The governing body of a county, upon the petition of 25 percent of the qualified voters, if any, residing within the limits of the territory proposed to be added, may, by ordinance, extend the boundaries and enlarge any sanitary district created under the provisions of this article, which ordinance shall prescribe the metes and bounds of the territory so added. Upon the filing of the petition a hearing shall be had as provided in §§ 21-114 and 21-115, and the notice of such hearing may require all interested persons to appear and show cause why any special tax levied or to be levied in the sanitary district for special sanitary district purposes may not be likewise levied and collected in the territory proposed to be added to such district, and to appear and show cause why the net operating revenue derived in the added territory from the operation of any system or systems established under the provisions of § 21-118 may not be set apart to pay the interest on and retire at maturity the principal of any bonds theretofore issued in connection with such system or systems. Nothing in such ordinance enlarging a sanitary district as provided herein shall be construed to limit or adversely affect the rights and interests of any holder of bonds issued by the district, and such ordinance shall expressly preserve and protect such rights and interests. All interested persons who reside in or who own real property in (i) a proposed district or (ii) an existing district in cases of enlargement shall have the right to appear and show cause why the property under consideration should or should not be included in the proposed district or enlargement of same at such hearing.