[PPT] - Bioelectrochemical Upgrading of Anaerobic Digestion Biogas Spyros G. PowerPoint Presentation

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Bioelectrochemical Upgrading of Anaerobic Digestion Biogas

Spyros G. Pavlostathis School of Civil & Environmental Engineering Georgia Institute of Technology Atlanta, GA 30332‐0512, USA NAXOS 2018 6th International Conference on Sustainable Solid Waste Management Naxos Island, Greece 14 June 2018

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 Opportunities for CO2 reuse and energy recovery in municipal wastewater treatment plants (WWTP), now referred to as Water Resource Recovery Facilities (WRRF)

Municipal Wastewater Treatment

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Anaerobic Digestion

Biogas (CO2, CH4, trace gases) Liquid digestate, Biosolids

Complex organic compounds

Carbohydrates, Proteins, Lipids

Simple organic compounds

Sugars, Amino acids, Fatty acids

Organic acids and alcohols CO2, CH4 H2, CO2 Acetate

Hydrolysis Acidogenesis Acetogenesis Methanogenesis

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Anaerobic Digestion – Biogas Composition

Assumes complete mineralization; ignores microbial growth

Mean Oxidation State of Carbon (OS) = 4 - 1.5(COD/TOC) CH4 (%) = 100 - 12.5 (OS + 4)

Gujer and Zehnder, Water Sci. Technol., 1983

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CO2 Capture & Sequestration

Absorption

Chemical (MEA, caustic, etc.)
Physical (Selexol, Rectisol, etc.)

Adsorption

Alumina, zeolite, activated carbon

Cryogenics Membrane separation

Gas separation (Polyphenyleneoxide,

polydimethylsiloxane)

Gas absorption (Polypropelene)
Ceramics

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CO2 Conversion & Valorization

CO2 CH4, Acetate, C3, C4 …. BES

Bioelectrochemical Systems (BES) for Direct CO2 Conversion

Pan et al. Crit. Rev. Environ. Sci. Technol., 2018

Roadmap of Valorization Technologies for Captured CO2 Microbial CO2 Fixation (Microalgae, Phototrophic Bacteria) CO2  Biomass  Products

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Biomethane Valorization – New Concepts

(2018)

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Reduction

Microbial Fuel Cell (MFC)

Produces electrical current

Microbial Electrolysis Cell (MEC)

Produces hydrogen (H2)

Microbial Electromethanogenesis

Produces methane (CH4)

Microbial Electrosynthesis (MES)

Produces 1+ carbon compounds (e.g., acetate, etc.) A, Resistor (MFC) or applied potential (MEC) B, Proton exchange membrane R1, Reactant in the anode (oxidation half reaction) P1, Product in the anode R2, Reactant in the cathode (reduction half reaction) P2: Product in the cathode

2H+ + 2e‐ → H2 EH°' = ‐0.414 V CO2 + 8H+ + 8e‐ → CH4 + 2H2O EH°' = ‐0.244 V CO2 + 4H2 → CH4 + 2H2O ΔE°' = 0.170 V

At 25 °C, 1 atm, pH 7.

Oxidation

Bioelectrochemical Systems (BES)

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e‐

(1) Direct Electron Transfer (DET) CO2 CH4 CO2 CH4 H2O H2 H2 H2O CH4 (2) H2‐Mediated Electron Transfer (MET) Mox Mred H+ CO2 Mred Mox CO2 CH4 (3) Non‐H2‐Mediated Electron Transfer

Electron Transfer Mechanisms in Biocathode

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BES Performance

BES performance depends on:

 Electron donor (anode)  Cathode potential  System design (e.g., PEM surface area, electrode type and surface area)  Inoculum type  Reactor type (One‐ vs. two‐chamber systems; batch vs. continuous flow)  Operational parameters (e.g., pH, temperature)

Methane production rate depends on

 Cathode potential (V)  Current density (A/m2)  Current‐to‐methane efficiency (%)

Geppert et al., Trends Biotechnol., 2016

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Biocathode Performance – Effect of Inoculum

ACETATE (mg COD/L)

1 2 3 4

CURRENT DENSITY (A/m2)

5 10 15 20 5 10 15 20

TIME (d) HEADSPACE CH4 (mmol)

1 2 3

A C B

MM-B EHM-B MM-B EHM-B MM-B EHM-B

Biocathode methanogenic inocula: MM, mixed; EHM, pre‐enriched hydrogenotrophic

Dykstra, C.M.; Pavlostathis, S.G. 2017. Methanogenic biocathode microbial community development and the role of Bacteria. Environ. Sci. Technol. 51(9) 5306‐5316.

