Benchtop COD Analyzer with Digestion Reactor

What is the Benchtop COD Analyzer with Digestion Reactor?

A benchtop COD analyzer combines a heated digestion reactor for sealed tubes with a colorimeter that reads the dichromate colour change. It is the standard laboratory configuration for wastewater and discharge testing.

Overview

Samples are pipetted into sealed reagent tubes containing dichromate, catalyst and mercuric sulfate, then heated in a reactor at 150 °C for two hours. After cooling, the tubes are placed in the colorimeter, which measures absorbance at two wavelengths depending on the range, and the instrument calculates COD in mg/L from a stored calibration. Ranges normally span 0 to 150 mg/L, 0 to 1500 mg/L and 0 to 15,000 mg/L, with the sample volume set by the range. Digestions can be run in batches of 12 to 25 tubes, and reactors hold a stable temperature to within 1 °C, since oxidation completeness depends on it. Some systems read the tubes directly without transfer, reducing handling and contamination.

How does it work?

Chemical oxygen demand is determined by oxidising the sample with potassium dichromate in strong sulfuric acid at about 150 °C for two hours, usually in sealed tubes. Silver sulfate catalyses the oxidation of most organic compounds, and mercury sulfate masks chloride, which would otherwise be oxidised and inflate the result. The dichromate consumed is proportional to the oxidisable material and is measured either photometrically, from the colour change of dichromate to chromium(III) at 600 nm or by the decrease in dichromate absorbance at 440 nm, or by titration of the remaining dichromate with ferrous ammonium sulfate. Results are reported as milligrams of oxygen per litre. COD is faster than BOD and includes material that is not biodegradable, which is why it is used for discharge compliance and process control.

What are the key features?

• Digestion reactor with stable 150 °C control
• Two-wavelength colorimetric reading of sealed tubes
• Three standard ranges covering 0–15,000 mg/L
• Batch capacity of 12–25 tubes
• Stored calibration and direct COD calculation
• Data logging and result export

What are the technical specifications?

A typical benchtop cod analyzer with digestion reactor configuration offers digestion temperature of 150 °C, ±1 °C, digestion time of 120 min, reactor capacity of 12–25 tubes, measurement ranges of 0–150, 0–1500, 0–15,000 mg/L, wavelengths of 440 nm and 600 nm and photometric accuracy of ±2 percent of reading. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Benchtop COD Analyzer with Digestion Reactor is used in municipal wastewater influent and effluent testing, industrial discharge compliance analysis, treatment plant performance evaluation and contract laboratory wastewater testing. Across the wider COD Analyzers class, laboratories also deploy it for wastewater treatment influent and effluent monitoring, industrial discharge compliance testing and municipal plant process control.

Which standards and certifications apply?

Relevant standards and methods include ISO 6060, ISO 15705, EPA 410.4, Standard Methods 5220 D and ISO/IEC 17025. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

COD chemistry is hazardous: dichromate is a carcinogen and strong oxidant, sulfuric acid is corrosive, and mercury salts are toxic, so digestion must be performed in sealed tubes or closed reflux systems with fume control and separate waste collection for heavy-metal-bearing residues. Chloride interferes seriously and is masked with mercury sulfate, so the expected chloride concentration must be known and the masking ratio respected; high-chloride samples may need dilution or a low-range method. Quality control requires blanks, standards, spiked samples and duplicates in each batch, and the dichromate solution should be standardised. Sealed tubes should be mixed thoroughly before reading, and the reading should be taken after the tubes cool to avoid temperature bias.

How do I select the right Benchtop COD Analyzer with Digestion Reactor?

Select a benchtop system when routine COD testing is needed at standard ranges with good throughput and traceability. Confirm that the reactor temperature control meets the method, that the ranges match your expected values, and that an appropriate waste collection plan exists for dichromate and mercury residues.

How does it compare with other COD Analyzers variants?

Choose the measurement format from where the sample is taken and how the result will be used. Sealed-tube colorimetric systems with a digestion reactor are the standard for laboratories, offering ranges from 0 to 15,000 mg/L with small sample and reagent volumes. Portable colorimeters bring the same chemistry to the plant or river bank for rapid screening. Titrimetric analysis is used for high-concentration or coloured and turbid samples, where photometry is unreliable, and remains the classic reference for difficult matrices. Automated analysers with autosamplers reduce reagent handling and improve traceability where sample numbers are high. Online UV analysers provide continuous trend data for treatment control but must be correlated with the dichromate method, since UV absorbance responds to aromatic compounds rather than total oxidisable matter.