Characteristics of water quality and bacterial communities in three water supply pipelines

Many cities in China have implemented urban water supply pipe network renovation projects; however, at the beginning of new pipeline replacements, customers often complain about water quality problems, such as red water, odour and other water quality problems. To overcome these frequent water quality problems, this study selected a commonly used ductile cast iron (DCI) pipe, stainless steel (SS) pipe and high-density polyethylene (HDPE) pipe for laboratory simulations of the water quality regularity of new pipes, the variations in pipe inner walls, and the presence of microbial communities. Based on the research results, combined with actual water sample analysis, the stabilisation time of the interaction between the tubings inner walls and bulk water was determined, to allow pipeline cleaning and water quality maintenance. The results showed that the water quality change in the DCI was the most significant, while the SS and the HDPE pipes showed consistent changes with severe initial deterioration, then later stabilisation to meet the required standard. The DCI inner wall changed from a loose porous particle shape to a relatively dense and irregular three-dimensional shape, with the constituent elements mainly being O and Ca. The SS inner wall had a uniform structure in the early stage, but are obvious spherical balls of different sizes formed later, with the elemental composition here mainly being C and O. The HDPE inner wall was smooth and had small perforations in the early stage, while the perforation in the middle and late stages increased to become rough and scale-like at a much later stage. The proportion of Proteobacteria in effluents (72.82% to 86.87%) was significantly increased compared with the influent (48.45%), while the proportion of Proteobacteria (86.87%) in the DCI was significantly higher than in the SS (74.28%) and HDPE pipes (81.68%). Moreover, compared with the influent (23.33%), the Bacteroidetes (2.79% to 3.32%) levels in the effluents were significantly reduced, indicating that the pipe material affects the microbial abundance in water.