Biodegradation of\nWater-Soluble Polymers by Wastewater\nMicroorganisms: Challenging Laboratory Testing Protocols

For water-soluble polymers (WSPs) that enter environmental\nsystems\nat their end-of-life, biodegradability is a key functionality. For\nthe development and regulation of biodegradable WSPs, testing methods\nthat are both scientifically validated and economically practicable\nare needed. Here, we used respirometric laboratory tests to study\nthe biodegradation of poly(amino acids), poly(ethylene glycol), and\npoly(vinyl alcohol), together with appropriate low-molecular-weight\nreference substrates. We varied key protocol steps of commonly used\ntesting methods, which were originally established for small molecules\nand tested for effects on WSP biodegradation. We found that avoiding\naeration of the wastewater inoculate prior to WSP addition, incubating\nWSP with filter-sterilized wastewater prior to biodegradation testing,\nand lowering the WSP concentration can increase biodegradation rates\nof WSPs. Combining the above-mentioned protocol variations substantially\naffected the results of the biodegradation testing for the two poly(amino\nacids) tested herein (i.e., poly(lysine) and poly(aspartic acid)).\nOur findings were consistent between microbial inocula derived from\ntwo municipal wastewater treatment plants. Our study presents promising\nbiodegradation dynamics for poly(amino acids) and highlights the importance,\nstrengths, and limitations of respirometric laboratory methods for\nWSP biodegradation testing.