control of alkalinity of a full-scale biogas plant

1

Control of alkalinity of a full-scale biogas plant treating wastewaterfrom the cleaning of car tanks transporting food and fodder

adaption of biogas production to the demand andverification of Nordmann titration method for measuring VOA and alkalinity

Wolfgang Pfeiffer2, Van Than Nguyen1,2, Jan Neumann3, Dirk Awe4, Jens Tränckner1

1The University of Rostock, Germany2The University of Wismar, Germany3TS-Clean Tank- und Siloreinigung Neumann GmbH, Germany4Rotaria Energie-und Umwelttechnik GmbH, Germany

Leipzig, 26-27 March 2019

2

Contents

• Cleaning of tanks for food and fodder road transports

• Characteristics of the highly polluted WW from the cleaning

• Old and new concept for highly polluted WW disposal

• Physicochemical model for anaerobic digestion process

• Experimental data

• Verification of Nordmann titration method with McGhee equation

• Full-scale biogas plant – construction, performance, feasibility

TS Clean Company (Fahrbinde, Germany)three cleaning sites: Fahrbinde, Kavelstorf, Neudientendorf

• 38 different types of food and fodder are cleaned at 3 sites

sugar, chocolate, fat and oil, milk, glycerol…

• App. 200 tanks/week are cleaned in site Fahrbinde (app. 35m3 highly polluted WW)

• App. 100 tanks/week are cleaned in sites Kavelstorf, Neudietendorf(app. 25m3 highly polluted WW)

• All cleaning with softened tap water

Figure 01: Cleaning lanes at TS-Clean plant Fahrbinde3

Introduction

0 20 40 60 80 100 120 140 160 180 200 220 240

0

10

20

30

40

50

60

70

80

90

100

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

COD and VS of WW (g/L)

Dis

trib

utio

n(%

)

pH and COD/VS ratio of WW

pH

COD/VS

COD

VS

Figure 02: Characteristic of cleaning WW of TS Clean company 4

• Highly polluted wastewater

average 110 gCOD/L

Characteristic of the highly polluted wastewater from tank cleaning

• Widely pre-acidified

pH < 4

• due to softened water usedin cleaning

low buffer capacity

Figure 03: Old concept of WW treatment at Fahrbinde, Germany

old concept

Natural gas

Tap water

Tank car

Tank car

Steam generator

Collection tank50m3

WWTP Rastow

Rastow community

1st phase cleaning(160oC, 80oC)

2nd phase cleaning (80oC, cold water)

45m3/d

Grease traps 16tons/month

Blowdown salt water

Domestic wastewater

Co-digestion

2-3g/l COD

7m3/d,110g/l CODWWTP

5

Wastewater disposal site Fahrbinde

Figure 04: New concept of WW treatment at Fahrbinde, Germany6

old concept

new concept

Research focus

Digester effluent

Natural gas

Tap water

Tank car

Tank car

Steam generator

Collection tank50m3

WWTP Rastow

Rastow community

1st phase cleaning (160oC, 80oC)

2nd phase cleaning (80oC, cold water)

45m3/d

Grease traps 16tons/month

Blowdown salt water

Domestic wastewater

Co- digestion

2-3g/l COD

7m3/d,110g/l COD

NaHCO3

Micronutrients

Flocculation

Anaerobic digester Sludge

OLR

Anaerobic digestion stability

No effect on the aerobic treatment process

Storage

Filtrate

Biogas

WWTP

Solid removal

Wastewater disposal site Fahrbinde

7

Physicochemical model

Biogas CH4 %-vol 59.4

kg CO2 %-vol 31.3

m3 N2 %-vol 2.5

O2 %-vol 0.7

Q-WW m3/d 12 H2O %-vol 5.0

COD-WW kg/m3 100 P bar 1.063 H2S ppm 110

mg/L mmol/L Digestate mg/L mmol/L

Na+ 200 8.7 Na

+ 703.3 30.6

K+ 515 13.2 T °C 39±0.5 K

+ 577.7 14.8

Mg2+ 70 2.9 Mg

2+ 43.33 1.8

Ca2+ 215 5.4 Y Ca

2+ 186.7 4.7

Total N 632 45.1 N-NHx 174 12.4

Total P 165 5.3 P-PO4 150 4.8

S 95 2.7 S 56.67 1.8

Cl- 295 8.3

Biogas composition

NaHCO3 X

pH

Alkalinity

VOA

Figure 05: Steady state physicochemical model for anaerobic pretreatment of strongly polluted WW

