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 CH4CO2 & 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.
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