Comparing respirometric systems for standardized biodegradation testing: a case study with polyethylene glycol and activated sludge microbiomes

Water-soluble polymers (WSPs) are key ingredients in personal care products, cleaning agents, and water treatment formulations, and are often released into wastewater systems after use. Biodegradability of WSPs by wastewater microbiomes enables appropriate end-of-life management and helps prevent their release into the environment. Standardized methods to assess WSP biodegradability using robust and reliable instrumentation are essential for the development and regulation of biodegradable WSPs. In this study, we compared three commercial respirometry systems (i.e., BSBdigi-CO2, OxiTop, and ECHO ER12) for testing the biodegradation of polyethylene glycol (as model WSP) by municipal wastewater microbiomes following OECD 301 B/F guidelines. Specifically, we aimed to determine how the different measurement principles and biodegradation endpoints between the systems affect the biodegradation test outcomes. Additionally, we evaluated practical aspects such as system setup, data validation and processing, and compatibility with complementary analytical techniques. All three tested systems produced similar biodegradation curves, with PEG biodegradation extents exceeding 75% after 28 days of incubation. Dissolved organic carbon (DOC) measurements were conducted complementary to respirometric analyses. In summary, we highlight the advantages and key considerations of all three respirometric systems, offering practical guidance when assessing the biodegradation of WSPs.