DBNPA, biocide

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. 

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. 

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. 

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 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... 

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. 

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. 

Klaine SJ, Cobb GP, Dickerson RL, Dixon KR, Kendall RJ, Smith EE, Solomon KR. 1996. An ecological risk assessment for the use of the biocide, dibromonitrilopropionamide (DBNPA), in industrial cooling systems. Environ Toxicol Chem 15 21-30. 

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. ... 

General information. DBNPA is a halogenated amide and is considered a fast kill biocide. It has seen widespread use in water treatment and pulp and paper applications but in the oilfield is used primarily to treat the water used to prepare fracturing fluids. Its main attribute seems to be that its biocidal action is very fast, but the active then hydrolyzes to less toxic by-products. This may be advantageous in applications where water is stored prior to discharge so deactivation may not be necessary. 

Oxidants also provide additional benefits such as enhancing the performance of other biocides. Biocides like isothiazolinone, Bronopol, and DBNPA work much more effectively in an oxidising environment than in a reducing environment. Oxidants can also alleviate anaerobic conditions and decrease the problems caused by anaerobic bacteria such as odors. 

DBNPA 2,2-dibromo-3-nitrilo-propionamide, a nonoxidizing biocide discussed in this section. 

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. 

DBNPA Is a non-oxldlzlng, moderate electrophile biocide that is compatible with membranes. Its mode of action is similar to oxidizers, but is not as aggressive it acts on the cell wall as well as with the cell cytoplasm, but it does not interact with the slime (EPS). Application for membranes can either involve shock treatment, such as 6-12 ppm as active for 60 minutes, every two to three days, or continuous treatment at 2-3 ppm as 20% product. Due to the expensive nature of the treatment, continuous treatment is typically not economical. Work by Schook et al. has shown the use of 8.5 ppm as active DBNPA for three hours once per week can be more effective that 20 ppm (as active) exposure for one hour once per week (see figure 8.28). ... 

DBNPA is well rejected by RO membranes, up to 99.98% °, so on-line treatment is acceptable for most industrial applications. DBNPA can be used for potable applications if the treatment occurs offline (due to the limited passage of the biocide) , and the system is rinsed and monitored properly. The key factor for DBNPA effectiveness is to eliminate the active biological slime from the system via a cleaning process before using DBNPA, since DBNPA is a moderate electrophile, that does not attack the ESP. Thus, DBNPA is most effective on membranes that are relatively free of mature biological colonies and slime. At a pH above 8, the product tends to hydrolyze, so application at neutral pH is recommended The half life of DBNPA is 24 hours at pH 7,2 hours at pH 8, and 15 minutes at pH 9. 

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