VOLTAGE (V)

1.0 -0.8 -0.6 -0.4 -0.2

0.0 0.2 CURRENT (mA)

20
10

10 20 30 40 50 MM-biocathode EHM-biocathode

Biocathode Final Biofilm Biomass (mg) Mean CH4 Production (mmol CH4/mg biomass‐ day) MM‐ inoculated 0.54 ± 0.07 0.15 ± 0.01 EHM‐ inoculated 0.64 ± 0.19 0.59 ± 0.03

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Biocathode Performance – Effect of Inoculum

Biocathode methanogenic inocula: MM, mixed; EHM, pre‐enriched hydrogenotrophic

Dykstra, C.M.; Pavlostathis, S.G. 2017. Methanogenic biocathode microbial community development and the role of Bacteria. Environ. Sci. Technol. 51(9) 5306‐5316.

MM MM-biocathode EHM EHM-biocathode

RELATIVE ABUNDANCE (%)

20 40 60 80 100 Methanobrevibacter spp. Methanobrevibacter arboriphilus Methanoculleus spp. Methanolinea spp. Methanomethylovorans spp. Methanosaeta spp. Methanobacterium spp.

Biocathode archaeal communities

converged on the same phylotypes, Methanobrevibacter arboriphilus

Inoculum pre‐enrichment with H2/CO2

selects for methanogens that are also selected for by biocathode conditions (faster biocathode start‐up)

MM MM-biocathode EHM EHM-biocathode

RELATIVE ABUNDANCE (%)

20 40 60 80 100 Bacteroidetes Protoebacteria Actinobacteria Firmicutes Spirochaetes Synergistia Thermotogae Anaerolineales Acidobacteria Deferribacteres Chloroflexi Unclassified

Cathode

Cell lysis products Methanogens CO2, Oxidized carbon Exoelectrogen e‐, H+, CO2 CH4

Archaea Bacteria

MM‐biocathode enriched in

Spirochaetes and other non‐ exoelectrogenic, fermentative Bacteria

EHM‐biocathode enriched in

Proteobacteria, exoelectrogens and putative producers of electron shuttle mediators

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Biocathode Performance – Effect of H2S

Cathode Headspace H2S (1% v/v)

5 10 15 20

CURRENT DENSITY (A/m2)

20 40 60 80

TIME (d)

5 10 15 20

METHANE (mmol)

2 4 6 8

A B

BES1 (Control) BES2 (H2S amended) Headspace H2S (% v/v) CE (%) CCE (%) 11 100 4 19 99 5 58 13 6 58 15

Two competing effects:

Depression of CH4 production (≥4% H2S):

Inhibition of methanogens?

Enhancement of CH4 production (≤3% H2S):

What is/are the process(es) involved?

CE, Coulombic efficiency CCE, cathode capture efficiency

Cathode Headspace H2S (0‐6%)

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Biocathode Performance – Effect of H2S

CO2 CH4 CH4

e‐ e‐ H+

H2S is the most toxic of the sulfide species

80% 20% H2S

H2S HS‐ S2‐ CO2 CO2 H2S

High local pH Neutral pH

The methanogenic biocathode is protected from sulfide inhibition by biofilm formation and a local high pH at the cathode surface.

Cathode

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Biocathode Performance – Effect of H2S

Anode N2 CO2 CO2

Potential anode H2S

xidation products

S0 Sx

2‐

S4O6

2‐

S2O3

2‐

SO4

2‐

Sun et al., ES&T 2009

N2

e‐

Acetate H2S SO4

2‐

Acetate CO2

SRB

Low H2S → more electrons donated to the anode → higher biocathode CH4

production

High H2S → smulate sulfur cycling → divert acetate eeq from the anode → lower

biocathode CH4 production

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Biocathode Performance – Effect of H2S

Bacteroidetes Proteobacteria Actinobacteria Firmicutes Spirochaetes Synergistia Unclassified

RELATIVE ABUNDANCE (%)

10 20 30 40 50 60 70 80 90 100

B BES1 BES2 Biofilm Susp. Biofilm Susp. RELATIVE ABUNDANCE (%)

10 20 30 40 50 60 70 80 90 100

A BES1 BES2 Biofilm Susp. Biofilm Susp.

Anode Cathode

Deltaproteobacteria were not detected in any anode or cathode biofilm or

suspended growth samples, except in the BES2 anode biofilm.

SRB phylotypes in the BES2 anode biofilm represented 32% of

Deltaproteobacteria and 1% of total Bacteria.

