Pyrolysis of Municipal Wastes

Pyrolysis is rapidly developing biomass thermal conversion technology and has been garnering much attention worldwide due to its high efficiency and good eco-friendly performance characteristics. Pyrolysis technology provides an opportunity for the conversion of municipal solid wastes, agricultural residues, scrap tires, non-recyclable plastics etc into clean energy. It offers an attractive way of converting urban wastes into products which can be effectively used for the production of heat, electricity and chemicals.


Pyrolysis of Municipal Wastes

Pyrolysis process consists of both simultaneous and successive reactions when carbon-rich organic material is heated in a non-reactive atmosphere. Simply speaking, pyrolysis is the thermal degradation of organic materials in the absence of oxygen. Thermal decomposition of organic components in the waste stream starts at 350°C–550°C and goes up to 700°C–800°C in the absence of air/oxygen.

Pyrolysis of municipal wastes begins with mechanical preparation and separation of glass, metals and inert materials prior to processing the remaining waste in a pyrolysis reactor. The commonly used pyrolysis reactors are rotary kilns, rotary hearth furnaces, and fluidized bed furnaces. The process requires an external heat source to maintain the high temperature required.

Pyrolysis can be performed at relatively small-scale which may help in reducing transport and handling costs.  In pyrolysis of MSW, heat transfer is a critical area as the process is endothermic and sufficient heat transfer surface has to be provided to meet process heat requirements.

The main products obtained from pyrolysis of municipal wastes are a high calorific value gas (synthesis gas or syngas), a biofuel (bio oil or pyrolysis oil) and a solid residue (char). Depending on the final temperature, MSW pyrolysis will yield mainly solid residues at low temperatures, less than 4500C, when the heating rate is quite slow, and mainly gases at high temperatures, greater than 8000C, with rapid heating rates. At an intermediate temperature and under relatively high heating rates, the main product is a liquid fuel popularly known as bio oil.

Wide Range of Products

Bio oil is a dark brown liquid and can be upgraded to either engine fuel or through gasification processes to a syngas and then biodiesel. Pyrolysis oil may also be used as liquid fuel for diesel engines and gas turbines to generate electricity.

Bio oil is particularly attractive for co-firing because it can be relatively easy to handle and burn than solid fuel and is cheaper to transport and store. In addition, bio oil is also a vital source for a wide range of organic compounds and specialty chemicals.

Syngas is a mixture of energy-rich gases (combustible constituents include carbon monoxide, hydrogen, methane and a broad range of other VOCs). The net calorific value (NCV) of syngas is between 10 and 20MJ/Nm3. Syngas is cleaned to remove particulates, hydrocarbons, and soluble matter, and then combusted to generate electricity.

Diesel engines, gas turbines, steam turbines and boilers can be used directly to generate electricity and heat in CHP systems using syngas and pyrolysis oil. Syngas may also be used as a basic chemical in petrochemical and refining industries.

The solid residue from MSW pyrolysis, called char, is a combination of non-combustible materials and carbon. Char is almost pure carbon and can be used in the manufacture of activated carbon filtration media (for water treatment applications) or as an agricultural soil amendment.

Bioenergy Resources in MENA Countries

The Middle East and North Africa (MENA) region offers almost 45 percent of the world’s total energy potential from all renewable sources that can generate more than three times the world’s total power demand. Apart from solar and wind, MENA also has abundant bioenergy energy resources which have remained unexplored to a great extent.


Around the MENA region, pollution of the air and water from municipal, industrial and agricultural operations continues to grow.  The technological advancements in the biomass energy and waste-to-energy industry, coupled with the tremendous regional potential, promises to usher in a new era of energy as well as environmental security for the region.

The major biomass producing countries in MENA are Saudi Arabia, Egypt, Yemen, Iraq, Syria and Jordan. Traditionally, biomass energy has been widely used in rural areas for domestic purposes in the MENA region, especially in Egypt, Yemen and Jordan. Since most of the region is arid or semi-arid, the major bioenergy resources are municipal solid wastes, agricultural residues and organic industrial wastes.

Municipal solid wastes represent the best source of biomass in Middle East countries. Bahrain, Saudi Arabia, UAE, Qatar and Kuwait rank in the top-ten worldwide in terms of per capita solid waste generation. The gross urban waste generation quantity from Middle East countries is estimated at more than 150 million tons annually.





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Solid Waste Management – History and Future Outlook

The disposal of municipal solid waste is the second most major concern for public health in developing countries because of population explosion, rampant poverty and high urbanization rates combined with poor government funding to curb waste management. Factors such as waste composition, technologies and lack of infrastructure have been found to set apart the good management of solid wastes in developing nations. Municipal waste is mainly comprised of paper, vegetable matter, plastics, metals, textiles, rubber and glass. In some countries (developing as well as developed), municipal solid waste is mixed with medical wastes and this may pose health risk to waste handlers and general public.

Historically, burying the wastes is the most preferred method for waste management in many countries. This method is still used in many more countries. Tackling environmental issues has become more important and more preferred than pollution and consumption of unsustainable utilization of resources. Most importantly, the primary objective of waste management is to put emphasis on protecting the people and environment from potentially harmful effects of waste.

Methods of Solid Waste Management

Depending on the types of wastes generated, four methods of solid waste management has been used throughout the history, i.e. dumping, incineration, recycling and waste prevention. Waste generated from household is much different from industrial waste, agricultural waste, medical waste or mining wastes.

