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 <-10oC. 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 CO32- 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, CO32- or carbonate precipitates will be the dominant form.