A dog waste collecting system that is fully compostable or biodegradable, and fully sustainable. The system is made of a cardboard box, a biodegradable liner, an optional cardboard cell divider, an absorbent coconut layer and a retaining coconut fiber mat that keeps the absorbent layer in place. The absorbent coconut layer absorbs the dog waste fluids while the coconut fiber mat holds the dog waste solids for removal by the owner. Perforations in the box define a lid that is removed prior to use to expose the mat. The system, after a few weeks of use, can be directly discarded in whole, in the compost.