be include: inappropriate bore plumbing design or material choice, or construction and poor choice of water treatment. Flaws in construction may for example cause extra chemical oxidation or restriction in screens, pipes and valves. Periods of little or no use allows the fouling growth to build-up. Overuse can encourage sand or mineral clogging and extra oxidation. In either event, Iron bacteria exacerbates the problems.
How can I tell if Iron Bacteria has infected my bore hole?
Usually with the advent of winter, summer irrigation is generally winding down. This is a good time to evaluate any affects micro-organisms may have had on your Irrigation system in the form of biofouling during the pumping period. How does your system measure up against the following check list?
- Measure a timed amount of water through the flow meter. (How does it compare with the last figures?)
- Read the voltage/amp. meters. (compare it with the last reading.)
- Line shaft pumps, check packing gland for sediment build-up around the gland and bore head.
- Open inspection port at bore head. check for sediment inside pipe.
- Remove sprinklers, check for sediment build-up inside
- Remove a section of pipe work. Check for internal diameter reduction due to deposits.
- Send sample of sediment for analysis. No matter how small. It may be the start of a problem.
If during this process you discover reduced water flow or increased amp. loading, combined with any red/yellow sediment accumulation it is time to act. You may have an Iron Bacteria problem. Iron Problems are increased by bacteria in the groundwater Fouling by Iron and sulphur bacteria is likely to occur in ground water bores and plumbing where:
- An unusual number of problems associated with biological clogging and corrosion have occurred already in other bores in the area
- There are unsealed abandoned ground water bores in the area.
- Aquifers in contact with the surface, these are usually at risk from contamination.
- There are areas with carbonate or fractured crystalline rocks or highly productive sands and gravel.
- Shallow aquifers which contain high microbial populations.
- Confined aquifer rock contains gypsum or hydrocarbons which often have problems with bacterially produced sulphides (SRB) or slime-forming sulphide oxidizing bacteria (SOB).
How do I go about collecting samples for analysis?
Use this simple method to check for visible (insoluble) iron:
- After a period of idleness (>12 hours) start the bore hole pump and gather from a suitable point at the bore head a water sample. The water sample should be representative of that which has been in the bore hole for the full 12 hours. This means the sample should be collected within a few seconds of the pump start. In badly contaminated bores a slug of brown material is usually observed in the water column within the first few seconds. Ideally this material is collected for analysis and is particularly good for bacterial detection by microscope. Send this sample to the lab for testing. If no slug was observed miss (ii.) and go to (iii.)
- Allow the pump to run for a further >10 minutes and collect another sample at the same point. The new sample will be water that is new into the bore hole and can only have had contact with any microbes for the time it passed though the equipment etc. This sample is representative of the normal water flow/quality.
- To allow us to see the insoluble (visible) iron as it would pass into the irrigation or storage system a very fine micron filter (0.45 Um) is used to filter the insoluble iron from the water. It is useful to do this at the time of collection so that when the sample goes to the lab iron can be measured in both samples. The subtraction of the soluble from the insoluble (which ever is greater) Will give a good indication of the severity or type of problem that may exist. It may be necessary filter up to a litre or a least until the filter will not allow anymore water through.
- A filter membrane that is coated in brown material after a small amount of water has passed through is suggests a high level of insoluble iron and conversely a large flow indicates a lesser problem. However it is important to note that under normal circumstances there should be none or a very small amount detectable iron by this method. Calculate the amount iron deposited in the irrigation system by the difference in the types of iron.
- Should the water sample contain mostly insoluble iron then further oxidation would only have superficial benefits in expelling the remaining soluble iron. While high levels of soluble iron would benefit from additional aeration to assist with oxidation and precipitation. Iron bacteria cause the water chemistry to change and it is questionable whether air will be and advantage to enhance the quality of the water further. In fact further oxidation may add to the slime that simply floats atop the water storage.