Thermodynamic method for analyzing and optimizing pretreatment/anaerobic digestion systems

Document Type : Research Paper


1 Dept. Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA.

2 Verde Technologies, Springville, UT, USA.


This paper builds a quantitative thermodynamic model for the microbial hydrolysis process (MHP, which uses Caldicellulosiruptor bescii at 75°C for pre-digestion) for producing biogas from a 5-10% aqueous suspension of dairy manure (naturally buffered near pH 7.8 by ammonium bicarbonate) by anaerobic digestion with a mix of acetoclastic and syntrophic methanogenesis. Standard Gibbs energy changes were calculated for the major reactions in pre-digestion, for reactions producing H2, acetate, and CO2 in the digester, and for methanogenesis reactions in the digester. The available data limit the study to analyzing reactions in the digester to reactions of short-chain volatile fatty acids anions. Results are presented as curves of ΔrxnG (Gibbs energy change) vs. acetate concentration. The H2(aq) concentration must be above 1.2×10-9 M to get significant syntrophic methanogenesis, i.e., for ΔrxnG to be negative. The results show syntrophic methanogenesis of propionate, butyrate, and valerate slows as acetate concentration increases because hydrogen production also decreases, and consequently, biogas production from syntrophic methanogenesis slows as acetate increases. Bicarbonate also inhibits both acetoclastic and syntrophic methanogenesis but is necessary to prevent acidification (souring) of the digester. At identical steady-state conditions, acetoclastic methanogenesis runs about 1.4 times faster than syntrophic methanogenesis. Because syntrophic methanogenesis produces acetate catabolized by acetoclastic methanogens, both types of methanogens are necessary to maximize biogas production. The culture in the digester is predicted to evolve to optimize the ratio of acetoclastic methanogens to syntrophic methanogens, a condition signaled by a constant, low acetate concentration in the digester effluent. Obtaining volatile solids reduction as high as 75% with MHP requires a feedstock with less than 25% lignin and a culture of acetoclastic methanogens and syntrophic methanogens and their symbiotic bacteria.

Graphical Abstract

Thermodynamic method for analyzing and optimizing pretreatment/anaerobic digestion systems


  • Dairy manure digestion with pre-digestion with Caldicellulosiruptor bescii is modeled with thermodynamics.
  • Syntrophic methanogenesis is inhibited by acetate.
  • Acetoclastic methanogenesis is accelerated by increasing acetate.
  • Acetoclastic methanogenesis is ≈1.4 times faster than syntrophic methanogenesis.
  • The correct ratio of acetoclastic and syntrophic methanogenesis maximizes biogas.


