Environmental Conditions Shape Biofilm Formation And Water Quality In Drinking Water Distribution Systems

The safety of drinking water supply has been threatened by the deterioration of water quality, which resulted mainly from microbial proliferation. Although numerous studies have been conducted on the biofilm formation in drinking water distribution systems (DWDS), the comprehensive performance of biofilm formation and bulk water quality in response to environmental conditions remains unclear. This study aims at investigating the impacts of environmental conditions on the comprehensive performance of biofilm formation and water quality, and untangling the mechanisms of biofilm formation. It could provide theoretical guidance and scientific basis for optimized functioning of DWDSs, thereby securing the safety of drinking water quality.Firstly, this study investigated the role of environmental conditions on biofilm formation and bulk water quality, in terms of flow velocity, residual chlorine concentration and nutrient availability (carbon and phosphorus).Results showed that flow velocity had opposing influences on the propagation of microbial population in biofilm and bulk water. Addition of chlorine suppressed proliferation of suspended cells while chlorine disinfection at moderate levels clearly promoted biofilm formation. Enhanced nutrient supplements were observed to favor suspended cell growth and biofilm formation. In addition, the changes in both suspended and biofilm-embedded cells propagation collectively induced by environmental fluctuations were mostly associated with turbidity variations, concentrations of TOC, NH4+-N and soluble phosphorus compared to the other water quality parameters tested.Secondly, the fuzzy pattern recognition technique was adopted to quantify the effects of environmental conditions on comprehensive performance of DWDSs. Results indicated that concentration of residual chlorine (0.5 mg/L) without nutrient supplement at the flow velocity of 0.5 m/s was the most favorable condition for comprehensive performance of bulk water quality and biofilm formation. However, high concentration of residual chlorine (2.0 mg/L) and addition of nutrient supplement at the velocity of 1.5 m/s yielded the worst performance.Lastly, this study investigated the extracellular polymers and surface aggregation under environmental conditions. Results showed that residual chlorine and flow velocity at low levels yielded enhanced EPS production and surface aggregation. In contrast, when the velocity greater than1.5 m/s and residual chlorine concentration greater thanl.5 mg/L inhibited microbial metabolism and physiology activity, which resulted in the decrease of EPS. The EPS production of biofilm-embedded and suspended cells reduced, and thus the aggregation behavior was surpressed with increasing the nutrient supplements.