| 摘要 |
PURPOSE:To obtain colorless transparent treated water by removing COD present in chemical washing waste water, containing citric acid-washing liquid and rust- inhibiting liquid, from the cleaning operation of boiler, etc. CONSTITUTION:Calcium hydroxide or calcium oxide is added to a chemical washing waste water containing citric acid-washing liquid and rust-inhibiting liquid in order to sediment the precipitates of hevy metals (mainly iron), citric acid, and phosphates dissolved in the waste water in the form of the hydroxides of heavy met als (mainly ferrous hydroxide), calcium citrate, and calcium phosphate. Then, after oxidizing the ferrous hydroxide (Fe(OH)2) formed to ferric hydroxide (Fe(OH)3) by aeration, a persulfate, e.g., ammonium persulfate, sodium persulfate, or potassium persulfate, is added to the waste water in a proportion of 1 equivalent, preferably 1.6 equivalent, on the basis of COD, and furthermore and alkali, e.g., sodium hydroxide or potassium hydroxide, is added to the water to regulate its pH to more than 12. Subsequently, the waste water is subjected to sedimentation to separate it into supernatant and precipitates which are, in turn, dehydrated and then incinerated, or treated by other methods. |
