The council may, at or before the confirmation of the assessment or assessment roll in proceedings under this article, by resolution, determine that improvement bonds be authorized and issued to represent the assessments. The bonds shall be issued in the name of the municipality, but shall be made payable only from the special fund collected by the municipality from special assessments levied and assessed upon the lots included within the limits of the assessment district. All sums collected from the special assessment shall be placed in the special fund and shall be used for no other purpose than payment of the principal and interest of the bonds.