“Tanning” refers to the process by which collagen fibers in a hide react with a chemical agent (tannin, alum or other chemicals). However, the term leather tanning also commonly refers to the entire leather-making process. Hides and skins have the ability to absorb tannic acid and other chemical substances that prevent them from decaying, make them resistant to wetting, and keep them supple and durable. The flesh side of the hide or skin is much thicker and softer. The three types of hides and skins most often used in leather manufacture are from cattle, sheep, and pigs.
A large amount of waste produced by these tanneries is discharged in natural water bodies directly or indirectly through two open drains without any treatment. The water in the low lying areas in developing countries, like India and Bangladesh, is polluted in such a degree that it has become unsuitable for public uses…
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Vermicomposting is a type of composting in which certain species of earthworms are used to enhance the process of organic waste conversion and produce a better end-product. Vermicomposting is a mesophilic process utilizing microorganisms and earthworms. Earthworms feeds the organic waste materials and passes it through their digestive system and gives out in a granular form (cocoons) which is known as vermicompost. Like regular compost, vermicompost also benefits the environment by reducing the need for chemical fertilizers and decreasing the amount of waste going to landfills/dumpsites.
Vermicompost is primarily earthworm excrement, called castings, which can improve biological, chemical, and physical properties of the soil. The chemical secretions in the earthworm’s digestive tract help break down soil and organic matter, so the castings contain more nutrients that are immediately available to plants.
Earthworms consume various organic wastes and reduce the volume by 40–60 percent. Each earthworm weighs about 0.5 to 0.6…
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The global market for WTE technologies was valued at US$19.9bn in 2008. This has been forecasted to increase to US$26.2bn by 2014. While the biological WTE segment is expected to grow more rapidly from US$1.4bn in 2008 to approximately US$2.5bn in 2014, the thermal WTE segment is nonetheless estimated to still constitute the vast bulk of the entire industry’s worth. This segment was valued at US$18.5bn in 2008 and is forecasted to expand to US$23.7bn in 2014.
The global market for waste to energy technologies has shown substantial growth over the last five years, increasing from $4.83 billion in 2006, to $7.08 billion in 2010 with continued market growth through the global economic downturn. Over the coming decade, growth trends are expected to continue, led by expansion in the US, European, Chinese, and Indian markets. By 2021, based on continued growth in Asian markets combined with the maturation of European…
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Food waste is an untapped energy source that mostly ends up rotting in landfills, thereby releasing greenhouse gases into the atmosphere. Food waste is difficult to treat or recycle since it contains high levels of sodium salt and moisture, and is mixed with other waste during collection. Major generators of food wastes include hotels, restaurants, supermarkets, residential blocks, cafeterias, airline caterers, food processing industries, etc.
In United States, food waste is the third largest waste stream after paper and yard waste. Around 12.7 percent of the total municipal solid waste (MSW) generated in the year 2008 was food scraps that amounted to about 32 million tons. According to EPA, about 31 million tons of food waste was thrown away into landfills or incinerators in 2008. As far as United Kingdom is concerned, households throw away 8.3 million tons of food each year. These statistics are an indication of tremendous amount of…
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Selection of an appropriate biogas storage system makes a significant contribution to the efficiency and safety of a biogas plant. A biogas storage system also compensates fluctuations in the production and consumption of biogas as well as temperature-related changes in volume. There are two broad categories of biogas sto
rage systems: Internal Biogas Storage Tanks are integrated into the anaerobic digester while External Biogas Holders are separated from the digester forming autonomous components of a biogas plant.
The simplest and least expensive storage systems for on-site applications and intermediate storage of biogas are low-pressure systems. Floating gas holders on the digester form a low-pressure storage option for biogas systems. These systems typically operate at pressures below 2 psi. Floating gas holders can be made of steel, fiberglass, or a flexible fabric. A separate tank may be used with a floating gas holder for the storage of the digestate and also…
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The typical composition of raw biogas does not meet the minimum CNG fuel specifications. In particular, the CO2 and sulfur content in raw biogas is too high for it to be used as vehicle fuel without additional processing. Biogas that has been upgraded to biomethane by removing the H2S, moisture, and CO2 can be used as a vehicular fuel. Biomethane is less corrosive than biogas, apart from being more valuable as a fuel.
