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Based on: Industry Standards and Best Practices

Languages: English

Sample Transcript

The activated sludge process introduces recycled sludge from the secondary clarifier downstream of the basin into the feed. The additional microorganisms and additional oxygen added to support them increases the efficiency of a basin beyond that of a simple aerated basin. Some activated sludge systems are enclosed and oxygen enriched air is introduced into the enclosure. The higher levels of oxygen, once again, increase the efficiency of BOD reduction. In evaluating the types of systems there is a trade off. As they become more efficient they become more complex and expensive to operate.

Wastewater - Secondary Treatment

Training Time: 21 minutes

Secondary wastewater treatment is the second stage in wastewater treatment, following what is known as primary treatment. Secondary treatment takes suspended solids and dissolved organic material, captures the solids, and removes greater than 85% of the biological oxygen demand, also known as BOD. Secondary treatment is a biological process which utilizes bacteria to remove BOD followed by secondary clarification.

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While the BOD test is a true test of the Biochemical Oxygen Demand it takes several days to complete the test. The COD test is faster and can be correlated to the BOD results.

While the BOD test is a true test of the Biochemical Oxygen Demand it takes several days to complete the test. The COD test is faster and can be correlated to the BOD results.

Aerobic microorganisms perform best around 35 deg C (95 deg F).

Aerobic microorganisms perform best around 35 deg C (95 deg F).

The activated sludge process introduces recycled sludge from the discharge of the secondary clarifier into the feed of aerated basin.

Learning Objectives

  • Define secondary wastewater treatment
  • Identify the purpose of secondary wastewater treatment
  • Define BOD and COD
  • Describe the different forms of secondary wastewater treatment plants
  • Identify and describe the key equipment and process flows of secondary wastewater treatment
  • List the bacterial growth factors in secondary wastewater treatment plants
  • Describe the principles of a secondary clarifier
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Wastewater - Secondary Treatment FAQs

What parameters are typically monitored in order to meet discharge permits?
Some of the parameters monitored include flow, BOD, suspended solids and pH.

What are growth pressures in secondary treatment pond?
Any factor which will affect the health of the microbial community in a treatment vessel is called a growth pressure.

What is the difference between an oxidation basin and an aerated stabilization basin?
Oxidation basins rely on natural diffusion to get the oxygen that microbes in the water need to metabolize organic matter. Aerated stabilization basins use mechanical means to increase the transfer of oxygen.

What is BOD?
BOD is Biochemical Oxygen Demand, it is a measure of the concentration of biologically consumable organic materials in a water sample.

What is anaerobic treatment?
Aerobic microbes need oxygen to grow and thrive, anaerobic microbes live and consume organic material in an oxygen-free environment.

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