Degradation Of Halobenzoquinones During UV/Chlorination And UV/Chloramination:Kinetics And DBPs Formation

Halobenzoquinones are a class of aromatic disinfection by-products（DBPs）with high detection frequencies and concentrations.In this paper,the degradation characteristics and formation of low-molecular-weight DBPs of 2,6-dichloro-1,4-benzoquinone（2,6-DCBQ）and 2,6-dibromo-1,4-benzoquinone（2,6-DBBQ）were studied under different conditions during chloramination,UV,UV/chlorination,UV/chloramination.The order of the degradation rate of 2,6-DCBQ and 2,6-DBBQ was UV>UV/chlorination>UV/chloramination>chlorination>chloramination>hydrolyzation.In chloramination,the half-life(t_1/2)of 2,6-DCBQ and 2,6-DBBQ ranged from1.05 h to 7.39 h and from 0.98 h to 5.10 h.Increasing the monochloramine dosage and pH accelerated the degradation of 2,6-DCBQ or 2,6-DBBQ;The degradation rates with different mass ratio of Cl:N were in the order of 4:1>3:1>5:1.The yields of chloroform（TCM）and 1,1-dichloro-2-propanone（1,1-DCP）from 2,6-DCBQ were32.70%and 1.54%.The yields of TCM,monobromodichloromethane（BDCM）and dibromochloromethane（DBCM）,bromoform（TBM）and 1,1-DCP from 2,6-DBBQ were 12.50%,5.86%,6.35%,3.67%and 2.48%,respectively.In UV,the t_1/2 of 2,6-DCBQ and 2,6-DBBQ ranged from 9.22 s to 484.7 s and from 26.0 s to 282.9 s.Increasing pH accelerated the degradation of 2,6-DCBQ and2,6-DBBQ.In UV/chlorination,the t_1/2 of 2,6-DCBQ and 2,6-DBBQ ranged from 20.8 s to541.5 s and from 4.88 s to 359.1 s.Increasing the monochloramine dosage and pH accelerated the degradation of 2,6-DCBQ or 2,6-DBBQ.The yields of TCM,1,1-DCP and 1,1,1-trichloro-2-propanone（1,1,1-TCP）from 2,6-DCBQ were 20.0%,6.2%and0.7%,respectively.The yields of TCM、BDCM、DBCM、TBM、1,1-DCP and 1,1,1-TCP from 2,6-DBBQ were 5.48%,6.86%,1.89%,0.63%,2.92%and 0.16%,respectively.In UV/chloramination,the t_1/2 of 2,6-DCBQ and 2,6-DBBQ ranged from 271.8 s to 815.5 s and from 202.7 s to 554.6 s.Increasing the monochloramine dosage and pH accelerated the degradation of 2,6-DCBQ or 2,6-DBBQ.The yields of TCM,1,1-DCP and 1,1,1-TCP from 2,6-DCBQ were 20.9%,1.6%and 0.1%,respectively.The yields of TCM、BDCM、DBCM、TBM、1,1-DCP and 1,1,1-TCP from 2,6-DBBQ were14.80%,4.82%,1.03%,0.77%,1.12%and 0.10%,respectively.Haloacetonitriles（HANs）and trichloronitromethane（TCNM）were detected in UV/chloramination.The yields of dichloroacetonitrile（DCAN）and trichloroacetonitrile（TCAN）from 2,6-DCBQ were 4.50%and 0.84%.The yields of monobromo-chloroacetonitrile（BCAN）,DCAN and TCAN from 2,6-DBBQ were 1.71%,0.82%and 0.21%,respectively.The yields of TCNM from 2,6-DCBQ and 2,6-DBBQ were 8.16%and 4.77%,and the TCNM formation was maximum at pH 7.0.