Iron, manganese and hydrogen sulfide (“the trio”) are the three most common water problems in private well systems. These contaminants, picked up by water as it flows through the ground into aquifers, will cause many different problems in home plumbing systems. As little as 0.3 mg/l of iron can cause orange or reddish/brown staining, a musty odor and metallic taste. Not all iron is the same, however. Iron comes in a number of different forms, including ferrous, ferric and bacterial.
Ferrous iron, or clear water iron, is not immediately visible when drawn. Once exposed to an oxidant such as air or chlorine, the iron oxidizes into visible particles. Ferrous iron is the most common form found in well systems.
Ferric iron, or red water iron, is oxidized iron that is visible to the eye when drawn and settles when left standing. It is less common than ferrous iron.
Bacterial iron is formed when ferrous iron is consumed by harmless bacteria that then carries the iron throughout the plumbing system, coating pipes and water using appliances with a slimy orange or brown coating that can plug up pipes to a point where water will hardly flow through them. This form of iron is most commonly noticed as a slimy orange or brown growth in toilet tanks.
Manganese is another dissolved metal that exists in some ground water systems. Although not as common as iron, it can cause staining with as little as 0.05 mg/l, and causes more of a dark brown to black stain in water using appliances. Manganese will impart a metallic taste and a musty odor. Canada recently imposed a MAC (maximum allowable concentration, also known as: MCL, or maximum contaminant level) for manganese and lowered the aesthetic objective, which is similar to the secondary MCL.
Hydrogen sulfide, or H₂S, exists in ground water as a dissolved gas and causes a very distinctive “rotten egg” odor in the water. H₂S can cause this smell with as little as 0.1 mg/l concentration. It can also be corrosive to metals, tarnish silver very easily and cause the water to turn black in severe cases, resulting black staining. Testing for H₂S is different than most other contaminants. You must test for it on-site because it oxidizes rapidly. Taking your sample to a laboratory is ample time for H₂S to oxidize in the water.
If the water containing H₂S has a rotten egg smell, determine if it is in both the cold and hot water or only present in the hot water. If it is present in the cold water, then it is coming from the well system and must be treated when the water enters the home. If it is only detectable in the hot water, then the H₂S problem is likely being created in the water heater itself.
Most water heaters come with a sacrificial anode rod. This rod, usually made of magnesium, is designed to prolong the life of the water heater by preventing corrosion. However, in some water supplies H₂S gas is created as the anode rod corrodes. If this is the case, most water heater manufacturers offer other types of anode rods made from zinc or aluminum.
Changing the rod to one of these other metals can stop the creation of H₂S. In other cases, a sulfate-reducing bacteria can get into the water heater and create H₂S. The only way to eliminate these bacteria is to shock the water heater with chlorine or bleach and flush it out.
In the case of boilers, H₂S can also be a problem. Boilers operating above 1,000 psi (generally reserved for power regeneration) can also have H₂S be generated within the boiler.
All of these troublesome contaminants will show up as stains in toilet bowls, laundry, showers and sinks, corrode faucets and washing machines to a point where they leak or no longer work properly. This troublesome trio will also build up in water heaters and cause the hot water to become rusty or black in severe cases.
In most cases, a water softener will be required after an iron filter to soften the water from excessive hardness minerals normally present in well water. If the water is coming from a well that is not biologically safe, then ultraviolet (UV) filtration will be required, and perhaps chlorination for residual protection downstream. A UV system will require that “the trio” and hardness are removed from the water before reaching the system. This gives the UV light an unobstructed view of the water it is disinfecting. Chlorine, when used for residual disinfection, can also be consumed by this trio, meaning that your disinfection isn’t as effective as it should be, potentially leading to problems.
In terms of available treatment technologies, they are varied and rely tremendously on the water quality. H₂S needs to be oxidized before filtration. Depending on your choice of oxidant and the water quality, you may end up creating sulfate compounds which may complicate down stream processes.
Filtering iron and manganese will also depend on your water. You may have dissolved minerals, particulate compounds, or you may want to treat the dissolved minerals by converting them into particulate compounds. Dissolved iron and manganese can be handled by a water softener, however special care must be taken with designing the system and extra maintenance costs and maintenance frequency must be considered. Particulate iron or manganese can be filtered out quite easily. Generally, a 5-micron filtration system is sufficient to remove them. These filtration systems can either be cartridge style filters or back washable media filters, depending on your application requirements.
Converting dissolved contaminants to particulate is a little more complicated as there are many things to consider. Does the pH of the water lend itself to easy oxidation of iron or manganese? Generally, iron requires a pH of 7 or greater, and manganese requires a pH of 8 or greater in order to be converted easily to the particulate form. If you do want to oxidize, what oxidant would you like to use? Typically, chlorine (normally in the form of sodium hypochlorite), potassium permanganate, ozone, hydrogen peroxide and oxygen can all be used. When people ask to avoid the use of “chemicals” they generally mean they want some type of air/oxygen-based oxidation system. While these are attractive and effective in residential applications, they come with their own challenges that usually restrict their use in commercial applications.
Biofilters are also becoming increasingly popular as a “chemical” free option. However, their use is limited to municipal water treatment plants as the knowledge required to run them is highly specialized.
Typically, people stick to sodium hypochlorite or potassium permanganate as their reactions are well known and easy to design. Hydrogen peroxide and ozone are also popular because their reactions to filtration are also becoming well understood. Understanding the composition of the water you’re working with as well as the expected reactions and limitations of each option is important before choosing a system.
For example, hydrogen peroxide is very effective at iron oxidation, because iron gets involved in the primary decomposition of hydrogen peroxide.
However, hydrogen peroxide isn’t nearly as effective on manganese because it doesn’t get involved in that reaction, and relies on the extra oxygen that the hydrogen peroxides provides once it decomposes.
Water is critical to any building infrastructure and, as you can see, understanding each of these contaminants and how to best treat it can be complicated. When encountering any of these contaminants, it’s always best to get the advice of the people who know it best. Water treatment professionals work in this space everyday and can provide invaluable advice that can save future headaches for your project and client. Removing the contaminants as the earliest possible point, will save your building’s plumbing system from unnecessary operational issues in the future.