User:RalphLindeboom/Autogenerative high pressure digestion

'Autogenerative High Pressure Digestion' is a relatively novel concept of anaerobic digestion, in which the methanogenic biomass generates biogas pressure inside the bioreactor^[1]. Because CO₂ has a higher solubility than CH₄, it will proportion more to the liquid phase at higher pressures. Therefore, AHPD biogas is characterised by a high CH₄ content, reaching equilibrium values between 80-99% at pressures between 3 and 90 bar. In addition, also H₂S and NH₃ are theoretically more soluble in the bulk liquid than CO₂. Moreover, the water content of the already compressed biogas is calculated to have a dew point <-10^oC. Ideally, high-quality biogas can be directly used for electricity and heat generation, or injected in a local natural gas distribution net.

The acid neutralizing capacity (ANC) also referred to as alkalinity, determines to what extent the produced CO₂ can influence the pH of the solution. Typically the ratio between ANC and produced Total Inorganic Carbon, determines whether CO₂ will dissociate to form HCO₃^- or CO₃^2- or migrate to the gas phase. When ANC << TIC, typically the biogas contains a relatively higher CO₂-content, because biogas separation is only based on Henry's law. When ANC = TIC, CO₂ will form HCO₃ and when ANC >> TIC, CO₃^2- or carbonate precipitates will be the dominant form.

References

1. Lindeboom, R.E.F., Fermoso, F.G., Weijma, J., Zagt, K., Van Lier, J.B. (2011) Autogenerative high pressure digestion: Anaerobic digestion and biogas upgrading in a single step reactor system. Water Science and Technology 64 647-653.
2. Lindeboom, R.E.F., Weijma, J., and van Lier, J.B., (2012). High-calorific biogas production by selective CO2 retention at autogenerated biogas pressures up to 20 bar. Environmental Science & Technology, 46(3), 1895-1902.

External links

• example.com