Since production of such fuel typically exceeds immediate on-site demand, the biomethane must be stored for future use, usually either as compressed biomethane (CBM) or liquefied biomethane (LBM). Biomethane can be liquefied, creating a product known as liquefied biomethane (LBM). Two of the main advantages of LBM are that it can be transported relatively easily and it can be dispensed to either LNG vehicles or CNG vehicles. Liquid biomethane is transported in the same…
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A biorefinery is a facility that integrates biomass conversion processes and equipment to produce fuels, power, and value-added chemicals from biomass. The biorefinery concept is analogous to today’s petroleum refinery, which produces multiple fuels and products from petroleum.By producing several products, a biorefinery takes advantage of the various components in biomass and their intermediates, therefore maximizing the value derived from the biomass feedstock. A biorefinery could, for example, produce one or several low-volume, but high-value, chemical products and a low-value, but high-volume liquid transportation fuel such as biodiesel or bioethanol. At the same time, it can generate electricity and process heat, through CHP technology, for its own use and perhaps enough for sale of electricity to the local utility. The high value products increase profitability, the high-volume fuel helps meet energy needs, and the power production helps to lower energy costs and reduce GHG emissions from traditional power plant facilities.
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The main problem with anaerobic digestion of crop residues is that most of the agricultural residues are lignocellulosic with low nitrogen content. To improve the digestibility of crop residues, pre-treatment methods like size reduction, electron irradiation, heat treatment, enzymatic action etc are necessary. For optimizing the C/N ratio of agricultural residues, co-digestion with sewage sludge, animal manure or poultry litter is recommended.
Several organic wastes from plants and animals have been exploited for biogas production as reported in the literature. Plant materials include agricultural crops such as sugar cane, cassava, corn etc, agricultural residues like rice straw, cassava rhizome, corn cobs etc, wood and wood residues (saw dust, pulp wastes, and paper mill. Others include molasses and bagasse from sugar refineries, waste streams such as rice husk from rice mills and residues from palm oil extraction and municipal solid wastes, etc. However, plant materials such as crop residues are more…
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Thailand’s annual energy consumption has risen sharply during the past decade and will continue its upward trend in the years to come. While energy demand has risen sharply, domestic sources of supply are limited, thus forcing a significant reliance on imports. To face this increasing demand, Thailand needs to produce more energy from its own renewable resources, particularly biomass wastes derived from agro-industry, such as bagasse, rice husk, wood chips, livestock and municipal wastes.
In 2005, total installed power capacity in Thailand was 26,430 MW. Renewable energy accounted for about 2 percent of the total installed capacity. In 2007, Thailand had about 777 MW of electricity from renewable energy that was sold to the grid. Several studies have projected that biomass wastes can cover up to 15 % of the energy demand in Thailand (Thailand-Danish Country Programme for Environmental Assistance 1998-2001, Ministry of Environment and Energy, 2000). These estimations are…
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The unavailability of sufficient feedstock and lack of R&D to evolve high-yielding drought tolerant Jatropha seeds have been major stumbling blocks. In addition, smaller land holdings, ownership issues with government or community-owned wastelands, lackluster progress by state governments and negligible commercial production of biodiesel have hampered the efforts and investments made by both private and public sector companies.
Another major obstacle in implementing the biodiesel programme has been the difficulty in initiating large-scale cultivation of Jatropha. The Jatropha production program was started without any planned varietal improvement program, and use of low-yielding cultivars made things difficult for smallholders. The higher gestation period of biodiesel crops (3–5 years for Jatropha and 6–8 years for Pongamia) results in a longer payback period and creates additional problems for farmers where state support is not readily available. The Jatropha seed distribution channels are currently underdeveloped as sufficient numbers of processing industries are…
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Renewable energy systems have been used in Jordan since early 1970s. Infact, Jordan has been a pioneer in renewable energy promotion in the Middle East with its first wind power pilot project in Al-Ibrahemiya as early as 1988. Systematic monitoring of the technological developments and implementation/execution of demonstration and pilot projects has been the hallmark of Jordan’s foray into clean energy sector.
