Nutrient Removal

Question 1

Why remove nitrogen?

Answer 1

It can cause excessive algae growth in receiving waters in combination with phosphorus

It stimulates aquatic plant growth

Ammonia can be toxic

It can reduce chlorine disinfection efficiency

It can cause disease in babies

It can deplete the receiving waters of O2 if nitrification occurs

Question 2

Treatment methods for nutrient removal

Answer 2

Physical

• sedimentation
• gas stripping

Chemical

• breakpoint chlorination
• ion exchange

Biological
-nitrification and denitrification

Question 3

What is nitrification?

Answer 3

The conversion if Ammonia or ammonium into oxidized nitrogen using aerobic bacteria

Question 4

What are the nitrifying bacteria?

Answer 4

Nitrosomonas - NH3 to NO2
Nitrobacter - NO2 to NO3

Strict aerobic bacteria
Slower growing than carbonaceous

Question 5

How much O2 and alkalinity does nitrification require?

Answer 5

4.6 mg/L O2 and 7.14 mg/L of alkalinity

Question 6

What is denitrification?

Answer 6

Conversion of nitrate into nitrogen gas with facultative bacteria and anoxic conditions

Question 7

How much O2 and alkalinity does denitrification produce?

Answer 7

2.86 mg/L O2 and 3.6 mg/L alkalinity

Question 8

What are the nitrification process requirements in suspended media?

Answer 8

DO levels between 2-4 mg/L in the aeration zone

MCRT > 5 days

15-35 degrees celcius

Appropriate alkalinity, pH towards 8.5

Question 9

What are the requirements for nitrification in trickling filters?

Answer 9

Synthetic media, sufficient ventilation, second stage filter with BOD <10mg/L

Question 10

What are the requirements for nitrification in an RBC?

Answer 10

Natural aeration or enhanced
Secondary unit with soluble BOD <10mg/L
1-2 mg/L DO

Question 11

Denitrification process requirements in suspended media

Answer 11

An anaerobic or anoxic zone
Presence of nitrates
Facultative bacteria

Question 12

Denitrification process requirements in fixed film

Answer 12

Separate independent process using fluidized sand beds or denitrification columns

Question 13

What are the 3 phosphorous compounds in municipal wastewater?

Answer 13

Organically-Bound phosphorous

• settles in primary
• biologically converted to PO4

Polyphosphate

• soluble
• biologically converted in secondary

Orthophosphate

• Soluble
• biologically converted in secondary
• precipitated with mettle salts

Question 14

What are examples of metal salts?

Answer 14

Aluminum sulfate
Sodium aluminate
Poly aluminum chloride
Poly aluminum silicate sulfate
Aluminum chloride
Ferric chloride
Ferrous chloride
Ferric sulfate
Ferrous sulfate

Question 15

What are some problems that may occur when nitrifying?

Answer 15

Dispersed growth
Filamentous bulking
Loss of chlorine disinfection
Low pH
Denitrification in final clarifiers

Question 16

How can we control problems associated with nitrification?

Answer 16

Lower aeration rates

Lower MLSS concentration (nitrifying bacteria are slow growing so lower MLSS will be younger)

Adding alkalinity

Question 17

What is a bulking sludge?

Answer 17

One that settles or compacts slowly

SVI >150

Question 18

What are some problems associated with bulking sludge?

Answer 18

Loss of sludge in effluent
Environment damage and permit violation
Compromises disinfection
Excessive return rates
Sludge disposal

Question 19

What are the primary filaments that cause bulking?

Answer 19

Nocardia
Microthrix parvicella
Type 1863

Question 20

What does nocardial foam look like?

Answer 20

Thick, stable, brown

Found in aeration basins or clarifiers

Question 21

How can you correct a filament problem?

Answer 21

Identify the filament and remove conditions favorable for its growth

Temporary foam control methods include polymer and chlorination

Question 22

How can you control foaming associated with filaments?

Answer 22

Limit FOG
Lower Sludge Age
Carry sufficient DO
Chlorinated sprays