Simultaneous recovery of coagulant and acid

A process for recovering coagulant and acid in a water treatment system, the process comprising:

• upon utilizing the coagulant in the water treatment system where sludge is produced, mixing the sludge in a mixing tank with the acid to produce waste solids and acidified sludge liquids, wherein the coagulant is a polyvalent metal coagulant;
• and
• in a membrane assisted capacitive deionization system having at least one cathode that is separated with a first flow spacer from at least one cation exchange membrane and at least one anode that is separated with a second flow spacer from at least one anion exchange membrane,
• (1) initiating a charging phase by applying an electric voltage difference between the at least one cathode and the at least one anode to separate aluminum or iron ions from anions during the charging phase, wherein the aluminum or iron ions diffuse across the at least one cation exchange membrane and the first flow spacer to temporarily immobilize at the at least one cathode, and the anions diffuse across the at least one anion exchange membranes and the second flow spacer to temporarily immobilize at the at least one anode during the charging phase,
• (2) initiating a charge relaxation/reversal phase to recover the aluminum or iron ions as they diffuse into the first flow spacer between the at least one cathode and the at least one cation exchange membrane, wherein the aluminum or iron ions react with a sulfuric acid solution or a hydrochloric acid solution to form recovered coagulant during the charge relaxation/reversal phase, and
• (3) recovering the anions as they diffuse into the second flow spacer between the at least one anode and the at least one anion exchange membrane to form recovered acid during the charge relaxation/reversal phase.