Introduction

Hydroclave is a recently introduced technique in the methods of sterilization. It is a simple method that is affordable and allows a high level of sterility at a very low cost. Hydroclave uses steam to indirectly heat and completely dehydrate the waste. At the end, the waste is reduced by weight and volume. The structure of the hydroclave consists of a hot cylindrical vessel outside and a shredding system inside. The blades are used to vigorously mix and fragment the waste. The hydroclave ensures even distribution of heat inside it. It can also be defined as an advanced autoclave. The use of hydroclave for biomedical wastes lead to a lesser negative impact on the environment. (Sharma, 2013) Hydroclave presents an array of exclusive features. It can achieve a higher degree of sterility when compared to other methods of sterilization. It is a safer method and is also faster. It has a holding time of 15 minutes. This method of sterilization is also cost-friendly. It can lead to complete overall sterilization of the waste. All types of infectious wastes can be treated using this apparatus. (Farshad, 2014) Various studies have been conducted using Hydroclave. It has been studied as an alternative treatment for infectious waste management. (Rafiee, 2016) Its use is also seen in the treatment of healthcare waste management. (Ciplak, 2016) The safety of such non-incineration based waste disposal devices have also been analyzed in a study. Hydroclave method of sterilization plays an important role when it comes to the management of medical and hospital wastes. (Dastpak, Golbaz, & Farzadkia, 2017; Farzadkia, Emamjomeh, Golbaz, & Sajadi, 2015)

There are a few drawbacks of using this method of sterilizing wastes. Initially, the system requires more steam to heat up. Since the blades are used in fragmenting the wastes, they may get clogged. The end product of using this method is shrunken dry waste because of highly fragmented waste; it is difficult to recycle this type of waste. The waste hence produced goes to the landfills in the end. The use of hydroclave also leads to release of certain emissions into the air. This review is done to understand the various fields in which hydroclaves are used. It can sterilize a wide range of objects like needles, plastics, metals, etc. It has a high level of sterility. One plus point of this method is that it is not dependent on the operator; it is an automatic machine. It is low maintenance and a low-cost alternative to conventional methods. It ensures a low odour because the waste at the end is a dry product. Hydroclave has various advantages over conventional Autoclave. This review was done to analyze in detail the Hydroclave method of sterilization.

General Sterilisation

Sterilization is best defined as the complete destroying of microorganisms, endospores and pathogens. (Yoo, 2018) An object that is completely free of these organisms can be called sterile. (Laneve, 2019) The technique of sterilisation should be chosen carefully. It should not cause any changes in structural or the biochemical properties of the object that has to be sterilised. (Dai, 2016) Sterilization is a basic necessity for instruments. This is because if not sterilised, the instruments may lead to spread of infection. Sterilization is necessary to prevent transmission of infection. (Rutala & Weber, 2004) Some pathogens if not removed may bring about serious infection. They may even cause severe complications (like periodontal destruction) if instruments are not sterilised. (Shahana & Muralidharan, 2016) Newer pathogens are emerging in recent times that can pose as a threat and bring about infections. It is necessary to sterilise to completely erase the pathogens. (Ashwin & Muralidharan, 2015) Some bacteria like A. baumannii have even gained multi-step resistance and hence can cause serious nosocomial infections. (Girija, 2019; Girija, Jayaseelan, & Arumugam, 2018). These organisms gain resistance through different mechanisms. These mechanisms include alterations in membrane permeability and chromosomal mutations (J V Priyadharsini, 2018; Smiline, Vijayashree, & Paramasivam, 2018) Bacteria like these gain high resistance and enter the oral cavity and cause infections. (Girija & Priyadharsini, 2019; Priyadharsini, 2018) Newer sterilisation techniques have to be searched and developed since bacteria and other microorganisms develop resistance and hence cannot be eliminated. (Shahzan, Girija, & Priyadharsini, 2019) Sometimes this resistance of organisms is attributed to the post-transcriptional changes that it undergoes. (Paramasivam, Priyadharsini, & Raghunandhakumar, 2020). Disinfection, Cleaning and sterilisation are all important to control disease spread and cross infections. (Hovius, 1992) In a dental set-up, infections can spread through multiple modes like aerosols, droplets, etc. Hence, it is necessary to disinfect even surfaces that are possibly contaminated. (Pratha & Geetha, 2017) Antimicrobials are substances that inhibit the growth of microorganisms. These substances are also used on inanimate objects as disinfectants. (Vaishali & Geetha, 2018) In a dental clinic, even extracted teeth have to be sterilised to prevent the spread of infection if any. They are sterilised using sodium hypochlorite, formalin, glutaraldehyde, etc. (Sandhu, 2012). Various chemical solutions like Chlorhexidine, Metronidazole gel, etc., are also proven to be effective against microorganisms. (Marickar, Geetha, & Neelakantan, 2014) Herbal extracts are also used in certain conditions to kill selected pathogens. (Selvakumar & Muralidharan, 2017) These extracts may have good medicinal properties that may be helpful in selective situations. (Geetha, Thangavelu, & L, 2019) Sterilization usually includes incineration, boiling, etc. But now these present a lot of harm to the environment and to health status. Hence, newer approaches are being used to sterilise objects. (Laroussi, 1996) These new approaches include the usage of different liquids to sterilise and disinfect objects and surfaces.