  1. Ahring, B.K., Sandberg, M., Angelidaki, I.J.AM., 1995. Volatile fatty acids as indicators of process imbalance in anaerobic digestors. Appl. Microbiol. Biotechnol. 43, 559-565.
  2. Baird, R.B., Eaton, A.D., Rice, E.W., Bridgewater, L. eds., 2017. Standard methods for the examination of water and wastewater, 23rd edition. American Public Health Association, Washington, D.C.
  3. Batstone, D.J., Keller, J., Angelidaki, I., Kalyuzhnyi, S.V., Pavlostathis, S.G., Rozzi, A., Sanders, W.T.M., Siegrist, H.A., Vavilin, V.A. 2002. The IWA anaerobic digestion model no 1 (ADM1). Water Sci. Technol. 45(10), 65-73.
  4. Batstone, D.J., Pind, P.F., Angelidaki, I., 2003. Kinetics of thermophilic, anaerobic oxidation of straight and branched chain butyrate and valerate. Biotech. Bioeng. 84(2), 195-204.
  5. Berghuis, B.A., Yua, F.B., Schulzc, F., Blainey, P.C., Woykec, T., Quake, S.R., Hydrogenotrophic methanogenesis in archaeal phylum Verstraetearchaeota reveals the shared ancestry of all methanogens. Proc. Natl. Acad. Sci. 116(11), 5037-5044.
  6. Bertacchi, S., Ruusunen, M., Sorsa, A., Sirviö, A., Branduardi, P., 2021. Mathematical analysis and update of ADM1 model for biomethane production by anaerobic digestion. Fermentation. 7(4), 237.
  7. Christensen, J.J., Hansen, L.D., Izatt, R.M., 1976. Handbook of proton ionization heats and related thermodynamic quantities. John Wiley and Sons, New York.
  8. Conrad, R., 1999. Contribution of hydrogen to methane production and control of hydrogen concentrations in methanogenic soils and sediments. FEMS Microbiol. Ecol. 28(3), 193-202.
  9. Conrad, R., 2020. Importance of hydrogenotrophic, aceticlastic and methylotrophic methanogenesis for methane production in terrestrial, aquatic and other anoxic environments: a mini review. Pedosphere. 30(1), 25-39.
  10. Denbigh, K.G., 1951. The Thermodynamics of the Steady State. John Wiley and Sons, New York.
  11. Goldberg, R.N., Kishore, N., Lennen, R.M., 2002. Thermodynamic quantities for the ionization reactions of buffers. J. Phys. Chem. Ref. Data. 31(2), 231-370.
  12. Gupta, K.K., Aneja, K.R., Rana, D., 2016. Current status of cow dung as a bioresource for sustainable development. Bioresour. Bioprocess. 3, 28.
  13. Hansen, J.C., Aanderud, Z.T., Reid, L.E., Bateman, C., Hansen, C.L., Rogers, L.S., Hansen, L.D., 2021. Enhancing waste degradation and biogas production by pre-digestion with a hyperthermophilic anaerobic bacterium. Biofuel Res. J. 31, 1433-1443.
  14. Holtzapple, M.T., Wu, H., Weimer, P.J., Dalke, R., Granda, C.B., Mai, J., Urgun-Demirtas, M., 2022. Microbial communities for valorizing biomass using the carboxylate platform to produce volatile fatty acids: a review. Bioresour. Technol., 344, 126253.
  15. Kataeva, I., Foston, M.B., Yang, S.J., Pattathil, S., Biswal, A.K., Poole II, F.L., Basen, M., Rhaesa, A.M., Thomas, T.P., Azadi, P., Olman, V., Saffold, T.D., Mohler, K.E., Lewis, D.L., Doeppke, C., Zeng, Y., Tschaplinski, T.J., York, W.S., Davis, M., Mohnen, D., Xu, Y., Ragauskas, A.J., Ding, S.Y., Kelly, R.M., Hahn M.G., Adams, M.W.W., 2013. Carbohydrate and lignin are simultaneously solubilized from unpretreated switchgrass by microbial action at high temperature. Energy Environ. Sci. 6(7), 2186-2195.
  16. Kato, S., Watanabe, K., 2010. Ecological and evolutionary interactions in syntrophic methanogenic consortia. Microbes Environ. 25(3), 145-151.
  17. Kato, S., Yoshida, R., Yamaguchi, T., Sato, T., Yumoto, I., Kamagata, Y., 2014. The effects of elevated CO2 concentration on competitive interaction between aceticlastic and syntrophic methanogenesis in a model microbial consortium. Front. Microbiol. Systems Microbiol. 5, 575.
  18. Lyu Z., Shao N., Akinyemi T., Whitman W.B., 2018. Methanogenesis. Curr. Biol. 28(13), R727-R732.
  19. Mackie, R.I., White, B.A., Bryant, M.P., 1991. Lipid metabolism in anaerobic ecosystems. Crit. Rev. Microbiol. 17(6), 449-479.
  20. Miller, S.L., Smith-Magowan, D., 1990. The Thermodynamics of the Krebs Cycle and Related Compounds. J. Phys. Chem. Ref. Data. 19(4), 1049-1073.
  21. Millero, F.J., Pierrota, D., Lee, K., Wanninkhof, R., Feely, R., Sabine, C.L., Key, R.M., Takahashi, T., 2002. Dissociation constants for carbonic acid determined from field measurements. Deep Sea Res. Part I. 49(10), 1705-1723.
  22. Nikafshar, S., Zabihi, O., Hamidi, S., Moradi, Y., Barzegar, S., Ahmadi, M., Naebe, M., 2017. A renewable bio-based epoxy resin with improved mechanical performance that can compete with DGEBA. RSC Adv. 7(14), 8694-8701.
  23. Pind, P.F., Angelidaki, I., Ahring, B.K., 2003a. Dynamics of the anaerobic process: effects of volatile fatty acids. Biotechnol. Bioeng. 82(7), 791-801.
  24. Pind, P.F., Angelidaki, I., Ahring, B.K., 2003b. A new VFA sensor technique for anaerobic reactor systems. Biotechnol. Bioeng. 82(1), 54-61.
  25. Popovic, M., Woodfield, B.F., Hansen, L.D., 2019. Thermodynamics of hydrolysis of cellulose to glucose from 0 to 100°C: cellulosic biofuel applications and climate change implications. J. Chem. Thermo. 128, 244-250.
  26. Qian, H., Chen, W., Zhu, W., Liu, C., Lu, X., Guo, X., Huang, D., Liang, X., Kontogeorgis, G.M., 2019. Simulation and evaluation of utilization pathways of biomasses based on thermodynamic data prediction. Energy. 173, 610-625.
  27. Rehman, M.L.U., Iqbal, A., Chang, C.C., Li, W., Ju, M., 2019. Anaerobic digestion. Water Environ. Res. 91, 1253-1271.
  28. Schink, B., 1997. Energetics of syntrophic cooperation in methanogenic degradation. Microbiol. Molecular Biol. Rev. 61(2), 262-280.
  29. Sinbuathong, N., Sillapacharoenkul, B., Palakas, S., Kahraman, U., Dincer, I., 2022. Using sugarcane leaves and tops for exploiting higher methane yields: an assessment study. Int. J. Hydrog. Energy. 47(77), 32861-32875.
  30. Skorek-Osikowska, A., 2022. Thermodynamic and environmental study on synthetic natural gas production in power to gas approaches involving biomass gasification and anaerobic digestion. Int. J. Hydrogen Energy. 47(5), 3284-3293.
  31. Thauer, R.K., Jungermann, K., Decker, K., 1977. Energy conservation in chemotrophic anaerobic bacteria. Bacteriol. Rev. 41(1), 100-180.
  32. Vanwonterghem, I., Evans, P.N., Parks, D.H., Jensen, P.D., Woodcroft, B.J., Hugenholtz, P., Tyson, G.W., 2016. Methylotrophic methanogenesis discovered in the archaeal phylum Verstraetearchaeota. Nature Microbiol. 1, 16170.
  33. Wagman, D.D., Evans, W.H., Parker, V.B., Schumm, R.H., Halow, I., Bailey, S.M., Churney, K.L., Nuttall, R.L., 1982. The NBS tables of chemical thermodynamic properties. selected values for inorganic and C1 and C2 organic substances in SI units. J. Phys. Chem. Ref. Data. 18(4), 1807-1812.
  34. Westerholm, M., Calusinska, M., Dolfing, J., 2022. Syntrophic propionate-oxidizing bacteria in methanogenic systems FEMS Microbiol. Rev. fuab057, 46(2), fuab057.