Chemical consideration of biodegradeability We hear the term 'biodegradeability' being thrown around alot in science, but rarely ever is the science itself explained. 

What are the chemical properties in a substance that make it biodegradeable? 

Furthermore, what exactly are the chemical processes involved in biodegradation?
Biodegradability is not a chemical property, much like a price for which you can buy a compound is not its chemical property. Both are the properties caused by some external circumstances, which are not necessarily related to chemistry.

As for the processes, there is hardly anything they have in common. Life is pretty versatile and can consume a wide range of chemical compounds. Wide as it is, though, this range does not constitute all chemistry. There are a great deal of compounds that just never happened to appear in nature before humans made them, so no life form had the chance to develop the ability to consume them. Those are not biodegradable.