Laboratory Investigation of Non-Intrusive Biofilm Monitoring Techniques for Drinking Water Distribution Systems

“Effective biofilm monitoring in drinking water distribution systems (DWDS) is crucial for ensuring water quality and infrastructure longevity [1, 2]. Traditional biofilm measurement techniques are often invasive and/or offline, limiting their applicability in real-world networks [3, 4]. This study presents an experimental investigation of two novel, non-intrusive biofilm thickness measurement techniques. One method is based on monitoring heat resistance alterations caused by biofilm growth [5], and the other is based on monitoring hydraulic residence time alterations induced by the biofilm restricting flow through the pipe [6]. Both were investigated using a controlled laboratory setup designed to replicate DWDS conditions. The experimental facility, “Slimer,” consists of a 50-meter-long plasticized polyvinyl chloride (PVCp) pipe, where biofilm was allowed to develop over a
ten-month period under realistic flow and temperature conditions [7]. Biofilm presence and thickness were then assessed using the two proposed methods and validated against destructive pigging, biofilm volume and Adenosine triphosphate (ATP) measurements. Heat resistance measurements were obtained by monitoring temperature variations at the inlet, outlet and the
ambient air, while hydraulic residence time was measured through measuring electrical conductivity at the inlet and outlet and dosing of a NaCl tracer. Experimental results demonstrated that the hydraulic residence time method provided stable and reproducible thickness estimates (7–75 μm), closely aligning with biofilm volume acquired through pigging. Conversely, the heat
resistance method exhibited significant variability (-153 to 588 μm), particularly at higher flow rates. Sensitivity analyses confirmed that hydraulic residence time was the more robust of the two approaches. By conducting a rigorous laboratory evaluation, this study highlights the potential of hydraulic residence time as a reliable, scalable biofilm monitoring tool while exposing the limitations of heat resistance-based sensing in its current form. The potential of testing these methods in a larger network is worth
investigating.”

(Citation: Glynis, K.G., Blokker, E.J.M., et.al. – Laboratory Investigation of Non-Intrusive Biofilm Monitoring Techniques for Drinking Water Distribution Systems – https://doi.org/10.15131/shef.data.29921054.v1 –
This paper was presented at the 21st Computing and Control in the Water Industry Conference (CCWI 2025) at the University of Sheffield (1st – 3rd September 2025))