Chapter 5 - CSTR

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Chapter 5 - CSTR
2012-04-21 18:23:55
Biological wastewater treatment

SRT, biomass
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  1. Assumptions
    • aerobic heterotrophs
    • COD is limiting nutrient
    • Hydraulic residence time
    • = V/F
  2. c
    • mean cell residence time
    • SRT
    • VX/FwXw
  3. 4 mass balance equations needed
    Ss, XB,H, XD, Oxygen
  4. iO/XB,V
    1.42 g COD/g VSS
  5. iO/XB,T
    1.20 g COD/g TSS
  6. Mass Balance on Biomass Equation
    H= (1/c) + bH
  7. Monod equation
  8. Mass balance on soluble substrate tells us:
    • The amount of biomass will increase if SSO increases
    • 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
  9. fA
    • active fraction of biomass
    • Concentration of active biomass divided by total biomass concentration
    • XBH / Xtotal
  10. Active fraction of biomass ______ as SRT increases. Why?
    • decreases
    • Buildup of biomass debris in the bioreactor
  11. Observed yield definition
    • Actual net biomass formed per unit mass of substrate destroyed
    • takes into consideration loss from decay
  12. Larger SRT _______ observed yield. Why?
    decreases. greater opportunity of biomass decay and greater need for maintenance energy, leaving less energy for new cell synthesis
  13. Wtotal
    • total biomass wastage rate
    • FWXtotal
  14. Wtotal depends on these 3 things:
    • SRT
    • flowrate
    • concentration of substrate in rxr
  15. 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
  16. 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.
  17. Phosphorus requirement is about ______ the nitrogen requirement
  18. As SRT increases, Ss __________. Why?
    • decreases
    • growth can be established and substrate removal increases.
  19. As SRT increases, total biomass (g) _________.
  20. 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
  21. SI
    • Soluble non biodegradable organic matter.
    • Influent concentration = effluent concentration
  22. XI
    • Inert suspended solids
    • Mass leaving = mass entering, but some get stuck inside and spend longer.
  23. XM,T
    • Mixed liquor suspended solids on TSS basis
    • Includes acive biomass and biomass debris
    • Used when influent has inerts
  24. The presence of active biomass in the influent _________ specific growth rate relative to SRT.
    • reduces
    • 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.
  25. 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