Whenever a sewer district, or any part thereof, in any county of the first class not having a charter form of government, is embraced within the corporate limits of any municipality, all of the sanitary sewage system, treatment plant, facilities, and appurtenances thereto, including both land and rights-of-way and main and submain sewers of any sewer or joint sewer district, shall vest in said municipality, and it shall be the duty of said municipality to assume, take charge of, and exercise control over said sewage system. Whenever said district shall have issued bonds payable from taxes or from revenue, such municipality shall retain as to the area in such district all of the powers and authority theretofore conferred upon said district by law. All unexpended assessments and taxes in the operation and maintenance account of said district shall be paid into the county treasury, and all unexpended assessments, taxes, funds and deposits in the revenue and general obligation bond fund shall be applied toward the payment of the obligations of said district.