CIVL 456: Wastewater Treatment

Homework #8- Fall 1996

Due Date: 8 November 1996




Background
The City of Fort Wayne (Indiana) currently operates a single-CFSTR activated sludge treatment system under the following conditions:
Flow = 11.5 mgd
Influent Total CBOD = 180 mg/L
Influent Total Nitrogen (Organic-N+Ammonia-N+Ammonium-N) = 18 mg/L
SRT=10 days
HRT=6 hours
Aeration Hardware=Coarse bubble diffusers
Specific Aeration-Mixing Horsepower=0.12 HP/1000 gal
Operating D.O.=2 mg oxygen/L
Reactor Operating Temperature: 20 deg C (assumed constant)
Reactor pH=8.2 (controlled by on-line acid and base addition)
Influent Alkalinity=125 mg as CaCO3/L
Underflow Solids=3 times `X' (MLSS in the reactor)
Based on on these conditions, complete the following `problems.'


Problem 1
Estimate the amount of influent nitrogen which will end up being consumed by the `organotrophic' (i.e., CBOD consuming) fraction of the MLVSS.


Problem 2
Estimate the relative distribution of `organotrophs' and `nitrfiers' in this same MLVSS (% organotrophs versus % nitrifiers).


Problem 3
Would this system likely have enough aeration horsepower (in terms of oxygen supply, not mixing intensity) if the available diffuser system were known to be capable of transfering 2.8 lbs oxygen per HP per hour (at maximal gradient).


Problem 4
Estimate the amount of alkalinity likely to be `consumed' by nitrification of the ammonium-nitrogen (after `organotrophic uptake for anabolism).


Problem 5
If this City were to add a subsequent `denitrification' reactor system, which would then need a supplemental addition of organic carbon to metabolically `drive' this reaction, how much methanol [answer in gallons per day!] would be needed (assuming this was the selected form of organic carbon).


Problem 6
In lieu of installing the latter `post-denitrification' system, suppose that one-half of this existing single stage reactor was to be converted to an anoxic condition, and that an internal recycle of `8Q' was to be installed to facilitate an `MLE' flowscheme. Would the remaining `aerobic' reactor volume still be able to nitrify this wastewater's reduced nitrogen?


Problem 7
Roughly estimate what fraction of the incoming `fixed' nitrogen (i.e., organic + ammonia + ammonium) could be removed using this latter design scheme (with removal including both organotrophic assimilation plus combined nitrification-denitrification).

Last Modified: 2 November 1996; alleman@ce.ecn.purdue.edu