Improving Biogas Quality by Recirculation of Wastewater Through a Silicone Membrane Located in An Aeration Tank.

By passing swine wastewater through a silicone hose located in an aeration chamber, we were able to reduce carbon dioxide concentration of biogas.  In the first series of experiments, carbon dioxide concentrations in the biogas were reduced by approximately 80%. This resulted in methane comprising about 90% of biogas compostion whereas methane comprised only about 70% of control biogas.  The lowering of carbon dioxide concentrations in the biogas was due to an increase in wastewater pH resulting in greater bicarbonate buffering and alkalinity. In the first experiment, some biogas production was sacrificed, due to loss of methane through the silicone membrane. In later experiments, wastewater was only circulated through the silicone hosing in early stages of the experiment in order to acheive greater bicarbonate buffering in the treated wastewater. In these experiments, biogas quality and total biogas production were increased above that biogas produced from control wastewater digestates.