Processes and systems are provided for simultaneously recovering coagulant and acid in a water treatment system. Sludge produced by the water treatment system is contacted with acid to form acidified sludge liquids. The acidified sludge liquids flow into a membrane assisted capacitive deionization system having both cation and anion exchange membranes. Metal cations from the acidified sludge liquids diffuse across at least one cation exchange membrane to form recovered coagulant, while anions from the acidified sludge liquids diffuse across at least one anion exchange membrane to form recovered acid. The diffusion rate of the metal cations across the cation exchange membranes is equal to or greater than the diffusion rate of the anions across the anion exchange membranes.