2008 USC-UAM Conference on biofiltration for
air pollution control
Long Beach, October 2008
OPERATIONAL ASPECTS OF THE
BIOLOGICAL SWEETENING OF ENERGY
GASES MIMICS IN A LAB-SCALE
BIOTRICKLING FILTER
M. A. Deshusses
M. Fortuny; A. GonzalezSánchez; C. Casas; D. Gabriel; J.
Lafuente
Duke University
Dep. Civil & Environmental
Engineering
Universitat Autònoma de Barcelona
Departament d’Enginyeria Química
Xavier Gamisans
Universitat Politècnica de Catalunya
Escola Politècnica Superior d’Enginyeria
de Manresa.
Outline
Introduction
Background
Previous results
Objectives
Materials & Methods
Setup
Methodology
Results & Discussion
EBRT
Intermittent substrate supply
Trickling liquid velocity
pH
Conclusions
INTRODUCTION
2/18
2008 USC-UAM Conference on biofiltration for air pollution control
Background
ENERGY capacity of doing, transforming or moving
Renewable
INTRODUCTION
3/18
Non-Renewable
2008 USC-UAM Conference on biofiltration for air pollution control
Background
BIOGAS
H2S, halogenated compounds,
other RSC, etc.
(1-3 %)
CH4 & CO2
(97-99 %)
H2S tipical concentrations 500-2,000 ppmv
but can reach up to 2% (20,000 ppmv)
Biogas energy recovery needs clean up
INTRODUCTION
4/18
2008 USC-UAM Conference on biofiltration for air pollution control
Background
Chemical processes (dry and wet scrubbing technologies)
Biological RSC oxidation
Sulfur Oxidizing Biomass +
CO2 + Nutrients
Biomass + By-products
H2S +1/2 O2 → S0 + H2O + 3/2 O2 → SO4= + 2H+
E
E
H2S +2 O2 → SO4= + 2H+
E
Successfully applied for H2S abatement at low concentrations and low pH (Gabriel and
Deshusses, 2003, PNAS-USA)
Successfully applied for H2S abatement at high concentrations and high pH (Buisman
et al., 1989, Acta Biotechnol.)
Successfully applied for H2S abatement at high concentrations and neutral pH
(Fortuny et al., 2008; Chemosphere, 71, 10-17)
INTRODUCTION
5/18
2008 USC-UAM Conference on biofiltration for air pollution control
Previous results
USC-TRG CONFERENCE 2006, L.A., USA. (Fortuny et al., 2008, Chemosphere, 71 (1): 10-17)
• Interesting alternative with high removal efficiencies for high inlet concentrations (>80 and 90% for
10,000 and 6,000 ppmv respectively)
• Sulfur production and accumulation at very high (>6,000 ppmv) is the main handicap
• O2 availability is the most important and limiting factor
• Proved system robustness
• pH plays a main role
BIOTECHNIQUES 2007, A Coruña, SPAIN
• Improved O2 supply considerably reduces sulfur accumulation
• Efficient start-up and inoculation
• pH control implementation
• Study on the O2/H2S supply ratio and sulfur speciation
• Preliminary research on the EBRT and maximum Elimination Capacity
INTRODUCTION
6/18
2008 USC-UAM Conference on biofiltration for air pollution control
Objectives
To further study some of the operational parameters
influencing the process performance:
- EBRT
- Substrate supply shutdowns
- Liquid recirculation velocity
- pH changes
INTRODUCTION
7/18
2008 USC-UAM Conference on biofiltration for air pollution control
Experimental
Setup setup B
Schematic of the lab-scale reactor
1: Main reactor
2: Air supply
compartment
3: Gas inlet
4: Gas outlet
5: HCO3- supply
6: Gas monitoring
7: MM supply
8: Recirculation pump
9: pH control
10: Liquid monitoring
11: Air supply
12: Level control
13: Liquid purge
MATERIALS & METHODS
8/18
2008 USC-UAM Conference on biofiltration for air pollution control
Setup
Parameter
Normal value
Inlet concentration (ppmv)
2000
Loading rate g H2S m-3 h-1
55.6
Operational pH
6.5 – 7
Packing material
HD Q-PAC
Specific surface area (m2 m-3)
433
Reactor packed volume (L)
2.0
Reactor liquid volume (L)
4.5 ± 0.2
Fresh liquid flow (L d-1)
2.5 ± 0.2
Recirculation velocity (m h-1)
3.8
EBRT gas (s)
180
HRT liquid (h)
24 - 48
MATERIALS & METHODS 9/18
HD Q-PAC (Lantec Products, CA, USA)
2008 USC-UAM Conference on biofiltration for air pollution control
Methodology

Effect of the EBRT:
Stepwise decrease from 180 s. down to 25 s at an inlet H2S = 2,000 ppmv => LR
from 55 up to 400 g H2S m-3h-1.

Effect of an intermittent substrate supply:
Gas and carbonate supply shutdown with liquid recirculation, purge and make-up
water on. pH control kept on as an indirect measure of biological activity.