Identified SRB phylotypes include Desulfobulbus propionicus, Desulfovibrio sp.

and Syntrophobacterales spp.

Control H2S‐amended Control H2S‐amended

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Methanogenic BES Performance

 Methane production rate (L CH4/L reactor/day)

0.27‐27 calculated assuming a current density of 1‐100 A/m2 (Geppert et al., 2016)(High‐rate anaerobic digesters 1.4‐9.8 L CH4/L reactor/day)

 Cell voltage

From ‐0.7 to ‐1.5 V

 Current‐to‐methane efficiency

23 to 99% (>100% microbially induced cathode corrosion)

 Energy (electrical) input (Wh/L CH4)

Water anode electron donor: 19 calculated; 74‐97 observed (Geppert et al., 2016) Acetate anode electron donor (observed; Dykstra & Pavlostathis, 2017)

CO2‐fed System Wh/L CH4 Control BES 27.0 BES with 3% H2S 31.0 BES with 1 g/L ZVIa 7.6

aZVI, zero valent iron added to the biocathode

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Methanogenic BES – Remaining Challenges

 Choice of anode electron donor  Reduction of energy losses (internal resistance; cathode

verpotential)

 Reduction of gas transport through the membrane  New electrode materials  Increase of methane production rate  Scale‐up

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BES AD Biogas Upgrading

Biogas (CH4 + CO2)

CH4

Acetate CO2

PEM ≤ ‐0.8 V

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Acknowledgement

 Experimental data presented here are from Dr. Christy Dykstra’s PhD dissertation entitled “Bioelectrochemical Conversion of Carbon Dioxide to Methane for Biogas Upgrading”.  This material is based in part upon work supported by the US National Science Foundation Graduate Research Fellowship under Grant No. DGE‐1148903.

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Bioelectrochemical Upgrading of Anaerobic Digestion Biogas

Spyros G. Pavlostathis School of Civil & Environmental Engineering Georgia Institute of Technology Atlanta, GA 30332‐0512, USA NAXOS 2018 6th International Conference on Sustainable Solid Waste Management Naxos Island, Greece 14 June 2018

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Extra Slides

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Substrate vs. Biomass Yield, Gas Composition

Waste Component Molecular Formula ThOD g O2/g Biomass Yield g VSS/g COD consumed Gas Composition % CH4 CO2 Carbohydrates C6H12O6 1.067 0.138 48 52 Proteins C16H24O5N4 1.500 0.040 69 31 Lipids (Fatty Acids) C16H32O2 2.875 0.030 72 28 Municipal Sludge C10H19O3N 1.990 0.054 70 30

aCalculated from stoichiometric equations developed based on bioenergetic

principles

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Materials & Methods

ANODE

Carbon felt

electrode/SS collector

Acetate‐fed (1.5 g

COD/L)

N2‐flushed headspace
Potential allowed to

fluctuate; measured against an adjacent Ag/AgCl reference electrode

300 mL total volume
250 mL liquid anolyte

(phosphate buffer, pH 7.0; trace minerals; vitamins)

Inoculated with

biofilm‐attached carbon felt from an active MFC CATHODE

Carbon felt

electrode/SS collector

CO2‐fed (1.6 atm,

absolute)

CO2‐flushed headspace
Potential fixed at ‐0.8 V

(vs. SHE) using an adjacent Ag/AgCl reference electrode

300 mL total volume
250 mL liquid catholyte

(phosphate buffer, pH 7.0; trace minerals; vitamins)

Inoculated with a

suspended‐growth, enriched hydrogenotrophic culture CO2 CH4 Acetate CO2

PEM Batch‐fed systems at 22±2oC Hydraulic retention time, 7 days

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Materials & Methods

Gases

Pressure transducer GC‐TCD for gas composition

Liquids

GC‐FID for acetate measurement Dissolved CO2 measured by sample acidification (6 N H2SO4) followed by composition analysis of evolved gas (conditional calibration)

Solids and Biomass

TSS/VSS for suspended biomass Protein analysis of biofilm and suspended biomass Molecular Analysis DNA extraction using UltraClean Soil DNA Kit and PowerSoil DNA Isolation Kit (Mo Bio Laboratories, Carlsbad, CA) 16S rRNA gene sequencing (Illumina MiSeq) Phylogenetic analysis using Mega 7.0 software Diversity analyses performed with QIIME 1.9.0 and R

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Biocathode Performance – Effect of Inoculum

Dykstra, C.M.; Pavlostathis, S.G. 2017. Methanogenic biocathode microbial community development and the role of Bacteria. Environ. Sci. Technol. 51(9) 5306‐5316.

