JP2925352B

PURPOSE:To reduce initial, running and maintaining costs and to enable an operator to make operate and manage the device even without having highly advanced specialized knowledge as well as to allow the purification up to a prescribed water quality level by subjecting the waste liquid of surface treatments to pH adjustment, then changing the metal complex salts in the waste liquid to hydroxides by the contact reaction with ozone, then precipitating the hydroxides and removing the same from the liquid. CONSTITUTION:A 1st pH adjusting stage for adjusting the pH to an alkaline side, an ozone treating stage for changing the metal complex salts in the waste liquid to the hydroxides by the contact reaction with the ozone and precipitating the hydroxides, a solid-liquid separating stage for flocculating and thickening the hydroxides precipitated in the liquid in the previous stage and separating the hydroxides from supernatant water and a 2nd pH adjusting stage from neutralizing the above-mentioned supernatant liquid as the base treatment of the waste liquid of surface treatments. The waste liquid is adjusted to a 10 to 13.5 pH range and about 0.1% NaCl is added to the waste liquid in the above-mentioned 1st pH adjusting stage. Further, the waste liquid is subjected to an ozone treatment by irradiating the liquid with UV rays, ultrasonic waves, etc., in the ozone treating stage; thereafter, the hydroxides precipitated in the waste liquid are separated and recovered. The supernatant water is released into public water basins.