Applications

PULSE-FLOW RESPIROMETER SYSTEMS

Are ideally suited to aerobic and anaerobic applications for:

  • Biodegradation studies
  • Toxicity assessments
  • Biomass activity monitoring
  • Assessing factors affecting treatment plant performance
  • Conducting intrinsic and extant kinetic analyses
  • Research and development applications
  • Industrial waste treatability assessments
  • Conducting oxygen uptake fingerprints (OUR respirograms)
  • Measuring oxygen uptake or gas production in laboratory-scale pilot plants
  • Measuring oxygen uptake for OECD, ASTM, EPA biodegradation protocols.


Biodegradation Tests PDF Print


Biodegradation tests involve testing samples in response to various parameters: dilution, nutrient addition, pH, temperature, and others. The pattern of oxygen uptake in aerobic tests; nitrogen gas production in anoxic denitrification tests; methane production in methanogenic tests; hydrogen production during glycolysis; and carbon dioxide production during fermentation reactions gives a measure of the rate and extent of biodegradation of the organic constituents of the test sample. Examples are shown below:


Aerobic Biodegradation Tests

The pattern of oxygen uptake– relative to that for a control substrate – gives a measure of the rate and extent of biodegradation of the organic constituents of the test sample. In this case, samples #2 and #3 showed a much lower biodegradation rate than the Control.


 

Nitrification Tests

This case study shows how respirometers were used to measure the impact of an industrial wastewater on the nitrification reaction in a treatment plant.

In this case, samples containing up to 60% wastewater by volume showed evidence of nitrification inhibition.

 

 

 










Anoxic Denitrification Tests

Anoxic denitrification requires the presence of an organic substrate to serve as an electron donor.

This case study shows how respirometry was used to determine the effect of C/N ratio on denitrification rates.


 

Anaerobic Biodegradation (BMP) Tests

Anaerobic biodegradation tests – often referred to as Biochemical Methane Production (BMP) tests – involve addition of known amounts of a chemical or wastewater to anaerobic cultures. The quantity of methane production – relative to that from a control or per unit of COD added – indicates the biodegradation potential.

This case study shows methane production for a Control reactor and three test reactors that were operated at 20-, 30- and 45-day retention times and received three doses of industrial wastewater. The tests indicate that culture acclimation was required and incomplete methane production occurred for the lower SRT reactors.



 
Biomass Activity Tests PDF Print

 

Pulse-Flow respirometers can be used to assess biomass activity for aerobic and anaerobic reactions. In aerobic tests, cultures are combined with nutrients, trace minerals, and an organic substrate – such as acetic acid or ethanol. The maximum oxygen uptake rate reflects the amount of active biomass in the test culture. Examples are shown below:

Aerobic Biomass Activity

In the case illustrated here, a culture having a VSS concentration of 2,000 mg/L was exposed to 300 mg/L of acetate COD. The active biomass concentration was determined from kinetic modeling to be 320 mg/L so that the VSS in the test culture was the 16 % active acetate-utilizing microorganisms.



Anaerobic Biomass Activity

In anaerobic tests, the active biomass is indicated by the maximum specific methane production (SMP) rate in the presence of high concentrations of acetic acid, ethanol or other organic substrates.

In this example, the maximum SMP for Sample #1 was 1.4 g CODCH4/g VSS/day. The maximum SMP for 100% active acetoclastic methanogens is 6 g COD/g VSS-d. Therefore, the test culture contained 23% active methanogens.

 

 
Toxicity Tests PDF Print

 

Toxicity of pure chemicals is assessed using respirometers by adding increasing concentrations to an active culture. The concentration at which oxygen uptake or gas production begins to decrease is known as the “threshold toxicant concentration.” Examples are shown below:

Aerobic Toxicity Testing

This example shows the results of dosing respirometer tests in which three concentrations of cyanide were added to a test culture that receive phenol as an organic substrate. The threshold toxic concentration of cyanide was 1 mg/L.


 

Anaerobic Toxicity Testing

This example shows the results of dosing an anaerobic culture with three concentrations of an industrial cleaning agent followed by respirometric measurement of methane production. The threshold toxic concentration was less than 80 mg/L of product and 800 mg/L produced a 50% decrease in methane production rate.

 

 
Determination of Biodegradation Kinetics by Respirometry PDF Print

 

Intrinsic kinetic tests involve adding relatively high concentrations of organic substrate to small concentration of acclimated microorganisms so that the COD/VSS ratio typically is greater than 10. Kinetic parameters are then determined by non-linear modeling using well-known relationships between biological growth and oxygen uptake. Examples are shown below:

 

 

In this example, 700 mg/L of glycerin COD was added to a test culture containing 45 mg/L of active biomass. Modeling showed the following kinetic parameters: Yield coefficient, Yg = 0.42 mg VSS/mg COD removed; specific substrate conversion rate, qm = 0.35 mg COD/mg VSS/hr; specific growth rate, μmax = 0.10 g VSS/g VSS-hr.



Extant kinetic tests
involve adding relatively low concentrations of organic substrate to large concentrations of biomass so that the COD/VSS ratio usually is less than 0.1. Extant kinetic parameters are then determined by using non-linear modeling techniques. Examples are shown below:

 

In this example case, 600 mg/L of acetate was added to a test culture containing 2000 mg VSS/L, followed by measurement of oxygen uptake by respirometers. Modeling showed the following: Active biomass = 390 mg/L; yield coefficient, Yg = 0.45 mg VSS/mg COD removed; specific substrate conversion rate, qm = 0.33 mg COD/mg VSS/hr; specific growth rate, μmax = 0.15 g VSS/g VSS-hr; biomass decay rate (active basis), b = 0.01/hr; half-saturation coefficient, K¬S = 1 mg/L. The shaded zone represents oxygen uptake associated with biodegradation of biopolymer that was stored in the original seed biomass.

 

 
Other Applications PDF Print

Pulse-Flow respirometer also can be used for the following applications:

  • Measuring oxygen uptake associated with compost reactions
  • Measuring oxygen uptake associated with carbon dioxide evolution from fermentation reactions
  • Assessing factors affecting treatment plant performance
  • Conducting intrinsic and extant kinetic analyses
  • Research and development applications
  • Industrial waste treatability assessments
  • Conducting oxygen uptake fingerprints (OUR respirograms)
  • Measuring oxygen uptake or gas production in laboratory-scale pilot plants
  • Measuring oxygen uptake for OECD, ASTM, EPA biodegradation protocols