Municipal solid wastes represent the best source of biomass in Jordan. In terms of quantity per capita and constituents, the waste generated in Jordan is comparable to most semi-industrialized nations. The per capita of waste generated in Jordan is about 0.9 kg/day. The total generation of municipal waste in Jordan is estimated at 1.84 million tons per year. The main resources of organic waste in Jordan that can be potentially used to produce biogas are summarized as follows:
- Municipal waste from big cities
- Organic wastes from slaughterhouse, vegetable market, hotels and restaurants.
- Organic waste from agro-industries
- Animal manure, mainly from cows and chickens.
- Sewage sludge and septic.
- Olive mills.
- Organic industrial waste
According to a study conducted by the Greater Amman Municipality, around 1.5 million tonnes of organic waste was generated in Jordan in 2009. In addition, an annual amount of 1.83 million cubic meter of septic and sewage sludge from treatment of 44 million cubic meter of sewage water is generated in greater Amman area. The potential annual sewage sludge and septic generated in Amman can be estimated at 85,000 tons of dry matter.
The Government of Jordan, in collaboration with UNDP, GEF and the Danish Government, established 1MW Biomethanation plant at Rusaifeh landfill near Amman in 1999. The Plant has been successfully operating since its commissioning and efforts are underway to increase its capacity to 5MW. Infact, the project has achieved net yearly profit from electricity sale of about US $ 100, 000. The project consists of a system of twelve landfill gas wells and an anaerobic digestion plant based on 60 tons per day of organic wastes from hotels, restaurants and slaughterhouses in Amman. The successful installation of the biogas project has made it a role model in the entire region and several big cities are striving to replicate the model.
The Middle East and North Africa (MENA) region is highly susceptible to climate change, on account of its water scarcity, high dependence on climate-sensitive agriculture, concentration of population and economic activity in urban coastal zones, and the presence of conflict-affected areas. Moreover, the region is one of the biggest contributors to greenhouse gas emissions on account of its thriving oil and gas industry.
The world’s dependence on Middle East energy resources has caused the region to have some of the largest carbon footprints per capita worldwide. Not surprisingly, the carbon emissions from UAE are approximately 55 tons per capita, which is more than double the US per capita footprint of 22 tons per year. The MENA region is now gearing up to meet the challenge of global warming, as with the rapid growth of the carbon market. During the last few years, many MENA countries, like UAE, Qatar, Egypt and Saudi Arabia have unveiled multi-billion dollar investment plans in the cleantech sector to portray a ‘green’ image.
There is an urgent need to foster sustainable energy systems, diversify energy sources, and implement energy efficiency measures. The clean development mechanism (CDM), under the Kyoto Protocol, is one of the most important tools to support renewable energy and energy efficiency initiatives in the MENA countries. Some MENA countries have already launched ambitious sustainable energy programs while others are beginning to recognize the need to adopt improved standards of energy efficiency.
The UAE, cognizant of its role as a major contributor to climate change, has launched several ambitious governmental initiatives aimed at reducing emissions by approximately 40 percent. Masdar, a $15 billion future energy company, will leverage the funds to produce a clean energy portfolio, which will then invest in clean energy technology across the Middle East and North African region. Egypt is the regional CDM leader with twelve projects in the UNFCCC pipeline and many more in the conceptualization phase.
The MENA region is an attractive CDM destination as it is rich in renewable energy resources and has a robust oil and gas industry. Surprisingly, very few CDM projects are taking place in MENA countries with only 22 CDM projects have been registered to date. The region accounts for only 1.5 percent of global CDM projects and only two percent of emission reduction credits. The two main challenges facing many of these projects are: weak capacity in most MENA countries for identifying, developing and implementing carbon finance projects and securing underlying finance.
Currently, there are several CDM projects in progress in Egypt, Jordan, Bahrain, Morocco, Syria and Tunisia. Many companies and consulting firms have begun to explore this now fast-developing field. One of them, the UK-based EcoSecurities, opened a regional office in Dubai. The company has offices in Bahrain and Lebanon and is planning for branches in Saudi Arabia and Qatar as well as intermediates in Egypt and Libya next year. The Masdar Company of Abu Dhabi, meanwhile, is the first local company in the region to pursue a CDM project.
