After the city has entered into a contract for construction of the district sewer improvements, the engineer or other officer having charge of the work shall compute the whole cost thereof and shall apportion the same against the lots or tracts of ground in the district, exclusive of the public highways, and the officer shall report the same to the governing body of the municipality by bill or otherwise, and the governing body shall therefore levy and assess a special tax by ordinance against each lot or piece of ground within the district; whereupon the clerk shall make out a certified tax bill under the seal of the city, town or village of the assessment against each lot or piece of ground within the district in the name of the owner thereof. Said certified tax bills shall be signed by the mayor and attested and recorded by the clerk and shall be delivered to the contractor in payment for the work upon completion of the project or deposited into a special fund as authorized by section 88.815, as appropriate.