According to Victoria’s environmental protection laws, hazardous waste, also known as prescribed industrial waste (PIW), is the “hazardous by-product of everyday goods and services, such as the manufacturing of motor vehicles, paint and plastics, dry-cleaning services, fast food outlets, dental surgeries and hospitals” (Environment Protection Authority Victoria 2017, para. 1). The guidelines for handling and disposing of such waste are stipulated in the Environment Protection (Industrial Waste Resource) Regulations 2009. The objectives of these regulations are to assist industry to
(a) Implement the principle of wastes hierarchy as set out in section 1I of the Environment Protection Act 1970; (b) prescribe requirements for assessing, categorizing, and classifying industrial waste and prescribed industrial waste for the purposes of the Environment Protection Act 1970. (c) encourage industry to utilize industrial waste as a resource through exempting material from categorization as prescribed industrial waste where secondary beneficial reuse is established; (d) prescribe requirements for the transport and management of prescribed industrial waste, including requirements for the tracking of prescribed industrial waste (Environment Protection (Industrial Waste Resource) Regulations 2009, para. 2).
This paper discusses the different classes of hazardous wastes and the available methods for treatment or disposal.
Classes of Wastes
Hazardous wastes have the potential to cause adverse damage to human beings and the environment. Such materials could be non-biodegradable, biologically magnified, highly toxic, or lethal even at low concentrations. Characterization of waste depends on the nature of contaminants that are likely to be present. Ultimately, hazardous wastes are classified into four categories – A, B, and C (Environment Protection Authority Victoria 2017). Each category has defining characteristics, which are used to ensure that all hazardous materials are classified appropriately. Category A waste is listed as industrial waste that is classified as dangerous goods. Under the Environment Protection (Industrial Waste Resource) Regulations 2009, dangerous goods are placed into eight classes for easy identification.
Class 1 covers explosives – solid waste that can produce gas to cause damage to the surroundings. Class 4.1 is flammable solids, which are easily combustible. Class 4.2 covers wastes liable to spontaneous combustion, while class 4.3 describes wastes that emit flammable gases when they contact water. Class 5.1 are oxidizing wastes, and class 5.2 are organic peroxide wastes. Class 6.1 is toxic wastes, which can cause infections through microbes. Finally, class 8 describes corrosive wastes with pH values of less than two or higher than 12.5 (Environment Protection Authority Victoria 2009). Category B and Category C wastes are defined using the level of concentration of substances stated in Category A classes. For instance, Category B waste has a higher concentration of substances than Category C but not exceeding that of Category A contaminants.
Treatment and Disposal of Category A Waste
All the waste materials under Category A should be treated before they can be accepted at any disposal facility. Different treatment methods are available for such wastes, including chemical, physical, thermal, and biological options. The selection of the best option for the treatment of hazardous waste depends on the nature of the involved materials or chemicals and the desired properties of the output stream. However, the chemical composition of waste plays a central role in determining the treatment method of choice.
Physical Treatment
Physical treatment of hazardous waste involves subjecting such materials to different processes to immobilize the hazardous elements or prepare if for further treatment. The processes involved in this treatment method do not destroy waste materials. On the contrary, wastes are changed into forms that could be treated further or disposed of. Physical treatment involves different processes depending on the nature of the waste materials under consideration (Muralikrishna & Manickam 2017). For example, encapsulation immobilizes or reduces the toxicity of hazardous materials by containerization. The main wastes treated using this method include organic polymers and asphalt, among other related materials. At times, heat is used to melt encapsulated waste in a process known as thermal encapsulation.
Another physical treatment method is wetting, whereby water is used to prevent the spread of harmful dust or fibers. Other physical methods include filtration, centrifuging, distillation, and flocculation, among others. Additionally, hazardous materials could be broken mechanically through shredding, pelletizing, and ripping (Muralikrishna & Manickam 2017). With the advancement in technology, other physical treatment methods have been invented for better and faster results. For instance, silica microencapsulation (SME) uses an impervious silica matrix to trap the involved waste, thus separating it totally from the environment. One of the advantages of physical treatment is that it is safe because it involves removing hazardous materials from the environment without using dangerous processes such as chemicals and high temperatures. However, this method can only be used with a limited number of hazardous materials. Additionally, it can be time-consuming and thus ineffective in cases where large volumes of waste are involved.
