1. Convert a flow of 600 gallons per minute to million gallons per day

2. Convert a Flow from 1.2 MGD to cubic feet per second

3. Estimate the velocity of wastewater flowing through a grit channel if a stick travels 32 feet in 36 seconds.

4. A grit channel removed 3.2 cu ft of grit during a period when the total flow was 0.8 MG. How many liters of grit are removed per cubic meter?

5. A circular secondary clarifier handles a flow of 0.9 MGD and suspended solids of 3,600 mg/L. The clarifier is 50 ft in diameter and 8.0 ft deep. Find the detention time, surface loading rate, weir over flow rate and solids loading.

Answers:

1. 0.86 MGD

(Flow, gal/min X 60 min/hr X 24 hr/day) / (1,000,000/M)

(600 gal/min X 60 min/hr X 24 hr/day) / (1,000,000/M)

2. 1.86 CFS

(Flow, MGD X 1,000,000/M) / (7.48 gal/cuft X 60 min/hr X 24 hr/day) =

3. 0.89 ft/sec

(Distance Traveled, ft) / (Time, sec)

(32 ft) / (36 sec) =

4. 4.0 cuft/MG

(3.2 cuft) / (0.8 MG) =

5.

Detention Time = 3.1 hr

Flow, gpd = 0.9 MGD X 1,000,000/M = 900,000 gpd

(Tank volume, cuft X 7.48 gal/cuft X 24 hrs/day) / (Flow, GPD)

Tank area, sqft = 0.785 X D, ft X D, ft OR 3.14 X R, ft X R, ft

Tank area, sqft = 0.785 X 50 ft X 50 ft = 1,962.5 sqft

Tank volume, cuft = area, sqft X Height, ft

1,962.5 sqft ft X 8 ft = 15,680 cuft

(15,680 cuft X 7,48 gal/cuft X 24 hr/day) / (900,000 gpd) =

NOTE: (R is Radius = 1/2 the diameter)

Surface Loading = 459 gpd/sqft

(Flow, gpd) / (Area, sqft)

(900,000 gpd) / (1,960 sqft)

Length of Weir, ft = 157 ft

3.14 X Diameter, ft

3.14 X 50 ft

Weir Overflow, GPD/ft = 5,730 GPD,ft

(Flow, GPD) / (Length of Weir, ft)

(900,000 GPD) / (157 ft)

Solids Applied lbs/day = 27,022 lbs/day

Flow, MGD X SS, mg/L X 8.34 lbs/gal

0.9 MGD X 3,600 mg/L X 8.34 lbs/gal

Solids Loading, lbs/day/sqft = 14 lbs/day/sqft

(Solids applied, lbs) / (Surface area, sqft)

(27,022 lbs/day) / (1,960 qft)