2. Factors determining nitrification rate in
MBBR
• The load organic matter.
• The oxygen concentration.
• The ammonium concentration.
• pH and alcalinity.
• Waste water temperature.
3. Nitrification design.Limiting factors.
Organic load.
Figure shows the effect of BOD loading on nitrification
rates at different oxygen levels
Conclusion :
Part of the aerobic reactor must be designed with a
Low loading rate for organic matter removal upstream
of nitrification reactor. This will helps that nitrification
rate can be achieved in the downstream nitrifying stage
resulting a more economical design.
Target of 1st part fo organic removal is that organic
surface loading rate on the nitrifications tanks to be
below 0.5 BOD5/m2 d
Low loading rate value for this chamber will be obtained
from
𝑅 𝐵𝑂𝐷5 = 4,5 ∗ 1.06 𝑇−10
4. Nitrification design.Limiting factors.
Oxigen and ammonia concentration
Figure illustrates the influence of ammonia concentration in
the nitrification rate at different dissolved oxygen levels. NH4-N
is only limiting at low concentrations (<1-2 mg NH4-N/l)
Nitrification rate( when NH4-N) is the limiting substrate will be
R𝑛 = 𝑘 ∗ 𝜃(𝑇−10)
𝑆𝑛 0.7
Rn=Nitrification rate
Sn=NH4-N concentration in the reactor
k = reactor rate constant k will be dependent upon the C/N-ratio (g BOD5/g NH4-
N) on of the incoming water to the bioreactor and vary from 0,7 at C/N = 0,5 (
with primary and pre-DN) to 0,5 at C/N = 4,5 (no primary or pre-DN)
θ= 1.09
At higher bulk concentration , Sn will eb replaced will be controlled by bulk
liquid DO concentratiom and Sn will be replaced by
Sn transition=
(𝐷𝑂−0,5)
3,2
DO=Dissolved oxygen level
5. Nitrification design.
Ammonium area loading rates ( SALR)
Ammonia area load ;gr NH4-N/m2*d
NITRIFICATION (1)
Ammonia area loading rate = Rn ( Nitrification rate)
(1) Provided that organic surface loading rate on the nitrifications tanks to be below 0.5 BOD5/m2 d , required ammonia removal efficiency below 90%
or target effluent ammonia concentration NH4-N below 2-3 mg/l
NITRIFICATION (2)
-1st compartment SLAR = Rn ( Nitrification rate)
-2nd compartment SALR= Half of the 1st compartment
(2) If required ammonia removal efficiency below 90% or target effluent ammonia concentration NH4-N below 2-3 mg/l, the nitrification volume will
be divided in two compartments
*An assimilation factor of approx. 4% of the organic matter removed in the organic matter removal chamber must be
taken into consideration in the nitrification design
6. Pre-Denitrification
Factors determining de nitrification rate
• Presence of suitable carbon source in a proper carbon to nitrogen
ratio in the reactor.
• Wastewater temperature.
• Oxigen carryover from upstream process steps or recirculation flow.
7. Factors determining pre-denitrification rate
in MBBR. Oxigen carry over
• Recirculation should be limited to a region where DO in
pre-DN stays low ( < 0,5 mg/l)
• Nitrification MBBR is operated at higher DO
concentrations ( 4-7 mg/l) , typically several times
higher than the values at the end of conventional
nitrification zones ( 2 mg/l) so nitrates recirculation
values must be limited to avoid oxygen recycled to
consume available carbon source
• Nitrate recirculation factor is limited to less < 250%
of Q aver. When recirculation flow of 250%, the
nitrogen removal efficiency will be limited between
65% to 75%. When it is required a higher efficiency
pre denitrification will not be enough
• De-oxygenation reactor in order to reduce the amount
of recycled 02 is usually include. Ammonium area load
< 0.225
8. Factors determining pre denitrification rate
in MBBR. Carbon source
• Figures shows the impact of low BSOCD
and low C/N on pre denitrification rate .
