Process for Treatment of Waste Water Exhausted From Water-Wash Spray Booth Using Water-Soluble Paint

Practical and presently preferred embodiments of the invention are illustratively shown in the following examples.

Waste water: Containing 5 % of a commercially available water-soluble paint ("Odesuper K-20" manufactured by Nippon Paint; epoxy-modified melamine alkyd type resin)

Acidic agent: Phosphoric acid (75 %)

Alkaline agent: Slaked lime

To the waste water (1 liter) under stirring, phosphoric acid is added to obtain a pH value of 6.5, then slaked lime is added thereto to make the pH value 8.5, and phosphoric acid is again added to obtain a pH value of 6.5. This addition operation is repeated until phosphoric acid (15 g) and slaked lime (30 g) are consumed, and stirring is continued for 1 hour thereafter. Then 10 ppm of an organic polymer coagulant ("Chemfloc A-10" manufactured by Nippon Paint; polyacrylamide coagulant) is added thereto to make the coagulated product gross under mild stirring. The resultant mixture is subjected to a procedure for isolation of solid and liquid. The thus obtained supernatant shows a calcium ion concentration of 22 ppm. It can be advantageously reused as washing water for a conventional water-wash spray booth without any trouble.

Waste water: Same as in Example 1

Acidic agent: Sulfuric acid (50 %)

Alkaline agent: Barium hydroxide

To the waste water (1 liter) under stirring, sulfuric acid is added to obtain a pH value of 6.5, then barium hydroxide is added thereto to make the pH value 8.5 and sulfuric acid is again added to obtain a pH value of 6.5. This addition operation is repeated until sulfuric acid (18 g) and barium hydroxide (15 g) are consumed, and stirring is continued for 15 minutes thereafter. Then, 10 ppm of the organic polymer coagulant as used in Example 1 is added thereto to make the coagulated product gross under mild stirring. The resultant mixture is subjected to a procedure for isolation of solid and liquid. The thus obtained supernatant shows a barium ion concentration of 2 to 4 ppm. It can be advantageously reused as washing water for a conventional water-wash spray booth without any trouble.

The same procedure as in Example 1 is repeated. To the resultant supernatant, tap water and the water-soluble paint are added to obtain "waste water" in the same condition as in Example 1, on which the same procedure as in Example 1 is again repeated. This operation is repeated 10 times. On each supernatant, the calcium ion concentration and the solubility of the water-soluble paint are examined, of which results are shown in Table 1. These supernatants can be advantageously reused as washing water.