Abstract
The development of biofilm on the surface of filtration membranes is the main fouling component of water filtration systems. Chemical cleaning is only partially effective in removing biofilm components from the membrane surface. In order to identify opportunities to improve the efficiency of commercial cleaning solutions used in nanofiltration, we compared the in vitro efficacy of different commercial treatments, with or without the addition of polysaccharidases, to clean fouled membrane samples. The treatments were tested at two stages of biofilm development corresponding to 80 (D80) and 475 (D475) days of filtration in an industrial plant. The cleaning efficiency was evaluated by comparing the ATR-FTIR spectra before and after cleaning. At D80 and D475, all cleaning solutions led to a reduction of infrared signals from the biofilm. At D80, enzymatic alkaline detergent (AEDT) treatment was significantly more effective than alkaline detergent (ADT) treatment in removing proteins, but no significant difference in efficacy between the two treatments was observed for polysaccharides. The addition of polysaccharidases to AEDT did not bring any significant efficiency gain. At D475, ADT and AEDT treatments had the same efficacy, but the addition of polysaccharidases to the AEDT treatment significantly increased the removal of polysaccharides and proteins from the membrane surface. In conclusion, polysaccharidases can increase the in vitro efficacy of a commercially available alkaline enzymatic detergent cleaning solution against sufficiently developed biofilms. These results pave the way for the development of new cleaning solutions containing polysaccharide degrading enzymes for the cleaning of membranes used in the production of drinking water. Further experiments are needed to characterize the mechanism of this polysaccharidase effect and to confirm this increase in cleaning efficiency in an industrial context.
Highlights
Membrane fouling during filtration is the main limitation of this type of process [1,2]
Further experiments are needed to characterize the mechanism of this polysaccharidase effect and to confirm this increase in cleaning efficiency in an industrial context
Biofouling is a sequential phenomenon harbouring initial stages of microbial attachment to the membrane and later stages of cell multiplication and extracellular polymeric substances (EPS) production leading to biofilm development [8,9]
Summary
Membrane fouling during filtration is the main limitation of this type of process [1,2]. During the maturation process of biofilms formed on nanofiltration (NF) membranes, there is a diversification of the polysaccharide residues of the matrix, development of the polysaccharide network and reinforcement of the cohesion of the matrix by increase of the viscosity and the elasticity [9] At this stage, shear forces can only tear off a fragment of biofilm when the structure becomes too prominent, limiting the growth of the biofilm in thickness and facilitating the colonization of other sites [10]. Shear forces can only tear off a fragment of biofilm when the structure becomes too prominent, limiting the growth of the biofilm in thickness and facilitating the colonization of other sites [10] Another factor facilitating the geographic expansion of the biofilm is the active detachment of microorganisms that return to the liquid phase [11,12]. This active detachment involves the production of microbial enzymes to degrade the matrix locally and release sessile bacteria [13]
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