The recovery and treatment of wastewater for cleaning boiler scale

• Main Authors: Kao-Teng Liu, 劉高登
• Other Authors: Sheng-Kun Chen
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/52105406118140118844

碩士 === 崑山科技大學 === 環境工程研究所 === 98 === High concentration of EDTA is hard to be degraded biologically, this paper research the phsiochemical recovery and treatment of the scale-cleaning wastewater containing EDTA from boiler. The water investigation showed that the COD and EDTA concentration in the original wastewater was as high as 48700 and 47695 mg/L，while the major metal contents of Fe, Zn, Cu were 1946, 232.8 and 93.1 mg/L respectively. The experimental process included chemical precipitation, crystallization, oxidization, and final activated carbon adsorption for the residual COD. The addition of sodium hydroxide, but not the hydrogen sulfide and sodium phosphate, was the best agent for chemical metal precipitation that resulted in the residual Fe contents decreased to 3 mg/L in the wastewater. The crystallization process recovered EDTA from the wastewater high than 72.3 percentage, and it was approved that the crystals contained 99.88 % of EDTA and the residual COD in the wastewater was declined to 13500 mg/L。The further oxidation treatment using hydrogen peroxide solution for 72 hours degraded EDTA in the results of EDTA concentration of 618 mg/L, but still left COD of 12016 mg/L in the wastewater. It indicated that the hydrogen peroxide degraded the EDTA structure partly but not removed COD. However, the final activated carbon adsorption for 24 hours did reduced the residual COD from 12016 to 310 mg/L. Thus, 99.4 % of the total COD in the original wastewater was removed in the whole treatment process. The recovery and treatment process needed 6~7 duration days, and consumed alkaline and acid for the industrial grade in the cost of about 400 NT dollars, the hydrogen peroxide and activated carbon for 15000 NT dollars, while recovered EDTA in the value of 2600 NT dollars per cubic metric wastewater. It was suggested that process for more time shorter and cost economical was needed to develop in the future.