Assessments provided for by this chapter shall be collected by the county trustee as county taxes are collected, except as provided otherwise in this part, and the funds collected shall be kept as a separate fund, and shall be paid out only for purposes properly connected with the improvement on the order or warrant of the county mayor; but the assessments may be collected by bill filed in chancery, as provided in §§54-12-412 —54-12-421, and no personal property of the owner of land assessed shall be liable or distrained upon for the assessment, but only the land assessed shall be liable for the assessment.