Chapter 5 - CSTR
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Chapter 5 - CSTR
Biological wastewater treatment
COD is limiting nutrient
Hydraulic residence time
mean cell residence time
4 mass balance equations needed
1.42 g COD/g VSS
1.20 g COD/g TSS
Mass Balance on Biomass Equation
) + b
Mass balance on soluble substrate tells us:
The amount of biomass will increase if S
small volume bioreactor has higher concentration of active biomass, although total mass is same as large rxr
as flow is increased with constant SRT, biomass increases
active fraction of biomass
Concentration of active biomass divided by total biomass concentration
Active fraction of biomass ______ as SRT increases. Why?
Buildup of biomass debris in the bioreactor
Observed yield definition
Actual net biomass formed per unit mass of substrate destroyed
takes into consideration loss from decay
Larger SRT _______ observed yield. Why?
decreases. greater opportunity of biomass decay and greater need for maintenance energy, leaving less energy for new cell synthesis
total biomass wastage rate
depends on these 3 things:
concentration of substrate in rxr
As SRT increases, biomass wastage rate ________. Why?
increases at first and then decreases
increased importance of decay, and decrease in excess biomass
more and more active biomass is oxidized and converted to debris and less must be disposed of
COD balance states that the amount of oxygen that must be supplied to a bioreactor must equal ____________.
The total COD in minus the total COD out, including COD of biomass and biomass debris.
Phosphorus requirement is about ______ the nitrogen requirement
As SRT increases, S
growth can be established and substrate removal increases.
As SRT increases, total biomass (g) _________.
As SRT increases, oxygen demand ____________. Why?
sharply increases, then steadily increases.
little oxygen required at short SRT because substrate removal isn't complete
as SRT increases, to the point where removal is complete, all oxygen is associated with biomass growth
Increasing further means more decay and increase in oxygen requirment is associated with decay
Soluble non biodegradable organic matter.
Influent concentration = effluent concentration
Inert suspended solids
Mass leaving = mass entering, but some get stuck inside and spend longer.
Mixed liquor suspended solids on TSS basis
Includes acive biomass and biomass debris
Used when influent has inerts
The presence of active biomass in the influent _________ specific growth rate relative to SRT.
If biomass is present in the influent the biomass in the reactor does not have to grow as fast to maintain itself as it does when the influent contains no biomass.
If 2 reactors have the same HRT and SRT but one receives active biomass in the influent, it will produce an effluent with ________ substrate concentration