Online UV COD Analyzer

What is the Online UV COD Analyzer?

An online UV COD analyzer estimates organic load continuously from ultraviolet absorbance at 254 nm and correlates the signal with dichromate COD. It provides real-time trend data for wastewater treatment control and alarm functions.

Overview

Many organic compounds, particularly those with aromatic rings and conjugated double bonds, absorb ultraviolet light at 254 nm, and turbidity is measured at a second wavelength to compensate for suspended solids. The instrument records absorbance continuously in a flow-through cell or with an immersion probe and converts it into an estimated COD using a site-specific correlation established against laboratory dichromate results. Multi-wavelength or spectral versions use several wavelengths and chemometric models to improve accuracy across different effluent types. Because the UV response depends on the composition of the organic matter, the correlation must be re-established when the process or raw materials change. Applications include influent load monitoring, aeration control, spill detection and discharge alarm systems.

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?

• Continuous absorbance measurement at 254 nm
• Second wavelength for turbidity compensation
• Site-specific correlation with dichromate COD
• Multi-wavelength or spectral models for mixed effluents
• Alarm outputs for load and spill detection
• Automatic cleaning of the optical path

What are the technical specifications?

A typical online uv cod analyzer configuration offers measurement principle of UV absorbance at 254 nm with turbidity compensation, wavelengths of 254 nm plus reference, or spectral range, range of 0–1000 mg/L COD equivalent, resolution of 0.1 mg/L, measurement interval of 5–60 s and path length of 2–10 mm, model specific. 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 Online UV COD Analyzer is used in influent organic load monitoring and aeration control, discharge alarm and spill detection, industrial effluent trend monitoring and treatment plant energy optimisation. 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 Online UV COD Analyzer?

Choose an online UV analyzer when continuous trend data are needed for control or alarms and the effluent composition is reasonably stable. Confirm that a correlation with dichromate COD can be established and maintained, and plan regular cleaning and verification against grab samples.

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.