What is Permanganate Index?
The permanganate index is a water quality parameter used to assess the amount of oxidizable material present in water. It is commonly applied to freshwater sources and treated drinking water. It provides a measure of the oxygen demand associated with oxidizable compounds present in the water under defined test conditions, serving as an indicator of overall water quality and treatment performance.
The standardized method is outlined in ISO 8467:1993, Water quality: Determination of permanganate index. During analysis, a water sample is heated in a boiling water bath for 10 minutes with a known amount of potassium permanganate and sulfuric acid. Oxidizable substances in the sample consume a portion of the potassium permanganate. The remaining permanganate is then determined through the addition of oxalate followed by titration with permanganate.
ISO 8467 applies to waters with chloride concentrations below 300 mg/L. Samples with a permanganate index greater than 10 mg/L should be diluted before analysis, and the lower end of the optimum measurement range is 0.5 mg/L.
Why is the Permanganate Index Measured?
Measuring oxidizability can help water treatment operators understand the presence of oxidizable organic matter in source and treated drinking water. This is relevant when monitoring natural organic matter (NOM), which can influence treatment performance and drinking water quality.
Although NOM itself is not associated with direct health effects, Health Canada notes that it can interfere with drinking water treatment, increase disinfectant demand, contribute to the formation of disinfection by-products (DBPs), encourage biofilm development, and affect corrosion control. For this reason, knowing both the amount and characteristics of NOM can help utilities optimize treatment processes.
The current EU Drinking Water Directive (Directive (EU) 2020/2184) includes oxidizability as an indicator parameter with a parametric value of 5.0 mg/L O₂. The directive also states that the oxidizability does not need to be measured when total organic carbon (TOC) is analyzed. Health Canada’s guidance on NOM similarly identifies COD as an indicator of oxidizable organic matter and suggests a treated-water target of less than 5mg/L O₂.
Methods for Measuring Permanganate Index and Oxidizability
Automated Permanganate Index Analysis
Traditional permanganate index testing involves several manual steps, including reagent addition, heating and titration. To simplify this process, MANTECH offers automated permanganate index solutions to conform to ISO 8467.
MANTECH’s MT30 analyzer can automate critical portions of the analytical process, including sample handling, pipetting, titration, rinsing, and analysis. The MT30 also protects analysts from handling hot samples and hazardous potassium permanganate. Automated systems can accommodate multiple samples and use MANTECH Pro software to control and monitor the analysis. By performing batch analysis, the system saves time by leveraging the 10-minute wait period between samples, rather than requiring each analysis to be completed one by one.
Automating the method can reduce repetitive manual tasks while providing laboratories with a standardized approach to permanganate index analysis. Watch the automated PI here: https://www.youtube.com/watch?v=D-THu6ds1RE
PeCOD for Rapid Oxidizability Measurement
In addition to permanganate index testing, photoelectrochemical oxygen demand (PeCOD) offers another approach for evaluating oxidizable material in source and treated drinking water. PeCOD also acts as a faster and safer tool to use compared to PI.
PeCOD uses a UV-activated TiO₂ photocatalyst to oxidize organic material in the sample and measure oxygen demand. The method is standardized under ASTM D8084 for freshwater sources used by drinking water treatment plants and treated drinking water. Unlike conventional COD and PI methods, it does not require hazardous reagents such as potassium permanganate, dichromate, mercuric sulfate, or silver sulfate.
Health Canada’s Guidance on Natural Organic Matter in Drinking Water identifies COD as an indicator of oxidizable organic matter and references PeCOD as an approach for measuring COD.
With analysis taking less than five minutes, MANTECH’s PeCOD is available in benchtop, automated, and online configurations, providing operators with rapid results for source-water monitoring, treatment optimization, and process decision-making.