other processes

anaerobic digestion

The practice of sending grease to the digester is widely accepted in Anglo-Saxon countries. It requires thorough 6 mm straining of either all the effluent or just the grease. Methane fermentation of grease will be satisfactory when the grease is thoroughly combined with the sludge. The SUEZ biogas mixing system prevents the formation of a crust (one of the earlier criticisms of this option).

composting

This process consists in mixing grease (having previously removed as much water as possible) with a substance (sawdust, shavings, straw …) in order to ensure that process air can pass through the grease.

This method requires lengthy contact times (7 months) and extensive ground areas. Additionally, this method can create nuisances (odours, leaching …).

The quality of the compost is often poor.

incineration

This process consists in eliminating grease by «recovering» their high calorific value.

This process has the advantage of converting grease into an inert residue. This technique can only be entertained for large treatment plants that already include a sludge furnace. There are also a few instances of incineration with household waste.