Activated Sludge Design for Industrial Wastewaters Presented by AquAeTer, Inc. W. Wesley Eckenfelder, Jr. D.Sc., P.E.
Activated Sludge Design for Industrial Wastewaters
Presented by AquAeTer, Inc.y q ,W. Wesley Eckenfelder, Jr. D.Sc., P.E.
F t ff ti th A ti t d Sl dFactors affecting the Activated Sludge Design for Industrial Wastewaters:
1. Aeration Power Density affects floc size and active masssize and active mass
2. MLVSS composition, active and inactive biomass, degradable and non-inactive biomass, degradable and nondegradable influent VSS
3. Reaction coefficient K, a function of3. Reaction coefficient K, a function of wastewater composition
4. Biological reaction, a function of4. Biological reaction, a function of temperature
Variation in Kinetic Constant with Mixing IntensityMixing Intensity
K(day-1)K(day )
B h 10Bench 10
Pilot 5.3
Full Scale 2.8
Activated Sludge Kinetics
• Conventionally related to the mixed and lower volatile solids, MLVSS.
• The MLVSS however is comprised of active and inactive biomass non degradableand inactive biomass, non-degradable influent VSS and residual degradable VSS.
• Only the Active biomass contributes to the organic removal.
• The active fraction of the biomass can be computed: p
a bf
θ2011
=c
a bf
θ2.01+
This is shown in the following figure.
• The degradable VSS are oxidized as a function of sludge age. This g gfollows a first order reaction.
• The degradation of municipal primary VSS is shown in theprimary VSS is shown in the following figure.
Oxidation of Degradable VSS• Degradable particulate VSS degradation is a
function of sludge age, θc.
A j it ll d d ithi 10 d• A majority usually degrades within a 10-day sludge age.
(Data for a municipal wastewater)
• The VSS are completely degraded with a sludge age of 10 days. The degradation properties of industrial VSS would have to be experimentally determineddetermined.
• Non-degradable primary VSS will accumulate in the ML.
• The fraction of non-degradable VSS in the ML can be calculated:
=xvt
vf ci
ND
θ
==
xx
v
i Influent non degradable VSS
MLVSS
=t Hydraulic detention time
• This relationship is shown in the following figure.
Biological Fraction of Mixed Liquor Volatile Suspended Solids (MLVSS)
1.0
0 9
o Inert influent volatile suspended solids also accumulate in the mixed
ctio
n
0.9
0.7
0.8
0.6
solids also accumulate in the mixed liquor as a function of sludge age.
olog
ical
Frac
0.5
0.6
0.3
0.4
Bio
0.2
0.1
0.0
Influent Non-biodegradable VSS
10-day Sludge Age 30-day Sludge Age
0 20 40 60 80 100 120 140 160
Calculation of Active BiomassMLVSS = 2500 mg/LMLVSS 2500 mg/LNon-degradable VSS = 30 mg/LSludge Age = 20 daysSludge Age = 20 daysDetention Times = 1.5 daysNon-degradable MLVSS =Active Biomass
16.05.12500
2030=
⋅⋅
71.0200201
1==fic e o ass
Active Biomass=
2002.01 ⋅+f
l/52617108402500Active Biomass= lm /526,171.084.02500 =⋅⋅
• Most wastewaters consist of multiple organics of variable degradation rates.g g
• In an acclimated system most of these• In an acclimated system most of these organics are degraded simultaneously, but at different ratesbut at different rates.
Schematic Representation of Multi-component Substrate Removal
A
tion A + B + C
(a) (b)
B
CCon
cent
rat
CO
D
B + C
C
Timet1 t2
C
t1 t2Time
(c)
gC
OD
(c)
Log
Xvb*t
Biodegradation Coefficient (K)(Complete Mix System)
tXS
bv
r
erS
SK tX
S=
bv
obvStX
oe
SS
do
e
c
bX - SSK a
θ1
=
• In a batch or plug flow system the degradation follows a pseudo first order reaction.
• In a complete mix process the organic removal rate is a function of the fraction or
i i i i th biorganic remaining, since the biomass removes the more readily degradable first.
• Optimal design of activated sludge for industrial wastewater is a multistage gsystem. A maximum removal rate is achieved in the first stage at high g gorganic concentration. The limitation is a maximum power density of 750 p yHP/mg of aeration volume.
Effect of Temperature on Biological Oxidation Rate Constant, K
)20(TC20T θKK −°=
Fl Di iffici
ent,
K
Floc Dispersion
onR
ate
Coe
IncreasedEffluent TSS
Rea
ctio
Mixed Liquor Temperature, °C4 32 39
Temperature Coefficient
Industrial Wastewaters 1 065 1 10Industrial Wastewaters 1.065 – 1.10Municipal Wastewaters 1.015
Endogenous 1.04
Effect of Temperature on the Reaction Rate
for a Bleached Sulfite Mill Wastewaterfor a Bleached Sulfite Mill Wastewater
Denitrification
NO3– + BOD → N2 + CO2 + H2O +OH– + CELLS
~3.0 g BOD are consumed/g NO3-N reduced~0.45 g New Cells are produced/g BOD removedg p g~3.57 g of alkalinity are formed/g NO3-N reduced
RDN = Denitrification rate, g NO3-N/g VSS-dayRDN Denitrification rate, g NO3 N/g VSS dayandRDN T = RDN 20° • 1.09(T-20) • fa
ODN
V
R
SeSK
tXS
•=• OV StX •
S = BOD removedSR = BOD removedXV = MLVSS
t = detention timeS ffl BODSe = effluent BODSo = influent BOD
KDN = anoxic reaction rate coefficientDN
9
Comparison Between Aerobic and Anoxic Degradable Substrate Removal
9
8
7
g/L)
6
5
Subs
trat
e (m
g
4
3
2
1Aerobic Anoxic
Time (hr)
00 5 10 15 20 25
C i f A bi d A i Ki i
Anoxic Aerobic
Comparison of Aerobic and Anoxic Kinetic Coefficients (d-1)
Anoxic Aerobic
Pharmaceutical 9 2 21 0Pharmaceutical 9.2 21.0
E d 4 4 6 3Endogenous 4.4 6.3
6 0Pulp and Paper 6.0 --
Denitrification Rate vs. BOD/Ammonia Ratio for a given K
0.5
0.6
day
0.4
g N
o3/m
g V
SS
0.2
0.3
actio
n R
ate,
mg
0.1Den
itrifa
03 3.5 4 4.5 5 5.5
BOD/NO3-N ratio, mg BOD/mg NO3
AquAeTer, Inc.215 Jamestown Park, Suite 100
Brentwood, TN 37027(615) 373-8532
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