Biological fouling prevention

Dow Chemical Company, "Water Chemistry and Pretreatment Biological Fouling Prevention," form no. 609-02037-1004. 

Biofilms can promote corrosion of fouled metal surfaces in a variety of ways. This is referred to as microbiaHy influenced corrosion. Microbes act as biological catalysts promoting conventional corrosion mechanisms the simple, passive presence of the biological deposit prevents corrosion inhibitors from reaching and passivating the fouled surface microbial reactions can accelerate ongoing corrosion reactions and microbial by-products can be directly aggressive to the metal. 

Biological fouling biological organisms attach to heat transfer surface and build a surface to prevent good fluid contact with the tube surface. 

Membrane storage Einally at the end of washing, the membrane was stored in 0.5% solution of sodium metabisulhte (SMBS) preservative prepared in DM water. This helps to prevent biological fouling and irreversible destruction of the membrane. 

UF and MF membranes alone do not remove total organic carbon (TOC) and tri-halomethane (THM) precursors [13]. Hence, pre-treatment entails addition of chemicals such as coagulants (FeCl3 or FeS04), alum or polyaluminium chloride to increase the size of suspended solids and colloidal particles and thus prevent or minimise colloidal, organic, and/or biological fouling. In the case of seawater desalination, membrane filtration has proven to be superior to multimedia filtration [14,15]. 

Membrane can be maintained well through cleaning with a mixture of 1% NaOH + 0.5% EDTA in tap water, which removes stubborn foulants. Alternate washing with 1% citric acid can remove metal salts and mineral precipitates from the membrane surface. The membrane must be stored in 0.5% SMBS (NaS O ) during shutdown periods as well as over every weekend to prevent biological fouling, which is otherwise irreversible. 

Test Conditions Test conditions and test requirements are shown in Table 2.5. The test was aimed at satisfying the following plant specification. For prevention of biological fouling, it was shown that the ICI method provided effective chlorine injection. 

For a 12-month test period, RO performance of HB9155 based on CTA material was very stable and satisfied the test requirements. Therefore, it was demonstrated that RO plant performance could be recovered by replacement of existing polyamide membranes with CTA membranes. Differential pressure was stable at a low level of about 20 kPa without the need for chemical cleaning during the test period. Therefore, it is concluded that the ICI method worked effectively to prevent biological fouling. 

Chemicals are added to the circulation system to prevent fouling. Dispersants are added to prevent deposit of solids, corrosion inhibitors to prevent corrosion and biocides to inhibit biological growth. 

Another attractive application of polymer brushes is directed toward a biointerface to tune the interaction of solid surfaces with biologically important materials such as proteins and biological cells. For example, it is important to prevent surface adsorption of proteins through nonspecific interactions, because the adsorbed protein often triggers a bio-fouling, e.g., the deposition of biological cells, bacteria and so on. In an effort to understand the process of protein adsorption, the interaction between proteins and brush surfaces has been modeled like the interaction with particles, the interaction with proteins is simplified into three generic modes. One is the primary adsorption. 

Typically a limit of, say, 2.0 ppm total iron is set for the maximum permitted in a system, but this usually has more to do with the tolerance of ongoing corrosion processes than with an effort to prevent problems occurring in the first place due to the presence of incoming iron. Where iron is present in cooling water, not only can it form a precipitated sludge and foul the system but also it can cause both electrochemical and biologically induced corrosion processes to occur. 

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