(Enzymatic treatment as an environmental-friendly strategy for biofouling mitigation of reverse osmosis membranes (RO

Enzymatic treatment as an environmental-friendly strategy for biofouling mitigation of reverse osmosis membranes (RO)

Reverse osmosis (RO) membrane processes for desalination and wastewater reuse are known as a leading technology to provide industrial and drinking water needs. However, a major problem in the RO process is the deterioration of the operation performance or fouling caused by the deposition of undesirable matters including organic, inorganic, colloidal, and microbial constituents. Especially, biofouling of RO processes has been suggested as a critical issue due to the build-up of an irreversible biofilm induced by the sequential steps of initial attachment, formation of a microcolony, and maturation of the biofilm on a RO membrane surface. Moreover, a matured biofilm can hardly be removed due to selfsecreted extracellular polymeric substances (EPS), which provide structural strength and chemical endurance. Control of biofouling on seawater reverse osmosis (SWRO) membranes is a major challenge as treatments can be expensive, damage the membrane material and often biocides do not remove the polymers in which bacteria are embedded. Biological control has been largely ignored for biofouling control. The objective of this study was to demonstrate the effectiveness of enzymes as a new strategy and environmental-friendly compounds against complex fouling communities and removing biofilms. Among the newly developed biofilm prevention and control approaches are the ones focusing on the intrinsic cellular processes involved in biofilm establishment and maturation, such as motility, cell-to-cell aggregation, production of extracellular polymeric substances (EPS) and intercellular communication (quorum sensing, QS). The target of biofilm-disrupting enzymes is usually the EPS matrix surrounding the cells. However, their mode of action can greatly vary. Enzymes can: i) attack directly the biofilm components and degrade them; ii) induce cellular lysis; iii) interfere with the QS system; iv) or even catalyse the formation of antimicrobials. As enzymes can act on the biofilm EPS, the structural components of this matrix should be ideally identified before any enzymatic application. Carbohydrates, polysaccharides, proteins (frequently exhibiting amyloid-like properties), glycoproteins, lipids, phospholipids, glycolipids, and nucleic acids are usually identified as components of the EPS matrix. Given that biofilms can have heterogeneous composition, diverse types of enzymes are required to combat them and usually a mixture of enzymes should be applied, or combined with complementary treatments. There are four types of enzymes of particular interest for biofilm removal: anti-QS enzymes, oxidative enzymes, polysaccharide-degrading enzymes and proteolytic enzymes. These four types of enzymes belong to three of the main classes: hydrolases, oxidoreductases and lyases. Treatments with deoxyribonuclease (DNase) reduced biofilm accumulation of Enterococcus faecalis. DNase was also used to control Streptococcus pneumoniae biofilms. observed a decrease in the biofilm thickness higher than 85%. Polysaccharide-degrading anti-biofilm enzymes are composed by amylase, alginate lyase, cellulase and lysozyme. α-amylase was only capable of reducing Staphylococcus aureus biofilm by 79%. The lysozyme-immobilized membrane showed sufficient antibacterial activity against the Gram-positive bacteria, Bacillus subtilis, and the antibacterial activity remained for 5 months after storage at 5 ̊C.

Reverse osmosis (RO) membrane processes for desalination and wastewater reuse are known as a leading technology to provide industrial and drinking water needs. However, a major problem in the RO process is the deterioration of the operation performance or fouling caused by the deposition of undesirable matters including organic, inorganic, colloidal, and microbial constituents. Especially, biofouling of RO processes has been suggested as a critical issue due to the build-up of an irreversible biofilm induced by the sequential steps of initial attachment, formation of a microcolony, and maturation of the biofilm on a RO membrane surface. Moreover, a matured biofilm can hardly be removed due to selfsecreted extracellular polymeric substances (EPS), which provide structural strength and chemical endurance. Control of biofouling on seawater reverse osmosis (SWRO) membranes is a major challenge as treatments can be expensive, damage the membrane material and often biocides do not remove the polymers in which bacteria are embedded. Biological control has been largely ignored for biofouling control. The objective of this study was to demonstrate the effectiveness of enzymes as a new strategy and environmental-friendly compounds against complex fouling communities and removing biofilms. Among the newly developed biofilm prevention and control approaches are the ones focusing on the intrinsic cellular processes involved in biofilm establishment and maturation, such as motility, cell-to-cell aggregation, production of extracellular polymeric substances (EPS) and intercellular communication (quorum sensing, QS). The target of biofilm-disrupting enzymes is usually the EPS matrix surrounding the cells. However, their mode of action can greatly vary. Enzymes can: i) attack directly the biofilm components and degrade them; ii) induce cellular lysis; iii) interfere with the QS system; iv) or even catalyse the formation of antimicrobials. As enzymes can act on the biofilm EPS, the structural components of this matrix should be ideally identified before any enzymatic application. Carbohydrates, polysaccharides, proteins (frequently exhibiting amyloid-like properties), glycoproteins, lipids, phospholipids, glycolipids, and nucleic acids are usually identified as components of the EPS matrix. Given that biofilms can have heterogeneous composition, diverse types of enzymes are required to combat them and usually a mixture of enzymes should be applied, or combined with complementary treatments. There are four types of enzymes of particular interest for biofilm removal: anti-QS enzymes, oxidative enzymes, polysaccharide-degrading enzymes and proteolytic enzymes. These four types of enzymes belong to three of the main classes: hydrolases, oxidoreductases and lyases. Treatments with deoxyribonuclease (DNase) reduced biofilm accumulation of Enterococcus faecalis. DNase was also used to control Streptococcus pneumoniae biofilms. observed a decrease in the biofilm thickness higher than 85%. Polysaccharide-degrading anti-biofilm enzymes are composed by amylase, alginate lyase, cellulase and lysozyme. α-amylase was only capable of reducing Staphylococcus aureus biofilm by 79%. The lysozyme-immobilized membrane showed sufficient antibacterial activity against the Gram-positive bacteria, Bacillus subtilis, and the antibacterial activity remained for 5 months after storage at 5 ̊C.