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Achieving nitrification in pure oxygen activated sludge by seeding
e:>
Pergamon
Wat. Sci. Tech. Vol. 37, No. 4-5, pp. 573-577, 1998. 1998 IA wQ. Published by ElsevIer Science Lid Printed in Greal Brilain.
PH: S0273-1223(98)00162-0
0273-1223/98 $19 00 + 0'00
ACHIEVING NITRIFICATION IN PURE OXYGEN ACTIVATED SLUDGE BY SEEDING J. B. Neethling*. Carlo Spani**. Joe Danzer** and Bruce Willey*** • HDR Engineering Inc., 271 Turn Pike Drive, Folsom CA 95630, USA •• Unified Sewage Agency, 155 Nonh First Avenue, Hillsboro, OR 97/24, USA ••• HDR Engineering Inc., 4500 SW Kruse Way, Lake Oswego, OR 97035-2564, USA
ABSTRACf An innovative "seeding" approach was used to increase the nitrification capacity of a pure oxygen activated sludge plant. In Ihis approach, waste activated sludge from a parallel air activated sludge system was used 10 seed nitrifiers to the pure oxygen plant to increase the apparent sludge age and achieve nitrification under the high loading in the pure oxygen system. Calculations indicate that nitrification can be achieved at a traditional sludge age of 3 days with a seeding rate of 20 percent. Full-scale tests showed that nitrification can be achieved at a seed rate of 35 percent and a traditional sludge age of 4.6 days, producing effluent ammonia below 5 mgll. Secondary clarification remained good during the operation of the system even at the higher solids loading rates, with effluent TSS concentrations at 6 mgll. © 1998 IAWQ. Published by Elsevier Science Ltd
KEYWORDS Kinetics; nitrification; pure oxygen activated sludge; sludge age; startup. INTRODUCfION The Unified Sewage Agency (USA) of Portland, OR, Rock Creek Wastewater Treatment Plant has two side• by-side activated sludge plants: a dissolved air (DA) activated sludge process and a high purity oxygen (HPO) plant (Figure I). This allowed USA to meet seasonal discharge limits for nitrification in summer and treat high winter flows for BOD removal only. The HPO activated sludge process can achieve high rate treatment due to the high oxygen transfer rates possible. However, because nitrifiers grow relatively slowly, the required sludge age for nitrification is significantly higher than the I to 3 days used in a typical pure oxygen activated sludge. The unique combination of processes available at USA's Rock Creek plant provided for an innovative solution to achieve nitrification in the high rate pure oxygen system: by transferring waste activated sludge from the diffused aeration activated sludge plant to the pure oxygen system to serve as a seed to the nitrifier population in the pure oxygen system. 573
574
J. B. NEETIlLING et al.
MATERIALS AND METHODS Samples were collect daily using composite samplers. All measurements were conducted according to Standard Methods. The dynamic sludge age was used (Vaccari et at., 1985). On April 26, 1994, the sludge age in the DA activated sludge basin was increased to 12 days to start nitrification, and by May 20, the air side was fulIy nitrifying. On May 26, 1994, waste activated sludge from the air side was sent to the HPO side. Dissolved Air (DA) Activated Sludge
' - - - - - - - - - . . . . . - ,...... ~ WAS
High Purity Oxygen (HPO) Activated Sludge
Figure I. Flow schematic of rock creek activated sludge processes.
