Membrane biofouling

Would you agree that membrane hidrophilcity is not enough to mitigate bacteria attachment?

Taxonomy

• Membranes
• RO & MSF Fouling
• Desalination

2 Answers

1. Yes, membrane hidrofobicity will not enough to mitigate bacteria attachment on the surface of RO memrbanes.

   1 Comment

   1. So instead of trying to enhance membrane hydrophilicity we should not address our researches to increase the resistance of polymeric membrane (polyamide) to chlorine?

2. Membrane chemical cleaning is an integral part of operation for micro- and ultrafiltration systems in the water industry and has significant impact on process operations. However, this issue has not been adequately addressed primarily for two reasons:

   1. Cleaning protocols are typically recommended from membrane manufacturers and some cleaners are proprietary;
   2.  The issues of membrane fouling are poorly understood and related to site-specific water quality issues.

    As advances in aquatic chemistries and the analytical tools of membrane fouling occur, a broad understanding of the interactions between fouling materials and membranes, among fouling materials, and between fouling materials and cleaning chemicals becomes possible, although there still are many gaps in the understanding of the basic chemistry of fouling. Algae, bacteria, and certain natural organic matters fall into the size range of particle and colloids. However, they are different from inert particles and colloids such as silts and clays. Biofouling is a critical issue in membrane water and wastewater treatment as it greatly compromises the efficiency of the treatment processes. It is difficult to control, and significant economic resources have been dedicated to the development of effective biofouling monitoring and control strategiesTo distinguish the different fouling phenomena, particles and colloids here are referred to biologically inert particles and colloids that are inorganic in nature and are originated from weathering of rocks. Microbial fouling is a result of formation of biofilms on membrane surfaces. Once bacteria attach to the membrane, they start to multiple and produce extracellular polymetric substances (EPS) to form a viscous, slimy, hydrated gel . EPS typically consists of heteropoly saccharides and have high negative charge density. This gel structure protects bacterial cells from hydraulic shearing and from chemical attacks of biocides such as chlorine. The attachment of microbial cells to the membrane surface is the first step of membrane biofouling, leading to the formation of the biofilm layer. The biofilm may comprise populations of different types of microorganisms (e.g., bacteria, algae, protozoa and fungi). Initial microbial attachment is mediated by electrokinetic and hydrophobic interactions [16], and is generally followed by cell growth and multiplication at the expense of soluble nutrients in the feed water or adsorbed organics on the membrane surface . The extracellular polymeric substances (EPS) excreted by microorganisms anchor the cells to the substratum and further condition and stimulate additional microbial colonization of the membrane surface .

   Surfactants are compounds that have both hydrophilic and hydrophobic structures. They can form micelles with fat, oil, and proteins in water and help to clean the membranes fouled by these materials. Some surfactants may also interfere hydrophobic interactions between bacteria and membranes . In addition, surfactants can disrupt functions of bacteria cell walls. Therefore, surfactants affect fouling dominated by the formation of biofilms.