Water sterilisation

Liquid chlorine dioxide, ClOj, boils at 284 K to give an orange-yellow gas. A very reactive compound, it decomposes readily and violently into its constituents. It is a powerful oxidising agent which has recently found favour as a commercial oxidising agent and as a bleach for wood pulp and flour. In addition, it is used in water sterilisation where, unlike chlorine, it does not produce an unpleasant taste. It is produced when potassium chlorate(V) is treated with concentrated sulphuric acid, the reaction being essentially a disproportionation of chloric(V) acid ... 

I water sterilisation ii the manufacture of organic chlorine compounds, such as the plastic PVC and the herbicide 2,4-D... 

The overkill process is often used in daily practice and is based on the principle that the process should be sufficiently powerful to reduce a severe contamination with a very thermo-resistant organism, i.e. circa 10 spores of Geobacillus stearothermophilus, to the SAL 10 . The standard process for steam or hot water sterilisation in the... 

The Z-value is a measure for the change in resistance of the micro-organism following the change in temperature. Therefore, the Z-value should always be mentioned in the notation of the F-value. For steam and hot-water sterilisation, usually a Z-value of 10 °C is used. 

Hot water sterilisers are also called hot water (immersion) autoclaves. In these sterilisers, hot distilled water, freshly filled in the stainless steel steriliser bath and heated in a sanitary heat exchanger is pumped around inside the autoclave and is continuously and with high flow sprayed top down over the load to be sterilised. The hot water autoclave contains a mixture of water and air before and during the sterilisation process no vacuum phase is used (see Fig. 30.5). 

Fig. 30.5 Schematic representation of a hot water steriliser. Source Recepteerkunde 2009, KNMP...

The abundant halogen element chlorine is a powerful oxidant used extensively in the chemical industry and for water sterilisation (e.g. communal swimming pools). It was first used as a weapon to incapacitate enemy troops on the battlefield during World War 1 and was recently used by Iraqi insurgents in 2007. Mixing household bleach with certain acidic agents can liberate chlorine gas. 

With continued filtration, the bacteria count on the membranes increases exponentially. Regular sterilization of the polishing loop is recommended to avoid biofouling. Commercially available external pressurized UF modules can withstand both hydrogen peroxide and hot water up to 98°C for the sterilization. Hot water sterilisation is preferred as it does not introduce any chemical into the polishing loop, and it provides a quicker rinse up time compared to hydrogen peroxide. It is important to control the ion exchange resin leach-ables in the UF feed water. The presence of such leachables can result in severe flux decline in polysulfone UF modules (Maki et al., 1992). 

Miscellaneous Applications. PEIs and their derivatives ate used as cementation auxihaties in cmde oil exploration (459), and for breaking cmde oil emulsions (460) in cmde oil extraction. Seed coatings of water-soluble copolymers containing polyethyleneimine have been developed (461). Polyethyleneimine derivatives have positive photoresist properties (462) amidated polyethyleneimines improve the flow properties of cement (463) and with few exceptions, A/-acyla2iddines act as chemical sterilisers for insects (464). 

In addition to these forms of water, several other official aqueous vehicles can be used. These are isotonic injections that can be sterilised, eg, sodium chloride. Ringer s, dextrose, dextrose and sodium chloride, and lactated Ringer s. Addition of water-miscible solvents such as ethanol or propylene glycol increases solubiUty and stabiUty. 

Phenols are considered to be low-to-intermediate level disinfectants, appropriate for general disinfection of noncritical and semicritical areas. They are not sporicidal and should not be used when sterilisation is required. They are dispensed in aqueous formulations or in mixed water—alcohol solutions. Levels of 400—1300 ppm in the diluted formulation are typical. 

Other, more recently developed, uses include microwave oven parts, transparent pipelines, chemical plant pumps and coffee machine hot water dispensers. One exceptional use has been to produce, by an extrusion moulding process, very large rollers for textile finishing for use where cast nylons cannot meet the specification. Also of growing interest are medical equipment applications that may be repeatedly steam-sterilised at 134°C, filtration membranes and cartridges for ink-jet printers. 

It is worthwhile drawing attention to health hazards associated with film infected water systems which also cause corrosion. Two of the most common are Legionnaires disease and so called humidifier fever . Because of strong adhesion of biofilms and diffusion rates through the film treatment based on cleaners and chemical sterilisers such as chlorine often fail similar considerations apply to other systems in industry, e.g. food, paint, oil and gas are examples where biofilm activities have given massive problems. 

The production-scale fermentation unit, with a projected annual capacity of over50,000 tonnes was fully commissioned in 1980. The bioreactor (Figure 4.8) is 60 m high, with a 7 m base diameter and working volume 1,500 m3. There are two downcomers and cooling bundles at the base. Initial sterilisation is with saturated steam at 140°C followed by displacement with heat sterilised water. Air and ammonia are filter sterilised as a mixture, methanol filter sterilised and other nutrients heat sterilised. Methanol is added through many nozzles, placed two per square metre. For start-up, 20 litres of inoculum is used and the system is operated as a batch culture for about 30 h. After this time the system is operated as a chemostat continuous culture, with methanol limitation, at 37°C and pH 6.7. Run lengths are normally 100 days, with contamination the usual cause of failure. 

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