• The C/N-ratio in incoming water to pre-DN
reactor should be guaranteed to be > 4 g
BOD5/g NO3-Nequiv. Below this ratio ( 4 ) as
shown in figure , predenitrification will have
a very limited efficiency
9. Factors determining post-denitrification
rate in MBBR. Carbon source
• C/N ratio of incoming water to post
DN stage is a limiting factor. It must be
guaranteed> 3gr BOD5/gr NO3-Nequi
• As long as BOD soluble , biodegradable
BSCOD-conc is> 10 mg/l, carbon is not
a limiting source
10. Factors determining postdenitrificaion rate
in MBBR.
• Post D-N are dependent on
choice of external source with a
limited impact of temperature.
Ethanol gives the best results as
external carbon source
• If very low effluent NO3-N (< 1-4
mg/l) is required, NO3-N may be the
limiting factor and determining
the DN-rate (KS = 0,5-2,0 mg NO3/l)
11. Design values . Pre-denitrification and
post-denitrification loading rates
NOx-Nequi area load: gr NOx-N/m2*d
• PRE-DENITRIFICATION (1)
NOx-Nequi area load < 0.5 Norweain guidelines
(1) Provided that the C/N-ratio in in-coming water to pre-DN reactor is > 5 g BOD5/g NO3-Nequiv,in and residual concentration out can be >3 mg NOx-N/l. If the C/N-ratio
is < 5 g BOD5/g NO3-Nekviv,in,the rate is to be reduced from the given value at C/N-ratio = 5 g BOD5/g NO3-Nekviv,in to 0 at C/N-ratio = 2 g BOD5/g NO3-Nekviv,in . If
there are two pre-DN stages in series, the first one is to be designed as indicated in the table, while the second is to be designed for < 0,30 g NOx-N/m2d 4 Provided that
recycled flow from nitrification reactor is = 250% of Qaver if 70 % tot N-removal is to be achieved by pre-denitrification alone
• POSTDENITRIFICATION (2)
NOx-Nequi area load < 1.5 Norweain guidelines
(2) Provided that external carbon source is added equiv. to C/N-ratio of incoming water to post-DN stage > 3 g BOD5/g NO3-Nequiv. And residual concentration of NO3-N
may be > 3 mg NO3-N/l. If residual concentration can be > 3 mg NO3-N/l.
If NO3-N must be <3 mg NO3-N/l. the DN step must be divided in two reactors, designed for maximum rate if norweian guidelines in 1st reactor and half of that value
in second reactor. If only one reactor is possible, design it for half of the maximum design rate
If NO3-N must be <1 mg NO3-N/l. the DN step must be divided in three reactors, with the 3rd ine for a quarter of the maximum rate
12. Design values . Predenitrification and
post denitrification values.
NOx-Nequi area load: gr NOx-N/m2*d
• COMBINED PRE AND POST DENITRIFICATION
Predenitrification (1)
NOx-Nequi area load < 0.5 gN0z-n/m2d Norweain guidelines
(1) Provided that the C/N-ratio in in-coming water to pre-DN reactor is > 5 g BOD5/g NO3-Nequiv,in and residual concentration out can be >3 mg
NOx-N/l. If the C/N-ratio is < 5 g BOD5/g NO3-Nekviv,in,the rate is to be reduced from the given value at C/N-ratio = 5 g BOD5/g NO3-Nekviv,in to
0 at C/N-ratio = 2 g BOD5/g NO3-Nekviv,in . If there are two pre-DN stages in series, the first one is to be designed as indicated in the table, while
the second is to be designed for < 0,30 g NOx-N/m2d 4 Provided that recycled flow from nitrification reactor is = 250% of Qaver if 70 % tot N-
removal is to be achieved by pre-denitrification alone
Post denitrification (2)
NOx-Nequi area load < 0.9 gN0z-n/m2d
(2) Provided that external carbon source is added equiv. to C/N-ratio of incoming water to post-DN stage > 3 g BOD5/g NO3-Nequiv. And residual
concentration of NO3-N may be > 3 mg NO3-N/l. If residual concentration can be > 3 mg NO3-N/l.
