title: Synergetic inactivation of microorganisms in drinking water by short-term free chlorination and subsequent monochloramination.
abstract: OBJECTIVE
  To introduce synergetic inactivation of microorganisms in drinking water by short-term free chlorination for less than 15 minutes followed by monochloramination.
  
  
  METHODS
  Indicator microorganisms such as Escherichia coli, Staphylococcus aureus, Candida albicans, and spores of Bacillus subtilis were used to assess the efficiency of sequential chlorination and free chlorination.
  
  
  RESULTS
  The sequential chlorination was more efficient in inactivating these microorganisms than free chlorination, indicating that synergy was provided by free chlorine and monochloramine. Ammonia addition time, temperature and pH had influences on this synergy.
  
  
  CONCLUSIONS
  The possible mechanism of this synergy might involve three aspects: free chlorine causing sublethal injury to microorganisms and monochloramine further inactivating them; different ability of free chlorine and monochloramine to penetrate and inactivate microorganism congeries; and higher concentration of residual chlorine in sequential chlorination than in free chlorination.
authors.affiliation: Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China.
authors.forename: Xiao-Jian
authors.initials: XJ
authors.lastname: Zhang
authors.forename: Chao
authors.initials: C
authors.lastname: Chen
authors.forename: Yun
authors.initials: Y
authors.lastname: Wang
mesh_terms: D002700:Chloramines / Q000737:chemistry* / Q000494:pharmacology*; D002713:Chlorine / Q000737:chemistry*; D004203:Disinfection / Q000379:methods*; D054879:Halogenation; D014867:Water / Q000737:chemistry; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods*
chemical_list: D002700:Chloramines; D014867:Water; D002713:Chlorine; C030816:chloramine