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COD analysers: how can the organic load of water be quantified?

Measuring the COD means quantifying the oxidisable organic matter in water – a decisive indicator for treatment control, regulatory compliance and process optimisation. From photometers with sealed-cuvette reagents to online process analysers, today’s instruments deliver rapid, traceable and reproducible results. Compliant with ISO 15705 (sealed cuvettes) and ISO 6060 (reflux), they secure your decision-making, from the QC lab to the wastewater treatment plant. Bottom line: accuracy, management of chlorides, automated digestion, connectivity and reduced hazardous waste.

What are the different types of COD analysers?

Three approaches dominate. In the lab, cuvette COD tests run in a thermoreactor oxidise the sample with dichromate in sulphuric acid, then a photometer reads the absorbance: a rapid, ISO 15705-compliant method, ideal for batch work. The more comprehensive closed reflux method (ISO 6060) combines digestion and determination (photometric or titrimetric) for challenging matrices.

TypePrincipleApplications
COD cuvette testsDichromate oxidation + optical readoutRoutine checks, QC laboratories
Online analyserAutomated digestion + measurementWastewater treatment plants, industrial processes
UV254 probeAbsorbance correlated to CODReal-time monitoring, deviation alerts


Key criteria: measurement range and LOD, tolerance to chlorides (masking with HgSO4), analysis time, maintenance (cleaning, reagents), safety (reduction of Cr(VI)), connectivity (LIMS, MQTT/Modbus) and total cost of ownership.

In which fields is a COD analyser used?

Everywhere organic load needs monitoring. In water treatment (municipal and industrial), COD (Chemical Oxygen Demand) guides the sizing and control of treatment trains, from pre-treatment through to compliant discharge. In food & beverage (dairies, breweries, abattoirs), it tracks the variable loads linked to production campaigns. In chemicals, cosmetics, pharma/biotech, it checks cleaning effluents (CIP) and pilot batches. In environmental monitoring, it documents the quality of surface waters and wastewater. Quality control and process R&D laboratories rely on reproducible measurements to compare formulations, adsorbents, coagulants and removal efficiencies.

The different types of COD analysers available

Frequently asked questions about COD analysers

Which method should I choose: cuvette tests or an online analyser?
Cuvette tests (ISO 15705) suit batch checks. An online process analyser automates and monitors continuously. Use both together for calibration and ongoing monitoring.

Do chlorides interfere with COD measurement?
Yes, they are oxidisable. Use a masking agent (e.g. mercuric sulfate) and check the chloride tolerance range stated by the manufacturer for your matrices.

What is the difference between COD, BOD and TOC?
COD quantifies the chemically oxidisable load, BOD the biologically oxidisable fraction, TOC the organic carbon. These are complementary indicators, not one-to-one substitutes.

Typical analysis time?
With cuvette tests, digestion typically takes about 2 h, then you can read immediately.

How can I reduce the environmental impact of COD reagents?
Favour low-dose kits, route Cr(VI)-bearing waste via a dedicated stream, and use UV254 probes for reagent-free early warning.

Which maintenance points have priority?
Check pumps and peristaltic tubing, clean lines, verify digestion temperatures, calibrate photometry, and replace reagents before expiry.

Should a process analyser be calibrated?
Yes. Validate with traceable standards and adjust the UV254?COD correlation against reference analyses (cuvette tests or reflux) for your matrices.