Biological Treatment

Topic: Ch 7

Announcements

1. HW2 going out today, due next Friday

2. Wiley next Wed3. March 20th Field trip w/ Jason

Assoiline4. Email me about DimDim Recordings5. Tentative Carpool Plan –

Time/Location1. Merced to Clovis is 1hr drive

6. Experiment with mic’s and video

Roadmap

1. Background Review - Today2. Stoichiometry - Today3. Energetics - Wed4. Microbial Growth Kinetics - Wed

Background Review

Purpose of Biological Treatment Capture nonsetteable solids into a

biological floc or biofilm Biomass has specific gravity greater

than water Must remove settled bacteria or won’t

reduce BOD Transform or remove nutrients (N

and P) Oxidize consituents into an

acceptable end product

Suspended Growth

Typically aerobic (need aeration… energy!)

Sometimes anaerobic for cases of highly concentrated wastewater Anaerobic typically used for sludge

treatment but this is not usually suspended growth

Bacteria

C5H7O2N Growth rates

double every 10ºC until optimum temp reached

pH optimum 6.5-7.5

Nutrients may be limited in industrial wastewaters

Metabolism

Bacteria Growth in Batch Reactor

Why does death phase occur?

Draw DO curve?

Draw BOD curve?

Quantifying Biomas

Bacteria Cells = Biomass Often measured as volatile suspended solids

(VSS) Is VSS entirely biomass? Other approaches: particulate COD, protein, ,DNA

Biomass yield (Y) = g biomass produced / g substrate consumed Substrate is typically the constituent in the

wastewater that is electron donor (energy source) What would be the units for the yield for

nitrification bacteria (what is the substrate)?

Stoichiometry

Biomass Yield (Y = g cell/g substrate)

Cellular Mass Balance (Stoichiometry) Assume substrate as glucose Neglect nutrient other than N

How much substrate leaves system as sludge vs. gas?

What is the yield (Y) based on this stoichiometry?

Biomass Yield (Y = g cell/g substrate)

COD Mass Balance (Stoichiometry) Assume substrate as glucose Neglect nutrient other than N

What is the yield (Y) based on this stoichiometry?

COD of Glucose (g O2 / g glucose)

Cellular Mass Balance (Stoichiometry) Assume substrate as glucose Neglect nutrient other than N

What is the yield (Y) based on this stoichiometry (change in O2 over change in glucose)?

COD of Glucose (g O2 / g glucose)

Cellular Mass Balance (Stoichiometry) Assume substrate as glucose Neglect nutrient other than N

What is the yield (Y) based on this stoichiometry (change in O2 over change in glucose)?

Theoretical Yield [(g cell / g glucose) / (g COD O2 / g glucose)]

Maximum yield… actual yield will be more because not all substrate is converted to cell mass (synthesis) since some is needed for cell maintenance

Solve for the theoretical yield given the following

Theoretical Yield [(g cell / g glucose) / (g COD O2 / g glucose)]

Solve for the theoretical yield

COD of Cell Tissue (g O2/g cell)

Recall that biomass must be removed by settling (as sludge) or effluent will have large BOD

Calculate COD of Cells given,

COD of Cell Tissue (g O2/g cell)

Organics molecules are converted into cellular molecules but still are BOD

Recall that biomass must be removed by settling (as sludge) or effluent will have large BOD

Calculate COD of Cells given,

Example 7-1

Example 7-1

Draw Schematic?

Example 7-1

Calculate Observed Yield (g cell / g substrate COD removed) ?

Example 7-1

Calculate Observed Yield?

vs. Theoretical Yield?

Example 7-1

Oxygen Used per COD removed? “Oxygen Used”: oxygen consumed by

bacteria during synthesis of substrate.▪ Calculate as difference between CODin and total

COD out (substrate COD out + biomass COD out) “COD removed”: Decrease in substrate

COD. Ignores COD of biomass.▪ Calculate as difference of CODin and CODout

“Oxygen Used”: oxygen consumed by bacteria during synthesis of substrate.▪ Calculate as difference between CODin and

total COD out (substrate COD out + biomass COD out)

Example 7-1

“COD removed”: Decrease in substrate COD. Ignores COD of biomass.▪ Calculate as difference of CODin and CODout

Example 7-1

Oxygen Used per COD removed?

In-Class Problem

• Why is theoretical yield less than actual yield?

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