BOD, COD and you use a lab sample? 2nd Water/Wastewater and Automatic Controls Conference Orlando August 9, 2007
Presenter Robert Lagrange Co author Business Manager Tracy Doane-Weideman Water and Wastewater Product Manager Analysis Endress+Hauser Inc.
Schedule • Organic Load • Importance for plant operation • Laboratory Measurements • BOD 5 • COD • On-Line Measurements • BOD • COD • Questions
Is it important to know the organic load ? • A change of organic load requires process adjustments • Controlling the Dissolved Oxygen concentration in the aeration tank is a typical way to compensate for this • But !!!! It could be too late if the plant capacity is limited It is better to know ahead of time, much more if there is a possibility to equalize the load or limit the intake of high load from industrial plants
BOD variations at a municipal WWTP Reference: Finbarr O Riordan
Measurement of Organic Load • TOC • COD • BOD “the fundamental purpose of the treatment plant is to reduce the bio-digestible organics”
Issues with laboratory measurement • BOD 5 Lab • Takes 5 days • Accuracy/Repeatability
Accuracy of lab measurement Reference: M. Köhne
Issues with laboratory measurement • BOD 5 Lab • Takes 5 days • Accuracy/Repeatability • COD • Takes 2 hours • Maintenance of the lab instrument • Disposal of waste stream depending on method
O2 Uptake mg/l Michaelis- Menten Kinetics Model 3 mg O CONTROL POINT 2 5 m g B O D / l Nutrient Concentration in mg BOD / l Michaelis- Menten Kinetic Model
How does it work? • Thousands of small plastic rings within the bioreactor provide a growth surface for the biomass. • The biomass is fed a mixture of wastewater and oxygen saturated dilution water • The dilution is constantly adjusted to maintain a 3mg/l oxygen consumption • The ratio of wastewater to dilution water defines BOD based on the Michaelis- Menten Kinetic Model
Before Calibration After Calibration Trending & Calibration Reference: Alexander Borys
Another trending example Reference: Finbarr O Riordan
Reference: Finbarr O Riordan Reference: Alexander Borys Maintenance On-line BOD
On-Line COD • Ozone is mixed with dilution water. The resulting concentration is measured by the first ozone sensor. • In the reaction chamber the waste water is oxidized by the ozonized dilution water • The ozone concentration in the reactor is measured by the second ozone sensor. • The consumption of Ozone is proportional to the COD
Thank you ! Questions ?