The tremendous increase in the quantum and diversity of waste materials generated by human activities has focused the spotlight on waste disposal methods. Waste generation rates are affected by standards of living, degree of industrialization and population density. Generally, the greater the economic prosperity and the higher percentage of urban population, the greater the amount of waste produced. Reduction in the volume and mass of wastes is a crucial issue due to limited availability of final disposal sites in almost all parts of the world. There is, no doubt, an obvious need to reduce, reuse and recycle wastes but recovery of energy from wastes is also gaining ground as a vital method for managing wastes.
Wastes can be transformed into clean and efficient energy and fuel by a variety of technologies, ranging from conventional combustion process to state-of-the-art plasma gasification technology. Besides recovery of energy, such technologies leads to substantial reduction in the overall waste quantities requiring final disposal. Waste-to-energy projects provide major business opportunities, environmental benefits, and energy security. Feedstock for waste-to-energy plants can be obtained from a wide array of sources including municipal wastes, crop residues and agro-industrial wastes.
Let us explore some of major waste resources that are readily available in MENA countries:
Municipal Solid Wastes
Atleast 150 million tons of solid wastes are collected each year in the MENA region with the vast majority disposed of in open fields and dumpsites. The major energy resource in municipal solid waste is made up of food residuals, paper, fruits, vegetables, plastics etc which make up as much as 75 – 80 percent of the total MSW collected.
Municipal wastes can be converted into energy by thermochemical or biological technologies. At the landfill sites the gas produced by the natural decomposition of MSW (called landfill gas) can be collected, scrubbed and cleaned before feeding into internal combustion engines or gas turbines to generate heat and power. The organic fraction of MSW can be biochemically stabilized in an anaerobic digester to obtain biogas (for heat and power) as well as fertilizer. Sewage sludge is a big nuisance for municipalities and general public but it is a very good source of biogas, which can efficiency produced at sewage treatment plants.
Crop residues encompasses all agricultural wastes such as bagasse, straw, stem, stalk, leaves, husk, shell, peel, pulp, stubble, etc. Large quantities of crop residues are produced annually in the MENA region, and are vastly underutilised. Wheat and barley are the major staple crops grown in the Middle East region. In addition, significant quantities of rice, maize, lentils, chickpeas, vegetables and fruits are produced throughout the region, mainly in Egypt, Tunisia, Saudi Arabia, Morocco and Jordan. Current farming practice is usually to plough these residues back into the soil, or they are burnt, left to decompose, or grazed by cattle. Agricultural residues are characterized by seasonal availability and have characteristics that differ from other solid fuels such as wood, charcoal, char briquette. Crop wastes can be used to produce biofuels, biogas as well as heat and power through a wide range of well-proven technologies.
The MENA countries have strong animal population. The livestock sector, in particular sheep, goats and camels, plays an important role in the national economy of respective countries. Many millions of live ruminants are imported each year from around the world. In addition, the region has witnessed very rapid growth in the poultry sector. The biogas potential of animal manure can be harnessed both at small- and community-scale. In the past, this waste was recovered and sold as a fertilizer or simply spread onto agricultural land, but the introduction of tighter environmental controls on odour and water pollution means that some form of waste management is now required, which provides further incentives for waste-to-energy conversion. The most attractive method of converting these waste materials to useful form is anaerobic digestion.
Wood processing industries primarily include sawmilling, plywood, wood panel, furniture, building component, flooring, particle board, moulding, jointing and craft industries. Wood wastes generally are concentrated at the processing factories, e.g. plywood mills and sawmills. In general, processing of 1,000 kg of wood in the furniture industries will lead to waste generation of almost half (45 %), i.e. 450 kg of wood. Similarly, when processing 1,000 kg of wood in sawmill, the waste will amount to more than half (52 %), i.e. 520 kg wood. Wood wastes has high calorific value and can be efficiency converted into energy by thermal technologies like combustion and gasification.
The food processing industry in MENA produces a large number of organic residues and by-products that can be used as biomass energy sources. These waste materials are generated from all sectors of the food industry with everything from meat production to confectionery producing waste that can be utilised as an energy source. In recent decades, the fast-growing food and beverage processing industry has remarkably increased in importance in major countries of the region.
Since the early 1990s, the increased agricultural output stimulated an increase in fruit and vegetable canning as well as juice, beverage, and oil processing in countries like Egypt, Syria, Lebanon and Saudi Arabia. Wastewater from food processing industries contains sugars, starches and other dissolved and solid organic matter. A huge potential exists for these industrial wastes to be biochemically digested to produce biogas, or fermented to produce ethanol, and several commercial examples of waste-to-energy conversion already exist around the world.
An environmentally sound and techno-economically viable methodology to treat wastes is highly crucial for the sustainability of modern societies. The MENA region is well-poised for waste-to-energy development, with its rich resources in the form of municipal solid waste, crop residues and agro-industrial waste. The implementation of advanced waste conversion technologies as a method for safe disposal of solid and liquid biomass wastes, and as an attractive option to generate heat, power and fuels, can greatly reduce environmental impacts of a wide array of wastes.