The Al-Shaheen project is the first of its kind in the region and third CDM project in the petroleum industry worldwide. The Al-Shaheen oilfield has flared the associated gas since the oilfield began operations in 1994. Prior to the project activity, the facilities used 125 tons per day (tpd) of associated gas for power and heat generation, and the remaining 4,100 tpd was flared. Under the current project, total gas production after the completion of the project activity is 5,000 tpd with 2,800-3,400 tpd to be exported to Qatar Petroleum (QP); 680 tpd for on-site consumption, and only 900 tpd still to be flared. The project activity will reduce GHG emissions by approximately 2.5 million tCO2 per year and approximately 17 million tCO2 during the initial seven-year crediting period.
Potential CDM projects that can be implemented in the region may come from varied areas like sustainable energy, energy efficiency, waste management, landfill gas capture, industrial processes, biogas technology and carbon flaring. For example, the energy efficiency CDM projects in the oil and gas industry, can save millions of dollars and reduce tons of CO2 emissions. In addition, renewable energy, particularly solar and wind, holds great potential for the region, similar to biomass in Asia.
With Indonesia’s recovery from the Asian financial crisis of 1998, energy consumption has grown rapidly in past decade. The priority of the Indonesian energy policy is to reduce oil consumption and to use renewable energy. For power generation, it is important to increase electricity power in order to meet national demand and to change fossil fuel consumption by utilization of biomass wastes. The development of renewable energy is one of priority targets in Indonesia.
It is estimated that Indonesia produces 146.7 million tons of biomass per year, equivalent to about 470 GJ/y. The source of biomass energy is scattered all over the country, but the big potential in concentrated scale can be found in the Island of Kalimantan, Sumatera, Irian Jaya and Sulawesi. Studies estimate the electricity generation potential from the roughly 150 Mt of biomass residues produced per year to be about 50 GW or equivalent to roughly 470 GJ/year. These studies assume that the main source of biomass energy in Indonesia will be rice residues with a technical energy potential of 150 GJ/year. Other potential biomass sources are rubber wood residues (120 GJ/year), sugar mill residues (78 GJ/year), palm oil residues (67 GJ/year), and less than 20 GJ/year in total from plywood and veneer residues, logging residues, sawn timber residues, coconut residues, and other agricultural wastes.
Sustainable and renewable natural resources such as biomass can supply potential raw materials for energy conversion. In Indonesia, they comprise variable-sized wood from forests (i.e. natural forests, plantations and community forests that commonly produce small-diameter logs used as firewood by local people), woody residues from logging and wood industries, oil-palm shell waste from crude palm oil factories, coconut shell wastes from coconut plantations, as well as skimmed coconut oil and straw from rice cultivation.
The major crop residues to be considered for power generation in Indonesia are palm oil sugar processing and rice processing residues. Currently, 67 sugar mills are in operation in Indonesia and eight more are under construction or planned. The mills range in size of milling capacity from less than 1,000 tons of cane per day to 12,000 tons of cane per day. Current sugar processing in Indonesia produces 8 millions MT bagasse and 11.5 millions MT canes top and leaves. There are 39 palm oil plantations and mills currently operating in Indonesia, and at least eight new plantations are under construction. Most palm oil mills generate combined heat and power from fibres and shells, making the operations energy self –efficient. However, the use of palm oil residues can still be optimized in more energy efficient systems.
Other potential source of biomass energy can also come from municipal wastes. The quantity of city or municipal wastes in Indonesia is comparable with other big cities of the world. Most of these wastes are originated from household in the form of organic wastes from the kitchen. At present the wastes are either burned at each household or collected by the municipalities and later to be dumped into a designated dumping ground or landfill. Although the government is providing facilities to collect and clean all these wastes, however, due to the increasing number of populations coupled with inadequate number of waste treatment facilities in addition to inadequate amount of allocated budget for waste management, most of big cities in Indonesia had been suffering from the increasing problem of waste disposals.
The current pressure for cost savings and competitiveness in Indonesia’s most important biomass-based industries, along with the continually growing power demands of the country signal opportunities for increased exploitation of biomass wastes for power generation.
Gasification with pure oxygen or hydrogen
Gasification with pure oxygen or pure hydrogen (or hydrogasification) may provide better alternatives to the air blown or indirectly heated gasification systems. This depends greatly on reducing the costs associated with oxygen and hydrogen production and improvements in refractory linings in order to handle higher temperatures. Pure oxygen could be used to generate higher temperatures, and thus promote thermal catalytic destruction of organics within the fuel gas. Hydrogasification is an attractive proposition because it effectively cracks tars within the primary gasifying vessel. It also promotes the formation of a methane rich gas that can be piped to utilities without any modifications to existing pipelines or gas turbines, and can be reformed into hydrogen or methanol for use with fuel cells.
