In order to increase the use of low-cost digestion systems, the systems must be optimized for methane production to increase energy availability and profitability. Low-cost digesters are optimal for co-digestion due to the dispersed nature of small-scale waste production (Gavala et al., 1996). In addition, a digester will create a safe and profitable method for disposal of household grease, whey, and restaurant waste, which will extend the life of septic tanks, the only waste system available in most rural areas. Due to the low volume of wastewater being treated in small-scale systems, knowing correct proportions is extremely important.
This study investigated co-digesting swine manure and used cooking grease in 12 field-scale digesters with three replications of each mixture in a nine-month study. Additionally, a methane production batch study was conducted after the nine-month study to determine if manure loading could be interrupted in co-digestion systems without an additional stabilization period. By utilizing simple systems that treat ample waste sources, this study seeks to determine the optimal ratio of grease and manure for increasing methane production in existing systems and adding economic incentives for further dissemination of low-cost digestion systems. Additionally, the results of this study will help determine if co-digestion is feasible in non-mixing conditions due to the immiscible nature of wastewater and oil.