Suspended Media Biological Treatment

Question 1

What is the activated sludge process?

Answer 1

An aerobic process with suspended microorganisms suspended in a tank where they convert dissolved and suspend solids into cellular mass

Question 2

Basic components of activated sludge process

Answer 2

Wastewater
Activated sludge
Aeration tank
Aeration system
Secondary settling tank with RAS/WAS

Question 3

What is MLSS?

Answer 3

The amount of suspended solids in the mixed liquor of an aeration tank

Question 4

What is MLVSS?

Answer 4

The amount of organic or volatile suspended solids in the mixed liquor of an aeration tank

Question 5

What are the EPA secondary treatment standards?

Answer 5

BOD and TSS removal no less than 85% and 30 day average not to exceed 30 mg/L

Question 6

What is the fundamental principle of operating an activated sludge process?

Answer 6

Maintaining the proper food to microorganism ratio by wasting excess microorganisms

Question 7

What is sludge age?

Answer 7

The average amount of time that solids or bacteria remain in an aeration tank. Also called mean cell residence time or solid retention time

Question 8

What are examples of process control tests for the activated sludge process?

Answer 8

Microscopic exam and TSS tests

Question 9

What are examples of calculations used in process control of activated sludge?

Answer 9

Sludge volume index
F/M ratio
MCRT

Question 10

What is the settleometer test?

Answer 10

Place a sample of MLSS in a 1-liter settleometer and measure the settled sludge volume every 5 minutes for 30 minutes. Then every 10 minutes until 60 minutes. Good SSV is <500

Question 11

What does SVI measure?

Answer 11

Compactibility/settlability of sludge

- how much volume 1g of ML occupies after 30 minutes

Question 12

What can SVI help to identify?

Answer 12

The presence of filaments if >150

Question 13

What is mechanical aeration?

Answer 13

Agitates the surface creating turbulence that entraps oxygen as the mixed liquor travels through the air

Question 14

What is diffused aeration?

Answer 14

Large volume of low pressure air is delivered near the bottom of the tank which allows mixing and oxygen diffusion as it rises

Question 15

What is pure O2 aeration?

Answer 15

Pure O2 is delivered to mixed liquor with a sealed cover on the aeration tank

Question 16

Describe the operating parameters of conventional activated sludge process

Answer 16

Plug flow aeration tank
Air evenly distributed
DO increases towards the effluent end
Detention time 4-12 hours
MLSS 1500-3000mg/L
MCRT 5-15 days
F/M 0.2-0.4 lbs BOD/day/lb MLVSS

Question 17

Provide examples of modifications to the conventional activated sludge process

Answer 17

High rate aeration
Contact stabilization
High-purity oxygen
Step-feed
Complete mix
Extended aeration
Oxidation ditch
Batch decant
Sequencing batch reactor
Counter current aeration system

Question 18

What is a lagoon?

Answer 18

AKA stabilization pond
Earthen basin excavated and lined with clay or plastic
Sludge collects on the bottom of lagoon cells

Question 19

What is the lagoon process?

Answer 19

Aerobic bacteria stabilize dissolved and suspended organic matter while producing CO2 and N and P

Algae use the CO2, N, and P for photosynthesis

Dissolved oxygen provided by mechanical or diffused aeration, photosynthesis, or wind/wave action

Question 20

Types of lagoons

Answer 20

Aerobic
Anaerobic
Facultative
Aerated

Question 21

What is pinpoint floc?

Answer 21

Small, dense, pinpoint shaped flocs

Indicates older sludge that flocculates poorly

Question 22

What is straggler floc?

Answer 22

Floppy, transparent, very light, buoyant floc

Typical of young sludge