The impact of disinfection processes on biofilm formation in potable water distribution systems

[摘要] In this study, surface and ground water were used to evaluate the impact of disinfectionprocesses (chlorination, chloramination, ozonation, UV irradiation and hydrogen peroxide) onbacterial regrowth and bioftlm formation in potable water distribution systems using laboratoryscaleunits. Disinfection was carried out using disinfectant concentrations which were as closeas possible to those used in practise. The parameters that were used to evaluate the bactericidaleffectiveness of each disinfectant were coliform bacteria, heterotrophic plate count and totalbacteria. Membrane filter and standard spread plate procedures were used to enumeratecoliform and heterotrophic plate count bacteria respectively. The epifluorescence direct countinvolving DAPI was used to enumerate total bacteria. The scanning electron microscopy technique was used to visualize biofilm formation on stainless steel and cement coupons.The microbial disinfection efficacy of all disinfectants was found to be equal in theelimination of coliform bacteria in surface water although recovery of coliforms occurred 24h after disinfection in all treated water systems with the exception of chloraminated watersystems. For the groundwater, all disinfectants were found to remove coliform bacteriawithin the first hours of disinfection with the exception of hydrogen peroxide. Completeremoval of coliform bacteria by hydrogen peroxide occurred only 48 h after disinfection.In surface water systems, more than 99 % (average kill percentage) of heterotrophicbacteria were removed by all the disinfection processes. Chloramination and hydrogen peroxidedisinfection, however, resulted in a higher effective disinfection (average 99.99 %) althougha longer period of time (between 24 and 72 h for chloramination and 72 h for hydrogenperoxide) was required to achieve this kill percentage. In groundwater systems, more than99.90 % (average kill percentage) heterotrophic bacteria were removed by all the disinfectantswith the exception of hydrogen peroxide (99.88 % average kill percentage). However, ozonewas highly effective within the first 2 has shown by the average kill percentage of 99.999 %of heterotrophic bacteria. These results led to the conclusion that the microbial disinfectionefficacy was greater when using groundw~ter than when using surface water.The phenomenon of bacterial regrowth was linked to the absence of concentrations ofdisinfectant residuals. In both water sources, bacterial regrowth occurred earlier in chlorinated,ozonated and UV treated water than in chloraminated and hydrogen peroxide treated water.Significantly higher heterotrophic bacteria counts were noted in chlorine, ozone and UV treatedwaters than either in chloramine or hydrogen peroxide treated waters. The greater persistenceof monochloramine and hydrogen peroxide residuals was found to inhibit bacterial regrowthin both test waters.

[发布机构] University of Pretoria