Making and harvesting VFA using high nitrogen substrates Yue Zhang - - PowerPoint PPT Presentation

ADNet Research Colloquium 11-12 September 2017, Southampton

Making and harvesting VFA using high nitrogen substrates

Yue Zhang

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• Context
• VFA/carboxylate platform
• Previous laboratory experience
• ADNet PoC 2014016: production and extraction of C3 and

C4 aliphatic carboxylic acids from the anaerobic digestion of waste blood as a model substrate

• Results
• Reflection
• The next step

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Content

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• Volatile fatty acids (VFA) serve as platform molecules for the

production of chemicals and polymers from organic waste streams

• Recalcitrant materials: gasification & syngas fermentation
• Independent of CO:CO2:H2 ratios
• Tolerant to gasification by-products, e.g. NH3, NOx, H2S
• Putrescible materials: direct fermentation
• Microorganisms for VFA fermentation are naturally

abundant

VFA/carboxylate platform

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• Alcohol production via VFA platform vs direct production
• VFA production does not require sterile conditions
• No external enzymes are required to carry out the

hydrolysis step

• All biodegradable organic wastes can be used for VFA

production

VFA/carboxylate platform

Previous studies

• The high nitrogen content of substrates results in a high digester total

ammonia nitrogen and this can lead to raised concentrations of VFA, and in particular of propionic acid.

2000 4000 6000 8000 10000 12000 14000 16000 50 100 150 200 250 300 Time (days) FW 1 VFA profile (mg l -1) Acetic Propionic Iso-Butyric n-Butyric Iso-Valeric n-Valeric Hexanoic Heptanoic

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• High ammonia content
• Methanogen inhibitor
• High buffering capacity, no need to add base solution for

pH control

• Rich in nutrients
• Again, minimal input of chemicals
• Waste blood chosen as a model substrate
• Readily available
• No need for particle size reduction

High nitrogen substrates

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• Open culture fermentation
• Operational modes: batch, fed-batch, semi-continuous
• Methanogen inhibitor
• Enzymatic pretreatment
• Recovery
• Esterification
• Membrane based solvent extraction

Experiments

Results – VFA production

• Due to high ammonia concentration in fermentation broth, a range of high VFA

concentration up to 100 g L-1 was achieved with a blood VS of 13.5%, without addition

• f external methanogen inhibitor.
• In general, acetic, n-butyric and iso-valeric acids were the dominant species, although

different operational conditions affected the VFA concentration, profile, production rate and yield.

• 70-90% of the population was from the Clostridiales order with a large participation

from the Sporanaerobacter genus.

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Semi-continuous test Fed-batch test

Results – Esterification

9 water Waste blood Mixed culture fermentation Biomass removal water removal Acidification Esterification H2SO4 Methanol VFA-methyl esters (NH4)2SO4 Biomass

Results – Membrane based extraction

10 Water/VFA Biomass Octanol

• TOA

Octanol-TOA/VFA Waste blood Mixed culture fermentation Biomass removal Membrane based solvent extraction VFA recovery VFA

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Amino acid contents of blood

Reference: Kramer S.L., Waibel P.E., Behrends B.R. and El Kandelgy S.M. (1978) Amino acids in commercially produced blood meals. J. Agric. Food Chem. 26, 979-981.

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Amino acid fermentation

References: Ramsay I.R. and Pullammanappallil P.C. (2001) Protein degradation during anaerobic wastewater treatment: derivation of stoichiometry. Biodegradation 12: 247-256. Schönheit P., Buckel W. and Martin W.F. (2016) On the origin of heterotrophy. Trends in microbiology 24: 12-25.

Previous studies - revisit

• Other VFA was degraded to biogas; propionic acid has the slowest

degradation rate

2000 4000 6000 8000 10000 12000 14000 16000 50 100 150 200 250 300 Time (days) FW 1 VFA profile (mg l -1) Acetic Propionic Iso-Butyric n-Butyric Iso-Valeric n-Valeric Hexanoic Heptanoic

Selective propionic acid production, but:

• 100 mg HPr L-1 day-1
• ~5% of VS

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• Alcohol production via VFA platform vs direct production
• VFA production does not require sterile conditions
• All biodegradable organic wastes can be used for VFA

production

• No external enzymes are required to carry out the

hydrolysis step

• Challenges
• Selectivity
• Solids in the effluent

VFA/carboxylate platform

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Follow up

Leach-bed fermenter Selective VFA extraction Anaerobic digestion VFA, Other chemicals Liquor Solids Biogas High nitrogen substrates Digestate

An additional unit?

• Chain elongation
• BES

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Acknowledgements

Thanks to Anaerobic Digestion Network PoC 2014016 Dr Jersson Plácido … and to Newton Fund Institutional Links and AD Network for continuing support to take this work forward Miss Victoria Outram Mrs Jing Lu