Iron: A Nuisance Contaminant
Many water treatment professionals turn to chemicals in order to remove or suspend ferrous iron in their method of water treatment. Clear water iron must be transformed into a filterable ferric iron in order to remove this nuisance contaminant, or it must be suspended with chemicals to keep it from staining.
Softeners can be used and ion exchange will work for low levels of iron, but there are applications where ion exchange is not possible or practical. Let’s take a look at a filter media that works very well at removing iron without chemicals or regeneration.
Filter Media
Basic iron removal media (BIRM) is effective in removing low levels of iron. There are some parameters and specifications that must be met in order for this very dense oxygen catalyst to work properly and successfully.
- The iron levels should not exceed 10 parts per million (ppm);
- The dissolved oxygen has to be 15% of iron present;
- The flow rates have to be matched with no more than 3.5 to 5 gal per minute per sq ft (gpm/sq ft); and
- A good water pressure must be used to lift and backwash this dense media.
There are some other specifica- tions that have to be met in order to achieve optimum results and successful iron removal.
The proper testing of the water cannot be stressed enough when employing this type of media for water treatment because there are other contaminants that can cause failure or premature reduction of this media’s activity. Chlorine and ozone are not very compatible, oil and hydrogen sulfide hinder performance, and polyphosphates can coat the outside of the BIRM, thus reducing the catalyst capabilities. Matching the correct media and proper flow rate with each application in water treatment determines the success of the water treatment professional. Understanding what contaminants need to be removed in order to achieve the best effluent water is the most important thing to remember when designing a system.
BIRM is very low maintenance. It requires backwashing only. No chemicals are needed for regeneration and if backwashed often and properly, the life of the BIRM is exceptional. We applied this media to an irrigation system that also was used as a pre-filter for a softener. The softener worked very well and the system also removed the iron and prevented staining in the irrigation process. This same system was used to fill a small pond, swimming pool and hot tub, but after about five years the media became fouled and was replaced. The oxygen levels were low and the tannin levels of the influent water was very high, so in theory the expected life of the media exceeded the expectations of the system designers. The filter was overrun many times and after constant bleed-through, it was determined that the time had come to re-bed the filter.
Mixing Media
With the performance of BIRM, the system designers also mixed in some Filox-R in the re-bed mixture. This media is a higher concentration of manganese dioxide than BIRM, but also increases cost. There was a tradeoff because less BIRM was used, and, with using the Filox-R, the designers hoped for a longer run and better filtration performance. The specifications for the Filox-R are much different, however, from the BIRM; therefore, the manufacturer should be contacted before implementing any application. Again, proper water testing cannot be stressed enough when designing a system that will deliver desirable results.
The iron filter that was used consisted of a 21-by-69-in. vessel and the distributor had laterals to help in backwashing the media thoroughly. The control head used was a Fleck 2850 flat cap, time clock, backwash valve. The unit used 6 cu ft of BIRM, but we found with use that 9 gpm was the best flow rate with no bleed-through. According to specifications, the unit should have been good for a higher flow rate, but that was not feasible or practical. The shortfalls of the filter were explained in detail to the customer before installation, so any failure to reach desired results did not present any dissatisfaction.
The irrigation system was designed to keep each zone at a lower flow rate and more zones were implemented. It was very crucial that the flow levels were not exceeded and also that the amount of water on each run was not overextended. Constant overruns and high flow rates will cause premature fouling of the filter because of iron buildup and not backwashing contaminants thoroughly from the unit. The whole system worked remarkably well for many years. In the long run, the unit was cost-effective and provided iron-free water. The treated water was brown when coming out of the faucet and exceeded the specifications set forth by the manufacturer. The iron level was 3.5 ppm, tannins were high, manganese was 0.5 ppm, hardness was 22 grains and there were high sulfates. We had to chlorinate the water at least once per year to help control iron bacteria.
Effective Application
A good water treatment professional can be successful if he or she tests the influent water properly and applies the effluent water correctly. Water treatment professionals must also explain the system sufficiently to the user so that if there is dissatisfaction, the user does not feel cheated or ripped off. Sometimes a trial and error method needs to be used to test a system design. But if there is enough time for understanding the application and doing the math, a water treatment system can be implemented without problems, and customers are very pleased with performance.
Always refer to the manufacturer’s specifications and supplier’s engineers for help in the design process. This is just one method of dealing with iron removal and not a cure-all. It is environmentally friendly so you can think green while removing the brown.
Author’s note: Manufacturer’s specifications can be found at www.clackcorp.com for BIRM and www.watts.com for Filox-R.
Jeff Roseman, CWS-VI, is a consultant and freelance writer in the water industry. Roseman is a member of the WQP Editorial Advisory Board.
Source: Water Quality Products February 2010