6. Dimensioning and Design of Nitrogen_Stefan Rettig
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Transcript of 6. Dimensioning and Design of Nitrogen_Stefan Rettig
Dimensioning and design of nitrogen removal technologies
Dipl.-Ing. S. RettigTU Berlin, Department of Urban water management
Gustav-Meyer-Allee 25, D - 13355 Berlin
Phone: +49 / (0) 30 / 314 72356; Fax: +49 / (0) 30 / 314 72248e-mail: [email protected]
Departement of urban water management 2
Introduction
Biological wastewater treatment: Fixed film (trickling filter, rotating diskfilter) or suspended biomass (activated sludge system)
Predominantly the activated sludge system is practiced
Municipal and industrial wastewater treatment
Basic of the activated sludge system:Combination of aeration tank
+ subsequent sedimentation (clarifier) + return of the separated biomass (return sludge)
Carrier of biological treatment - activated sludge -
Invention of the activated sludge system 1914 (Ardern, Lockett)
Departement of urban water management 3
Basis of dimensioningbasic possibilities
1. Evaluation of available data (normal case)2. Additional specific investigations (series of
measurements), if data is insufficient3. Mathematical determination with known (exceptional
case) Consideration of future development
(mostly with the help of characteristic values) Demography (population development) Residential areas Industry Tourism
Departement of urban water management 4
Cumulative frequency / Undercut frequency
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600
Qo in m3/d
Sum
men
häuf
igke
it [%
]
Undercut [%]
COD-load, inflow
Cum
ulat
ive
frequ
ency
[%]
Bd,COD[1000 kg/d] COD-load
Inflow rate
Departement of urban water management 5
Dimensioning Flows and Loads
The following values are required from the influent to the biologicalreactor:
lowest and highest wastewater temperature
organic load (Bd,BOD Bd,COD), load of suspended solids (Bd,SS) and of phosphorus (Bd,P) for the determination of the sludge production and thus the calculation of the volume of the aeration tank
organic load and nitrogen load for the design of the aeration facilityfor (as a rule) the highest relevant temperature
–Loading condition: BOD/N; highest saisonal peak
maximum inflow rate with dry weather QDW,h (m³/h) for the design of the anaerobic mixing tank and the internal recirculation flow rate
dimensioning inflow rate QWW,h (m³/h) for the design of thesecondary settling tanks
Departement of urban water management 6
Biological Standard ProcessesActivated sludge processes
Elimination of: COD, BOD5, NH4-N, NO3-N, P
Effluent
Aeration
Clarifier
Return sludge
Excess sludge
anoxic zonedenitrification
aerobic zoneCOD-elimination
& nitrification
Recirclation sludge
Influent(primary-treated)
Departement of urban water management 7
Inhabitant-specific loads
g/(Inhabitant·d)
German standard (ATV-DVWK A 131)During biological wastewater treatment process for each kg BOD5 about 0,04-0,05 kg Nitrogen and about 0,01 kg Phosphorus are needed for the development of biomassand discharged in the waste sludge. *) The share returned in the sludge liquor has to be concerned. Thus the loads in theinfluent of the biological treatment stage can increase up to 20 %.
Departement of urban water management 8
Dimensioningof the activated sludge process I
1. Determination of the relevant flows and loads2. Selection of the treatment process
=> Nitrification/Denitrification
Activated sludge tank (Part 1) Set up of a Nitrogen-balanceSelection of the treatment process
Nitrification/Denitrification; P-Elimination; SelectorSelection of the return sludge ratio;
intermitting DN timeDetermination of the denitrification capacityDetermination of the required sludge ageCalculation of the sludge production
Departement of urban water management 9
N in influent:Co,N = Co,org.N + Co,NH4-N+ Co,NO3-N+ Co,NO2-N
Nitrogen balance
Effluent
anoxic zonedenitrification
aerobic zoneCOD-elimination
& nitrification
Excess sludge
aeration
Clarifier
Return sludge
Recirculation sludge
Influent(primary-treated)
N in effluent:Ce,N = Ce,org.N + Ce,NH4-N+ Ce,NO3-N+ Ce,NO2-N
N in sludge:CNWS = 0,04 - 0,05 · Co,BOD5
Co,TKN
Departement of urban water management 10
German effluent regulations for municipal sewage; monitoring values
113 **)10 15 75 > 100.0005218 **)10 20 90 10.000 bis < 100.0004
––10 20 90 5.000 bis < 10.0003
–––25 110 1.000 bis < 5.0002
–––40 150 < 1.0001
tot P
mg/l
Ntot anorg.*
mg/l
NH4-N *)
mg/l
BOD5
mg/l
COD
mg/l
PE based on BOD inlet
60 g BOD5/(PEd)
SizeCategory
PE: population equivalent Abwasserverordnung (AbwV vom 2004)
Departement of urban water management 11
Nitrogen removal procedures (DWA-A 131e, 2000)
Departement of urban water management 12
The operating conditions in aeration tank and secondarysettling tank are influenced through Mixed-liquor suspended solids concentration in the influent to the
secondary settling tank SSEAT
Mixed-liquor suspended solids concentration of the return sludgeSSRS
Return sludge ratio RS = QRS/Q.
