Two-step double-chambered wastewater electrolysis to recover separated fractions of heavy metals and phosphate

The separated recovery of heavy metals and phosphate through a two-step water electrolysis is investigated. The use of carbon-polymer composite cathode with non-sticking properties and a dimension-stable anode in two-chamber cells is investigated to treat original industrial wastewater from metal industry by minimal addition of salts to support process water recovery. The heavy metals and phosphates are precipitated as metal-hydroxides and magnesium/calcium-phosphates, respectively. For phosphate precipitation the addition of magnesium chloride, calcium oxide as well as a reverse osmosis (RO) concentrate of artificial water reservoir were investigated. The pH value in the first steps affects both the amount of heavy metals and phosphate precipitated and an optimal pH for the first step is found to increase the phosphate recovery at low heavy metal content. Moreover, the use of RO concentrate enables a chemical input free phosphate recovery.