Transcript NUTRIENT REMOVAL - Newcastle University

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
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
Nutrient levels in a Conventional
Aerobic Treatment Plant
Pretreatment
Sed
Tank
Influent
BOD 300
SS 300
TKN 50
PO4 15
Primary
Sludge
Final Effluent
BOD
SS
TKN
PO4
Aerobic
Biological
Process
<20
<30
>20
>10
Sed
Tank
Secondary
Sludge
Nutrient Cycles
• Eutrophication potential
– Nutrient balance
C:N:P (100:5:1)
10,000 pe x 200 l/d x 15mgN/l 
algae/d
10,000 pe x 200 l/d x 5mgP/l
algae/d

500kg
1200kg
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”)
Chemical Methods
• Nitrogen
– Ammonia stripping at high pH (Lime, CaO)
NH4+ + OHNH3  + H2O
• Phosphorus
– Precipitation by metal ions
Ca(OH)2 + HPO42-
Ca5(OH)(PO4)3
Al2(SO4)3 + PO43-
AlPO4 + SO42-
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)
Biological Nitrogen Removal
• Wastewaters contain: Org-N, ammonia, (nitrate)
• Dissimilatory metabolism
• Nitrification
1.
NH4+ + 1.5 O2
NO2- + 2H+ + H2O
Nitrosomonas
2.
NO2- + 0.5 O2
NO3-
(nitrified effluent)
Nitrobacter
• Denitrification
NO3- + CH2 + H+
N2 + CO2 + H2O
denitrifying bacteria (many)
Basic Nitrogen Removal System
(Ludzak-Ettinger Process)
Effluent
N2
Influent
Anoxic
(denitrification)
Aerobic
QR
RAS
Sedimentation Tank
Modified L-E Process
has recycle (QR)
Alternative Nitrogen Removal System
Effluent
Influent
Aerobic +
Nitrification
RAS
Sedimentation Tank
N2
Methanol
Anoxic
(denitrification)
RAS
Aerobic
Re-aeration for
Excess Methanol
Removal
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)
Selection of Bacteria
Anaerobic
High BOD
Carbon uptake
(fatty acids stored as
poly hydroxy alkanoates PHA)*
Phosphate released from cells
(polyP  PO4, energy released)
Aerobic
Low BOD
Carbon Oxidation
(PHA oxidised to CO2,
releases energy)
Phosphate uptake (Luxury)
(PO4  polyP)*
* These processes need energy to drive them
PhoStrip Process (Sidestream)
Influent
Aeration
Tank
Sed.
Tank
Effluent
RAS
Waste Sludge
Phosphorus Stripped Sludge
Anaerobic
Stripper
Primary Effluent
(BOD, Elutriation)
Supernatant Return
P
Lime
Waste Chemical
Sludge (P)
Combined N & P Removal
Methanol
Aeration
BOD Rem
Nitrific
-ation
N2
Denitrification
RAS
Phosphorus Free
Sludge
Aerobic
PhoStrip
P
Waste Chemical
Sludge (P)
Anoxic
Sedimentation
Anaerobic
Final
Effluent
Combined N & P Removal (Mainstream)
(UNIVERSITY OF CAPE TOWN PROCESS , UCT)
Anoxic
Re-cycle
(100%Q)
Q
HRT=
0.5-1.0h
Anaerobic
Anoxic
Aerobic
Nitrified Re-cycle (100-200%Q)
N2
HRT=
0.5-1.0h
NH3 to NO3
HRT= 3-6 h
RAS (50-100%Q)
Settling Tank
WAS (P)
(= 6% P)
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)