The main component of biofilms is water, which can make up to over 90% of the wet weight. Biofilms are therefore considered as hydrogels. Water binding and mobility are crucial for diffusion processes in biofilms as well as for dewatering of sludges. In a FTIR-ATR study, the hydrogen-deuterium exchange in native drinking water mixed population biofilms was investigated non-destructively in a flow-through cell. The exchange process of water is characterized by two steps, the first completed after 49 seconds and the second after 21 minutes, indicating different water retention mechanisms. The process is fully completed after about 2 hours. If the biofilm is treated with chlorine (6 mg L−1 for 12h), exchange happens faster and no steps can be observed, indicating a change in the matrix with respect to water binding properties. It is concluded that the water in the EPS matrix is organized in a fine structure which influences the properties of the biofilm.

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