Other Non-Oxidizing Biocides

Isothiazolone has also been used as a non-oxidizing biocide for RO applications. However, the residence time required is much longer than for DBNPA. For example, a dosage of 50 to 100 ppm requires a 4-hour contact period. Thus, isothiazolone is not recommended for shock feed or continuous feed, but is recommended for cleaning events. Isothiazolone is more effective than DBNPA in high-organic waters. 

Quaternary germicides, phenolic compounds and iodine are not recommended as sanitizing against for polyamide membranes as these compounds can cause losses in water flux through the membrane.15 

3 Combination Mechanical Plus Chemical Fretreatment—Lime Softening 

Lime softening is used to remove the following species from water  

Species Raw Water Cold Lime Cold Lime- Soda Warm Lime Hot Lime Hot Lime- Soda 

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General information. Glutaraldehyde is a 5-carbon dialdehyde that has seen extensive use in industrial water treatment applications. In addition to its use as a biocide in oil and gas operations, it is also used in cooling water, paper making, and preservative applications, medical instrument sterilization, and as a non-biocidal crosslinker for leather. X-ray films, and enzyme immobilization. It is often used in oilfield applications in combination with other non-oxidizing biocides such as QAC s and formaldehyde and is compatible with the oxidizing biocides typically used in cooling water applications. 

Most of non-oxidizing biocides are liquids, and they can be classified rather vaguely by mode of action, by speed of kill, by active chemical group, etc. We will address here only significant practical aspects of most commonly used non-oxidizers. An information on other non-oxidizers can be found in the recently published reviews by Puckorius and Associates (Puckorius, 1998a, Puckorius, 1998b). 

The following sections discuss the primary biocide used today, chlorine, and alternative physical and chemical techniques to address membrane biofouling control. The most common alternative techniques examined here include chloramine, chlorine dioxide, ozone, UV, and non-oxidizing biocides such as DBNPA and isothiazolone. Table 8.12 summarizes advantages and limitations of these techniques (adapted from Kim, 2009). It is important to note that some of these biocides/disinfectants can contact the membranes, and others must be removed or destroyed before the water is introduced to the membrane system itself. 

Other chemicals. Oxidants are very non-specific in their reactivity. Therefore, the presence of chemicals susceptible to oxidation can affect oxidant performance. For example, many oxidants are known to react with dyes which results in a loss of oxidant and increased dye usage. Some oxidants can react with non-oxidising biocides. Some oxidants can even react with each other (e.g., hypochlorite and hydrogen peroxide). Interferences with OBA (optical brighteners), starch, sizing, unbleached groundwood have been reported. 

When plastics come in contact with microorganisms it can cause changes (negative) in the properties of plastics. Typical material parameters which are altered by the microbial action are mechanical properties, (e.g., tensile strength, flexibility), or simply the colour. Biocorrosion is usually an unwanted process which is to be avoided, e.g., by the addition of biocides to the material. The mechanism of biocorrosion is often a selective degradation of one component of the plastic, e.g., a plasticiser, and is accompanied in many cases by other, non-biological mechanisms such as hydrolysis or oxidation. 

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