Iron and manganese often are associated with hard groundwater and can create problems for homeowners with private wells. They are responsible for staining fixtures and laundry in shades of orange, red and brown. In extreme cases, the discoloration can ruin these items, which is why these contaminants are a main focus of well water treatment systems. Water softeners can be used to treat low concentrations of these minerals, but higher concentrations can damage cation exchange resin and require specialized treatment upstream of the water softener to prevent damage.
Treatment typically involves oxidation and filtration. The reduced states of iron and manganese are soluble, but the oxidized states are insoluble in water and can be mechanically filtered. Iron is easily oxidized, and exposure to oxygen in the air is sufficient for treatment, with some devices utilizing Venturi-type systems prior to filtration. Manganese is more stable and not as easily oxidized, so typically a strong oxidizer such as chlorine or potassium permanganate is injected to achieve oxidation prior to filtration when manganese is present. Ozone also is an effective oxidant for treatment of water contaminated with iron or manganese.
Test Methods
NSF/ANSI Standard 42 defines test protocols and criteria for verifying the effectiveness of iron and manganese treatment systems. It addresses all forms of treatment for iron and manganese, including oxidation and filtration technologies.
Although testing methodologies are available for both point-of-entry (POE) and point-of-use systems, most systems that treat iron and manganese are POE. Many NSF/ANSI drinking water treatment unit standards require testing two POE systems in parallel, but NSF/ANSI 42 only requires testing one system for iron or manganese reduction claims. This is because many iron and manganese systems have high treatment capacities, which can lead to high testing costs, and because the treatment devices address aesthetic claims only, not health effects.
The iron and manganese influent challenge concentrations and maximum treated water concentrations are shown in Table 1. The influent challenge concentrations are based on typical well water scenarios involving iron and manganese contamination.
The 9 to 11 mg/L iron challenge was added to the standard in 2017 to allow evaluation of systems intended for use with very high-iron source water. The maximum treated water concentrations are based on the U.S. EPA’s National Secondary Drinking Water Regulations, which are advisory only and provide guidelines for water systems to help control the aesthetic quality of drinking water.
POE systems are tested continuously at the manufacturer’s rated service flow for 16 hours per day. Prior to testing, the system is conditioned in accordance with the manufacturer’s instructions, and then operated for testing. Samples of the influent and treated water are collected after 10 unit volumes have been treated. Additional samples are collected in increments of 10% of the manufacturer’s recommended treatment capacity up to 100% of capacity, with a final pair of samples collected at 120% of manufacturer’s recommended treatment capacity.
For a treatment unit to be certified, 90% of the treated water samples, including the 100% capacity sample, must meet the requirements specified in Table 1.
Table 1. Iron and Manganese Concentrations
Additional Requirements
In addition to the test requirements for iron and manganese reduction, systems also must meet criteria for:
- Materials in contact with drinking water. Extraction testing is conducted on the system to ensure contaminants will not leach from the system into drinking water at concentrations of toxicological significance. Systems that incorporate adsorptive or absorptive treatment media are tested with and without the media.
- Structural integrity. Two tests for structural integrity, each on a separate test specimen, are conducted. One of the tests is 100,000 cycles from 0 to 150 psi, and the other is a 15-minute hydrostatic test at 300 psi or three times the system’s maximum pressure rating, whichever is higher. The hydrostatic test requires a pressure of 150 psi or 1.5 times the system’s maximum pressure rating if the diameter of the pressure vessel is greater than or equal to 8 in. • Pressure drop and rated service flow. POE systems must have a pressure drop of no more than 15 psi at the manufacturer’s rated service flow, which must be at least 4 gal per minute.
- Product literature. Systems must have a data plate, performance data sheet, installation and operation instructions, and, if applicable, replacement element packaging that meets the requirements of Section 8 of NSF/ANSI 42. This helps consumers and end users understand product specifications, capabilities and service-related requirements to assure proper and effective operation.
Consumer Confidence
Certification to all voluntary NSF/ANSI drinking water treatment unit standards, including NSF/ANSI 42, helps instill consumer confidence that the product performs as advertised, does not leak when installed properly and is clearly understood by the end user.
Iron and manganese well water contaminations can be extremely aggravating to consumers dealing with staining problems and ruined laundry. These well owners are willing to bring in professionals to identify the source of the problem and recommend treatment equipment. Because of the technical nuances and cost of the recommended solution, confidence in the product can be a major factor in the purchasing decision. A third-party certification to NSF/ANSI 42 can be the key to instilling the confidence to help consumers move towards purchasing a system and solving their problem.
