CIVL 456: Wastewater Treatment

Homework #9- Fall 1996

Due Date: 15 November 1996




Background
The City of South Bend (Indiana) currently operates a single-CFSTR activated sludge treatment under the following conditions:
Flow = 32 mgd
Influent Total CBOD = 180 mg/L
Influent Total Nitrogen (Organic-N+Ammonia-N+Ammonium-N) = 18 mg/L
SRT=2 days
HRT=6 hours
Reactor Operating Temperature: 20 deg C (assumed constant)
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 in this initial reactor system. You should assume that there is 'NO' nitrification taking place in this first activated sludge reactor.


Problem 2
Develop a preliminary design for a subsequent (following the aforementioned reactor in series) fixed-film nitrification reactor (two each in parrallel), based on an ammonium-nitrogen loading of 1 pound N per 12,000 sq.ft. media surface area per day (i.e., determine the necessary reactor diameters assuming a tank media of 20 feet). You should also assume that the media to be used will have a specific surface area of 45 sq.ft. per cu.ft. of media volume (a somewhat conservative figure, as compared to media values which can be obtained as high as 60, but less apt to clog and foul due to unexpected excessive biofilm growth).


Problem 3
Would this system likely have enough aeration horsepower Develop a second preliminary design for an optional 'IDI Biofor' system assuming an ammonium-nitrogen loading of 2.0 kg N per cu.meter (of tank volume) per day. In this case, you should estimate the width and length (at a respective 2:1 ratio) dimensions (in meters) for the single 'Biofor' reactor with a media depth of 3.5 meters.


Last Modified: 7 November 1996; alleman@ce.ecn.purdue.edu