| Title |
Breakpoint Chlorination to Remove NH3 - N and PAC Dechlorination to Prevent THM Formation |
| Authors |
오상은 ; 왕창근 ( Sang Eun Oh ; Chang Keun Wang ) |
| Abstract |
Influent NH₃-N concentration in downstream Keum River during winter period was as high as 3.5㎎/l. Although NH₃-N itself is not reported harmful at this level, it must be removed to meet drinking water quality standard of 0.5㎎/l. When high concentration of NH₃-N is not sufficiently removed during prechlorination, it is expected that too much chloramines are formed during post chlorination, and consumers` complaints are expected due to heavy smell of chloramine. Not sufficient disinfection efficiency by chloramine is also expected. Prechlorination and PAC dechlorination was adopted in the pilot plant study to prevent DBP formation by possible small amount of residual free chlorine after breakpoint. When chlorine dose is well controlled, NH₃-N removal is over 98% and THM formation is very low because of low free residual chlorine due to PAC dechlorination. In bench scale test, breakpoint appeared when Cl₂/NH₃-N ratio was 10∼11 on a weight basis and breakpoint reaction was almost completed within 10∼15min. After chlorination, PAC dose of l0㎎/l resulted in removal of 1∼1.5㎎/l free chlorine for 10 minutes. PAC reacted very slowly with NH₂Cl but very fast with free chlorine, and PAC removed more free chlorine at low pH than high pH. |