Pressure steam sterilisers

Industrial bioreactors can withstand up to 3 atmospheres positive pressure. Large fermenters are equipped with a lit vertical sight glass for inspecting the contents of the reactor. Side parts for pH, temperature and dissolved oxygen sensors are a minimum requirement. A steam sterilisation sample port is provided. Mechanical agitators are installed on the top or bottom of the tank for adequate mixing. 

The pressure during steam sterilising cycles should be recorded at least manually. 

Of the methods discussed for decontaminating a freeze-drier, in the absolute sense only pressurised steam can be regarded as a sterilant. Since 1970, the use of pressurised steam for sterilising pharmaceutical freeze-driers has become standard and freeze-drying manufacturers are conversant with the problems associated with the fabrication of steam-sterilisable machines. Exhaustive literature exists detailing the temper-ature/pressure relationship required to destroy individual micro-organism species and these conditions can be readily achieved within the freeze-drier. 

An empirical rule-of-thumb is often used in the design of sterilisation processes which uses the principle of substantial overkill to design a readily validated make-safe process. The MRC Working Party reports on pressure-steam sterilizers are often quoted as the intellectual source of the much-used sterilisation standard of saturated steam at 121.1 °C for 15 minutes. This treatment is widely regarded as giving a sufficient margin of safety in yielding a sterile product irrespective of the type and initial... 

Steam sterilisation (high steam pressure, 120-135 °C) No toxic residues Deformation/degradation owing to water attack, limited usage for PLA-PGA... 

PVC can be sterilised in a steam steriliser with pressure compensation. 

The principle of steam sterilisation for medical devices, pharmaceutical products and utensils is based on heat transfer by hot condensing steam under pressure. The steam condenses in the autoclave to pure water, releasing at that moment its heat content. This is a very effective means of heat transfer. Furthermore, the mechanism of inactivation by saturated steam (denaturation of proteins) is also very effective. Therefore, steam sterilisatirai in an autoclave is the preferred method for medical devices, utensils and some pharmaceutical products. It is of critical importance that the steam in a steam autoclave is completely saturated and not superheated, because only then the sterilisation is effective. For the details of steam sterilisation reference is made to other textbooks and guidance, such as [4,5]. The pressure of saturated steam at different temperatures is shown in Table 30.2. 

The steam steriliser is commonly referred to as an autoclave. The simplest steam steriliser, however, is a pressure cooker. In a pressure cooker, the added distilled or deionised water is heated and eventually begins to boil. The steam that is formed pushes the air out through the vent valve in the lid. This is not a very effective process because the vent valve is in the upper part of the steriliser and it takes time to remove the air just by continuous boiling. Air is heavier than steam, so these gases are slowly removed by upwards displacement to the upper part of the pressure cooker. 

The steam sterilisation process is pressure-controlled and temperature-monitored. The most important steps in the steam sterilisation process are (see also Fig. 30.4) ... 

Because of the fundamental difference between sterilisation of finished medicinal products and medical devices (temperature-controlled hot water process vs. -pressure-controlled steam process), both processes have their own validation directive. Most countries have then-own National legislation and standards on sterilisation and validation. International ISO standards are always useful or are implemented and commented in the own country for steam sterilisation see [6]. 

No stress through changing pressures as is the case with steam sterilisation. 

The fungus isolated from the wastewater was used as a seed culture. The media for seed culture as a starter of each experimental run was prepared by using 1.0 g of glucose and 1.0 g of peptone in 100 ml of distilled water. The nutrients and minerals were obtained from Merck. The media was sterilised in an autoclave at 121 °C, 15 psig steam pressure for 20 minutes. 

The direct sterilisation of particulafe solid foods in a gas-solid fluidized bed was proposed as long ago as 1968 by Lawrence et al. (1968) who sterilised wheat flour in steam-air mixtures at the pilot scale. However, Jowitt (1977) described an atmospheric pressure process for fhe sferilisation of canned foods in which the cans are immersed in a fluidized bed of inert particles. This has a number of advantages compared to the conventional retorting process using pressurised steam or hot water ... 

Heat-stable solutions, rubber bungs and liners, bottles with plastic caps, ultrafiltration apparatus etc. are all sterilised by steam treatment at elevated pressure. Although the time required to sterilise is usually only about 15 min at 15 lb pressure the cycle time for modem autoclaves is several hours. This is because of the safety precautions built into these machines to prevent the doors being opened until the temperature of liquid within bottles has fallen to 80°C. 

Partly filled bottles should have their caps firmly screwed on. The steam generated within the bottle will effectively sterilise the contents but changes in volume will be prevented. It is such bottles which create the hazard in autoclaves if the temperature and pressure outside the bottle is allowed to fall suddenly. This will happen if the autoclave door is opened prematurely leaving the bottle itself full of superheated steam. 

Other measures to improve the penetration of heat to deeper soil levels are the installation of a permanent steam-piping system under the plot (Nederpel, 1979) systems operating under reduced pressure provided by fan action (Runia, 1983) and the use of steam-air mixtures, provided by blowing air into the steam supply (Belker, 1990 Labowsky, 1990). The latter technique permits more control of the temperatures achieved, and is favoured where a soil pasteurisation procedure is desired rather than complete sterilisation. 

Autoclaving with steam involves time/temperature relationships, i.e. 134°C for 3 min or 121°C for 15 min or 115°C for 30 min or such combinations of temperature and time which ensure sterilisation. It is advisable to carry out autoclave tests on any plastic as part of the development programme. Now that autoclaves have balanced or overpressure facilities, experiments have to be carried out in order that the correct conditions can be selected. It should be noted that distortion or extension (initially due to internal pressure in the pack) is likely to occur during the cooling cycle and it is during this period that additional pressure is required to overcome the internal pressure. 

After harvesting, the FFBs are quickly transported to the PO mill where they are sterilised with steam and the fruit stripped off. The fruit is then pressed to obtain PO from the fleshy mesocarp. The nuts are hard and survive the pressure unbroken. They are separated from the fibres, cracked to remove the shell, and dried to a moisture content below 8% to prevent mould growth. 

Moist heat sterilisation is achieved by exposure to saturated steam under pressure in a suitably designed chamber. Under these conditions there is an exact relationship between steam temperature and pressure, but the pressure is used solely to obtain the temperature required and otherwise contributes nothing to the sterilisation process. The temperature and not the pressure must be used to control and monitor the process. 

System integrity shall be maintained after sterilisation. The system should then be purged of steam and condensate and maintained under positive pressure until ready for use. 

Thermally stable material such as glassware or metal instruments may be sterilised by heating them in an oven at 185°C for two hours. The material is wrapped in autoclave paper prior to heating, and after removal remains sterile until the wrapping paper is removed. Steam treatment in an autoclave is normally used for the sterilisation of aqueous material. The autoclave uses steam at a pressure greater than atmospheric and laboratory systems normally operate at 15 lbs in which corresponds to a temperature of 121 °C. This makes the assumption that the atmosphere inside the autoclave is composed only of steam and therefore it is necessary to expel all the air before the sterilisation process commences. 

Method of use. The chamber is evacuated and then warmed to 40 °C with hot air or steam to give an RH of 25-50%. Ethylene oxide is then injected into the chamber to a concentration of 400-1000 mg per litre and sterilising conditions maintained for 4—8 hours. The freeze-drier is then returned to atmospheric pressure and the ethylene oxide vented from the drier. An explosion-proof mixture of 60% ethylene oxide and 40% methyl bromide has been used for decontamination. Ethylene oxide has been more widely used in the USA than in the UK for sterilising freeze-driers. 

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