When the lands are offered for sale by the sheriff, as provided by this chapter, and the sum of the tax due, together with interest, costs and penalty, is not bid, the sheriff making such sales shall bid the whole amount due thereon as aforesaid in the name of the district and shall sell the lands to the district and execute his deed therefor, conveying to such district such lands so sold to it. Such lands may be held and disposed of by the board of supervisors as the interest of the district may demand.