Over and above the charges established herein, there may be established in special instances and upon special agreement between the City and the owner of any lot, parcel of land or premises which is served by the system, such additional charges for sewage wastes, industrial or otherwise, of unusual strength or composition which are accepted by the City for treatment, as may be determined to be fair and equitable. Each such special agreement and the charge established thereby shall not become effective until ratified by ordinance, duly passed by Council. (Ord. 47-56. Passed 7-24-56.)