The invention discloses a biotechnological process for the treatment of hydroxide sludge containing As produced in potable water production processes which use FeCI.sub.3 as a coagulant. The process seeks to modify the physicochemical properties of the produced sludge in such a way to facilitate the use of mechanical dehydration methods that allow decreasing the sludge volume and facilitating its final disposal. The process entails: Preparation of an inoculum of sulfate reducing microorganisms from the sludge to be treated; Combining the sludge to be treated, the SRB inoculum, and nutrients at a controlled temperature for about 5 days in an anaerobic reactor with enough mixing to allow sludge homogenization such that no untreated zones remain; Decanting the treated sludge for a period of approximately 3 days, recovering the clarified liquid and subjecting the sediment to a dewatering process through filtration or centrifugation; Filtering the solid residue coming from the decanter; and Characterizing the final residue.