THEORETICAL CONSIDERATIONS Consider the simple complete mixed activated sludge system with seed (stream 2) added (see Nomenclature for definition). The conventional sludge age of the system is defined as:
Mass in System Mass removed per day
o =-------":------:-• x
(I)
The sludge age determines the efficiency of the reactor operation (Lawrence and McCarty, 1970). The bacterial growth rate is related to the sludge age as follows for a system without seeding: Without seed: -
1
Ox
f.Jrm.'S
= Net growth rate = - - - b K, +S
(2)
However, if the influent seed is added to the system, the effective growth rate of the bacteria is increased and the sludge age can be calculated as:
Mass in System X V o'.' = Net mass =-----'--'---removed per day QsX +Q6X6 -Q2X2 7
7
(3)
s
From equations 2 and 3 we have: With seed:
1 1 -=--p
Ox.,
Ox
x
(4)
Achieving nitrification
In
pure oxygen
575
where P = Massseedadded per day = Q)X) .. Q2 X 2
•
MassinSystem
X,V,
(5)
X,V,
Figure 2 shows the effective or seeded sludge age as a function of the seed rate for systems operating at a conventionally calculated sludge age of I, 2, and 3 days. The seeded sludge age rapidly increases as seed is added and with nitrifiers in the seed, nitrification in the high rate system could readily be established. For the example. a system operating at a conventional sludge age of 2 days and seeding rate of 35 percent will have a seeded sludge age of nearly 7 days. 10 -r-----j>---t-...,..--,--,---t--,
i •
"
3.
..""
• 4
i
I Figure 2. Impact of seeding on effective sludge age of activated sludge system.
RESULTS AND DISCUSSION Table I shows the operating parameters for the DA and HPO activated sludge systems during the test. The seed consisted of 3,600 kgld waste activated sludge from the DA side to the HPO side. Table I. Typical Operating Parameters Activated Sludge Processes. Parameter Influent (primary emuent) Flow,MUd BOD,mgIL TSS,mgIL NH4,mgNIL pH Alkalinity, mgIL Bum Volume, mA 3 MLSS,mgIL OO,mgIL
Seed rate, per day
laOueat
Air S)'Item (DA)
Pure Oxnea S)'Item(HPO)
53 122 116 26
53 7 4 0.15 (0.01-0.8) 8.2 130
19 10 5 2.2 (0.03-6.4) 6.7 185
-
12,300
--0
3,500 4,100 5 0.35
Sludge age (without seed), day.
12
4.6
Net sludge age (with seed), days
N.A.
>10
Figure 3 shows that the effluent ammonia concentration rapidly decreased after seeding staned, and reached 1-5 mg Nil within two weeks, until operation stabilized below I mgll after about a month of operation. During this period the solids inventory in the aeration basin was increased slowly from 2.000 mgll to about 4.000 mgll. The sludge age (excluding seed) remained at about 3 days. The sludge age including seed increased steadily with time indicating the favorable environment for nitrifier growth. The only change in operation was the addition of the seed, as shown in Figure 3, and nitrification was established immediately.
576
J B NEETHLING et al. 25
"oi
Cl <{
-::--_ _..,
~
20
'"
Cl
"i"ii
15
;J
z
10
Cl
E
..; J:
5
Z
c:
'"
0.1-_-_-
~"
U...Ac:w".
-
-
--->-'"'
__
1• ..,Apr...
Effluont NH4 - - Siudgo Ago counting sood Siudgo ago oxcluding sood
Figure 3 Imp."t 01 ,eedmg on ,Iudge age and nllnficallon oj High Punty Oxygen (HPO) actIvated ,Iudge plant
The nitrification rate In the ~eeded HPO basin was 5.9 mg Nlllhr and hydraulic retention time 4.4 hours. The pure oxygen ,y'tem wa, able to mamtam the DO at about 5 mg/1. Note that the pH and alkalinity in the HPO basin wa~ quite low compared to the DA sIde. a~ typically found in pure oxygen ~ystems. Earlier batch tests ~howed a dramatic decrea,e In nItrification rate when the pH in the batch reactor dropped below 7.0. However. thi, inhibition was not observed In the full scale system. 30
~
i
'. j
:
'0
i20
~i E~
,
,---..,..--~--H------,-------_r 300
,_.\".";r
250
'",
200
:;;
ui~
~ '0 10
100 '"
~~
sw"
hgure
~
~
150 E
50 0 +-_-_ _-
...J-
0
Sewnd.lr} Clanllcr Perlormance Dunng Seedmg 01 High Purity Oxygen ACllvaled Sludge Plant
FIgure 4 ~how~ the 'econdary clarifier loading and performance during the test period. Effluent TSS concentration rema1l1ed excellent. averaging 5 mg/1. compared to 4 mg/I on the air ~Ide. The SVI increased during the cour~e of the ~ludy. It I~ not clear what Impact seeding had on the SVI of the proces,. The SVI on the DA '!de dUring thl~ period Increa~ed from about 100 to 200 mUg. Thl~ SVI Increa~e was cau~ed by S.IIt/(/II/.\ growth 111 the DA 'Ide. The growth I' thought to be cau,ed by an up~tream plant that dl~charges wa~te activated ,Iudge to the ,ewer CONCLUSION
,I
Seeding hIgh pUrity oxygen activated ~Iudge with waste activated sludge from a fully nItrifying activated ,Iudge ~y'tem produced nllrlflcatlon In the high loaded HPO 'y,tem. Adding 35 percent ,ceding to the ,olid~ Inventory reduced the ammOnIa concentration to below 5 mg/I WIthin 3 day~. It took over 3 week, to bring ammOnIa concelllr.ltlon, below 0.5 mg/1.