Physicochemical model:

• Relation of pH and alkalinity

Physicochemical model:

• CO2 absorption equilibrium

• Chemical equilibria for NH3, carbonic acid, phosphoric acid

• Ions balance

Input concentration:

• Digester effluent analysis of three independent steady state effluent analysis

Figure 06: Addition of NaHCO3 for control of the digester pH and digester alkalinity

8

Physicochemical model

1.7 2.2 2.7 3.2 3.7 4.2 4.7 5.2 5.7 6.2 6.7 7.2

6.6

6.7

6.8

6.9

7.0

7.1

7.2

7.3

7.4

7.5

7.6

7.7

0 1 2 3 4 5 6 7 8 9 10

Digester alkalinity (gCaCO3/L)

Dig

est

er

pH

Addition of NaHCO3 (kg/m3 of wastewater)

Literature

Finding:

• The addition of NaHCO3/Na2CO3 is crucial for maintaining the digester pH in the optimal range

• With no addition of NaHCO3, digester pH shall fall below 6.95

• 2.4 kg NaHCO3/m3 WW or

1.2 kg Na2CO3/m3 WW has to be added in

order to maintain digester pH and alkalinity in the optimal range

Figure 07: Results of bench scale experiments with provoked digester imbalance (a) and pilot scale experiments with digester stability (b)

Finding: No addition of NaHCO3

• Alkalinity decreased in operation

• Alkalinity below 3 gCaCO3/L caused:

o increase volatile organic acid (VOA),

o drop in pH,

o decrease of biogas production 9

Experimental data

Finding: Alkalinity is controlled by addition of NaHCO3

• pH is stable at 7.15-7.20

• Alkalinity is maintained at 3.5 gCaCO3/L

• Biogas yield = 1.48 m3/m3 reactor/day

6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

0

1

2

3

4

5

6

7

0 60 120 180 240 300 360 420 480 540 600 660 720 780

Dig

este

r pH

Bio

gas p

roduction

(m

3/m

3/d

ay)

VO

A a

nd a

lkalin

ity (g

/L)

Operation time(day)

Alkalinity VOA Biogas production pH

constant OLR increase OLR

foam

optimize OLR

(b)

6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

0

1

2

3

4

5

6

7

8

9

10

0 60 120 180 240 300 360 420 480 540 600 660

Dig

este

r pH

Bio

gas p

roduction (L/d

ay)

VO

A a

nd a

lkalin

ity (g/L

)

Operation time(day)

Alkalinity VOA Biogas production pH

(a)

10

Nordmann titration method

0

10

20

30

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14

%

pH

[HCOO-] [CH3COO-] [C2H5COO-] [C3H7COO-] [C4H9COO-] [HCO3-] [CO32-]

Alkalinity:From pH = initialto pH = 5.0

HCO3- CO2

Ac- HAc

73.7%

98%

64.5%

4.25%

VOA:From pH = 5.0to pH = 4.4

Ac- HAc

HCO3- CO2

1.1%

31.4%

Sample

Figu

re 0

8:

pH

dep

end

ent

dis

soci

atio

n o

f V

OA

an

d H

2CO

3

Figure 09: McGhee data (a) and equation versus physicochemical calculation (b)

11

Verification of Nordmann titration method with McGhee equation

(a)

Finding:

• The higher value of the factor of the McGhee empirical equation compensates the in general increasing alkalinity with increasing VOA concentration

• Without an increasing alkalinity (adding NaHCO3) with increasing VOA the initial pH drops below pH = 5.0 and a Nordmann titration is not possible

y = 2.06x + 0.15R² = 1

y = 1.84x + 0.07R² = 1

y = 1.84x + 0.16R² = 1

y = 1.84x + 0.26R² = 1

y = 1.84x + 0.43R² = 1

y = 1.84x + 0.63R² = 1

y = 1.84x + 1.06R² = 1

y = 1.84x + 1.26R² = 1

0

1

2

3

4

5

6

7

8

9

10

11

12

13

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 6.0

mL H

2S

O4/ p

H u

nit

VOA (gCH3COOH/L)

McGhee equation add 0.5gNaHCO3/L add 1.2gNaHCO3/L add 2gNaHCO3/L

add 3.36gNaHCO3/L add 5gNaHCO3/L add 8.4gNaHCO3/L add 10gNaHCO3/L

Measuring zone

Measuring zone

Measuring

zone

Measuring zone

Measuring zone

(b)

