By Rick Andrew
The presence of iron and/or manganese in groundwater can be a considerable problematic for homeowners with private wells. Iron and manganese can cause significant aesthetic issues for these homeowners, primarily orange-, red- or brownstained fixtures and possibly laundry. In extreme cases, the damage to fixtures and laundry can amount to essentially ruining them, making effective treatment essential. While water softeners can be used to treat low concentrations of these minerals, higher concentrations can cause damage to cation exchange resin. These situations require specialized treatment upstream of the water softener to prevent damage to the softener and provide a solution to the consumer. This treatment typically involves oxidation and filtration. The reduced states of both iron (Fe+2) and manganese (Mn+2) are soluble, whereas the oxidized states (Fe+3 and Mn+4) are insoluble in water and can be mechanically filtered. So, it is beneficial to first oxidize and then easily mechanically filter. Fe+2 is quite easily oxidized. Exposure to the oxygen in air can be sufficient for treatment purposes. Some iron treatment systems utilize air oxidation via Venturitype systems prior to filtration. Mn+2 is more stable and is not as easily oxidized, so typically chlorine or potassium permanganate, which are strong oxidizers, are injected to achieve oxidation prior to filtration when manganese is present. Ozone would also be an effective oxidant for treatment of water contaminated with iron and/or manganese. NSF/ANSI 42 Drinking Water Treatment Units–Aesthetic Effects includes test protocols and criteria for verifying the effectiveness of iron and manganese treatment systems. These protocols address all forms of treatment for iron and manganese, including the typical oxidation and filtration technologies, and any others that might be used.
Test methods for POE systems
Although testing methodologies are available for both POE and POU systems, the vast majority of systems being used for treatment of iron and manganese are POE, because the main issues with iron and manganese contamination in water are related to staining of fixtures and laundry. The standard requires that only one POE system must be tested for iron or manganese reduction claims, unlike many of the test methods in the NSF/ANSI Drinking Water Treatment Units standards that require testing of two systems in parallel. The reason behind the requirement of testing one system only is that these POE systems may have high treatment capacities, which can lead to high testing costs. The requirement to test only one system helps control testing costs and can be justified because these are aesthetic claims only and not related to health effects.
Iron and manganese influent challenge concentrations, along with the required maximum treated water concentrations, are indicated in Figure 1. Influent challenge concentrations are based on typical ‘problem well water’ scenarios involving iron and manganese contamination. The maximum treated water concentrations are based on US EPA’s National Secondary Drinking Water Regulations (NSDWRs) these regulations are advisory only.
They provide guidelines for water systems to help control the aesthetic quality of their drinking water. Additional information about NSDWRs can be found on US EPA’s website: http://water.epa.gov/drink/contaminants/secondarystandards.cfm.
Other certification requirements
In addition to conforming to the test requirements for iron and/or manganese reduction, these systems must meet additional criteria as specified in NSF/ANSI 42:
Materials in contact with drinking water. Extraction testing must be conducted on the system to assure that contaminants will not leach from the system into drinking water at concentrations of toxicological significance. Systems that incorporate adsorptive or absorptive treatment media must be tested with and without the media.
Structural integrity. Two tests for structural integrity must be conducted, each on a separate test specimen. One of the tests is 100,000 cycles from zero 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 eight inches (20.32 cm).
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 four gpm (15.14 L/m).
Product literature. Systems must have a data plate, performance data sheet, installation and operation instructions and, if applicable, replacement element packaging that meet the requirements of Section 8. The purpose of this information is to help consumers and end users understand product specifications, capabilities and service-related requirements to assure proper and effective operation. Specific informational requirements for these pieces of literature are spelled out in the standard.
Iron and manganese contamination of well water can be extremely aggravating to consumers dealing with staining problems and possibly ruined laundry. These well owners are willing to bring in professionals to help them identify the source of the problem and recommend and specify treatment equipment. They may ultimately spend thousands of dollars to treat their water. Because of the aggravating nature of the problem, the technical nuances of the recommended solution and the cost, confidence can be a major consideration. The purpose of the NSF/ ANSI Drinking Water Treatment Units standards, including NSF/ANSI 42, is to help instill confidence that the product is safe, will not leak when installed properly, is clearly understood by the end user and perhaps most importantly, that it performs as advertised. Having a third-party certification to NSF/ANSI 42 can be the key to instilling the confidence to help consumers move forward toward purchasing a system and solving their problem.
About the author