ENVIRONMENTALLY SOUND MANAGEMENT OF WASTE PET BOTTLES
This study has been carried out to assess the waste management of PET bottles and effectively manage the PET plastic bottles by identifying practical means and introducing recycling as a cleaner production tool to achieve sustainable development goals. The science of post-consumer PET recycling is based on the fact that this polymer is non-degradable by nature. There has been a growing need for chemical recycling processes as a successful method for post-consumer PET transformation into monomers that can be used in the production of new bottles, textile materials, drug production, etc. This research focused on the depolymerization of waste PET bottles in an alkaline medium with the aim of response surface methodology.PET flakes from waste bottles were depolymerized at atmospheric pressure in an alkaline solution of potassium hydroxide in selected aliphatic alcohols and glycol to produce terephthalic acid. Response Surface Methodology (RSM) based on Central Composite Design model was used, with design variables being temperature, reaction time, and alkali concentration. The solid product was analyzed using FTIR and its acid value was determined.From the results obtained, it was found that reaction models obtained are significant (p < 0.05 for alcohols), accounting for 98% of the variations observed. For ethanol media, the optimum condition for PET decomposition was 0.35g/L, 66.82mins, and 2000C, which gave the decomposition of 79.4%. For propylene glycol, an optimum decomposition of 74.6% was obtained at a reaction temperature, time, and alkali concentration of 2200C, 60mins, and 0.5g/L respectively. For propylene glycol, the reaction time had more effect on the percentage decomposition, while the temperature was the dominant factor for the ethanol media. Comparing the IR spectra of the final product obtained from the alcohol with that of pure terephthalic acid, it can be concluded that the solid product obtained was terephthalic acid which can be used in pharmaceutical industries as a raw material in producing certain drugs.
CHAPTER ONE INTRODUCTION 1.1 Background of the Study Wastes are materials of solid or semi-solid character that the possessor no longer considers of sufficient value to retain (Gilpin, 1976). The New York State Department of Environmental Conservation also defined solid wastes in simple words as any discarded (abandoned or considered waste-like) materials. There are different types of waste: municipal waste (including household and commercial waste), industrial waste (including manufacturing), hazardous waste, construction and demolition waste, mining waste, waste from electrical and electronic equipment, biodegradable municipal waste, packaging waste, and agricultural waste. Solid wastes can be solid, liquid, and semi-solid or containerized gaseous material. Also, there are various sources of waste: residential, industrial, commercial, institutional, construction, and demolition waste; municipal services manufacturing process, agriculture. Municipal solid waste (MSW) is defined to include refuse from households, nonhazardous solid waste from industrial, commercial, and institutional establishments (including hospitals), market waste, yard waste, and street sweepings. MSW is defined by Cointreau (1982) as non-air and sewage emissions created within and disposed of by a municipality, including household garbage, commercial refuse, construction and demolition debris, dead animals, and abandoned vehicles. Municipal solid waste is generally made up of paper, vegetable matter, plastics, metals, textiles, rubber, and glass (USEPA, 2003). The waste management problem in Nigerian cities is becoming more alarming. The volume and range of solid wastes generated daily in Nigeria has been 2 increasing within the last few years. This is mainly due to the high population growth, urbanization, industrialization, and general economic growth (Ogwueleka, 2004). The common waste disposal methods are Sanitary landfill which is the disposal of waste material or refuse by burying it in natural or excavated holes, depressions, incineration; burning the refuse to ashes. There is also the compost heaps where the refuse is left to degrade by aerobic microorganism and it's used as fertilizer, then the resource recovery, a process of recovering energy and reusable materials from solid waste before decomposition or landfill. The resources also goes further to be utilized by the principle of 3Rs (Reduce, Reuse and Recycle) (Taiwo, 2011). Environmentally sound waste management is a crucial problem not only for developing countries but for the developed countries as well. However, the plastic waste as a significant portion and component of the municipal solid waste is a quite problematic for its non-biodegradability and therefore can stay in the environment for a considerable length of time carrying all sorts of problems. There are two major categories of plastics include thermoplastics and thermosets. Thermoplastics refer to plastic materials that can be formed into other products by re- melting or processing into different shapes by the application of heat and pressure. These are easily recyclable into other products. These thermoplastics include polyethylene, low and high density (LDPE, HDPE) polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyethylene terephthalate (PET), etc. Thermoset plastics contain alkyd, epoxy, ester, melamine-formaldehyde, polyurethane, etc. which are cross-linked on curing and will not soften with heat to allow these to be formed into different shapes. 3 Polyethylene terephthalate (PET) is widely used in several key products, as fiber for textile applications and into backing materials for audio and videotapes. Biaxially oriented polyester film is used for packaging and as thermoformed sheets in a frozen meal trays for microwave ovens. Pet films are used in electric devices as well. The best-known product made from aromatic polyester (PET); however is the blow-molded water and soda bottles for soft drinks and other household and consumer products. PET is a relatively new packaging resin. Soft drink bottles remain the biggest the user of PET resin. ’Consumer' bottles are used for other products such as salad dressing, peanut butter and jellies. Half of the polyester carpet made in the United States is made from recycled PET bottles. The rise of the use of custom bottle and the increased consumption of water and soft drinks away from home have created challenges for increasing the PET recycling rate. PET use has reduced the size of the waste stream because PET has replaced heavier steel and glass containers. The use of Polyethylene terephthalate also known as PET (a plastic resin materials used for making packaging materials such as bottles and food containers) is increasingly becoming paramount among