Plasma gasification or plasma discharge uses extremely high temperatures in an oxygen-starved environment to completely decompose input waste material into very simple molecules in a process similar to pyrolysis. The heat source is a plasma discharge torch, a device that produces a very high temperature plasma gas. Plasma gasification has two variants, depending on whether the plasma torch is within the main waste conversion reactor or external to it. It is carried out under oxygen-starved conditions and the main products are vitrified slag, syngas and molten metal. Vitrified slag may be used as an aggregate in construction; the syngas may be used in energy recovery systems or as a chemical feedstock; and the molten metal may have a commercial value depending on quality and market availability.
Such processes use high-energy microwaves in a nitrogen atmosphere to decompose waste material. The waste absorbs microwave energy increasing the internal energy of the organic material to a level where chemical decomposition occurs on a molecular level. The nitrogen blanket forms an inert, oxygen free environment to prevent combustion. Temperatures in the chamber range from 150 to 3500C. At these temperatures, metal, ceramics and glass are not chemically affected.
Sugarcane is one of the most promising agricultural sources of biomass energy in the world. It is the most appropriate agricultural energy crop in most Cane producing countries due to its resistance to cyclonic winds, drought, pests and diseases, and its geographically widespread cultivation. Due to its high energy-to-volume ratio, it is considered one of nature’s most effective storage devices for solar energy and the most economically significant energy crop. The climatic and physiological factors that limit its cultivation to tropical and sub-tropical regions have resulted in its concentration in developing countries, and this, in turn, gives these countries a particular role in the world’s transition to sustainable use of natural resources.
According to the International Sugar Organization (ISO), Sugarcane is a highly efficient converter of solar energy, and has the highest energy-to-volume ratio among energy crops. Indeed, it gives the highest annual yield of biomass of all species. Roughly, 1 ton of Sugarcane biomass-based on Bagasse, foliage and ethanol output – has an energy content equivalent to one barrel of crude oil. Sugarcane produces mainly two types of biomass, Cane Trash and Bagasse. Cane Trash is the field residue remaining after harvesting the Cane stalk and Bagasse is the milling by-product which remains after extracting the Sugar from the stalk. The potential energy value of these residues has traditionally been ignored by policy-makers and masses in developing countries. However, with rising fossil fuel prices and dwindling firewood supplies, this material is increasingly viewed as a valuable Renewable Energy resource.
Sugar mills have been using Bagasse to generate steam and electricity for internal plant requirements while Cane Trash remains underutilized to a great extent. Cane Trash and Bagasse are produced during the harvesting and milling process of Sugar Cane which normally lasts 6 to 7 months.
Around the world, a portion of the Cane Trash is collected for sale to feed mills, while freshly cut green tops are sometimes collected for farm animals. In most cases, however, the residues are burned or left in the fields to decompose. Cane Trash, consisting of Sugarcane tops and leaves can potentially be converted into around 1kWh/kg, but is mostly burned in the field due to its bulkiness and its related high cost for collection/transportation.
On the other hand, Bagasse has been traditionally used as a fuel in the Sugar mill itself, to produce steam for the process and electricity for its own use. In general, for every ton of Sugarcane processed in the mill, around 190 kg Bagasse is produced. Low pressure boilers and low efficiency steam turbines are commonly used in developing countries. It would be a good business proposition to upgrade the present cogeneration systems to highly efficient, high pressure systems with higher capacities to ensure utilization of surplus Bagasse.
Southeast Asia, with its abundant biomass resources, holds a strategic position in the global biomass energy atlas. There is immense potential of biopower in Southeast Asian countries due to plentiful supply of diverse forms of wastes such as agricultural residues, woody biomass, animal wastes, municipal solid waste, etc. The rapid economic growth and industrialization in the region has accelerated the drive to implement the latest waste-to-energy technologies in order to tap the unharnessed potential of biomass resources.
The Southeast Asian region is a big producer of wood and agricultural products which, when processed in industries, produces large amounts of biomass residues. According to conservative estimates, the amount of biomass residues generated from sugar, rice and palm oil mills is more than 200-230 million tons per year which corresponds to cogeneration potential of 16-19 GW.
