Lecture 7 Flashcards
(29 cards)
How is ammonia removed from wastewater?
Two sequential processes: Nitrification (ammonium oxidised to nitrate) and Denitrification (nitrate reduced to nitrogen gas)
What happens in Nitrification?
Ammonia is oxidised sequentially by two groups of bacteria:
AOB oxidise ammonia to nitrite,
NOB oxidise nitrite to nitrate.
What are the equations for Nitrification?
Step 1:
NH4+ + 1.5O2 → NO2-+ 2H+ + H2O
Step 2:
NO2- + 0.5O2 → NO3-
Overall
NH4+ + 2O2 → NO3- + 2H+ + H2O
What happens in Denitrification?
Reduction of nitrate to any gasseous nitrogen.
Performed by facultative aerobic microorganisms.
2NO3− + 12H+ → N2+ 6 H2O
What is Annamox?
Anaerobic Ammonium Oxidation.
Microroganisms that use ammonium as electron donor and nitrite as electron acceptor.
Shortcut in N removal.
NH4+ + NO2- –> 2H2O + N2
What factors affect microbial activities?
Temperature
pH
Toxic or inhibitory compounds
Bioavailability
Oxygen
Nutrients
Amount of subtrates
What conditions are needed for Nitrification?
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 is there low oxygen in aerated system?
Centre of floc has low DO.
Post denitrification make first reactor oxic and second reactor anoxic
Pre denitrification make first anoxic second oxic
What conditions are needed for Denitrification?
5-60 degrees
pH range of 6-8 below 6 incomplete reduction, nitrite accumulates.
Low dissolved O2.
What conditions for Annamox?
Anoxic conditions.
Slow growers so slow startup
elevated temperatures
mesophilic conditions
Outcompeted by nitrifiers
Advantages of annamox?
No external carbon needed.
Less O2 required.
No CO2 emissions.
Lower sludge treatment cost
What are the considerations for N removal?
Nitrification: two N2O producing pathways
Oxidation of Hydroxylamine or reduction of NO2-.
Denitrification: incomplete denitrification produces N2O
What is the most common method of P removal?
dosing metal salts to the CAS reactors, or to the outlet of secondary clarifiers.
What happens to the added salt?
Added salt precipitates which can be filtered.
Separation of chemically bonded P is difficult.
What are phosphate accumulationg organisms?
PAOs are bacteria that store excess P in their cells.
What is Enhanced Biological Phosphorus Removal?
PAOs are encouraged to grow and consume P, in reactor configurations that give them advantages over other bacteria.
Design considerations for EBPR?
Presence of VFAs in anaerobic phase of cycle.
Influent BOD:P ratio of 25:1.
Strict anoxic conditions.
Aerobic treatment.
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.
Anaerobic degradation.
both respiration and fermentation.
No external electron acceptors, uses internal cell products.
Less energy+ partial subtrate breakdown + less cells.
What is anaerobic digestion?
Breakdown of organic material to biogas, CO2, trace amount of H2S.
Very little energy.
Glucose-> 3CO2+3CH4.
Energy is renewable from methane produced.
Anaerobic Digestion process.
Hydrolysis
Acidogenesis
Acetogenesis
Methanogenesis
What is hydrolysis?
External process.
Leads to release of monomeric producs.
Carried out by hydrolytic bacteria.
Produce enzymes.
What is Acidogenesis?
Many non hydrolytic fermantitive species scavenge monomeric products.
Very wide range of fermentation products depending on pathways.
What is Acetogenesis?
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.