577
Achieving nitrification in pure oxygen
Secondary clarifier performance remained excellent during the seeding, even though the solids loading to the clarifiers increased. SVI increases during the period, is attributed to filamentous seed to the plant. REFERENCES Lawrence. A. W.• McCarty. P. L. (I970). Unified Basis for Biological Treatment Design and Operation. J. Sani,. Eng. Div. Am. Soc. Civ. Engrs.• 96. 757-778. Vaccari, D. A.. Fagedes, T., Longtin. I. (1985). Calculation of Mean Cell Residence Time for Unsteady-State Activated Sludge Systems. Biotechnol. Bioeng.• 27. 695-703. NOMENCLATURE
b Px Q S V
X
ex ex•s
Jimax
= = = = = = = = =
Endogenous decay rate, d-I Seed rate, d-I Flow, Mild Substrate concentration, mgll Volume.MI Solids concentration, mgll Conventional sludge age, d Seeded sludge age, d Maximum growth rate, d-I
=Seed
-h1lFS2: r 2
6
5
Pergamon
Wat. Sci. Tech. Vol. 37, No. 4-5, pp. 573-577, 1998.
PH: S0273-1223(98)00162-0
0273-1223/98 $19 00 + 0'00
ACHIEVING NITRIFICATION IN PURE OXYGEN ACTIVATED SLUDGE BY SEEDING J. B. Neethling*. Carlo Spani**. Joe Danzer** and Bruce Willey*** • HDR Engineering Inc., 271 Turn Pike Drive, Folsom CA 95630, USA •• Unified Sewage Agency, 155 Nonh First Avenue, Hillsboro, OR 97/24, USA ••• HDR Engineering Inc., 4500 SW Kruse Way, Lake Oswego, OR 97035-2564, USA
ABSTRACf An innovative "seeding" approach was used to increase the nitrification capacity of a pure oxygen activated sludge plant. In Ihis approach, waste activated sludge from a parallel air activated sludge system was used 10 seed nitrifiers to the pure oxygen plant to increase the apparent sludge age and achieve nitrification under the high loading in the pure oxygen system. Calculations indicate that nitrification can be achieved at a traditional sludge age of 3 days with a seeding rate of 20 percent. Full-scale tests showed that nitrification can be achieved at a seed rate of 35 percent and a traditional sludge age of 4.6 days, producing effluent ammonia below 5 mgll. Secondary clarification remained good during the operation of the system even at the higher solids loading rates, with effluent TSS concentrations at 6 mgll. © 1998 IAWQ. Published by Elsevier Science Ltd
KEYWORDS Kinetics; nitrification; pure oxygen activated sludge; sludge age; startup. INTRODUCfION The Unified Sewage Agency (USA) of Portland, OR, Rock Creek Wastewater Treatment Plant has two side• by-side activated sludge plants: a dissolved air (DA) activated sludge process and a high purity oxygen (HPO) plant (Figure I). This allowed USA to meet seasonal discharge limits for nitrification in summer and treat high winter flows for BOD removal only. The HPO activated sludge process can achieve high rate treatment due to the high oxygen transfer rates possible. However, because nitrifiers grow relatively slowly, the required sludge age for nitrification is significantly higher than the I to 3 days used in a typical pure oxygen activated sludge. The unique combination of processes available at USA's Rock Creek plant provided for an innovative solution to achieve nitrification in the high rate pure oxygen system: by transferring waste activated sludge from the diffused aeration activated sludge plant to the pure oxygen system to serve as a seed to the nitrifier population in the pure oxygen system. 573
