Dissolved Oxygen

Question 1

What are typical measurements of organics in wastewater?

Answer 1

1. Biochemical oxygen demand (BOD)
2. Chemical oxygen demand (COD)
3. Total/dissolved organic carbon (TOC/DOC)

Question 2

What is biochemical oxygen demand (BOD)?

Answer 2

It is a measurement of dissolved oxygen used by microorganisms in the biochemical oxidation of organic matter

Question 3

What do BOD tests determine?

Answer 3

They determine the approximate quantity of oxygen required to “stabilize” organic matter

Question 4

What are some challenges pertaining to conducting BOD tests in labs?

Answer 4

• For most wastewaters, oxygen quickly depletes

- Some wastewaters may not contain enough organisms to start the degradation process

Question 5

What is nitrification?

Answer 5

Ammonia reacts with oxygen to form nitrate.

Question 6

How long does it take for nitrifiers to acclimate and function?

Answer 6

Nitrifiers (organisms that perform nitrification) take 6-10 days to acclimate and function.

For 5 day BOD test, we don’t have to worry about nitrification.

Question 7

What are some limitations of the BOD_5 test?

Answer 7

• takes 5 days to complete, doesn’t provide a means for operational control
• only measures biodegradable organics (not good for toxic wastes)
• 5 days may not always fully capture carbon degradation (complex organics take more time to degrade)

Question 8

What does chemical oxygen demand (COD) measure?

Answer 8

• Measures oxygen required to oxidize organic materials using a strong chemical oxidant
• used to measure organic matter in industrial and municipal wastes containing toxic compounds

Question 9

What are some advantages to COD over BOD?

Answer 9

• COD values are typically higher than BOD (easier to chemically oxidize than biologically)
• COD analysis only takes several hours (much faster than BOD, and can be used for process control)

Question 10

What does total organic carbon (TOC) measure?

Answer 10

• measures total organic carbon in a sample (ok this answer seems obvious…)

Total organic carbon does not indicate type or biodegradability of carbon

Question 11

What are the limitations of Streeter-Phelps? (the additional processes that may occur)

Answer 11

1. Removal of BOD by adsorption or sedimentation
2. Addition of BOD by tributary flow
3. Addition of BOD or removal of DO by benthic layer
4. Addition of oxygen by photosynthesis
5. Removal of oxygen by respiration