The bacterial community of a biocathode has a significant effect on archaeal CH4 production
Increased biocathode CH4 production occurs with a bacterial community enriched in:
Putative producers of electron shuttles/mediators
Proteobacteria
Exoelectrogens

Acetate CO2 H2 CH4 Cell lysis debris Recycle lysed cells Produce electron shuttles cathode Mox Mred CH4 CO2 Role of Bacteria

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EFFECT OF CATHODE H2S ON BES PERFORMANCE 27

Corrosive, toxic (NIOSH, IDLH = 100 ppm)
Produced by sulfate‐reducing bacteria during

anaerobic digestion and by the breakdown of HS‐ containing compounds (e.g., cysteine)

Inhibitory to methanogenesis during anaerobic

digestion [1]

Feedstock C:S ratio predicts biogas H2S [2]

Desulfovibrio vulgaris

[1] Chen, Y., et al., 2008. Biores.

Technol. 99(10), 4044‐4064.

[2] Peu, P., et al., 2012. Bioresource

Technol. 121, 419‐424.

Feedstock C/S (g/g) Theoretical Biogas H2S (%, range) Grease trap waste 798 0.0 – 0.1 Biological sludge 59 0.6 – 1.9 Industrial WW biological sludge 46 0.8 – 2.0 Pig bristles 19 2.0 – 4.9 Harvested green seaweed 7 5.5 – 17.7

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TIME (d)

2 4 6 8 10

METHANE (mmol)

1 2 3

R2 = 0.997 R2 = 0.999

EFFECT OF CATHODE H2S ON BES PERFORMANCE 28 7 cycles 3 cycles 3 cycles 3 cycles 1 cycle 1 cycle 1 cycle

100% CO2, no H2S 99% CO2, 1% H2S 98% CO2, 2% H2S 97% CO2, 3% H2S 96% CO2, 4% H2S 95% CO2, 5% H2S 94% CO2, 6% H2S

Linear biocathode CH4 production during the first 3 days of a feeding cycle

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Biocathode Performance – Effect of H2S

Gas transport between biocathode and bioanode Anode Cathode

Potentiostat

PEM

CO2 H2S CO2 N2 N2 N2 CO2 CO2

Ag/AgCl reference electrode

CH4 N2, CO2, CH4

H+ H+ H+ H+ e‐ e‐

H2S H2S CO2 CH4 Acetate

Dykstra, C., Pavlostathis, S.G. (2017), “Evaluation of gas and carbon transport in a methanogenic bioelectrochemical system (BES)”, Biotechnology & Bioengineering, 114(5), 961-969.

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Biocathode Performance – Effect of H2S

CARBON (mmol)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 Suspended Biofilm BES1 Anode BES1 Cathode BES2 Anode BES2 Cathode

H2S stimulated total biomass growth in

both anode and cathode

H2S stimulated SRB growth in the anode

biofilm

BES1 cathode BES2 cathode

Control H2S‐amended

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EFFECT OF CATHODE H2S ON BES PERFORMANCE 31 Abiotic H2S Transport within a BES H2S Transport Across the Membrane

Abiotic BES with Pt‐coated carbon cloth anode and

carbon felt cathode

Open circuit conditions
Magnetically mixed
3% H2S added to the headspace of the cathode
Cyclic voltammetry from ‐1.2 V to 0.2 V (vs. Ag/AgCl)

at 100 mV/s

Sodium sulfide calibration curve constructed to

convert current at 0.2 V vs. Ag/AgCl to sulfide ions

H2S Dissolution in the Cathode

Abiotic BES with Pt‐coated carbon cloth cathode and

carbon felt anode

Open circuit conditions
Magnetically mixed
3% H2S added to the headspace of the cathode
Cyclic voltammetry from ‐1.2 V to 0.2 V (vs. Ag/AgCl)

at 100 mV/s; Measured current at 0.2 V.

TIME (min)

20 40 60 80

TOTAL SULFIDE IONS (mM)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

TIME (min)

5 10 15 20 25 30

CURRENT (mA)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18

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EFFECT OF CATHODE H2S ON BES PERFORMANCE 32

‐0,03 ‐0,02 ‐0,01 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 ‐1,2 ‐1,0 ‐0,8 ‐0,6 ‐0,4 ‐0,2 0,0 Current (mA) Voltage (V vs. Ag/AgCl) 0% H2S 4% H2S 5% H2S 6% H2S

H2S (%) CE (%) CCE (%)

11 100 4 19 99 5 58 13 6 58 15

2 2 2 2

Above 4% H2S v/v, the cathode biofilm is significantly inhibited.