Due to slow decomposition, typically fat, oil, and grease in wastewater is hard to treat. This study investigated weather adding a pea gravel cap above the coarse sand would help with pre-treatment of the wastewater. The results indicate that the pre-treatment does help the COD/BOD5 ratio stay around 1.0. This means that the organic matter is readily biodegradable. In conclusion, sand bioreactors are able to treat fat, oil, and grease that is in wastewater.