PROCESS CONTROL WITH A FLOWMETER, PART 3

Some of you are going to whine and say, "but Jim, you forgot about the clarifier inventory!"  I haven't forgotten.  I am just bringing you along one step at a time, and lots of you never consider the clarifier inventory, or use the OEPA calcualation, which is WRONG ( I hope Andy Barienbrock doesn't read this, or he'll never renew my license: I'm already in trouble for standing up to Dear Leader).  I will show you 2 ways to calculate the clarifier inventory as MLSS gallons.

The first way is to assume that the clarifier inventory is pounds is 25-35% of the aeration tank inventory and then add it to the aeration gallons, like this

Total inventory = aeration tank volume X 1.25 = 1, 250,000 from our earlier examples

For an 8 day MCRT, then 1,250,000 gallons/8 =156,250 gallons of mixed liquor to waste, or for mixed liquor as determined in part 2, 156,250/3 = 52,100 gallons of RAS.

Alternatively, you can measure the blanket volume and calculate an MLSS equivalent inventory, like so

Inf. Flow = 2 MGD
RAS Flow = 1 MGD
Aeration Tank Volume = 1MG
Clarifier Diameter = 70'
Blanket Volume = 1'

If the blanket is 1 ft. deep, I would assume that all the blanket is the same concentration as the RAS.  If it is deeper, you should make a different assumption.  Thats for part 4.

the volume of one foot of blanket is pie are squared x 1 ft. or
35' x 35' x 3.14 x 1ft x 7.48gal/cf = 28,800 gallons
The MLSS equivalent is 3 x 28,800 = 86,300 gallons

Therefore, total MLSS inventory as gallons of MLSS are 1, 086,300

For an 8 day MCRT of MLSS to waste it's, 1,086,300/8 = 135,787 gallons
as RAS it's 135,787/3 = 45,262 gallons

That wasn't so hard, was it?

NOTE: when you waste RAS you should do it with a timer on the pumps so you can waste out during all parts of the day.  RAS concnetration changes during the day and to have an accurate portion, you need to remove some several times during the day,