Online Respirometric BOD Analyzer

What is the Online Respirometric BOD Analyzer?

An online respirometric BOD analyzer measures oxygen uptake continuously in a small reactor fed with a sample stream. It provides trend data for wastewater treatment control and early warning of organic load changes.

Overview

The analyzer draws a small, defined volume of sample into a reactor containing a stable microbial population or fixed biomass, aerates it, and measures the oxygen consumed by respirometry over a short cycle, typically 5 to 30 minutes. The result approximates the short-term oxygen demand, and the instrument reports a value correlated with BOD5 through a site-specific relationship. Because the biomass is retained and acclimatised, results are more reproducible than with a fresh seed each time, but the reactor must be protected from toxic shock loads and periodic calibration against the laboratory method is required. Analysers suit aeration control, load-based dosing and spill detection, and they need automatic cleaning and stable sample conditioning to avoid fouling.

How does it work?

BOD is determined by allowing microorganisms to oxidise biodegradable matter under controlled conditions and measuring the oxygen they consume. In the dilution method, sample is diluted with seeded, oxygen-saturated water, filled into bottles and incubated at 20 °C, and dissolved oxygen is measured before and after five days; the difference, corrected for the seed blank and dilution factor, gives BOD5. In respirometric systems, the sample is incubated in a sealed bottle with a carbon dioxide absorber, and the pressure drop caused by oxygen consumption is measured and converted continuously into oxygen uptake. Combining manometric BOD measurement with nitrification inhibition focuses the result on carbonaceous demand. Results are reported in milligrams of oxygen per litre, and the ratio of BOD to COD indicates how readily the wastewater can be treated biologically.

What are the key features?

• Continuous short-cycle respirometric measurement
• Retained or fixed biomass reactor for stability
• Outputs correlated with laboratory BOD5
• Automatic aeration, cleaning and sample conditioning
• Alarm on high load or toxic shock
• Trend logging and plant control outputs

What are the technical specifications?

A typical online respirometric bod analyzer configuration offers measurement principle of Continuous respirometry in a bioreactor, measuring range of 0–500 mg/L BOD equivalent, cycle time of 5–30 min, resolution of 0.5 mg/L, sample conditioning of Filtration and temperature control and reactor volume of 0.5–2 L. 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 Respirometric BOD Analyzer is used in aeration control based on organic load, influent load monitoring and plant protection, industrial discharge trend monitoring and toxic shock and spill detection. Across the wider BOD Analyzers class, laboratories also deploy it for municipal wastewater treatment plant control, industrial effluent biodegradability assessment and discharge permit compliance monitoring.

Which standards and certifications apply?

Relevant standards and methods include ISO 5815-1, ISO 5815-2, Standard Methods 5210 B, EPA 405.1 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.

BOD measurement is sensitive to the seed, the dilution water and the incubation conditions, so dilution water must be free of chlorine and organic matter and should be aerated and seeded consistently. Nitrification inhibitors are added when only carbonaceous demand is required, since nitrifying bacteria consume oxygen and inflate results. Dilution must bring the final dissolved oxygen into the accepted window, typically at least 2 mg/L remaining and a depletion of at least 2 mg/L. Bottles, stoppers and seals must be clean and leak-free, especially in respirometric systems where a small leak ruins the pressure measurement. Incubation must be maintained at 20 ± 1 °C, and reference standards such as glucose-glutamic acid check the whole procedure.

How do I select the right Online Respirometric BOD Analyzer?

Select an online BOD analyzer when continuous organic load data are needed for aeration control or plant protection, and the effluent composition is stable enough for a correlation to hold. Confirm sample conditioning and cleaning arrangements for your stream, and plan periodic laboratory comparisons.

How does it compare with other BOD Analyzers variants?

Select the method from the data you need and the resources available. Respirometric systems automate incubation and readout, remove the need for titration and allow several bottles to run in parallel with continuous data, which suits routine plant control. Dilution methods with dissolved-oxygen measurement remain the reference approach for regulatory reporting and are used for samples with high or variable BOD. No measurement is valid without correct seeding, dilution and nitrification control, and the seed blank must be run with every batch. Choose a combined BOD and COD system if both parameters are reported routinely, since sharing incubation and reagents simplifies workflow. For continuous control, online respirometric instruments provide trend data but must be correlated with laboratory results.