Figure 10: Verifying VOA (a) and alkalinity (b) in spiked distilled water with the FOS/TAC 2000

12

Finding:

• The measured H2SO4 consumptions correlate well with the McGhee equation (R² = 0.92 – 0.97)

• The FOS/TAC 2000 is well performance measuring VOA and alkalinity in synthetic wastewater


y = 2.06x + 0.15R² = 1

y = 1.9954x + 0.1948R² = 0.9547

y = 1.8074x + 0.4034R² = 0.9768

y = 1.8136x + 0.5824R² = 0.9677

y = 1.8285x + 0.1419R² = 0.9717

y = 1.8362x + 0.0983R² = 0.9283

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

mL H

2S

O4/p

H u

nit

measure

d w

ith F

OS

/TA

C 2

000

VOA in spiked distilled water (gCH3COOH/L)

McGhee equation Add 1gNaHCO3/L Add 2gNaHCO3/L

Add 3.4g NaHCO3/L Add 5g NaHCO3/L Add 8.4g NaHCO3/L

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

Alk

alin

ity (gC

aC

O3/L

)

VOA in spiked distilled water (gCH3COOH/L)

Add 1gNaHCO3/L Add 2gNaHCO3/L Add 3.4g NaHCO3/L

Add 5g NaHCO3/L Add 8.4g NaHCO3/L Alkalinity calculated

(b)(a)

Figure 11: H2SO4 consumption over VOA in spiked filtrate of the biogas plant effluent Fahrbinde (a) and of spiked filtrate of digested sewage sludge from WWTP Wismar (b)

13

Finding:

• The FOS/TAC 2000 is well performance measuring VOA in filtrates; for the filtrates of the digested sewage sludge from WWTP Wismar is not so good, but acceptable with respect to the low concentrations evaluated


y = 2.06x + 0.15R² = 1

y = 2.1664x + 0.1065R² = 0.998

y = 1.932x + 0.0685R² = 0.9923

y = 2.1245x + 0.0976R² = 0.9973

y = 2.1066x - 0.0821R² = 0.9891

y = 1.7869x + 0.2392R² = 0.9956

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

mL H

2S

O4/p

H u

nit

VOA in spiked filtrate of the biogas plant Fahrbinde (gCH3COOH/L)

McGhee equation Without NaHCO3 Add 1.5g NaHCO3/L

Add 3g NaHCO3/L Add 5g NaHCO3/L Add 8g NaHCO3/L

y = 2.06x + 0.15R² = 1

y = 1.7402x + 0.7035R² = 0.9931

y = 1.75x + 0.1796R² = 0.9963 y = 1.7533x - 0.0908

R² = 0.9961

y = 1.7388x + 0.2013R² = 0.9994

y = 1.5421x + 0.3041R² = 0.9284

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

mL H

2S

O4/p

H u

nit

VOA in spiked filtrate of the sewage sludge from WWTP Wismar (gCH3COOH/L)

McGhee equation Without NaHCO3 Add 1.5gNaHCO3/L

Add 3gNaHCO3/L Add 5gNaHCO3/L Add 8gNaHCO3/L

(a) (b)

Figure 12: Verifying alkalinity and VOA in spiked filtrates of the effluent of the biogas plant Fahrbinde (a) and of spiked filtrates of digested sewage sludge from WWTP Wismar (b) with the

FOS/TAC 2000

14

Finding:

• The FOS/TAC 2000 is a good performance measuring the alkalinity in the spiked filtrates


0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

Alk

alin

ity m

easu

red

by

FO

S/T

AC

2000

(gC

aC

O3/L

)

VOA in spiked filtrate of the biogas plant Fahrbinde (gCH3COOH/L)

Without NaHCO3 Add 1.5g NaHCO3/L Add 3g NaHCO3/L

Add 5g NaHCO3/L Add 8g NaHCO3/L Alkalinity calculated

(a)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

Alk

alin

ity m

easu

red b

y F

OS

/TA

C 2

000

(gC

aC

O3/L

)

VOA in spiked filtrate of the sewage sludge from WWTP Wismar (gCH3COOH/L)

Without NaHCO3 Add 1.5gNaHCO3/L Add 3gNaHCO3/L

Add 5gNaHCO3/L Add 8gNaHCO3/L Alkalinity calculated

(b)

Full-scale operation: 1000 m3 working volume

• single stage, temperature 39±0.5 °C, intermittently mixing,12 m3 WW/day are treated

For monitoring and control the digestion process of the biogas plant:

