Nothing in Sections 17-17-33 through 17-17-41 shall be construed to prohibit local governments from the construction or operation of approved sanitary landfills, or of any other heretofore or hereafter approved solid waste disposal system, it being the intent of Sections 17-17-33 through 17-17-41 that their provisions shall be supplementary to, and not restrictive of, any previously authorized solid waste disposal system, facility or operation, nor of any other such system, facility or operation which may be authorized in the future.