Biodegradable waste can be recycled into useful material by biological decomposition. There are two mechanisms by which this can occur. The most common mechanism of recycling of household organic waste is home composting or municipal curbside collection of green wastes sent to large scale composting plants.
Alternatively organic waste can be converted into biogas and soil improver using anaerobic digestion. Here organic wastes are broken down by anaerobic microorganisms in biogas plants. The biogas can be converted into renewable electricity or burnt for environmentally friendly heating. Advanced technologies such as mechanical biological treatment are able to sort the recyclable elements of the waste out before biological treatment by either composting, anaerobic digestion or biodrying.
Sulabh International, an Indian NGO designed a cheap toilet system that recycles human waste into biogas and fertilizer.