DBNPA

Non-oxidizing biocides are used on membranes to prevent microbial fouling. By definition, these products will not oxidize polyamide composite membranes and can be used directly on the membranes. There two most common, non-oxidizing biocides used with RO membranes sodium bisulfite and 2,2,dibromo-3-nitrilo-proprionamide or DBNPA. 

Sodium bisulfite can be used as a biocide on a shock feed basis. Typically, 500 to 1,000 ppm as sodium bisulfite should be fed for 30 minutes. The frequency of use should be dictated by the temperature of the water and the concentration of nutrients for microbes (warmer water and higher concentrations call for more frequent application of the bisulfite). 

For potable water applications, only off-line treatment with DBNPA is recommended. This is to ensure that the single produce active concentration (SPAC) of 90 ppb of DBNPA in the permeate is not exceeded.14 

Sodium bisulfite and other reducing agents can decompose the active ingredient in DBNPA formulations. Hence, it is recommended to suspend use of reducing agents during addition of DBNPA to avoid decomposition of the biocide.14 

Although DBNPA is non-oxidizing, it does give an ORP response of about 400 milliVolts at 0.5 to 3.0 ppm. Chlorine gives a reading of about 700 milliVolts at 1 ppm concentration. It is recommended that the ORP set points be by-passed during addition of DBNPA. 

For potable water applications, only off-line treatment with DBNPA is recommended. This is to ensure that the single produce active concentration (SPAC) of 90 ppb of DBNPA in the permeate is not exceeded. Sodium bisulfite and other reducing agents can decompose the active ingredient in DBNPA formulations. Hence, it is recommended to suspend use of reducing agents during addition of DBNPA to avoid decomposition of the biocide.  

DBNPA can also be used as a cleaner to destroy microbes within the membrane modules. Dosage is about 100 ppm for 30 minutes at pH 6.0 to 7.5. This cleaning may be followed by an alkaline cleaning to help remove any biofilm that may be present (see Chapter 13.2 for more details on membrane cleaning formulations). 

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Disinfection of heavily fouled systems generally requires a lowering of the pH level to between 6 and 7 and addition of DBNPA at 25... 

DBNPA Paper food packaging Hot water extraction MEKC UV 1700 pg/g 53.0 16... 

The concept of dispensing biocides or biostats in tablet form has recently been extended to the supply of certain nonoxidizers, such as 2,2-dibromo-3-nitrilopropionamide (DBNPA) (which has been widely available for many years as a liquid product and to a lesser extent as a powdered product). 

Since those days, various other bromine-based biocides and biocide intermediates have been introduced onto the global market or found renewed favor. The most notable are sodium bromide, isocyanurate/NaBr blends, and DBNPA (a nonoxidizer available as a powder or solution, and recently introduced in tablet form). Most bromine biocides employ chlorine in some form as an activator to produce the primary biocidal species hypobro-mous acid (HOBr). 

From the preceding, it can be seen that there is a wide range of individual nonoxidizing biocides and blends available. None of the individual products are especially effective under all operating conditions or water qualities, although the newer individual biocides tend to perform better than older materials. However, several of these newer biocides are generally offered only by one or two primary manufacturers (examples are DBNPA, gluteraldehyde, isothiazolinones) and consequently are often the most expensive materials to use, on a cost-per-application basis. 

Chemical 4 (20% DBNPA) dosed periodically at 6 to 12 ppm, on system volume... 

Basic problem of poor biological control. The pH level of the recirculating water is too high for efficient use of chlorine. Much of the chlorine is used as a process contaminant oxidizer and not as a biocide. No biodispersant is used. Use of DBNPA was a poor choice. Most of the biocidal duty falls on isothiazoline, but even this cannot effectively deal with algae, given that the pH is over 8.0 and the weather is extremely sunny. 

Also, a new program would make use of a biodispersant, and the DBNPA... 

The customer required isothiazoline and DBNPA to be used on an alternating basis, but was agreeable to the supply of a biodispersant. However, the practice was for the biodispersant to be added 4 hours after each application of biocide, rather than before or at the same time, which tended to defeat the purpose. 

Stainless steel injection quills should not be used with DBNPA as they may corrode. 

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. 

Dow Chemical Company, "Water Chemistry and Pretreatment Biological Fouling Prevention of FilmTec Elements and DBNPA," form no. 609-02036-0808. 

Neutral-pH cleaners are usually used to address microbes. Most of these cleaners use a non-oxidizing biocide such as DBNPA (dibro-monitriloproprionamide) or isothiasolin, and are pre-packaged by vendors. 

While there may be many options to deal with RO reject, each one has advantages and limitations. Some offer cost savings, while others may increase costs, but eliminate the need to dispose of a relatively large waste stream. Reject is considered non-hazardous, and contains only those constituents that were present in the feed water (only more concentrated, which can be a problem) and any antisealants, biocides (such as DBNPA—see Chapter 8.2.5.2), or any other chemical added as pretreatment. Disposal techniques over the years have included ... 

For biocide treatment directly on the membranes, DBNPA is a good non-oxidizing biocide (see Chapter 8.2.5.2). For clean membranes, a dosage of about 100 ppm for 30 minutes 2 to 3 times per week is recommended. For heavier fouling, 100 ppm for 60 minutes 2 to 3 times per week should be fed. Alternatively, DBNPA can be fed continuously at about 2-3 ppm. Note that once biofouling gets out of control, it will be very difficult for DBNPA to work, because it is a non-oxidizer and cannot penetrate biofilm. DBNPA works best as a preventative treatment. 

Isothiazolone can be used as a cleaner, but not for slug treatment, as it requires a longer contact time than DBNPA (see Chapter 8.2.5.3). When cleaning with isothiazolone, it should be allowed to contact the membrane for at least 4 hours. 

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