title: Removal of genotoxicity in chlorinated secondary effluent of a domestic wastewater treatment plant during dechlorination.
abstract: OBJECTIVE
  Dechlorination with tetravalent sulfur is widely used in wastewater treatment processes after chlorination. Dechlorination can remove certain genotoxic disinfection by-products (DBPs). However, the reactions occurring during dechlorination of chlorinated secondary effluent and their genotoxic chemicals are still very complex, and the related genotoxicity changes remain unknown. Therefore, the effects of dechlorination on genotoxicity in secondary effluent and its fractions and typical genotoxic chemical after chlorination were evaluated.
  
  
  METHODS
  The dissolved organic matter in the secondary effluent sample was separated into four fractions with XAD-8 resin. Genotoxicity of secondary effluent and its fractions was evaluated by SOS/umu test, an ISO standard method. The concentration of typical genotoxic chemical named ofloxacin was determined by liquid chromatography with a mass spectrometer and a fluorescence detector.
  
  
  RESULTS
  Dechlorination with the addition of Na(2)SO(3) notably decreased the genotoxicity in the chlorinated secondary effluent, especially in the presence of high ammonia nitrogen concentration in the sample before chlorination. The Na(2)SO(3) addition significantly decreased the genotoxicity of the secondary effluent and its genotoxic ofloxacin prior to chlorination. The genotoxicity in the fractions containing hydrophobic acids (HOA) increased after chlorination, while addition of Na(2)SO(3) decreased the genotoxicity induced by chlorination. Tryptophan found in HOA exhibited genotoxicity after chlorination, while dechlorination decreased the genotoxicity in chlorinated tryptophan induced by DBPs.
  
  
  CONCLUSIONS
  Dechlorination was found to decrease the genotoxicity of chlorinated secondary effluent. The decrease was associated with the reduction of genotoxicity in genotoxic chemicals in secondary effluent prior to chlorination and DBPs.
authors.affiliation: Environmental Simulation and Pollution Control State Key Joint Laboratory, School of Environment, Tsinghua University, Beijing, People's Republic China. wuqianyuan@tsinghua.edu.cn
authors.forename: Qian-Yuan
authors.initials: QY
authors.lastname: Wu
authors.forename: Yi
authors.initials: Y
authors.lastname: Li
authors.forename: Hong-Ying
authors.initials: HY
authors.lastname: Hu
authors.forename: Ya-Nan
authors.initials: YN
authors.lastname: Ding
authors.forename: Huang
authors.initials: H
authors.lastname: Huang
authors.forename: Feng-Yun
authors.initials: FY
authors.lastname: Zhao
mesh_terms: D002713:Chlorine / Q000737:chemistry*; D004203:Disinfection / Q000379:methods*; D054879:Halogenation; D057927:Hydrophobic and Hydrophilic Interactions; D009152:Mutagenicity Tests; D009153:Mutagens / Q000737:chemistry / Q000302:isolation & purification* / Q000633:toxicity*; D013431:Sulfates / Q000737:chemistry; D014364:Tryptophan / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D009153:Mutagens; D013431:Sulfates; C012036:sodium sulfate; D002713:Chlorine; D014364:Tryptophan