Suspended solids mass balance (neglecting XSS,EST)
Return Sludge Ratio I
Departement of urban water management 13
Effluent
Return sludge
Influent QWW,h
QRS = 0.75·QWW,h
max.QRS = 1.0 ·QWW,h
Recirculation sludge
Return Sludge Ratio II
Departement of urban water management 14
Denitrification capacity
(DWA-A 131e, 2000)
Departement of urban water management 15
Sludge age tSS: [d]Average retention time of activated sludge in the activated sludge system
Amount of sludge in the aeration tank MLSSAT VATtSS = = Removed amount of sludge QES MLSSES + Q MLSSE
tSS = 1/(SPd·BSS) tSS = 1/µmax tSS …..10 to 12 days
MLSSAT: Total amount of solids (MLSS) (measured) [g/l or kg/m3]MLSSES: Total amount of solids in the excess sludge
Important design parameterfor activated sludge system
Enough time for the growth of microorganisms
Dimensioning sludge age in days dependent on the treatment target and thetemperature as well as the plant size (intermediate values are to be estimated)
Departement of urban water management 16
Required Sludge Age (DWA-A 131e, 2000)
Departement of urban water management 17
Sludge production SPd
SPd = SPd,BOD + SPd,P SPd,BOD= SPC,BOD * Bd,BOD,ZB
SPd,P [kg/d] = Qd [m³/d] (3 XP,BioP + 6,8 XP,Prec, Fe + 5,3 XP,Prec,Al)/1000(DWA-A 131e, 2000)
Departement of urban water management 18
Dimensioningof the Secondary Settling Tank
1. Selection of the sludge volume index2. Selection of the sludge thickening time tTh; dependent on the biological process
selected3. Determination of the return sludge suspend solids concentration (SSRS)4. Selection of the return sludge ratio (RS) and estimation of the permissible
suspended solids concentration of the activated sludge in the biological reactor(SSAT).VAT reduces with increasing SSAT.AST and tST rises with increasing SSAT.
5. Determination of the surface area of the scondary settling tank (AST) from thepermissible surface overflow rate qa or the sludge volume loading rate qav
6. Determination of the depth of the secondary settling tank from partial depths forthe functional zones and other sepcifications
7. Dimensioning of the sludge removal (scraper)8. Verification of the selected thickening time by the sludge removal (scraper)
performance9. Dimensioning of the return sludge and excess sludge pumps
Transfering: SS-content
Departement of urban water management 19
Sludge volume SV: Volume of sludge after 30 min. settling of 1000 ml activated Volume of sludge after 30 min. settling of 1000 ml activated
sludgesludge Measured value > 250 ml Measured value > 250 ml dilution the sample (factor)dilution the sample (factor) Common values: Common values: 200 200 –– 600 ml600 ml
Sludge volume index SVI: Quotient of sludge volume and liquor suspended solids SVI = SV / MLSS Common values: Common values: 75 75 -- 180 ml/g180 ml/g Bulking sludge Bulking sludge SVI > 150 ml/gSVI > 150 ml/g
Mixed liquor suspended solids MLSS: Content of biomass Content of biomass Common values: Common values: 3 3 -- 6 6 g/lg/l
Characteristic parameters
(Steinke, 2009)
Departement of urban water management 20
Approximate values for theMLSS concentration in thebiological reactor dependent on the sludge volume index forSSRS = 0.7·SSBS
= MLSS
Standard values for the sludge volume index
(DWA-A 131e, 2000)
Departement of urban water management 21
Settlement in horizontal flow tanks
(Austermann-Haun, 2011)
Departement of urban water management 22
2.0 - (2.5)Activated sludge plants with denitrification
1.0 - 1.5Activated sludge plants with nitrification
1.5 - 2.0Activated sludge plants without nitrification
Thickening time tTh [h]Type of wastewater treatment
An exceeding of the thickening time of tE = 2.0 h requires a very advanced denitrification in the biological reactor.