manufacturers, as they used these PET bottles to package their products because it is an excellent barrier material with high strength, thermostability and transparency. The consumer also prefer or choose PET because it is inexpensive, lightweight, resealable, shatter-resistant, and recyclable among other reasons. Every year not less than 200 billion bottles of bottled water are consumed globally. Only about 15% of this quantity is recycled in all recycling plants across the globe while the remaining ones end up in trash bins, landfills, or open dumpsites in cities across the globe (Abdulkarim and Abiodun, 2012). In Nigeria, all of the brands of bottled water, soft drinks, beverages, etc., are always available in different types of packaging materials – PET bottles, cans, glass 4 bottles, polythene sachet, and synthetic paper packages. According to Oni (2011), not less than 200 million PET bottles are produced in Nigeria per day. From his analysis, the consumption of the products creates waste which is above the ability of the producer to manage. One of the approaches to the solution of the plastic waste problem is through recycling for its numerous benefits justifying the aim of this study that essentially meant to contribute to sustainable consumption and production of PET bottles in particular. Recycling of plastics should be carried in such a manner to minimize the pollution level during the process and as a result to enhance the efficiency of the process and conserve the energy. Plastics recycling technologies have been historically divided into four general types -primary, secondary, tertiary, and quaternary. Primary recycling involves the processing of waste/scrap into a product with characteristics similar to those of the original product. Secondary recycling involves the processing of waste/scrap plastics into materials that have characteristics different from those of original plastics products. Tertiary recycling involves the production of basic chemicals and fuels from plastics waste/scrap as part of the municipal waste stream or as a segregated waste. Quaternary recycling retrieves the energy content of waste/scrap plastics by burning/incineration. 1.2 Statement of Research Problem In recent years, there has been a phenomenal increase in the volume of wastes generated daily in the country. This is due to a number of reasons including the increasing population growth rate, increasing urbanization, industrialization and economic growth. In addition, many urban areas of Nigeria 5 lack effective waste management systems. As a result, most urban households
resort to the haphazard dumping, burning, and or burying of solid wastes. (Agunwamba et al. 2003). The non – biodegradability of PET is the major obstacle to disposing of its waste using conventional methods such as landfilling and incineration. Recycling is assumed to be one of the best approaches to solve the accumulation of PET waste problem. Among the various method of PET recycling, only chemical recycling conforms to the principles of sustainable development because it has the potentials for yielding the raw materials from which PET is originally made. However, the various chemical recycling routes reported in various works (such as hydrolysis, alcoholysis, and aminolysis) are fraught with shortcomings such as the need for high pressure and corrosion-resistant equipment (Kondo and Genta, 2001), high temperature (Campanelli et al., 1993), and long reaction time (Yoshioka et al., 2003; Sunain et al., 2012). There is therefore a need to develop a relatively simple, yet effective means of depolymerizing postconsumer PET using inexpensive and readily available solvents. 1.3 Objectives of the study Major objective To assess the waste management and to effectively manage the waste PET bottles by identifying practical means to introduce cleaner production tools mainly recycling in order to achieve sustainable development goals. Specific objectives · To collect and study available data on plastic and PET plastic bottles in particular. 6 · To effectively manage the PET plastic bottles waste and minimize the volume (industrial/domestic). 1.4 Scope of the Study Solid Waste Management all over the world is a complex one. There is a proposed waste management hierarchy which is shown in Figure 1.1. However, the main the focus of this research work is on how to manage the PET waste menace through recycling. Recycling was chosen because it has numerous advantages over the other modes of waste disposal and comparatively less capital intensive. There are three recycling processes namely mechanical recycling, feedstock/chemical recycling and incineration/energy recovery. This thesis work however, adopted chemical recycling since that is more appropriate for a developing a country such as Nigeria. The thesis, therefore, covers the initial upgrading techniques, size reduction techniques, reprocessing techniques through to the final product manufacturing. An integrated waste management approach as shown in the waste hierarchy is however the preferred choice for an efficient and effective waste management for any country. Though the viability and feasibility of recycling would depend on a large extent to the availability of potential markets for the reprocessed products that are not discussed within this thesis work. However, considering the income levels of the majority of the populace, it is obvious that reprocessed products would attract high demand.
Figure 1.1: 7 Image Figure 1.1: Waste Management Hierarchy Source: Porteus, A., 2005 1.5 Justification of the Study The wastes in any environment spoil the aesthetics of that environment, especially as an academic environment. The major reason for this is poor waste management. Waste management is an important and integral part of our society and therefore needs to be acknowledged as one of the few things that may help to preserve the beauty and splendor of any environment for future generations. Waste generation increases with population expansion and economic development. Improperly managed solid waste poses a risk to human health and the environment. Uncontrolled dumping and improper waste handling causes a variety of problems, including contaminating water, attracting insects and rodents, and increased flooding due to blocked drainage canals or gullies. In addition, it may result in safety hazards from fires or explosions. Improper waste management also increases greenhouse gas (GHG) emissions, which contribute to climate change. Planning for and implementing a comprehensive program for waste collection, transport, and disposal-along with activities to prevent or recycle waste-can eliminate or at least reduce these problems. This study examines the need for effective municipal solid waste management (i.e. PET) in an environment in order to achieve a clean and hygienic environment..