• the FOS/TAC 2000 was used to measure VOA, alkalinity and VOA/alkalinity ratio

• biogas composition (CH4, O2, H2S) is analyzed online, and monitored every 2 hours

• digester pH is measured daily and biogas volume is recorded daily 15

Figure 13: Photo of full-scale biogas plant in Fahrbinde and the characteristic of the WW

Full-scale biogas plant 1200 m3

0

50

100

150

200

250

300

Jan-18Feb-18Mar-18Apr-18May-18Jun-18 Jul-18 Aug-18Sep-18Oct-18 Nov-18Dec-18Jan-19

CO

D a

nd

TS

of th

e w

aste

wa

ter (g

/L)

Operation of time (month)

COD TS

Figure 14: Full-scale biogas plant performance

The biogas plant is working well

• Biogas volume 800 m3/day

• Biogas yield is 68 m3/m3 WW

• CH4 is 63 % 16

• pH, alkalinity and VOA/alkalinity are stable

• Na2CO3 consumed 1.15 kg/m3 WW is very close to the calculated demand 1.20 kg Na2CO3/m

3 WW

Full-scale biogas plant performance

30

40

50

60

70

80

90

400

600

800

1000

1200

Jan-18Feb-18Mar-18Apr-18May-18Jun-18 Jul-18 Aug-18Sep-18Oct-18Nov-18Dec-18Jan-19

m3

bio

gas/

m3

WW

and C

H4(%

)

m3 b

iogas/d

ay


Biogas volume Biogas yield CH4(%)

0

1

2

3

4

5

6

7

8

9

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Jan-18Feb-18Mar-18Apr-18May-18Jun-18 Jul-18 Aug-18Sep-18Oct-18Nov-18Dec-18Jan-19

Dig

este

r p

H

VO

A a

nd

alk

alin

ity

(g/L

)


VOA Alkalinity pH

17

Variation of feed volume and biogas consumption

0

200

400

600

800

1000

1200

1400

1600

0

5

10

15

20

25

30

Wednesday Thursday Friday Saturday Sunday Monday Tuesday Wednesday

Bio

ga

s c

onsu

me

d (m

3/d

ay)

Fe

ed

ing

WW

(m

3/d

ay)

Operation time

Biogas consumed (Steam generator) Feeding WW

Figure 15: Feeding volume and biogas consumed

18

Variation of feed volume and biogas consumption

0

25

50

75

100

0 5 10 15 20 25 30

Dis

trib

utio

n(%

)

Feeding WW (m3/day)

Wed1-Feeding WW

Thu-Feeding WW

Fri-Feeding WW

Sa-Feeding WW

Sun-Feeding WW

Mon-Feeding WW

Tue-Feeding WW

Wed2-Feeding WW

0

25

50

75

100

0 500 1000 1500 2000 2500 3000

Dis

trib

ution(%

)

Biogas consumed (m3/day)

Wed1-Biogas consumed

Thu-Biogas consumed

Fri-Biogas consumed

Sa-Biogas consumed

Sun-Biogas consumed

Mon-Biogas consumed

Tue-Biogas consumed

Wed2-Biogas consumed

Figure 16: Sum distribution of feeding volume and biogas consumed

• The WW from the cleaning of tank cars is suitable for an anaerobic pre-treatment

• The substitution of natural gas thru biogas for steam generation saves 8.500€/month

• Return on investment (ROI) of full scale plant is less than 6 years

• In order to keep the full scale digestion process stable:

o OLR shall not to exceed 4.5 kgCOD/m3/day

o pH, VOA, alkalinity shall be monitored daily

o Addition of 1.2 kgNa2CO3/m3 WW is required for maintaining pH and alkalinity stable

o Addition of micronutrient is required

• Physicochemical model of digestion process was developed for:

o Simulation of the effect of NaHCO3/Na2CO3 addition on digester pH

• The FOS/TAC 2000 is a good performance measuring VOA and alkalinity

o McGhee equation and Nordmann titration method are verified

o FOS/TAC 2000 is tested both distilled water and filtrates spiked with CH3COOH and NaHCO3

• Biogas production is successfully adapted to the biogas demand by the WW-feeding regime19

Conclusion

Thank you very much for your attention and looking for the cooperation

please contact to us:

Professor Wolfgang PfeifferThe University of Wismar, GermanyEmail: [email protected]

Nguyen Van ThanThe University of Rostock, GermanyEmail: [email protected]

20

control of alkalinity of a full-scale biogas plant

Documents