newch 10-2 denitrification 2012-2 [호환 모드].pdf

7/24/2019 NewCh 10-2 Denitrification 2012-2 [ ].pdf

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Example 10.1 Stoichiometry of denitr ification reactions

Denitrification scheme

eterotrop c w t met ano

Heterotrophic with acetate

Autotrophic with H2

Parameters

f0s values : 0.36, 0.52, 0.21

Compute the overall Stoichiometric reactions for each system


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Example 10.1 Stoichiometry of denitrification reactions

1. Calculate the fs, fe

2. Cell synthesis (Rc) with NO3 ( Equation C-2, Table 2.4, same for all)

3. Acce tor e uation Ra E uation I-7 Table 2.2 same for all

4. Donor equation (Rd) ( methanol, acetate, H2, Table 2.3)

5. Compute the stoichiometric equation

[3.33]1

110 xdss b

b)f(ff

+

+=

]37.2[dcsae RRfRfR +=


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i) Heterotrophic with Methanol

Assumption : b = 0.05/day(Table 10.1) , fd=0.8 for all system

fs fe1. Calculate fs, fe0.267 0.733

2. Cell synthesis equation

OH2811NOHC

281eH

2829CO

285NO

281 2275

-2

-3 ++++

+

3. Acceptor equation OH5

3N

10

1eH

5

6NO5

122

--

3 +++ +

4. Donor equation OH1

OHCH1

eHCO1

23

-

2 +++ +


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1112951 -- +

2828282828. 227523

O)H5

3N

10

1eH

5

6NO5

1(0.733 22

--

3 +++ +

cs

aeRf

-

223 eHCO61OH

261OHCH

61 +++ +

dR

-33 0.1561HNO15610OH0.1667CH ++ +

.

222275 0.119COO0.3781HN07330NOHC009540 +++ ..


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i) Heterotrophic with methanol

222275

-

33

0.119COO0.3781HN07330NOHC009540

0.1561HNO15610OH0.1667CH

+++

++ +

..

.

ii) Heterotrophic with acetate

OH1542.00.0639CO0.125HCON0658.0NOHC0122.00.1438HNO1438.0COO0.125CH

22

-

32275

-

3

-

3

++++

++ +

0.1773HCO02460NO177300.5H 2-

32 +++ +

..

u o rop c w 2

. 22275 ..

Table 10.2.


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Summary of Example 10.1


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Summary of Example 10.1

1. The observed yield of denitrifiers (fs ) declines significantly from acetate tomethanol to H2 as the donor.

~ - - -. . .

The great % (13 %) is associated with the greatest fs (0.342).For acetate, e- eq as N-source =0.342 x (8/28) = 0.098 (eqns. at p.502)

% of e- eq = (0.098/0.756) x 100 = 13 %.

3. 28.6 % of the oxygen demand of the biomass is invested in reducing the N-source (NO3

-) to the -3 oxidation state.

4. For heterotrophic nitrification with acetate requires an input of

~ 4g BODL / g NO3- -N and produces ~ 0.69 g VSS of biomass (=sludgewasting rate) and 3.6 g as CaCO3 of alkalinity (= buffer requirement).


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10.3 One-Sludge Denitrification

Tertiary denitrification : the water does not contain the necessary electron

donor and thus an exogenous electron donor must be provided.

One-sludge denitrification : the water contains an electron donor that can

drive denitrification.

- One-sludge denitrification (= single-sludge = combined denitrification)

- Two goals in one-sludge denitrification :

1) Providing aerobic conditions that allow full nitrification

2) Providing anoxic conditions and Reserving BOD (organic electron donor)for denitrification.

*1) and 2) seems to conflict with each other, but they should be done simultaneously .

Conse uentl the task is to how to reconcile them.


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10.3.1 Basic One-Sludge Strategies

Influent wastewater contains TKN. In one sludge denitrification, the TKN must

be oxidized to NO3- - N without oxidizing all the BOD before denitrification

takes place.

Total Kjeldahl nitrogen (TKN) = organic BOD and reduced nitrogen (NH4+)

,

all one-sludge processes rely on one or more of three basic strategies.

Three basic strategies for reserving organic electron donor while nitrification

takes place :

1) Biomass storage and decay

2 Classical redenitrification

3) Simultaneous nitrif ication with denitrif ication


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10.3.1 1) Biomass storage and decay

- The synthesis of biomass stores electron equivalents that originally camefrom the BOD and can be released through endogenous respiration to

.

TKN NO3--N

BOD: partly oxidized and

NO3--N N2

Biomass as electron donorendo enous res iration

Fig.10.1 (a) biomass storage and decay


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10.3.1 1) Biomass storage and decay

- It is called Wuhrmann biomass decayer (Swiss engineer K. Wuhrmann, 1964)

-

employed as a stand-alone process due to two shortcomings:

= .

a high conc. of MLVSS (operating problems with settler and recycle)

high capital costs are necessary

2) the decay of biomass always releasesNH4 -N from the anoxic step although at

concentrations lower than in the influent.


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10.3.1 Classical predenitrification

- The first tank (anoxic) ; the influent BOD (electron donor) is directly utilizedfor denitrification.