In 2005, rice mills in the region produced 38 million tonnes of rice husk as solid residues. Sugar industry is an integral part of the industrial scenario in Southeast Asia accounting for about 10% of global sugar production. Malaysia, Indonesia and Thailand account for 90% of global palm oil production leading to the generation of thousands of tonnes of waste per annum in the form of empty fruit bunches (EFBs), fibers and shells, as well as liquid effluent. Woody biomass is a good energy resource due to presence of large number of forests and wood processing industries in the region.
The prospects of biogas power generation are also high in the region due to the presence of well-established food-processing and dairy industries. Another important biomass resource is contributed by municipal solid wastes in heavily populated urban areas. In addition, there are increasing efforts from the public and private sectors to develop biomass energy systems for efficient biofuel production, e.g. bio-diesel from palm oil.
Current technologies for biomass utilization need urgent improvement towards best practice by making use of the latest trends in the waste-to-energy sector. Southeast Asian countries are yet to make optimum use of the additional power generation potential from biomass waste resources which could help them to partially overcome the long-term problem of energy supply. There can be several routes for dedicated power generation from biomass at various scales of power output. Cogeneration of heat and power from residues in forest-based and agro industries is being increasingly promoted by the private sector, mostly for in-house consumption. In contrast, utility companies in Western countries already supply electricity and heat from biomass to national grids and local communities.
Energy is the driving force for development in all countries of the world. The increasing clamor for energy and satisfying it with a combination of conventional and renewable resources is a big challenge. Accompanying energy problems in different parts of the world, another problem that is assuming critical proportions is that of urban waste accumulation. The quantity of waste produced all over the world amounted to more than 12 billion tonnes in 2006, with estimates of up to 13 billion tonnes in 2011. The rapid increase in population coupled with changing lifestyle and consumption patterns is expected to result in an exponential increase in waste generation of upto 18 billion tonnes by year 2020.
Waste generation rates are affected by socio-economic development, degree of industrialization, and climate. Generally, the greater the economic prosperity and the higher percentage of urban population, the greater the amount of solid waste produced. Reduction in the volume and mass of solid waste is a crucial issue especially in the light of limited availability of final disposal sites in many parts of the world. Millions of tonnes of waste are generated each year with the vast majority disposed of in open fields or burnt wantonly.
Waste-to-Energy (WTE) is the use of modern combustion and biochemical technologies to recover energy, usually in the form of electricity and steam, from urban wastes. These new technologies can reduce the volume of the original waste by 90%, depending upon composition and use of outputs. The main categories of waste-to-energy technologies are physical technologies, which process waste to make it more useful as fuel; thermal technologies, which can yield heat, fuel oil, or syngas from both organic and inorganic wastes; and biological technologies, in which bacterial fermentation is used to digest organic wastes to yield fuel. Waste-to-energy technologies can address a host of environmental issues, such as land use and pollution from landfills, and increasing reliance on fossil fuels.
Around 130 million tonnes of municipal solid waste (MSW) are combusted annually in over 600 waste-to-energy (WTE) facilities globally that produce electricity and steam for district heating and recovered metals for recycling. Since 1995, the global WTE industry increased by more than 16 million tonnes of MSW. Incineration, with energy recovery, is the most common waste-to-energy method employed worldwide. Over the last five years, waste incineration in Europe has generated between an average of 4% to 8% of their countries’ electricity and between an average of 10% to 15% of the continent’s domestic heat.
Currently, the European nations are recognized as global leaders of the SWM and WTE movement. They are followed behind by the Asia Pacific region and North America respectively. In 2007 there are more than 600 WTE plants in 35 different countries, including large countries such as China and small ones such as Bermuda. Some of the newest plants are located in Asia.
The United States processes 14 percent of its trash in WTE plants. Denmark, on the other hand, processes more than any other country – 54 percent of its waste materials. As at the end of 2008, Europe had more than 475 WTE plants across its regions – more than any other continent in the world – that processes an average of 59 million tonnes of waste per annum. In the same year, the European WTE industry as a whole had generated revenues of approximately US$4.5bn. Legislative shifts by European governments have seen considerable progress made in the region’s WTE industry as well as in the implementation of advanced technology and innovative recycling solutions. The most important piece of WTE legislation pertaining to the region has been the European Union’s Landfill Directive, which was officially implemented in 2001 which has resulted in the planning and commissioning of an increasing number of WTE plants over the past five years.
