some sawdust is "toxic"...
I have heard that Walnut sawdust will kill plants in the garden. I don't use much Walnut so I compost all the rest of mine...Oak, some Maple or Pine. I also think Walnut is not good for animal bedding..I donno?
I collect all the leaves, grass clippings, sawdust and chips and then cover them with dirt for the winter. I turn the pile occasionally and in about a year or by fall I have some pretty rich soil.
There is a composting bacteria you can buy to speed up the process.
Some horse farms use sawdust in their bedding and I would suspect other animal farmers could use it also....chickens, goats etc. I would really check out if any other sawdust is "toxic" to animals.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)