Huge amounts of water treatment sludge are wasted annually in Egypt. One common practice of sludge handling is to discharge into waterways or by disposal after drying into landfills. Currently, there is a critical need for sustainable solutions that provide environmental protection as well as benefits for water producers. Coagulant recovery is not new but is still a good solution for sludge handling and reduction of operational costs. This work aims at completing the picture on coagulant recovery from alum sludge in El-Sheikh Zayed water treatment plant (ESZ-WTP) by acidification using hydrochloric acid. This study also investigates the effect of sequential recovery on the efficiency of the coagulant and treated water quality. Sludge characterization was done through determination of metals' concentration and composition, water content and organic matter concentration. The influence of acid concentration, sludge mass, acid/sludge mass ratio, mixing speed, temperature, and mixing time on aluminum leaching was studied. At optimum values of these parameters, 82.4% aluminum recovery was obtained. In addition, repeated recoveries were carried out at laboratory scale using raw water from ESZ-WTP. Our research revealed that recovered coagulant can be used for three times' recoveries as the trihalomethanes remain within acceptable limits.

acidification method, aluminum recovery, alum sludge, sequential recovery, water purification
© IWA Publishing 2017
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