If NO3-N must be <3 mg NO3-N/l. the DN step must be divided in two reactors, designed for maximum rate if Norweian guidelines in 1st reactor
and half of that value in second reactor. If only one reactor is possible, design it for half of the maximum design rate
If NO3-N must be <1 mg NO3-N/l. the DN step must be divided in three reactors, with the 3rd Line for a quarter of the maximum rate
13. The combined pre and post –DN MBBR
process
1 ST COMPARTMENT
Anoxic (pre-denitrification) and receives recycled nitrate
from the last aerobic compartment.
2ND COMPARTMENT
The second compartment may be operated both anoxically
(no air) and aerobically (with air).
3RD, 4TH COMPARTMENT
Used for residual organic matter removal and nitrification.
5TH COMPARTMENT
De oxigentaion tank used for nitrification and this
compartment may be operated with or without aeration.
Oxigen level must be kept below 2 mg/l
6th COMPARTMENT
carbon is added, is anoxic and for post denitrification.
7TH COMPARTMENT
optionally a small aerobic compartment for oxygenation as
well as for removal of any residual biodegradable organic
matter.
15. Conclusion denitrification
Predenitrification advantages
• Pre-anoxic denitrification is suitable if C/N > 4 and target %
Removal of N < 75%
• Ensures maximum utilization of the biodegradable COD
• Ensures partial recovery of the alkalinity consumed in the
nitrification process
Postdenitrification advantages
• Lower volume required (40-50%)Better control of nitrogen
removal process
• No limit for de-nitrification
• Post-anoxic de nitrification or combined ( recommended)
should be used if C/N < 4 or target % Removal of N > 75%
16. Combined pre and postdenitrification
• Treatment result independent upon C/N of raw water
• Total reactor volume may be optimally utilized with
respect to seasonal variations
• Phosphate will not limit post-denitrification
• Chemical consumption in post-denitrification is
reduced
• < 5mg Tot N/L can be achieved
Conclusion de-nitrification
17. MBBR separation alternatives.
Primary stage
Settling/Lamella settling
Typically is achieving STT<15 mg/l and <0.5 mg/l TotP at dosages of
around 10–15 mg/l Fe + 1–2 mg/l anionic polymer
Hydraulic flow rate 1 m/h
Microsand ballasted lamella settling
Typically is achieving SST <10 mg/l and <0.5 mg/l TotP at dosages of
around 10–15 mg/l Fe + 1–2 mg/l anionic polymer
The average rise rate in the clarifier tank of the plants that are in
operation is 72 m /h , ranging from 35 to 120 m/h
DAF
Outlet values : SST < 10 mg/l P< 0.5 mg/l ( with metal
coagulant addition )
Overflow rate: 5-7.5 m/h at design flow and 10m/h at
maximum flow
18. MBBR separation alternatives .Secondary
stage
Hydraulic capacity
Average hydraulic capacity at 20
mgS/L influent : 7,5 m/h
Effluent SS and P versus influent
SS
Effluent SS< 5 mg/l3.
Total P< 0.2 mg/l
19. MBBR separation alternatives .Secondary
stage
Filtration
After primary stage separation ( usually DAF)
Outlet values : SST < 5mg/l P< 0.2 mg/l ( with metal coagulant addition
Maximum filtration rate : 8.2 m/h
Direct filtration ( possible)
If SS and BOD removal is required a cationic polymer alone would be
enough
Maximum filtration rate : 4-5m/h
20. MBBR separation alternatives .Secondary
stage
MBBR+DISKFILTER+UF
TSS<1 mg/l and Total P<0.1 mg/l
40 μm disc filter for minimum foot print. to be optimized
A cationic polymer with/or metal salt ahead of the disc filter
Recommended design flux for ultrafiltration is 25 l m2 h
MBBR+DAF+UF
TSS<1 mg/l and <0.1 mg/l TotP
Recommended design flux for ultrafiltration is 25 l m2 h
MBBR+UF
Recommended design flux for ultrafiltration is 50l m2 h
