Why Anaerobic Digestion?

There are essentially three main options for dealing with organic wastes:

bury it - which means landfilling
burn it - which means incineration, gasification or pyrolysis
bio-digest it - which means either anaerobic digestion or composting

Technology	Sustainable	Impact on the environment	Energy recovery	Fertiliser output	Water recovery	Heavy metal recovery
Landfill	Unsustainable waste of resources	Some CH4 to atmosphere, leachate problems	Partial if landfill gas extracted	No fertiliser outputs	Lost in leachate	Not possible
Composting	Energy required	Damage to ozone layer, also leachate problems	None	Incomplete pathogen kill	Lost to atmosphere	Not possible
Incineration	Fertiliser loss negates any energy gain	Toxic ash	Some but Energy wasted	Some P&K output, but N destroyed	Burnt off	Secondary waste
Pyrolysis	Fertiliser loss negates any energy gain	Toxic ash, emmissions regulated	Some but Energy wasted	Some P&K output, but N destroyed	Burnt off	Secondary waste
Gasification	Fertiliser loss reduces energy gain	Pollutants locked in slag	Some but Energy wasted	Some P&K output, but N destroyed	Burnt off	Controlled not recovered
Anaerobic digestion	Carbon neutral	Total recovery of energy as CH4 CO2 & fertiliser	Maximum overall energy	Clean NPK fertiliser and trace elements	100%	Heavy metals can be recovered from digestate

Anaerobic digestion is the only system for dealing with organic waste which is sustainable, recovers the maximum energy, is a completely closed system with no emissions to air or land, which retains the fertiliser and water content, and facilitates the recovery of heavy metals.