Effect of the trickling velocity
Step-wise increase from 0.52 up to 19.5 m h-1 every 48h (5 HRT) at a LR of 83.5 g
H2S m-3 h-1 (3,000 ppmv), an O2/H2S supply ratio of 23.5 (v v-1) and an EBRT of
180 s.

Effect of pH changes
Initial imposition of a pH drop down to 2.5 with HCl 1M for a 34 h period and
resumption of normal pH 6-6.5. Afterwards, imposition of a pH increase up to 9.5
with NaOH 1M for a 24 h period before returning to pH 6-6.5.
MATERIALS & METHODS 10/18
2008 USC-UAM Conference on biofiltration for air pollution control
EBRT and maximum EC
Object: reduce the design EBRT of 180 s. and increase pollutant mass transfer
200
100
1
2
3
EC = Load
150
1
2
3
80
125
60
RE %
EC (g H2S m-3 h-1)
175
100
40
75
50
20
25
0
0
0
50
100
150
200
250
300
Load (g H2S m-3 h-1)
350
400
0
20
40
60
80
100
120
140
160
180
200
EBRT (s)
-3 -1
-3 -1
Run 3:
10after
daysinoculation:
of gas flow Max.
reversion:
Max.± EC
1: after
shortly
EC=125
3 g =H145
2S m± 2h g H2S m h
Run 2: after over a year’s operation: Max EC= 144 ± 4 g H2S m-3 h-1
Stimulation of biomass growth for a short period of time is not a good
strategy to improve the mass transfer
No biological limitation (no H2S accumulation) means improved
mass transfer
RESULTS & DISCUSSION 11/18
2008 USC-UAM Conference on biofiltration for air pollution control
Methodology

Effect of the EBRT:
Stepwise decrease from 180 s. down to 25 s at an inlet H2S = 2,000 ppmv => LR
from 55 up to 400 g H2S m-3h-1.

Effect of an intermittent substrate supply:
Gas and carbonate supply shutdown with liquid recirculation, purge and make-up
water on. pH control kept on as an indirect measure of biological activity.

Effect of the trickling velocity
Step-wise increase from 0.52 up to 19.5 m h-1 every 48h (5 HRT) at a LR of 83.5 g
H2S m-3 h-1 (3,000 ppmv), an O2/H2S supply ratio of 23.5 (v v-1) and an EBRT of
180 s.

Effect of pH changes
Initial imposition of a pH drop down to 2.5 with HCl 1M for a 34 h period and
resumption of normal pH 6-6.5. Afterwards, imposition of a pH increase up to 9.5
with NaOH 1M for a 24 h period before returning to pH 6-6.5.
MATERIALS & METHODS 10/18
2008 USC-UAM Conference on biofiltration for air pollution control
Intermittent substrate supply
Object: assess the capacity to overcome substrate shutdowns
100
200
7,5
Stop III
150
7,0
100
80
50
6,0
60
5,5
5,0
40
0
-50
ORP (mV)
6,5
pH
Load (g H2S m-3 h-1) and RE (%)
8,0
4,5
-100
Load
RE
pH
ORP
20
4,0
3,5
0
3,0
80
81
82
83
84
85
86
87
88
89
-150
-200
90
Time (days)
pH control: indicates changes in bio-activity
A pH control can be
used as a biological activity
and
sulfur balance:
continuity
in loss
the biological
activity by S0 oxidation
gasORP
supply
resumption
 basification
and
of RE
assessment tool
S0 “maintains”
few hours after resumption
 acidification biological activity
small
and brief
7 %) decrease on day 86.6
gasRE:
supply
shutdown
(<acidification
RESULTS & DISCUSSION 12/18
2008 USC-UAM Conference on biofiltration for air pollution control
Methodology

Effect of the EBRT:
Stepwise decrease from 180 s. down to 25 s at an inlet H2S = 2,000 ppmv => LR
from 55 up to 400 g H2S m-3h-1.

Effect of an intermittent substrate supply:
Gas and carbonate supply shutdown with liquid recirculation, purge and make-up
water on. pH control kept on as an indirect measure of biological activity.

Effect of the trickling velocity
Step-wise increase from 0.52 up to 19.5 m h-1 every 48h (5 HRT) at a LR of 83.5 g
H2S m-3 h-1 (3,000 ppmv), an O2/H2S supply ratio of 23.5 (v v-1) and an EBRT of
180 s.

