Primary Treatment

Question 1

Purpose of Clarifiers

Answer 1

To remove readily settleable or floatable solids

Question 2

Purpose of influent baffles

Answer 2

Provides for even flow, distribution, flocculation, and energy dissipation

Question 3

Purpose of effluent weirs

Answer 3

Provides even flow distribution out of the tank. Need to be level to prevent formation of currents in the tank

Question 4

Purpose of skimming device

Answer 4

To remove floating material

Question 5

Purpose of internal baffles

Answer 5

Negates the effect of density currents/short circuits

Question 6

Short circuits

Answer 6

Different velocities in any part of a tank that can effect settling and solids removal

Question 7

Detention time for clarifiers

Answer 7

2-3 hours

Question 8

How does temperature impact settle rate?

Answer 8

Lower temperature increases the density of water which increases settling time. 50% faster at 80 degrees F than 38F

Question 9

Horizontal velocities in a clarifier for settling

Answer 9

1-2 feet per minute

Question 10

Weir loading rate

Answer 10

A measure of flow over a defined amount of weir. Higher weir loading can result in poor settling. 10000-20000 gpd/ft

Question 11

Optimal Surface loading rate in a primary clarifier

Answer 11

Ranges from 300-1200 gpd/ft2. Lower rate leads to longer detention times.

Question 12

Percent solids of sludge removed from primary clarifier

Answer 12

4-6% is typical

Question 13

What role do chemical additions play in a clarifier?

Answer 13

Act as coagulent for improved settling and can precipitate phosphorous

Question 14

Primary Treatment settleable solids removal (%)

Answer 14

90-99%

Question 15

Primary Treatment TSS removal (%)

Answer 15

40-60%

Question 16

Primary Treatment TS removal (%)

Answer 16

10-15%

Question 17

Primary Treatment BOD removal (%)

Answer 17

20-50%

Question 18

Solids loading rate (secondary clarifiers)

Answer 18

12-30lbs/day/square foot

Question 19

Sludge gasification

Answer 19

Soluble and suspended organic matter undergoes anaerobic decomposition releasing gas. Can lead to popups.

Question 20

Bulking

Answer 20

Clouds of billowing sludge when it does not settle properly. Often cause by filamentous bacteria in activated slude.

Question 21

Clarifier efficiencies are affected by what factors?

Answer 21

Type of solids, time in the collection system, detention time, condition of equipment, sidestreams such as recycle flows

Question 22

What are the two most common methods of flow equalization?

Answer 22

In-line or side-line equalization

Question 23

In-line flow equalization

Answer 23

Blends all incoming flows into the holding tank and discharges at the average flow rate

Question 24

Side-line equalization

Answer 24

Diverts flows that are higher than average rate or concentration for release when flows are below average

Question 25

Advantages of in line flow equalization

Answer 25

Better at leveling out fluctuations in concentration