Bactericidal action of illuminated TiO_2 on pure Escherichia coli and natural bacterial consortia:post-irradition events in the dark and assessment of the effective disinfection time

摘要

Bactericidal action of illuminated TiO_2 on pure culture of Escherichia coli K12 and bacterial consortium was studied.Photocatalytic E.coli inactivation rate was dependent on the biological parameters such as:physiological state,generation and initial concentration of bacteria.The behavior of the bacterial suspension during the subsequent dark period was discussed in order to estimate the potential of using the photocatalytic treatment process in a real water disinfection situation.The effectie disinfection time(EDT)was defined as the time required for total inactivation of bacteria without re-grow in a subsequent dark period referenced at 48h.An increase of E.coli concentration was observed aftr illumination fo bacteria without TiO_2 (named here as photolysis).In the presence of TiO_2(photocatalysis),the decrease of bactria continues in the dark,and no regrowth was observed within the illumination period.Thus,EDT was reached in photocatalytic but not in photolytic treatment.Bacterial consortia present in two different wastewaters were phototreated with and without TiO_2 and a singificant difference in bacterial sensitivity to both phototreatments was observed.Enterococcus sp.appear to be less sensitive than coliforms and other Gram-negatie bacteria.Considerable differences in photoreactivity were observed for both samples taken at the same place but at different data.Bacterial consortia present in two different wastewaters were phototreated with and without TiO_2 and a significant difference in bacterial sensitivity to both phototreatments was observed.Enterococcus sp.appear to be less sensitive than coliforms and other Gram-negative bacteria.Considerable differences in photoreactivity were observed for both samples taken at the same place but at different date.The first sample named as wastewater 1,exhibited a bacteriostatic but no actericidal effect after both phototreatments;the addition of TiO_2 accelerated the solar disinfection.in the second sample,wastewter 2,a bactericidal effect was observed in photolytic and photocatalytic experiments and the solar disinfection.In the second sample,wastewater 2,a bactericidal effect after both photolytic and photocatalytic experiments and the EDT was attained in both cases,even if bacterial inactivation rate was the lowest in the pesence of the catalyst.the chemical oxyen demand (COD)decreases during photocatalytic treatment,but not during the photolytic one;wheras the Dissolved organic carbon (DOC) increases in both cases.COD/DOC ratio decreases durign phototreatments.