What Is An Autoclave?

An autoclave works similarly to a traditional pressure cooker. It is a pressurized chamber that operates at very high temperatures, usually around 120^oC. The waste management industry uses autoclaves to sterilize wastes before disposal. The chemical industry uses it to vulcanize rubber, and microbiologists use it to destroy or control bacteria and other microorganisms and to sterilize lab ware. The autoclave has been in use for more than 100 years. An autoclave uses pressure, heat, and water to create superheated steam.

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Autoclaves traditionally consume a large amount of water. Autoclaves mainly use water to generate steam, cool the wastewater, and create a vacuum for proper sterilization.

In this article, we’ll see the impact of autoclave on environment. We’ll learn about how autoclaves’ water and energy requirements are causing environmental damage.

Autoclave Water Requirements

Autoclaves use water in mainly three processes:

1. Steam generation

The design of the autoclave produces high-temperature, pressurized steam to kill viruses, bacteria, and other microorganisms that may exist on the instrument, equipment, or in the sterilization chamber. The sterilization chambers are usually double-walled. There is a small space called a ‘jacket’ between the walls. When we turn on an autoclave, steam fills this jacket to pre-heat the unit in preparation for operation. Tap water or purified water sources this steam.

2. Effluent cooling

Autoclaves also use water to cool waste. When an autoclave is in an idle state, or even during mid-sterilization, steam is constantly condensing within the autoclave. This condensed steam drains into a drainage in the floor of the chamber. Building codes require that all wastewater be cooled to below 140^oF before discharge. Autoclaves cool wastewater by introducing cold water to the sterilizer’s waste flow.

Older autoclave models had a constant flow of cold water to cool waste. This is called ‘constant bleed’. It means that even when the sterilizer is turned off, cold water continues to pass through it and down the drain. 1,500-2,500 gallons of water are lost this way since cold water flows through the autoclave 24/7. This amounts to 1 million gallons of water wasted every year.

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3. Vacuum generation

Certain equipment or instruments need air removed from within them to ensure proper sterilization. Autoclaves do this by producing a vacuum with the help of water. We can use a liquid pump ring or a venturi-based water ejector to create the vacuum. In either case, water immediately runs down the drain after creating the vacuum.

Autoclave Energy Requirement

Autoclaves are electricity-hungry devices. How and why an autoclave uses so much energy is actually pretty simple to understand.

We’ve already read that an autoclave sterilizes objects by achieving a temperature of 121^oC for 15 minutes or more. A temperature lower than 121^oC cannot assure sterilization. The heating process would be inefficient if autoclaves used just air and no water. Therefore, autoclaves use steam to sterilize objects. The steam has a specified quantity of liquid water droplets (5% by mass).

Now the problem with water is that the boiling point of water under normal room conditions is 100^oC. The pressure inside an autoclave is 2.068 Bar. At this pressure, water boils at 121^oC. Maintaining this pressurized condition for 15 minutes to ensure that water boils is what makes up the bulk of an autoclave’s energy use.

At 2.068 Bar, water needs 2,619 joules of energy per kg to boil. Some claim that using a heating device with lower wattage will lower an autoclave’s energy use. This is not true. Even with lower wattage, we would still need 2,619 J/kg of energy to convert water into steam. If we reduce the wattage of the heating element, we’d need double the time for water to boil. Reduce the wattage also heats the water slowly. This slow heating of water allows heat to escape the autoclave, thus increasing energy loss and overall energy use.

One change that can reduce energy use is reducing the amount of water the autoclave uses to produce steam. If you halve the water input to the autoclave, you halve energy use too.

Another feature that plays a part in autoclave energy use is the shape of the autoclave. The shape of an autoclave chamber is essential in saving energy. A cylindrical chamber allows us to use thinner metal for the vessel. The thinner material requires less energy to get heated. Rectangular autoclaves generally require more power than cylindrical ones to operate effectively.

Environmental Impacts and Solutions

We all know that our increasing energy demand is putting more greenhouse gases into the atmosphere. A majority of our energy today comes from fossil fuels. When fossil fuels burn, they release gases that trap heat in the atmosphere, causing global warming and accelerating climate change.

An autoclave requires an enormous amount of energy to run. Without improvements in energy efficiency, an autoclave can have disastrous environmental impacts. However, small changes in autoclaves, such as reducing water input, can help. New research has shown that s smaller volume of water in an autoclave requires only 16 kW (kilowatt) of heating elements compared to 72 kW of heating elements in normal autoclaves. Even using cylindrical autoclaves instead of rectangular ones saves energy.

Another thing to remember is to use an autoclave only when it is full. Let’s explain that with an example. Say you want some test tubes disinfected. Your autoclave can probably hold 30 test tubes. But, if you use the autoclave to sterilize just one test tube, you’ll be wasting around 97% of potentially useful energy.

With a changing climate, the world is rapidly running out of fresh water. On the other hand, we’re using autoclaves that waste enormous amounts of perfectly good water. One simple, zero-cost approach to saving water in autoclaves is to turn it off when not in use. Many labs keep autoclaves turned on 24/7. This means that the chamber continuously produces steam and condensate in preparation for sterilization. Keeping autoclaves on only during work times and during it off at night and on weekends can save 70% of water.

Many modern systems and manufacturers are beginning to address the energy and water consumption issues with autoclaves. Unfortunately, there are still many older models that constantly ‘bleed’ water still in use today. These systems waste around 10 billion gallons of clean, fresh water annually. Given this figure, universities and institutes must assess the types and the number of autoclaves they need on premises. They should consider autoclaves that come with water conservation solutions. The potential water and energy savings can be tremendous. These small actions can help reduce the impact of autoclave on environment.