Question

1. common settling times in primary clarifiers range from.

a. 15 to 30 minutes
b. 30 to 45 minutes
c. 1 to 2 hours
d. 2 to 3 hours

1. compute the lagoons detention time.

data: average depth = 3.0 ft
surface area = 6.0 acres
daily flow = 0.25 mgd
a. 3 days
b. 8 days
c. 24 days
d. 29 days

1. white fluffy foam on the biological reactors in an activated sludge process is usually

caused by _.
a. insufficient biomass to treat the incoming waste
b. low bod
c. high do
d. too little sludge being wasted from process

1. when organic wastes are discharged to receiving waters, oxygen is depleted by.

a. algae
b. bacteria
c. ducks
d. limestone rocks

1. three water born diseases are.

a. tuberculosis, diphtheria, chickenpox
b. mumps, measles, colds
c. scarlet fever, pneumonia, hay fever
d. typhoid fever, dysentery, cholera

1. typical components of grit removal systems include

a. belt press
b. comminutors
c. chain-and-flight scrapers
d. bar racks

Explanation:

Step1: Calculate the lagoon volume

First, convert the surface area from acres to square feet. Since 1 acre = 43560 square feet, the surface area \(A = 6.0\times43560=261360\) square feet. The volume \(V\) of the lagoon is given by \(V = A\times h\), where \(h = 3.0\) ft. So \(V=261360\times3.0 = 784080\) cubic feet.

Step2: Convert the daily flow to cubic feet per day

The daily flow \(Q = 0.25\) MGD (million gallons per day). Since 1 million gallons = 133680 cubic feet, \(Q=0.25\times133680 = 33420\) cubic feet per day.

Step3: Calculate the detention time

The detention time \(t=\frac{V}{Q}\). Substitute \(V = 784080\) cubic feet and \(Q = 33420\) cubic feet per day. \(t=\frac{784080}{33420}=23.46\approx24\) days.

Answer:

1. a. 15 to 30 minutes (Primary clarifiers have relatively short settling times as they are designed for initial separation of solids from wastewater).
2. c. 24 days (As calculated above).
3. b. Low BOD (Low BOD in the activated - sludge process can lead to the growth of filamentous organisms which cause white fluffy foam).
4. b. Bacteria (Bacteria decompose organic wastes through aerobic respiration, consuming oxygen).
5. d. Typhoid fever, dysentery, cholera (These are well - known water - borne diseases. Tuberculosis is airborne, mumps and measles are also not water - borne in the typical sense, and hay fever is an allergic reaction not a water - borne disease).
6. d. Bar racks (Bar racks are used to remove large debris in grit removal systems. Belt presses are for dewatering, comminutors are for grinding, and chain - and - flight scrapers are for sludge removal in clarifiers).