Newer Techniques of Sterilisation

Since the time conventional methods have been used, there have been certain drawbacks with many of the methods used. Over the years, extensive development has taken place regarding newer techniques of sterilization. Ultrasonic cleaners are a new method in which high-frequency electrical energy is converted into mechanical energy during the process. (Mensudar & Amudha, 2014) Endoclens is another new development which Is used in the sterilization process of endoscopes. Pulse light sterilization involves deactivation of microorganisms by pulses of light focused on the object. The targeted object is illuminated using this light and aids in sterilization. New endoscopes such as flexible ureteroscopes, chip on tip endoscopes etc. are sensitive to heat. Hence gamma irradiation is used to sterilise these instruments. (Sabnis, Bhattu, & Mohankumar, 2014)

Structure of Hydroclave

The hydroclave is a double jacketed, cylindrical shredding system. (Farshad, 2014) The Hydroclave functions in four stages. In stage one; the waste is introduced into the apparatus. The waste can be bagged waste, sharps, liquids, cardboard or even metals. Then it moves to the second stage, wherein; the waste is fragmented. The sturdy paddles inside are rotated to facilitate the mixing process. (Hossain, 2011) High-temperature steam is introduced into the outer jacket of the vessel. This steam indirectly facilitates heating of the waste. The liquids present in the vessel turn to steam. It takes about 20 minutes to completely sterilize the waste. In stage three, the vessel is opened and de-pressurised. Stage four involved the unloading of the waste. The door is opened and the waste is removed from the vessel. The weight of the waste is reduced to a great extent. (Lavanya & Majhi, 2018)

Features of Hydroclave

Hydroclave presents a wide range of exclusive features. It can take 15 kg of waste in a single cycle. The entire cycle takes about 50 minutes to complete. This includes the initial heat up, start-up, sterilization, de-pressurising, and dehydration. The major sterilization takes place within 20 minutes at a temperature of 126 degrees. (Mathew, 2017) The hydroclave can treat all the materials that can be treated by autoclave treatment. In addition, hydroclave can also treat sharps.

Uses of Hydroclave

As already discussed, hydroclave has a variety of uses in various fields. It is useful in fragmenting sharps and also the conventional types of wastes. It is useful in treating a range of infectious wastes, very efficiently. Its application is also seen in treating hospital wastes, which need proper care, treatment and disposal to avoid any accidents, contamination, etc. (Ferdosi, Ferdowsi, & Mehrani, 2016) The working takes place in four stages, they are Stage 1- Loading of Waste, Stage 2- Fragmentation of the Waste, Stage 3- Vessel venting and dehydration, Stage 4- Unloading of the waste.

Advantages of Hydroclave

Hydroclave is adaptable to future situations and also meets the capacity requirements. When it is compared to autoclave, the hydroclave has lesser cost and maintenance requirements. (Maamari, 2016) It creates steam pressure and a vacuum, and this process makes the sterilization more effective. It reduces the end waste product by weight and by volume to a great extent.

Disadvantages of Hydroclave

There are very few disadvantages to hydroclave sterilization. Initially, it takes a long time for the steam to heat up and build pressure inside the vessel. Next, the shredder blades may get clogged due to excess fragmenting of wastes. When the cycle is running for longer periods, there may be a lack of moisture. Hence, additional steam has to be injected into the outer jacket of the vessel. (Clark, 2018; Rao, 2004)

Conclusion

From this review, we can understand the role of Hydroclave. It is a newly introduced method of sterilisation. This method uses steam to heat up the vessel and dehydrate the waste. The Hydroclave sterilisation presents a low operating cost. It does not require any specific technique to operate this apparatus. The entire process takes 50 minutes, whereas the core sterilisation time takes only about 20 minutes at a temperature of 126^o. It can sterilise metals, plastics, sharps, cardboard, etc. Hydroclave is known to be widely used because of its advantages over the conventional autoclave.

Funding Support

The authors declare that they have no funding support for this study.

Conflict of Interest

The authors declare that they have no conflict of interest for this study.