Bisulfite feed

Bisulfite feed bisulfite is added to eliminate free chlorine, if carbon is not used. 

To prevent these failures, constant monitoring of the pretreatment system is necessary. Alarms should be installed on critical systems, such as the ORP associated with the sodium bisulfite feed. Particle monitors could be used to detect channeling or carry over through filters. Hardness analyzers with alarm should be installed on the effluent from softeners. 

Design criteria The required contact time = 1-5 min sulfur dioxide feed rate = 1.1 lb per lb of residual chlorine sodium sulfite feed rate = 0.57 lb per lb of chlorine sodium bisulfite feed rate = 0.68 lb per lb of chlorine sodium thiosulfate feed rate = 1.43 lb per lb of chlorine. 

HES is produced from 93—96% dextrose hydrolyzate that has been clarified, carbon-treated, ion-exchanged, and evaporated to 40—50% dry basis. Magnesium is added at a level of 0.5—5 mAf as a cofactor to maintain isomerase stabiUty and to prevent enzyme inhibition by trace amounts of residual calcium. The feed may also be deaerated or treated with sodium bisulfite at a level of 1—2-mAf SO2 to prevent oxidation of the enzyme and a resulting loss in activity. 

In addition to its industrial importance as an intermediate in the synthesis of vitamin K, menadione, or more specifically, salts of its bisulfite adduct, are important commodities in the feed industry and are used as stabilized forms in this appHcation. Commercially significant forms are menadione dimethyl pyrimidinol (MPB) (10) and menadione sodium bisulfite (MSB) (11). MSB is sold primarily as its sodium bisulfite complex. The influence of feed processing, ie, pelleting, on the stabiUty of these forms has been investigated (68). The biological availabiUties and stabiUty of these commercial sources has been deterrnined (69,70). 

Chlorine addition may be a prerequisite to sanitize the RO feed-water supply line and oxidize any organics (followed by dechlorination using sodium bisulfite, after the MM filtration stage). Where chlorine is required, it is usual to provide a 20- to 25-minute contact period by means of a temporary storage tank. This is then followed by a repressurization pump system. 

Chlorine can be removed from RO feed water using sodium bisulfite or carbon filtration (see Chapters 8.2.4 and 8.1.4, respectively). As discussed in Chapter 8.1.4, carbon in carbon filters can aide the growth of microbes so carbon filtration is typically not recommended for dechlorination of RO feed water unless the concentrations of organics is high enough to warrant its use, or if the dosage of sodium bisulfite is too low for accurate control. 

A note of caution when feeding sodium metabisulfite. If membranes are heavily fouled with heavy metals such as cobalt, iron, or manganese, residual sodium bisulfite actually converts to an oxidant in the presence of excessive oxygen. In this case, the membranes are in danger of being oxidized and destroyed.9... 

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). 

S. M. Billedeau, Fluorimetric determination of vitamin K3 (menadione sodium bisulfite) in synthetic animal feed by high-performance liquid chromatography using a post-column zinc reducer,... 

A. J. Speek, J. Schrijver and W. Schreurs, Fluorimetric determination of menadione sodium bisulfite (vitamin K3) in animal feed and premixes by high-performance liquid chromatography with post-column derivatization, / Chromatogr., 301,441,1984. 

As noted above, the polyamide and polyurea membranes cannot tolerate an oxidizing agent, such as residual chlorine in the feed. Consequently, if these membranes are used and the feed has a residual chlorine content, then it is necessary to remove it. This is usually done by adding a stoichiometric excess of sodium bisulfite or sodium thiosulfate in accordance with recommendations from the membrane manufacturer. 

Chlorine has been added to the feedwater upstream of reverse osmosis pretreatment. However, since chlorine will depolymerize the polyurea membrane barrier layer in the spiral wound element, with subsequent loss of desalination properties, the chlorine is removed in the pretreatment system dechlorination basin. This removal is chemically accomplished by the addition of sodium bisulfite. The chlorine level in the influent and effluent to the dechlorination basin is continuously monitored. The feedwater is then transferred from the dechlorination basin to the cartridge filter feed pumping station by gravity flow and it is then pumped to the cartridge filters. 

Figure 2. Uncatalyzed oxidation of calcium bisulfite. Comparison between computer code results and experimraital data [10] for different compositions of the gas feed (100%, 40% and 21% volume of oxygen).

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