574
J. B. NEETIlLING et al.
MATERIALS AND METHODS Samples were collect daily using composite samplers. All measurements were conducted according to Standard Methods. The dynamic sludge age was used (Vaccari et at., 1985). On April 26, 1994, the sludge age in the DA activated sludge basin was increased to 12 days to start nitrification, and by May 20, the air side was fulIy nitrifying. On May 26, 1994, waste activated sludge from the air side was sent to the HPO side. Dissolved Air (DA) Activated Sludge
' - - - - - - - - - . . . . . - ,...... ~ WAS
High Purity Oxygen (HPO) Activated Sludge
Figure I. Flow schematic of rock creek activated sludge processes.
THEORETICAL CONSIDERATIONS Consider the simple complete mixed activated sludge system with seed (stream 2) added (see Nomenclature for definition). The conventional sludge age of the system is defined as:
Mass in System Mass removed per day
o =-------":------:-• x
(I)
The sludge age determines the efficiency of the reactor operation (Lawrence and McCarty, 1970). The bacterial growth rate is related to the sludge age as follows for a system without seeding: Without seed: -
1
Ox
f.Jrm.'S
= Net growth rate = - - - b K, +S
(2)
However, if the influent seed is added to the system, the effective growth rate of the bacteria is increased and the sludge age can be calculated as:
Mass in System X V o'.' = Net mass =-----'--'---removed per day QsX +Q6X6 -Q2X2 7
7
(3)
s
From equations 2 and 3 we have: With seed:
1 1 -=--p
Ox.,
Ox
x
(4)
Achieving nitrification
In
pure oxygen
575
where P = Massseedadded per day = Q)X) .. Q2 X 2
•
MassinSystem
X,V,
(5)
X,V,
Figure 2 shows the effective or seeded sludge age as a function of the seed rate for systems operating at a conventionally calculated sludge age of I, 2, and 3 days. The seeded sludge age rapidly increases as seed is added and with nitrifiers in the seed, nitrification in the high rate system could readily be established. For the example. a system operating at a conventional sludge age of 2 days and seeding rate of 35 percent will have a seeded sludge age of nearly 7 days. 10 -r-----j>---t-...,..--,--,---t--,
i •
"
3.
..""
• 4
i
I Figure 2. Impact of seeding on effective sludge age of activated sludge system.
RESULTS AND DISCUSSION Table I shows the operating parameters for the DA and HPO activated sludge systems during the test. The seed consisted of 3,600 kgld waste activated sludge from the DA side to the HPO side. Table I. Typical Operating Parameters Activated Sludge Processes. Parameter Influent (primary emuent) Flow,MUd BOD,mgIL TSS,mgIL NH4,mgNIL pH Alkalinity, mgIL Bum Volume, mA 3 MLSS,mgIL OO,mgIL
Seed rate, per day
laOueat
Air S)'Item (DA)
Pure Oxnea S)'Item(HPO)
53 122 116 26
53 7 4 0.15 (0.01-0.8) 8.2 130
19 10 5 2.2 (0.03-6.4) 6.7 185
-
12,300
--0
3,500 4,100 5 0.35
Sludge age (without seed), day.
12
4.6
Net sludge age (with seed), days
N.A.
