Electrolytic coagulation has advantages compared with conventional chemicals coagulation treatment. First of all, the addition of alkaline agent is necessary in chemicals coagulation treatment as the addition of acid agents in coagulation of dense wash water makes pH decline. While not much change of pH is observed with electrolytic coagulation, where alkaline agent is not demanded. Secondly, it is easy to control the dose of additional coagulants. In this study, electrolytic coagulation sedimentation treatment is adopted for membrane retentate from membrane filtration treatment without using coagulants. As electricity can control the addition of coagulation, an automation method is applied in the experiment. The lower the iron as well as aluminum dissolved, the higher the sludge density becomes; especially aluminum has this tendency. It is possible to achieve 400 kg/m3 of condensed sludge density with artificial wash water and more than 80 kg/m3 for real retentate, in terms of electrolytic coagulation of iron anode. The sludge density of aluminum anode is higher, but its filtrate density is lower than iron anode.

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