Effect of pH changes
Initial imposition of a pH drop down to 2.5 with HCl 1M for a 34 h period and
resumption of normal pH 6-6.5. Afterwards, imposition of a pH increase up to 9.5
with NaOH 1M for a 24 h period before returning to pH 6-6.5.
MATERIALS & METHODS 10/18
2008 USC-UAM Conference on biofiltration for air pollution control
Trickling liquid velocity (I)
9
110
20
8
100
18
RE
Trickl. velocity
DO
90
7
6
5
4
3
14
70
RE %
DO (mg L-1)
80
16
12
60
10
50
8
40
6
30
2
20
4
1
10
2
0
0
Trickling liquid velocity (m h-1)
Object: effect on by-products and biomass accumulation
0
94
96
98
100
102
104
106
108
Time (days)
RE not affected (0.51 to 19.1 m h-1 and LR of 83.5 g H2S m-3 h-1)
Main effect on the O2 transfer
Oxygen availability increase
Interesting operational advantage since elemental sulfur
accumulation is diminished without an air supply increase
RESULTS & DISCUSSION 13/18
2008 USC-UAM Conference on biofiltration for air pollution control
Trickling liquid velocity (II)
500
200
400
150
100
Sulfur
Recirc. velocity
Biomass
S-SO42- average
20
15
300
10
200
5
50
100
0
0
0
10
8
6
4
2
Biomass as total N (mg L-1)
250
25
Recirculation velocity (m h-1)
600
S-S0 (mg L-1)
S-SO42- (mg h-1)
300
0
94
96
98
100
102
104
106
108
Time (days)
Biomass or S0 liquid concentration and trickling velocity not related
Increasing trickling velocity not efficient to reduce accumulated S0 (short run)
A high trickling velocity recommended (in this system) since increases O2
availability thereby reducing S0 production
RESULTS & DISCUSSION 14/18
2008 USC-UAM Conference on biofiltration for air pollution control
Methodology

Effect of the EBRT:
Stepwise decrease from 180 s. down to 25 s at an inlet H2S = 2,000 ppmv => LR
from 55 up to 400 g H2S m-3h-1.

Effect of an intermittent substrate supply:
Gas and carbonate supply shutdown with liquid recirculation, purge and make-up
water on. pH control kept on as an indirect measure of biological activity.

Effect of the trickling velocity
Step-wise increase from 0.52 up to 19.5 m h-1 every 48h (5 HRT) at a LR of 83.5 g
H2S m-3 h-1 (3,000 ppmv), an O2/H2S supply ratio of 23.5 (v v-1) and an EBRT of
180 s.

Effect of pH changes
Initial imposition of a pH drop down to 2.5 with HCl 1M for a 34 h period and
resumption of normal pH 6-6.5. Afterwards, imposition of a pH increase up to 9.5
with NaOH 1M for a 24 h period before returning to pH 6-6.5.
MATERIALS & METHODS 10/18
2008 USC-UAM Conference on biofiltration for air pollution control
pH
Object: effect in case of pH control failure
b)
10
4,0
120
100
300
3,5
200
8
80
4
40
-200
pH
RE
ORP
2
-300
-400
135
pH = 6 - 6.5
100
RE %
80
2,0
1,5
SO42S2O32-
1,0
% S-SO42-
60
40
% S-S2O32-
20
0,5
0
134
pH = 6 - 6.5 pH =9.5
2,5
20
0
133
g S day-1
-100
60
pH
ORP (mV)
0
pH =2.5
3,0
100
6
pH = 6 - 6.5
136
137
138
139
140
Time (days)
141
142
143
144
% S / Sremoved
a)
0,0
0
133
134
135
136
137
138
139
140
141
142
143
144
Time (days)
pH drop: no effect on RE
slightly affects biomass activity (25% reduction on SO4= production)
fast recovery of sulfate production (biological activity)
pH rise: significant reduction of RE
important reduction of biological activity
sulfide accumulation and chemical production of thiosulfate
Slower recovery of biological activity
Bioreactor much more susceptible to high pH than to low pH conditions
RESULTS & DISCUSSION 15/18
2008 USC-UAM Conference on biofiltration for air pollution control
Conclusions
• The EBRT could be reduced from 180 s. to 90 s. without affecting the removal of H2S,
but drastically reducing the investment costs of a full-scale reactor
• The main rate limiting process was found to be mass transfer of H2S which was not
affected by a full colonization of the packed column by bacteria
• Gas supply shutdowns for up to 5 days are not a concern if make-up water supply is
kept on, since elemental sulfur oxidation ensures continuous biological activity
• A high liquid trickling velocity is recommended because it favors sulfate production
through a better use of the supplied DO.
• There may be a small effect on the biomass activity from a short (34h) and sharp pH
drop down to a value of 2.5. However, a pH rise of only 24 hours up to a value of 9.5
has a significant effect on the overall reactor performance.
CONCLUSIONS
16/18
2008 USC-UAM Conference on biofiltration for air pollution control
2008 USC-UAM Conference on biofiltration for
air pollution control
Long Beach, October 2008
OPERATIONAL ASPECTS OF THE
BIOLOGICAL SWEETENING OF ENERGY
GASES MIMICS IN A LAB-SCALE
BIOTRICKLING FILTER
M. A. Deshusses
Marc Fortuny; A. GonzalezSánchez; C. Casas; D. Gabriel; J.
Lafuente
Duke University
Dep. Civil & Environmental
Engineering
Universitat Autònoma de Barcelona
Departament d’Enginyeria Química
Xavier Gamisans
Universitat Politècnica de Catalunya
Escola Politècnica Superior d’Enginyeria
de Manresa.