Impact of Biofilm in Distribution Water Systems on Water Characteristics and Attempts for Treatment

Biofilms formed by ubiquitous polymeric compounds in drinking water systems host opportunistic bacterial infections. Contact between these microbial communities and drinking water has major effects on water quality and may endanger human health to the point of pollution. Access to safe drinking water remains a goal for developing countries, so factors that affect the development and growth of biofilms must be controlled. This study aims to estimate the effect of biofilms on the physical, chemical, and biological properties of water inside drinking water pipes, study the bacterial content of the biofilm deposits and attempt to apply some chemical treatment for biofilms within water systems, Biofilm samples were collected from water distribution systems in a specific geographical area. The results of the hydraulic study on the sampling points indicated a decrease in the water flow rate to 0.05 m/s and 0.12 m/s, and an increase in the duration of water stagnation, which led to a loss of part of the residual chlorine percentage to 0.08, 0.1 ppm. The physical properties resulting from the dissolution of biofilm sediments within distilled water showed a decrease in dissolved oxygen concentration from 9.2 ppm to 5.9 ppm, effect on turbidity, odor, as well as raising the pH. The biological properties of distilled water were also negatively affected due to the presence of pathogenic Escherichia coli bacteria, which formed the main component of biofilm colonies, the bacterial plate count as a result of passing treated water through biofilm points within water systems increased to 170 CFU/cm³ for cast iron pipes and 110 CFU/cm³ for PVC pipes. The chemical properties changed in terms of ammonia, TOC, and iron parameters. The Scan Electron Microscopic (SEM) examination of the biofilm sample revealed the presence of exopolysaccharide aggregates, the main component of Extracellular polymeric substances EPS, within the biofilm during maturation stages, as well as E. coli Bactria in its cylindrical and rod-shaped forms, and Streptococcus species in clusters. The use of oxidizing agents such as 0.1% sodium hypochlorite mixed with 0.5% hydrogen peroxide as a strong disinfectant for a contact time of 4 hours resulted in 100% complete destruction of the bacterial content of E. coli, as well as make detachment for the biofilm layers formed inside the water pipe as a sticky deposit due to the degradation of a portion of the protein that forms the EPS material surrounding the bacterial colonies.