br 200 Biodegradable Dog Waste Bags, Pet Waste Bags, Green Eco Bags (2011 Jan Special) - My Doggie Supplies br The two main types of biodegradable plastics: oxo-biodegradable and hydro-biodegradable. In both cases degradation begins with a chemical process (oxidation or hydrolysis), followed by a biological process. Both types emit CO2 as they degrade, but hydro-biodegradables (usually starch-based) can also emit methane. Both types are compostable, but only oxo-biodegradable can be economically recycled.