portable composting toilet mediums

We have been using this toilet in our country house for 6 years now with no issues of odor or pathogens etc. The solid waste can also be handled like dog poop...bagged and burned cleanly. which allows the urine medium to go straight to garden plants. Or another method can be 2 toilets. One for solid waste and another for liquid.
The mediums i originally used were sawdust and wood ash. Recently my cat showed me, by digging in my garden, that the screened compost topsoil may be a superior medium, as it already contains microbes that help break down matter. We now prefer dried composted soil or dried earth.

I may like to add that our cat also utilizes the same medium in his cat litter box. Separately disposed in a hole in the bush.

I have started using rotted stump material which has been quite a bit better than saw dust. Likely due to already having microbes as well. Plus it is free, I just collect it around my property.