Methane production in low-cost, unheated, plug-flow digesters treating swine manure and used cooking grease

The T2.5 treatment had the greatest methane (CH4) production (45 L/day), a 124% increase from the control, with a total biogas production of 67.3 L/day and 66.9% CH4 in the produced biogas. Increasing the grease concentration beyond T2.5 produced biogas with a lower percentage of CH4, and thus, did not result in any additional benefits. A batch study showed that methane production could be sustained for three months in digesters that co-digested swine manure and used cooking grease without daily inputs. The investigation proved that adding small amounts of grease to the influent is a simple way to double energy production without affecting other digester benefits.