Characterisation and anaerobic digestion of fat, oil and grease (FOG) waste from wastewater treatment plants.

The materials removed in the oil separation units of wastewater treatment plants can be referred to as fat, oil and grease (FOG) waste. FOG waste accumulation in treatment plants can cause clogging of pipes, production of excessive scums and foams, and negatively affect air/liquid oxygen transfer. While conventional disposal routes of this material can be limited by its water and organic content, FOG can represent a source of bio-energy other than bio-diesel production. This research determined the chemical and physical characteristics of FOG waste collected at four different wastewater treatment plants and defined the potential for energy recovery via dark fermentation and anaerobic digestion as treatment options for final disposal. The FOG samples featured markedly distinct physical aspects in connection with the oil separation technologies: solid agglomerate with a high content of lipids from vortex-type separation and semi-solid agglomerate with a low content of oils and fats from horizontal-flow chambers. All FOG waste presented high potential for methane production with values ranging from 460 to 865 NmCH/tVS but low yields of biological hydrogen via dark fermentation. This study addresses a knowledge gap in the scientific literature on the characteristics of FOG waste from treatment plants and defines possible routes for sustainable management via bio-energy recovery.