Download - Nutrient Removal
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Nutrient Removal
Objective:•To understand the fundamental principles of nutrient removal using chemical and biological methods•To know examples of the major wastewater treatment processes for nutrient removal.
–Reference: “Operation of municipal wastewater treatment plants. Manual of Practice 11, Vol2 (1996). Water Environment Federation “
–http://www.staff.ncl.ac.uk/p.j.sallis/teach.html•see section ‘CIV912’; user and password both cassie
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Nutrient Removal
Introduction
Chemical Methods
Principle of Biological Nitrogen Removal
Biological Nitrogen Removal Processes
Principle of Biological Phosphorus Removal
Biological Phosphorus Removal Processes
Combined Biological N & P Removal Processes
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Pretreatment Sed Tank
Aerobic Biological
Process
SedTank
Final Effluent
InfluentBOD 300SS 300TKN 50PO4 15
BOD <20SS <30TKN >20PO4 >10
PrimarySludge
SecondarySludge
Nutrient levels in a Conventional Aerobic Treatment Plant
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Nutrient Cycles
• Eutrophication potential– Nutrient balance
C:N:P (100:5:1)
10,000 pe x 200 l/d x 15mgN/l 500kg algae/d
10,000 pe x 200 l/d x 5mgP/l 1200kg algae/d
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Nutrient Removal - Standards -
UWWT Directive (1991):
Pop >10,000 N<15mg/l P<2mg/l
Pop >100,000 N<10mg/l P<1mg/l
or 80% removal of Total P
70 - 80% removal of Total N
(The above applies to “sensitive waters”)
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Chemical Methods
• Nitrogen– Ammonia stripping at high pH (Lime, CaO)
NH4+ + OH- NH3 + H2O
• Phosphorus– Precipitation by metal ions
Ca(OH)2 + HPO42- Ca5(OH)(PO4)3
Al2(SO4)3 + PO43- AlPO4 + SO4
2-
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Biological Nutrient Removal
• Assimilation– C, N, P, S etc uptake for synthesis of new cells
• Dissimilation– C, N, S, oxidized/reduced to provide energy
• Aerobic (oxic)– in the presence of molecular oxygen (O2)
• Anoxic– very low concentration of molecular oxygen (O2) – significant levels of electron acceptors (NO3
-, SO4-)
• Anaerobic– no oxygen, lack of electron acceptors (only CO2)
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Biological Nitrogen Removal
• Wastewaters contain: Org-N, ammonia, (nitrate)
• Dissimilatory metabolism
• Nitrification1. NH4
+ + 1.5 O2 NO2- + 2H+ + H2O
Nitrosomonas2. NO2
- + 0.5 O2 NO3- (nitrified
effluent)Nitrobacter
• DenitrificationNO3
- + CH2 + H+ N2 + CO2 + H2O
denitrifying bacteria (many)
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Anoxic(denitrification)
Aerobic
Influent
Effluent
N2
Basic Nitrogen Removal System(Ludzak-Ettinger Process)
Sedimentation Tank
RAS
QR
Modified L-E Processhas recycle (QR)
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Aerobic +Nitrification
Anoxic(denitrification)
Aerobic
Methanol
Influent
Effluent
N2
Re-aeration for Excess MethanolRemoval
Alternative Nitrogen Removal System
Sedimentation Tank
RASRAS
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Biological Phosphorus Removal
• Selection of Bacteria in Sludge – Luxury uptake of Phosphorus
• (Acinetobacter, Pseudomonas)
– Cyclic Environmental Conditions• High BOD when anaerobic
• Low BOD when aerobic
• Sidestream – P is stripped from sludge in separate unit process
• Mainstream– P is concentrated to high levels in the sludge (biomass)
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Selection of Bacteria
AerobicLow BOD
Carbon Oxidation(PHA oxidised to CO2,
releases energy)
Phosphate uptake (Luxury)(PO4 polyP)*
AnaerobicHigh BOD
Carbon uptake(fatty acids stored as
poly hydroxy alkanoates PHA)*
Phosphate released from cells(polyP PO4, energy released)
* These processes need energy to drive them
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Aeration Tank
Sed.Tank
Waste ChemicalSludge (P)
Lime
RAS
Phosphorus Stripped Sludge
Supernatant Return
Waste Sludge
Influent Effluent
Primary Effluent(BOD, Elutriation)
PhoStrip Process (Sidestream)
AnaerobicStripper
P
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AerationBOD Rem
Nitrific-ation
PhoStrip
Denitrification
Final Effluent
Waste Chemical Sludge (P)
RAS
Phosphorus FreeSludge
Methanol
Aerobic
Anoxic
AnaerobicSedimentation
Combined N & P Removal
N2
P
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NH3 to NO3
HRT= 3-6 hHRT=
0.5-1.0hHRT=
0.5-1.0h
Anaerobic
AnoxicAerobic Settling Tank
Nitrified Re-cycle (100-200%Q)
RAS (50-100%Q)
(= 6% P)
AnoxicRe-cycle(100%Q)
Q
Combined N & P Removal (Mainstream) (UNIVERSITY OF CAPE TOWN PROCESS , UCT)
WAS (P)
N2
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Operational Considerations
• Maintain discrete environments– excess recycle rate gives completely mixed system
• Limitations– Combined System optimized for N (denitrification), biological P
removal non-optimized (requires chemical supplementation)
• Efficiency– denitrification re-uses Oxygen bound in the nitrate
• Contingency– provide P removal by chemical means (when biological process
fails)