Assessment of bacterial communities and residual chlorine dynamics within underground and overhead water storage tanks

Abstract

Biofilms are primary reservoirs for microbial communities within drinking water distribution systems (DWDSs) and exert considerable influence on the overall safety and quality of potable water. The current study centered on investigating the development of biofilms within water storage tanks of National University of Sciences and Technology (NUST) Islamabad, Pakistan. Two types of tank materials, Polyvinyl Chloride (PVC) and Reinforced Cement Concrete (RCC), were selected to study the impact of the material and residual chlorine on biofilm formation. This study analyzed biofilm development on these materials over 15 and 30 days, demonstrating the evolving biofilm dynamics over time. The findings revealed that water samples showed a high degree of bacterial contamination, with biofilm formation on both PVC and RCC surfaces attributed to low residual chlorine levels. The study also scrutinized the differences between PVC and RCC surfaces, highlighting their varied biofilm growth potentials. Bacterial quantity through Heterotrophic Plate Count (HPC) and images obtained from Scanning Electron Microscopy (SEM) showed that RCC surfaces promote denser biofilm growth owing to their roughness. Moreover, most biofilm samples showed more growth over 30 days time period compared at 15 days. Elemental analysis using Energy Dispersive X-ray Spectroscopy (EDX) revealed increased carbon content in biofilms, suggesting the role of organic compounds in microbial nourishment. This study underscores the significance of material selection for water distribution systems with rough surfaces, such as RCC, potentially promote enhanced bacterial attachment and proliferation. Moreover, current findings highlighted the significance of maintaining adequate residual chlorine levels to inhibit biofilm formation.