Chemical Treatment
Chemical treatment of materials entails exploiting the different chemical properties of the waste to alter the inherently hazardous nature. Such waste is treated by destroying dangerous materials or producing other compounds, which can be treated or disposed of easily. As such, chemical reactions are involved in this method of treatment. The common chemical reactions used include neutralization, oxidation, reduction, hydrolysis, and precipitation. In neutralization, substances with pH levels of less than two or more than 12.5 are treated to become neutral at a pH closer to 7. For instance, highly acidic wastes are mixed with alkalis, while highly alkaline wastes are treated with acids, and the ultimate product is neutral. In 2014/2015, 27,309 and 9,657 tonnes of acids and alkalis were treated chemically in four states across Australia, including New South Wales, Queensland, Victoria, and Western Australia (Blue Environment 2017). Oxidation involves using an oxidizing agent such as hydrogen peroxide to oxidize hazardous compounds, such as cyanide. On the other hand, in reduction, hazardous inorganic substances, such as chrome, are converted into less toxic or mobile forms using reducing agents. In hydrolysis, hazardous organic wastes are decomposed using caustic soda.
Heavy toxic metals are treated through precipitation, whereby they are converted into less mobile and insoluble forms before being disposed into landfills. One major advantage of this treatment method is that it is highly effective and cheap when dealing with compounds with similar chemical properties. However, when applied to waste substances with mixed chemical compositions, side reactions may interfere with the processes, thus reducing their effectiveness (Muralikrishna & Manickam 2017). Such an occurrence may create highly toxic products, thus negating the essence of the treatment in the first place. Other common chemical treatment methods include de-halogenation and catalytic detoxification. In de-halogenation, also known as de-chlorination, chlorine is removed from toxic waste materials, thus making them less harmful. The common wastes treated using this method are contaminated with polychlorinated biphenyl (PCB) and dioxin. Some of the advantages of this method include the contaminated materials could be treated on-site, thus avoiding the dangers of transportation. Additionally, the air is not emitted in the process as the produced gases are collected for further treatment and disposal. However, the lack of information regarding the toxicity of the contaminants and the required reagents may limit the application of this method.
Biological Treatment
In the context of the management of hazardous waste, biological treatment is normally referred to as bioremediation. In this case, waste materials are degraded biologically under controlled environments. This process works by introducing bacteria or enhancing their growth conditions to degrade identified chemicals in hazardous waste (Muralikrishna & Manickam 2017). For instance, bacteria are used to break down chlorinated pesticides. Biodegradation could occur under aerobic or anaerobic conditions in the presence of oxygen or lack of it, respectively. Hazardous wastes contaminated with hydrocarbons are mostly degraded using aerobic bioprocesses. On the other hand, alkylated aromatics and benzene are broken down using anaerobic biodegradation. Bioremediation could be in-situ or ex-situ, depending on the materials being treated. In-situ bioremediation involves the use of naturally occurring microorganisms to treat soils and groundwater. As such, the media used in this form of treatment is not removed from its natural environment and location. In-situ bioremediation requires the supply of oxygen and nutrients for aerobic processes to take place. One of the advantages of this method is that it causes minimal intrusion to structures above the ground, and it is useful in small operational sites. However, it may not be suitable for locations with free phase contaminants.
Ex-situ bioremediation involves relocating the contaminated materials from their natural environments to treatment sites. For example, contaminated soil could be excavated and transported to treatment locations before being disposed of. Additionally, contaminated water could be drawn from underground reservoirs and be placed in bioreactors for biodegradation to take place. Another emerging method for bioremediation is known as in-situ phytoremediation. In this case, higher plants are used to remove contaminants from soil and water. In 2014/2015, 31 tonnes of Category A chemicals used in plating and heat treatment were treated through bioremediation in New South Wales, Queensland, Victoria, and Western Australia (Blue Environment 2017). One of the main advantages of bioremediation is that it is a natural process. The microorganisms are used to clean up the environment without leaving harmful residuals. Additionally, in-situ bioremediation means that contaminated materials are treated on-site, thus avoiding the dangers that could be associated with transporting such materials. Moreover, this process is less expensive as compared to other methods of treating hazardous waste. However, this method is limited to only biodegradable waste. Additionally, it takes more time as compared to other methods, and thus harmful effects caused by hazardous waste could be felt for a long time. The method is also highly specific, and it may not be applicable in large-scale waste management.
Conclusion
Hazardous waste could cause long-term damage to the environment and human beings if not handled appropriately. Such materials are grouped into three categories – A, B, and C. In Victoria, the handling, treatment, and disposal of these hazardous wastes are guided by the Environment Protection (Industrial Waste Resource) Regulations 2009 S.R. No. 77/2009. Hazardous wastes are treated using physical, chemical, and biological means based on the nature of the contaminants in the materials under consideration. Each treatment method has associated advantages and disadvantages, as discussed in this paper.
References
Blue Environment 2017, Hazardous waste in Australia 2017, Web.
Environment Protection Authority Victoria 2009, Solid industrial waste hazard categorisation and management, Web.
Environment Protection Authority Victoria 2017a, Hazardous waste management in Victoria, Web.
Environment Protection (Industrial Waste Resource) Regulations 2009 S.R. No. 77/2009, Web.
Muralikrishna, I & Manickam, V 2017, Environmental Management: science and Engineering for Industry, Elsevier, Cambridge.