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Chemical Coagulation (CC) and Electrocoagulation (EC) processes using iron as coagulating agent were compared while treating aquifer water contaminated by a relatively high concentration of total chromium (CrT =19.0 mg L-1). A continuous semipilot comprising of EC (or CC), followed by flocculation, sedimentation and sandfiltration steps was used to remove CrT from water in order to get drinking water. A ratio of Fe/CrT ≥ 3 was required to reach the best efficiency of treatment using EC and CC. More than 99% of CrT was removed and residual CrT concentration below 0.05 mg L-1 (the limiting value recommended by WHO) could be obtained using the both configurations. However, CC increased the concentration of dissolved solids above the guideline recommended for drinking water.

This paper presents the results of a study on electrogeneration of aluminium, as a coagulant to remove silica in make-up water for cooling towers. Three electrochemical systems were tested, two with aluminium electrodes (one with polarity change and another without it), and a third one with aluminium anodes and cathodes of stainless steel. From the obtained results it was concluded that under the studied conditions, the most advantageous system to produce aluminium and remove silica is the one with both electrodes of aluminium working with direct current. Due to chemical production of aluminium at the cathode, the concentration of aluminium in the water at the outlet of the electrochemical reactor is much higher than the one calculated according to Faraday's law. Under the tested conditions it was possible to remove up to 66% of silica from water containing around 50 mg L(-1).

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Two reactors were tested to generate Al3+, that quickly form Al(OH)3 used to remove dissolved silica. Reactor (A) has parallel plates with a vertical zig-zag hydraulic path; this configuration has the disadvantage of important load lost due to the opposition between a going down water flux and the electrochemically generated gas bubbles naturally moving up in some regions. Reactor (B) consisted on an alternating arrangement of a reaction camera with only ascendant flow of water, followed by a chamber designed for water drop. The reaction zone, where bubbles generate is the same where the water moves up. Reactor (B) saves energy and had a better performance for equivalent conditions when compared with reactor (A) to remove silica.

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