Per the hierarchy of waste management, waste can be treated and disposed through five major pathways: reduction, reuse, recycling and composting, energy recovery, and landfill, each of which has its challenges in implementation. Several types of plastic, such as thermoset, for example, cannot be recycled. Unlike conventional thermoplastic, thermoset is highly popular because of its stronger dimensional stability and higher chemical resistance and is used in many automotive industries, adhesives, coatings, shore structures, clean energy production, solar cells, and electronic packaging utensils. Unfortunately, the material cannot be dissolved or melted (Yue et al., 2019).
Disposal into landfill is the most common treatment of wastes from municipal, construction and demolition, and industrial activities, but landfill is considered to be a source of marine plastic debris. Research on potential sources of microplastic demonstrates that microplastic can enter the environment through leachate leakage. The geomembrane component of a composite liner in landfills, which aims to prevent groundwater pollution, can leak even if operated under high control (Foose et al., 2001). Even though leachate treatment is more complex than municipal wastewater treatment because it comprises biological, physical, chemical, and membrane treatment to eliminate chemical contamination, the process cannot thermally, chemically, and biologically remove microplastic. The treatment only changes microplastic distribution, where high-density microplastic accumulates at the bottom of the basin and then becomes sludge and final effluent. Besides being disposed through leachate, microplastic can be found in the landfill itself. The fine soil-like fraction of landfill tends to accumulate microplastic, which is eventually distributed by wind or surface run-off to marine environment. The microplastic can be discharged from landfill through ventilation in aerated bioreactors or closed landfills. Yet, a huge amount of plastic is still disposed into landfills, contributing 21%–42% of global plastic waste production.
The Philippines, through Republic Act No. 9003 on Ecological Solid Waste Management Program, has endorsed the implementation of sanitary landfills instead of open and controlled dumps. Section 37 states that open and controlled dumps in local government units (LGUs) must be closed in 3–5 years after the issuance of the regulation. Sanitary landfill is defined as a site to dispose waste, and is designed, constructed, operated, and maintained under engineering control to reduce potential environmental impacts from development and operation of the facility. Section 41 states that to establish sanitary landfill, liners and leachate collection and treatment system must be provided. Liners aim to reduce or prevent groundwater contamination, while leachate collection and treatment system aim to collect leachate for storage and eventual treatment and discharge. Based on the Implementing Rules and Regulations of Republic Act 9003, sanitary landfill must have at least 6 inches of daily cover every day. Initially, the daily cover is applied to prevent waste from long-term contact with the environment. For a landfill area that will not be used for at least 180 days, an additional 6-inch-thick interim soil cover must be applied over the existing daily cover. Republic Act 9003 has had a significant impact, with illegal dumpsites decreasing from 806 to 353 in 10 years. The number of sanitary landfills grew, from 33 sanitary landfills serving 78 LGUs in 2010 to 165 sanitary landfills serving 353 LGUs in 2018 (Environmental Management Bureau, 2018). The combined liners, daily cover, and leachate collection and treatment in sanitary landfill can help reduce microplastic.
Bukit Tagar Sanitary Landfill in Malaysia, an advanced landfill treatment, is a government privatisation project with a capacity up to 120 million tonnes of waste. Although all landfills potentially leak, the design of Bukit Tagar Sanitary Landfill applies the highest level of sanitary landfill standards of the United States Environmental Protection Agency through a multi-layer base liner to block leachate infiltration to the soil. Collected leachate goes to a treatment plant that uses mainly a biological reaction process combined with chemical dosing. After being purified in the treatment plant, the leachate is further polished by reed beds technology to achieve zero residue.
Incineration has become the second most common option after landfill for waste treatment and disposal. Combustible wastes, such as municipal solid waste, hazardous waste, clinical waste, and industrial waste, are suitable for treatment by incineration (Williams, 2004). Combustion control is taken into account to prevent incomplete combustion, which can result in dioxins and furans. A well-designed incinerator enables controlled air flows, leading to generation of high temperatures and clean burn. Based on EPA 1990, the recommended temperatures for the primary chamber of the incinerator is 540–980 degrees Celsius, and for the secondary chamber 980–1,200 degrees Celsius (WHO, n.d.). Production of dioxin in large-scale incineration can be minimised through fast cooling combustion, where time spent in 200–450 degree Celsius is shortened, leading to generation of cleaner combustion (Environment Australia,1999; Soares, 2015).
Incineration technology has been a concern of the Government of Japan since the enactment of the Act on Emergency Measures Concerning the Development of Living Environment Facilities in 1963 (Ministry of Environment of Japan, 2014). Japan has incineration plants spread across the country that apply strict policies to reduce pollution. Japan has discovered that the conventional stoker furnace is the most reliable technology. As a result, stoker furnace technology is used in 70% of incineration plants. The main difference between a stoker furnace and a conventional one is that the former allows higher combustion quality derived from lower combustion air ratio, improvement of combustion gas and air mixing, improvement of oxygen-enriched combustion and combustion quality, and generation of evenly burnt materials with infusion of high temperature air. The secondary chamber of the latest stoker furnace technology reaches 1,000 degree Celsius to ensure complete combustion reaction (Ministry of Environment of Japan, 2012). In the city of Kyoto, the replacement of multiple-heart furnace by stoker furnace has shown positive impacts, including 50% ash reduction, 77% reduction of energy consumption, and 18% reduction of operating cost (Ito, 1991).
Waste treatment and disposal are highly dependent on cost. The United Nations Environment Programme notes that in waste management, the financial cost is divided into investment and operation costs. Investment cost is usually prioritised since it is related to modernisation of waste management infrastructure, such as equipment and technology. Operation cost, which accounts for up to 60%–70% total cost of waste management, covering labour, fuel, energy, maintenance and repair, emission control and monitoring, income collection, public communication, and management and administration, is frequently overlooked. While investment cost can be easily estimated, operation cost is difficult to estimate because of various aggregation methods used to calculate budgets. For example, allocation of operation cost in cities sometimes overlaps with other public utilities because waste management is not regarded as a common activity. This leads to cities’ lack of allocation for operation cost. Unavailable data on operation is another reason why determining operation cost is complicated and challenging.
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