Lecture 7 Flashcards

(29 cards)

1
Q

How is ammonia removed from wastewater?

A

Two sequential processes: Nitrification (ammonium oxidised to nitrate) and Denitrification (nitrate reduced to nitrogen gas)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What happens in Nitrification?

A

Ammonia is oxidised sequentially by two groups of bacteria:
AOB oxidise ammonia to nitrite,
NOB oxidise nitrite to nitrate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the equations for Nitrification?

A

Step 1:
NH4+ + 1.5O2 → NO2-+ 2H+ + H2O
Step 2:
NO2- + 0.5O2 → NO3-
Overall
NH4+ + 2O2 → NO3- + 2H+ + H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What happens in Denitrification?

A

Reduction of nitrate to any gasseous nitrogen.
Performed by facultative aerobic microorganisms.
2NO3− + 12H+ → N2+ 6 H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is Annamox?

A

Anaerobic Ammonium Oxidation.
Microroganisms that use ammonium as electron donor and nitrite as electron acceptor.
Shortcut in N removal.
NH4+ + NO2- –> 2H2O + N2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What factors affect microbial activities?

A

Temperature
pH
Toxic or inhibitory compounds
Bioavailability
Oxygen
Nutrients
Amount of subtrates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What conditions are needed for Nitrification?

A

min 0.5 mg O2/L.
High sludge retention time as nitrifiers grow slowly.
Produces protons decreasing pH so a buffer is needed so that AOB and NOB or not inhibited.
pH range of 5.5-9.
5-40 degrees.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How is there low oxygen in aerated system?

A

Centre of floc has low DO.
Post denitrification make first reactor oxic and second reactor anoxic
Pre denitrification make first anoxic second oxic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What conditions are needed for Denitrification?

A

5-60 degrees
pH range of 6-8 below 6 incomplete reduction, nitrite accumulates.
Low dissolved O2.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What conditions for Annamox?

A

Anoxic conditions.
Slow growers so slow startup
elevated temperatures
mesophilic conditions
Outcompeted by nitrifiers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Advantages of annamox?

A

No external carbon needed.
Less O2 required.
No CO2 emissions.
Lower sludge treatment cost

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the considerations for N removal?

A

Nitrification: two N2O producing pathways
Oxidation of Hydroxylamine or reduction of NO2-.
Denitrification: incomplete denitrification produces N2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the most common method of P removal?

A

dosing metal salts to the CAS reactors, or to the outlet of secondary clarifiers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens to the added salt?

A

Added salt precipitates which can be filtered.
Separation of chemically bonded P is difficult.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are phosphate accumulationg organisms?

A

PAOs are bacteria that store excess P in their cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is Enhanced Biological Phosphorus Removal?

A

PAOs are encouraged to grow and consume P, in reactor configurations that give them advantages over other bacteria.

14
Q

Design considerations for EBPR?

A

Presence of VFAs in anaerobic phase of cycle.
Influent BOD:P ratio of 25:1.
Strict anoxic conditions.

15
Q

Aerobic treatment.

A

Full breakdown of organic material.
Releases a lot of energy, microbial excess biomass must be disposed of.
Intense aeration required so costly and uses great amount of energy.

16
Q

Anaerobic degradation.

A

both respiration and fermentation.
No external electron acceptors, uses internal cell products.
Less energy+ partial subtrate breakdown + less cells.

16
Q

What is anaerobic digestion?

A

Breakdown of organic material to biogas, CO2, trace amount of H2S.
Very little energy.
Glucose-> 3CO2+3CH4.
Energy is renewable from methane produced.

17
Q

Anaerobic Digestion process.

A

Hydrolysis
Acidogenesis
Acetogenesis
Methanogenesis

18
Q

What is hydrolysis?

A

External process.
Leads to release of monomeric producs.
Carried out by hydrolytic bacteria.
Produce enzymes.

19
Q

What is Acidogenesis?

A

Many non hydrolytic fermantitive species scavenge monomeric products.
Very wide range of fermentation products depending on pathways.

20
Q

What is Acetogenesis?

A

Generates substrates for methanogens.
Catalysed by OHPA.
or homoacetic bacteria coverting H2 and CO2 to acetate.
OHPA can only direct energy producing reactions if H2 pressure is low.
H2 must be removed by species.

21
What is Methanogenesis?
catalyse final stage. Archaea not bacteria. grow slowly.
22
Factors affecting Methanogenesis.
Neutral pH High ammonia concentration is toxic Sulfide toxicity Heavy metal toxicity Toxicity from other compounds
23
Design considerations
Need to know about activity and growth rates. Fraction of energy available for cell synthesis. Growth yield of new cells. Rate of substance utilisation. Endogenous decay coefficent.
24
What is needed for digester?
Feedstock, includes wastewater,manure, food waste, green waste, sewage sludge, energy crops.
25
Consideration for wastewater treatment
Low strength high volume so less methane produced, short volumetric rates required, long retention times. Improved bioreactor design. For cooler climates: Low temperature reduces reaction rate, decay rate, specific growth rate, substrate utilisation. Even longer SRT required. Increased dissolved gasses and viscosity.