- The second tank aerobic the influent TKN is nitrified to NO-and

any remained BOD is oxidized.

- The nitrate formed in the aerobic tank is recycled to a anoxic tank (Qr2

; large)--(electron donor) for denitrification

3Remained BOD: aerobically consumed

. .

(b) classical predenitrification


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-Fractional removal of N = ~2

2

r

r

QQ

Q

+

Q : plant flow rate

Qr2 : mixed-liquor

recycle flow rate

- The large recycle flow of NO3-

from the second to the first tank

is necessary, because NO3-

not recycledleaves in the effluent.

- Recycle ratios of 400 percent or more

are employed to bring enough NO3

-

removals are substantial.


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Widespread use worldwide;

- Advantages:

i) direct use of influent BOD for denitrification

reduces aeration costs for the removal of BOD

aster net cs t an w t omass storage an ecay

iii) no release of NH4+-N in the effluent

- Disadvantage:

i) large mixed-liquor recycle rate

ncreases cos s o p p ng an pump ng


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10.3.1 Simultaneous nitrification with denitrif ication

Three factors allow all reactions to occur simultaneously.

1) Various nitrogen reductases using N as e- acceptor are repressed

only when the D.O. conc. is well above 1 mg/L.

2) However, inhibition of the nitrogen reductase is not severe when the D.O.

conc. is less than 1 mg/L.

2223 NONNONONO

ductaseNitriteOHNOHeNO

ductaseNitrateOHNOHeNO

Re2

Re22 223

+=++

+=++

+

+

ductaseOxideNitricOHONHeNO Re222 22 +=++

+

+

222


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Three factors allow all reactions to occur simultaneously.

. . .

treatment systems; thus, denitrification can occur inside the floc (or biofilm),

as long as the electron donor (BOD) penetrates inside.

- When D.O. concentration is poised at a suitably low level (< ~ 1 mg/L),

anoxic denitrification can occur in arallel to the aerobic reactions of

nitrification and aerobic BOD oxidation.

Fig.10.1 (c) simultaneous nitrification with denitrification


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- 100 percent N removal by simultaneous nitrification with denitrification

, ,

amounts of denitrification probably occur in most activated sludge

systems that nitrify and have D.O. conc. below saturation (deSilva, 1997)

- Simultaneous nitrification with denitrification offers all the advantages

of predenitrification, but overcomes the main disadvantage, the high

recycle rate.

- Maintainin a low D.O. conc. throu hout one reactor creates an infinitel

high recycle ratio and allows essentially 100 percent N removal.

-

: We do not yet know the combinations of SRT, HRT, and D.O. conc. that

.


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10.3.1Epilog for One-Sludge Processes

Common features of all one-sludge processes :

- one community (or one sludge) of microorganisms carries out all the

reactions.

- The heterotrophs switch back and forth between aerobic and

anoxic respiration, or they do both simultaneously.

- Because the nitrifiers are slow growing autotrophs,their growth rate controls the SRT needed. SRTs greater than 15 days

are requ re n mos cases, some mes muc onger s are use .

- The longer SRTs provide an added safety factor for the nitrifiers,who experience periods of low or zero DO.

- The long SRTs mean that accumulation of inert suspended solids is important.


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10.3.1Epilog for One-Sludge Processes

Common features of all one-sludge processes :

- A practical outcome of a long SRT is that the HRT (in settler) needs to

increase in order to keep the MLSS conc. within reasonable limits dictated by

Thats why settler parameters for one-sludge denitrification is similar to

those used for extended aeration activated sludge.

- HRTs for predinitrification and simultaneous nitrification with denitrificationare at least 10 h for typical sewage, and 24 h or greater are used in some

ns ances.

- To overcome the limitations of one-sludge denitrification, the Barnardprocess, sequencing batch reactor (SBR), and biofilm systems are

developed.


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10.3.2 Variations on the Basic One-Sludge processes

Barnard process (1975) by Dr. J. Barnard of South Africa

50 mg/L TKN Influent TKN : 50 mg/L

recycle ratio (Qr2 ) from reactor 2 to 1

: 400 % eac or : en r ca on ra e s o

recycled input and 80 % of the influent TKN(Qr2=400%) 10 mg/L (20%)

Reactor 2

NO3--N/L leaving : 10 mg/L (20%) 3 mg NH4

+-N /L

Reactor :endogenous decay of cells

- 0.3 mg NH4+-N is released per mg NO3-N

due to endogenous cell decay 3 mg NO3--N/L

-Because 10 mg/L of NO3-N is converted to

N2 gas, Reactor 3 releases 3mg NH3-N/L

(6 %)

Reactor 4 releases 3 mg NO3

-N/L

Final effluent TKN : 3 mg NO3-N/L

Total removal rate : 94 %Fig.10.2 Schematic of the Barnard process


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10.3.2 Variations on the Basic One-Sludge processes

50 mg/L TKN

Barnard process

-denitrification process (> 90% N removal)

10 mg/L

3 mg NH4+-N /L Drawbacks- need many tanks

3 mg NO3--N/L

- ong

- significant mixed-liquor recycle

(400 %)between reactors 2 and 1

Fig.10.2 Schematic of the Barnard process

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