Effect of chlorine and chloramine disinfection and the presence of phosphorous and nitrogen on biofilm growth in dead zones on PVC pipes in drinking water systems

Abstract

In drinking water systems, 'dead zones' may have higher biofilm counts than areas of higher flow rates, as there are limited/no shear stresses removing biofilms from the pipe material, and disinfectant concentrations are significantly lower due to no/low supply of disinfected water from the reservoir. Biofilms affect the quality of drinking water and may lead to severe health issues for downstream consumers. Biofilms can be controlled by disinfection, two common disinfectants being chlorine and monochloramine. The growth of biofilms is also affected by the presence of nutrients, as nutrients act as a food source to bacteria in the biofilms. To compare the growth of biofilms in 'dead zones' under different disinfectant (chlorine and chloramine) conditions, PVC coupons were placed in stagnant distilled disinfected waters inoculated with 10% pond water (environmental source), and the biofilm growth was monitored on the coupons using visual analyses. Chloramine has a better disinfectant inhibiting potential than chlorine. To compare the influence of nutrients on biofilms in 'dead zones', coupons were placed in distilled water inoculated with pond water from the same environmental source, and nitrogen and phosphorous concentrations were monitored. It was found that for 'dead zones' in drinking water networks, chloramine has a better biofilm inhibiting and inactivation potential, and the presence of nitrates in water influence biofilm growth, and to a lesser extent so does phosphorous.