Extractions of extracellular polymeric substances, be it in their soluble (soluble microbial polymers [SMPs]) or extractable (extractable extracellular polymers) form, are commonplace in activated sludge research. However, a large variety of extraction protocols exists. This study focuses on the SMP polymers extraction. A literature survey revealed the prevalence of four extraction protocols: centrifugation, centrifugation combined with filtration, filtration, and sedimentation; but even within each of these protocols, the applied extraction conditions vary extensively. To decrease this variety, the impact of different extraction conditions was first investigated. In a second step, the different extraction protocols were compared with each other in terms of the extracted amount of SMP and their repeatability. Finally, a validation test on the different types of sludge was performed. This led to the conclusion that centrifugation (5000 g for 10 min) followed by filtration (prerinsed filter of 11 μm pore size) is the most reliable and generic applicable SMP extraction protocol.
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