Permitted Thickening Time (tTh)
Departement of urban water management 23
Suspended Solids Concentrationin the bottom sludge
Achievable suspendedsolids concentration in the bottom sludge SSBS
can be estimatedempirically in dependence on the SVI and tTh
(DWA-A 131e, 2000)
Departement of urban water management 24
Surface Overflow Rate and Sludge Volume Surface Loading Rate
The surface overflow rate qA is calculated from thepermitted sludge volume loading rate qSV and the dilutedsludge volume DSV as:
(DWA-A 131e, 2000)
Departement of urban water management 25
QWW,h (m³/h) - Max. inflow rate
SVI (l/kg) - Sludge volume index
SSEAT (kg/m³) - Suspended solidsconcentration in the influent to settling tanks
Effluent
Return sludge
QRS
Dimensioning of the Secondary SettlingTank
Departement of urban water management 26
The required surface area of the secondary settling tank results as follows:
For vertical flow secondary settling tanks the effectivesurface area at the mid-point between inlet aperture and water level is to be set
With this the geometry of normal tank shapes is taken intoaccount
Settling Tank Surface Area
(DWA-A 131e, 2000)
Departement of urban water management 27
Settling Tank Surface Area
Horizontal flow circular secondary settlingtanks
(DWA-A 131e, 2000)
Departement of urban water management 28
Dimensioningof the activated sludge process II
Activated sludge tank (Part 2) Calculation of the volume of the biological reactorDimensioning of aeration (O2-demand; daily peak)Dimensioning of circulation units; design of circulation pumpsType of biological reactorChecking of acid capacity and pH
Takeover: concentration of SS
Departement of urban water management 29
Required mass of suspended solids in biological reactor:MSS,AT = tSS,Dim · SPd [kg]
The volume of the biological reactor is obtained as follows:
As comparative figures the BOD5 volume loading rate (BR) and the sludge loading rate (BSS) can be calculated:
Nitrification BSS= 0,10 kg BOD5/(kgSS·d)
Bd = BOD5 QoNitrification BR =0,35 kg BOD5/(m³·d)
Usual values of MLSS,AT: 2 - 6 g/l
Volume of the Biological Reactor
Departement of urban water management 30
Design of recirculation
t
RS
t
RZRStRC
t
RZ
t
RS
BMorgNeorgNONNNH
ANNO
NNH
QQRF
QQbzwQRFQQ
QQRC
therefore
XSCSwithSS
RC
.*][
:
1
,,,,4
,3
,4
Effluent
Return sludge
Influent QWW,h
Recirculation sludge
Departement of urban water management 31
Dimensioning of aeration (O2-demand)
Oxygen consumption for C-EliminationOUd,C [kg O2/d] = OUC,BOD,spez · Bd,BOD,I
Oxygen consumption for Nitrification
OUd,N [kg O2/d] = Qd * 4,3*(SNO3,D – SNO3,IAT + SNO3,EST)/1000Oxygen consumption for Denitrification (+)
OUd,D [kg O2/d] = Qd * 2,9 * SNO3,D / 1000
Specific oxygen consumption OUC,BOD [kg O2/kg BOD5, validfor CCOD,IAT/CBOD;IAT ≤ 2.2
(DWA-A 131e, 2000)
Departement of urban water management 32
Dimensioning of aeration (Daily peak OUh)
Load cases:
I fN = 1 with fC = x
II fN = x with fC =1
24*)(*
]/[ ,,,2
NdNDdCdCh
OUfOUOUfhkgOOU
with fC and fN = Peak factors for load peaks (appear at different times)
-
1.25
6
2.0
-
1.2
8
1.8
-
1.2
10
-
1.3
4
Sludge age in d
1.5
2.5
1.15
15
2.0fN for BC,BOD,I ≤ 1.200 kg/d
-fN for BC,BOD,I > 6.000 kg/d
1.1fC
25
Departement of urban water management 33
Summary
The calculated tank volumes are highly influenced by thecorrect evalution of the loads (Q, COD, BOD, N- and P-load)
Design based on sludge age
Design of denitrification: capacity of denitrification
Design of secondary settling tanks based on sludge volumeload
Simple calculation according to A 131
Computer-based models according to A 131 or equivalentapproaches