- Anaerobic digestion provides a variety of benefits. These may be classified into three groups viz. environmental, economic and energy:
- The environmental benefits include:
- Elimination of malodorous compounds.
- Reduction of pathogens.
- Deactivation of weed seeds.
- Production of sanitized compost.
- Decrease in GHGs emission.
- Reduced dependence on inorganic fertilizers by capture and reuse of nutrients.
- Promotion of carbon sequestration
- Beneficial reuse of recycled water
- Protection of groundwater and surface water resources.
- Improved social acceptance
Anaerobic digestion is advantageous in terms of energy generation in the following manner:
- Anaerobic digestion is a net energy-producing process.
- A biogas facility generates high-quality renewable fuel.
- Surplus energy as electricity and heat is produced during anaerobic digestion of biomass.
- Anaerobic digestion reduces reliance on energy imports.
- Such a facility contributes to decentralized, distributed power systems.
- Biogas is a rich source of electricity, heat, and transportation fuel.
The economic benefits associated with a biogas facility are:
- Anaerobic digestion transforms waste liabilities into new profit centers.
- The time devoted to moving, handling and processing manure is minimized.
- Anaerobic digestion adds value to negative value feedstock.
- Income can be obtained from the processing of waste (tipping fees), sale of organic fertilizer, carbon credits and sale of power.
- Power tax credits may be obtained from each kWh of power produced.
- A biomass-to-biogas facility reduces water consumption.
- It reduces dependence on energy imports.
- Anaerobic digestion plants increases self-sufficiency.
Recycling and reuse of plastics is gaining importance as a sustainable method for plastic waste disposal. Unfortunately, plastic is much more difficult to recycle than materials like glass, aluminum or paper. A common problem with recycling plastics is that plastics are often made up of more than one kind of polymer or there may be some sort of fibre added to the plastic (a composite). Plastic polymers require greater processing to be recycled as each type melts at different temperatures and has different properties, so careful separation is necessary. Moreover, most plastics are not highly compatible with one another. Apart from familiar applications like recycling bottles and industrial packaging film, there are also new developments e.g. the Recovinyl initiative of the PVC industry (covering pipes, window frames, roofing membranes and flooring).
Polyethlene terephthalate (PET) and high density polyethylene (HDPE) bottles have proven to have high recyclability and are taken by most curbside and drop-off recycling programs. The growth of bottle recycling has been facilitated by the development of processing technologies that increase product purities and reduce operational costs. Recycled PET and HDPE have many uses and well-established markets.
In contrast, recycling of polyvinyl chloride (PVC) bottles and other materials is limited. A major problem in the recycling of PVC is the high chlorine content in raw PVC (around 56 percent of the polymer’s weight) and the high levels of hazardous additives added to the polymer to achieve the desired material quality. As a result, PVC requires separation from other plastics before mechanical recycling.
Commonly Recyclable Plastics
- High Density Polyethylene (HDPE) used in piping, automotive fuel tanks, bottles, toys,
- Low Density Polyethylene (LDPE) used in plastic bags, cling film, flexible containers;
- Polyethylene Terephthalate (PET) used in bottles, carpets and food packaging;
- Polypropylene (PP) used in food containers, battery cases, bottle crates, automotive parts and fibres;
- Polystyrene (PS) used in dairy product containers, tape cassettes, cups and plates;
- Polyvinyl Chloride (PVC) used in window frames, flooring, bottles, packaging film, cable insulation, credit cards and medical products.
Five Steps in Plastics Recycling
Step 1: Collection
This is done through roadside collections, special recycling bins and directly from industries that use a lot of plastic.
Step 2: Sorting
At this stage nails and stones are removed, and the plastic is sorted into three types: PET, HDPE and ‘other’.
Step 3: Chipping
The sorted plastic is cut into small pieces ready to be melted down.
Step 4: Washing
This stage removes contaminants such as paper labels, dirt and remnants of the product originally contained in the plastic.
Step 5: Pelletization
The plastic is then melted down and extruded into small pellets ready for reuse.