What should be done with dirt from digging out sewer drain pipe?
EPA discussion of waste treatment with lime
One common sanitizer for sewage is lime.  A farm supply would have it.  You must layer the dirt and the lime, a 1:10 ratio (1 inch of lime to 10" of dirt)

Care must be used against touching or breathing the lime directly.  Hydrating and mixing each layer (or lift) will ensure the dispersal and neutralizing the bacteria (and smell).

Historically used in pit toilets and at disaster scenes for mass burials.