Recycling of filter backwash water and alum sludge for reuse in water treatment plants. Technical report

The feasibility of recycling backwash water and alum sludge generated from water-purification plants has been investigated. The waste recycle system presented here consists of (a) recycling the filter backwash water to the intake system for reproduction of potable water, (b) dividing the combined sludge into two fractions for alum solubilization, respectively, in an acid reactor and an alkaline reactor, (c) centrifugal filtering the inert silts from alum solutions by two separate water-solid separators for ultimate disposal, and (d) returning the solubilized alums from the two separate water-solid separators in proper proportions for reuse as flocculant(s). The proposed recycle process was designed to provide a cost-effective system for achieving zero water discharge and alum recovery from a water-purification plant. Recommended process-design parameters necessary to achieve the above stated goals were established. Experimental results tend to suggest that practical designs based on the proposed water recycle, sludge thickening, and alum recovery (STAR) system are both technically and economically feasible.