Biostability assessment of ultrapure water piping materials in the semiconductor industry and their susceptibility to Ralstonia growth

The pipes used for ultrapure water (UPW) distribution are constructed using high-quality materials to ensure purity. However, there remains a risk of contamination based on the pipe type. This study is the first to comprehensively evaluate the biological implications of various UPW pipe materials used in the semiconductor industry. The results showed that Polyvinylidene fluoride (PVDF) exhibited lower organic carbon leaching (0.08 mg/L) and a reduced biomass formation potential (BFP) (approximately 5 × 10⁵ cells/cm²) compared to chlorinated polyvinyl chloride (CPVC) pipes. In particular, Ralstonia, an oligotrophic bacterium commonly found in UPW systems, formed a significant biofilm on pipe surfaces, notably in stainless steel (SUS) and CPVC pipes. Furthermore, particle contamination, a critical concern in semiconductor manufacturing, was investigated, focusing on potential contamination sources generated by pipe leaching and the presence of bacteria. The bacterial composition of the selected UPW was investigated, revealing Herbaspirillum, a nitrogen-fixing bacterium, as the dominant species, account for 66.15 %. Notably, the composition of the feedwater was different from that of the UPW. This study also highlights the limitations of culture-based methods, particularly in detecting bacteria under oligotrophic conditions, which are often unculturable. Flow cytometry (FCM) shows promise for the quick detection of bacterial contamination by providing total cell counts. Moreover, cytometric fingerprinting analysis revealed phenotypic differences between the communities. Nevertheless, further development of a simplified and widely applicable cell counting protocol is required for its effective integration into UPW production.