>10
Figure 3 shows that the effluent ammonia concentration rapidly decreased after seeding staned, and reached 1-5 mg Nil within two weeks, until operation stabilized below I mgll after about a month of operation. During this period the solids inventory in the aeration basin was increased slowly from 2.000 mgll to about 4.000 mgll. The sludge age (excluding seed) remained at about 3 days. The sludge age including seed increased steadily with time indicating the favorable environment for nitrifier growth. The only change in operation was the addition of the seed, as shown in Figure 3, and nitrification was established immediately.
576
J B NEETHLING et al. 25
"oi
Cl <{
-::--_ _..,
~
20
'"
Cl
"i"ii
15
;J
z
10
Cl
E
..; J:
5
Z
c:
'"
0.1-_-_-
~"
U...Ac:w".
-
-
--->-'"'
__
1• ..,Apr...
Effluont NH4 - - Siudgo Ago counting sood Siudgo ago oxcluding sood
Figure 3 Imp."t 01 ,eedmg on ,Iudge age and nllnficallon oj High Punty Oxygen (HPO) actIvated ,Iudge plant
The nitrification rate In the ~eeded HPO basin was 5.9 mg Nlllhr and hydraulic retention time 4.4 hours. The pure oxygen ,y'tem wa, able to mamtam the DO at about 5 mg/1. Note that the pH and alkalinity in the HPO basin wa~ quite low compared to the DA sIde. a~ typically found in pure oxygen ~ystems. Earlier batch tests ~howed a dramatic decrea,e In nItrification rate when the pH in the batch reactor dropped below 7.0. However. thi, inhibition was not observed In the full scale system. 30
~
i
'. j
:
'0
i20
~i E~
,
,---..,..--~--H------,-------_r 300
,_.\".";r
250
'",
200
:;;
ui~
~ '0 10
100 '"
~~
sw"
hgure
~
~
150 E
50 0 +-_-_ _-
...J-
0
Sewnd.lr} Clanllcr Perlormance Dunng Seedmg 01 High Purity Oxygen ACllvaled Sludge Plant
FIgure 4 ~how~ the 'econdary clarifier loading and performance during the test period. Effluent TSS concentration rema1l1ed excellent. averaging 5 mg/1. compared to 4 mg/I on the air ~Ide. The SVI increased during the cour~e of the ~ludy. It I~ not clear what Impact seeding had on the SVI of the proces,. The SVI on the DA '!de dUring thl~ period Increa~ed from about 100 to 200 mUg. Thl~ SVI Increa~e was cau~ed by S.IIt/(/II/.\ growth 111 the DA 'Ide. The growth I' thought to be cau,ed by an up~tream plant that dl~charges wa~te activated ,Iudge to the ,ewer CONCLUSION
,I
Seeding hIgh pUrity oxygen activated ~Iudge with waste activated sludge from a fully nItrifying activated ,Iudge ~y'tem produced nllrlflcatlon In the high loaded HPO 'y,tem. Adding 35 percent ,ceding to the ,olid~ Inventory reduced the ammOnIa concentration to below 5 mg/I WIthin 3 day~. It took over 3 week, to bring ammOnIa concelllr.ltlon, below 0.5 mg/1.
577
Achieving nitrification in pure oxygen
Secondary clarifier performance remained excellent during the seeding, even though the solids loading to the clarifiers increased. SVI increases during the period, is attributed to filamentous seed to the plant. REFERENCES Lawrence. A. W.• McCarty. P. L. (I970). Unified Basis for Biological Treatment Design and Operation. J. Sani,. Eng. Div. Am. Soc. Civ. Engrs.• 96. 757-778. Vaccari, D. A.. Fagedes, T., Longtin. I. (1985). Calculation of Mean Cell Residence Time for Unsteady-State Activated Sludge Systems. Biotechnol. Bioeng.• 27. 695-703. NOMENCLATURE
b Px Q S V
X
ex ex•s
Jimax
= = = = = = = = =
Endogenous decay rate, d-I Seed rate, d-I Flow, Mild Substrate concentration, mgll Volume.MI Solids concentration, mgll Conventional sludge age, d Seeded sludge age, d Maximum growth rate, d-I
=Seed
-h1lFS2: r 2
6
5