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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
Verification of Nordmann titration method with McGhee equation
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
Verification of Nordmann titration method with McGhee equation
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
Verification of Nordmann titration method with McGhee equation
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
Operation of time (month)
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
)
Operation of time (month)
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