1. 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. Fortuny; A. Gonzalez-Sánchez; C. Casas; D. Gabriel; J. Lafuente
M. A. Deshusses
Xavier Gamisans
Duke University
Dep. Civil & Environmental Engineering
Universitat Autònoma de Barcelona
Departament d’Enginyeria Química
Universitat Politècnica de Catalunya
Escola Politècnica Superior d’Enginyeria de Manresa.

2. 2008 USC-UAM Conference on biofiltration for air pollution control
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

3. 2008 USC-UAM Conference on biofiltration for air pollution control
Background
ENERGY capacity of doing, transforming or moving
Renewable
Non-Renewable
INTRODUCTION 3/18
2008 USC-UAM Conference on biofiltration for air pollution control

4. Background BIOGAS Biogas energy recovery needs clean up
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

5. Background E Chemical processes (dry and wet scrubbing technologies)
Biological RSC oxidation
Sulfur Oxidizing Biomass + CO2 + Nutrients
Biomass + By-products
H2S +1/2 O2 → S0 + H2O E
SO4= + 2H+ →
+ 3/2 O2 E E
H2S +2 O2 → SO4= + 2H+
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

6. 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

7. 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

8. 2008 USC-UAM Conference on biofiltration for air pollution control
Experimental setup B
Setup
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

9. 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)
HD Q-PAC (Lantec Products, CA, USA)
MATERIALS & METHODS 9/18
2008 USC-UAM Conference on biofiltration for air pollution control

10. 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 Afterwards, imposition of a pH increase up to 9.5 with NaOH 1M for a 24 h period before returning to pH
MATERIALS & METHODS 10/18
2008 USC-UAM Conference on biofiltration for air pollution control

11. 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
Run 3: after 10 days of gas flow reversion: Max. EC = 145 ± 2 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
Run 1: shortly after inoculation: Max. EC=125 ± 3 g H2S m-3 h-1
Run 2: after over a year’s operation: Max EC= 144 ± 4 g H2S m-3 h-1
No biological limitation (no H2S accumulation) means improved mass transfer
RESULTS & DISCUSSION 11/18
2008 USC-UAM Conference on biofiltration for air pollution control

12. 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 Afterwards, imposition of a pH increase up to 9.5 with NaOH 1M for a 24 h period before returning to pH
MATERIALS & METHODS 10/18
2008 USC-UAM Conference on biofiltration for air pollution control

13. Intermittent substrate supply
Object: assess the capacity to overcome substrate shutdowns
pH control: indicates changes in bio-activity
gas supply shutdown  acidification
gas supply resumption  basification and loss of RE
few hours after resumption  acidification
RE: small and brief (< 7 %) decrease on day 86.6
ORP and sulfur balance: continuity in the biological activity by S0 oxidation
A pH control can be
used as a biological activity
assessment tool
S0 “maintains” biological activity
RESULTS & DISCUSSION 12/18
2008 USC-UAM Conference on biofiltration for air pollution control

14. 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 Afterwards, imposition of a pH increase up to 9.5 with NaOH 1M for a 24 h period before returning to pH
MATERIALS & METHODS 10/18
2008 USC-UAM Conference on biofiltration for air pollution control

15. Trickling liquid velocity (I)
Object: effect on by-products and biomass accumulation
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

16. Trickling liquid velocity (II)
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

17. 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 Afterwards, imposition of a pH increase up to 9.5 with NaOH 1M for a 24 h period before returning to pH
MATERIALS & METHODS 10/18
2008 USC-UAM Conference on biofiltration for air pollution control

18. pH Object: effect in case of pH control failure
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

19. 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

20. 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
Marc Fortuny; A. Gonzalez-Sánchez; C. Casas; D. Gabriel; J. Lafuente
M. A. Deshusses
Xavier Gamisans
Duke University
Dep. Civil & Environmental Engineering
Universitat Autònoma de Barcelona
Departament d’Enginyeria Química
Universitat Politècnica de Catalunya
Escola Politècnica Superior d’Enginyeria de Manresa.