Development of an Irish grease management strategy and evaluation of biological in-situ digestion

Abstract

This document evaluates Ireland’s management of fats, oils and greases (FOGs) and examines the role of in-situ bacterial treatment in Grease Retention Units (GRUs). The study includes a sixteen-week bacterial dosing evaluation and culminates in a proposed national Grease Management Strategy. There are clearly identifiable political, legal, social, economic and environmental drivers for a national strategy. The Department of Environment and Local Government is in an ideal position to draw it up, prior to Local Authorities tailoring it to suit their own functional areas. The bacterial digestion study found that dosed units experienced a reduction in retained grease o f between 2% and 81%. Three of the units experienced significant rises m BOD discharges (up to 372%) and all experienced rises in ammonia (up to 1180%). This may have been due to oxidation and reduction of FOG or merely from the degradation of other organic and proteinaceous compounds. There was no evidence to suggest that bacterial dosing elevated emulsified fats, oils or grease in discharges. Bacterial digestion will have a role to play in a Grease Management Strategy, but recovery of major sources of FOG for alternative energy production is the preferred long-term option. In the shorter term, thermal oxidisation, anaerobic digestion and composting also have a significant role to play. Any strategy must promote public awareness in order to reduce domestic FOG discharges.