When wastes contain any hazardous component, or it has capability to become hazardous with time, poses very serious threat to environment and health. Hazardous wastes generated needs to be handled very carefully, with special techniques. This is one of the major reasons of open landfills are getting replaced with sanitary landfills.

At a landfill, wastes are covered with thick layer of soil. By the late 1950, this practice was very common for waste management across the world. Earlier landfills had considerable sludge and methane emissions, which were harmful to the environment as well as animal and human health. But these issues have been resolved largely by modern disposal methods, which were developed around 20 years ago. Modern landfills are equipped with thick layer of clay followed by plastic sheets. This method was practiced by some nations and still going on.

In 1930-1940, many cities in USA adopted new technology to curb waste issues by burning at high temperature, this method is known as incineration. During initial years, this method was not very efficient and emit very large amount of poisonous gasses, this is the major reason of incinerators shut down during that period. During mid-1970s, scientists modified incinerators to generate energy, which are known as waste to energy plants. But after around a decade, it has become major issue to build these plants, again because of emission issues.

With development of technology, waste burning in advanced form of incinerators became common in 1970s, researchers across the world bet on incinerators or waste to energy plants for solution to energy crisis in 1973. However, with realisation of impact on environment and air quality, it become very difficult to find location to build any waste to energy plants, mainly because of public opposition. Another issue with incinerator is production of ashes, which contain huge amount of heavy metals, toxic and inorganic compounds.



Future of Solid Waste Management

The overall concept of wastes needs to be considered economically, it will be more considered as economically viable product if waste is considered as an inefficiency of the production process not as rejected residue of waste product. A permanent rejection or heavy restriction into products which produces waste that cannot be accumulated back into the environment safely.

The major challenge in waste management is to persuade people/community to consider waste as a resource, rather than a liability on society, which can be created with more innovation and technological development of manufacturing industry, waste processing industry and new business model and plans.

This planning system will create circular economy where product value created by inputs (e.g. energy, materials, labour etc.) is extended by enabling a material that goes into circular economy, beyond product life. We go from mineral to metals to product then back to minerals/metals. By understanding economic cycle of waste, people will understand the creation of opportunities to more sustainable product in future with limited resources.

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Recycling and Waste-to-Energy Prospects in Saudi Arabia

The Kingdom of Saudi Arabia produces around 15 million tons of municipal solid waste (MSW) each year with average daily rate of 1.4 kg per person. With the current growing population (3.4% yearly rate), urbanization (1.5% yearly rate) and economic development (3.5% yearly GDP rate), the generation rate of MSW will become double (30 million tons per year) by 2033. The major ingredients of Saudi Arabian MSW are food waste (40-51 %), paper (12-28 %), cardboard (7 %), plastics (5-17 %), glass (3-5 %), wood (2-8 %), textile (2-6 %), metals (2-8 %) etc. depending on the population density and urban activities of that area.


In Saudi Arabia, MSW is collected and sent to landfills or dumpsites after partial segregation and recycling. The major portion of collected waste is ends up in landfills untreated. The landfill requirement is very high, about 28 million m3 per year. The problems of leachate, waste sludge, and methane and odor emissions are occurring in the landfills and its surrounding areas due to mostly non-sanitary or un-engineered landfills. However, in many cities the plans of new sanitary landfills are in place, or even they are being built by municipalities with capturing facilities of methane and leachate.

Recycling Prospects in Saudi Arabia

The recycling of metals and cardboard is the main waste recycling practice in Saudi Arabia, which covers 10-15% of the total waste. This recycling practice is mostly carried out by informal sector. The waste pickers or waste scavengers take the recyclables from the waste bins and containers throughout the cities. The waste recycling rate often becomes high (upto 30% of total waste) by waste scavengers in some areas of same cities. The recycling is further carried out at some landfill sites, which covers upto 40% of total waste by the involvement of formal and informal sectors.


The recycled products are glass bottles, aluminum cans, steel cans, plastic bottles, paper, cardboard, waste tire, etc. depending on the area, available facilities and involved stakeholders. It is estimated that 45 thousand TJ of energy can be saved by recycling only glass and metals from MSW stream. This estimation is based on the energy conservation concept, which means xyz amount of energy would be used to produce the same amount of recyclable material.

Waste-to-Energy Potential in Saudi Arabia

The possibilities of converting municipal wastes to renewable energy are plentiful. The choice of conversion technology depends on the type and quantity of waste (waste characterization), capital and operational cost, labor skill requirements, end-uses of products, geographical location and infrastructure. Several waste to energy technologies such as pyrolysis, anaerobic digestion (AD), trans-esterification, fermentation, gasification, incineration, etc. have been developed. Waste-to-energy provides the cost-effective and eco-friendly solutions to both energy demand and MSW disposal problems in Saudi Arabia.

As per conservative estimates, electricity potential of 3 TWh per year can be generated, if all of the KSA food waste is utilized in biogas plants. Similarly, 1 and 1.6 TWh per year electricity can be generated if all the plastics and other mixed waste (i.e. paper, cardboard, wood, textile, leather, etc.) of KSA are processed in the pyrolysis, and refuse derived fuel (RDF) technologies respectively.


Waste management issues in Saudi Arabia are not only related to water, but also to land, air and the marine resources. The sustainable integrated solid waste management is still at the infancy level. There have been many studies in identifying the waste related environmental issues in KSA. The current SWM activities of KSA require a sustainable and integrated approach with implementation of waste segregation at source, waste recycling, WTE and value-added product (VAP) recovery. By 2032, Saudi government is aiming to generate about half of its energy requirements (about 72 GW) from renewable sources such as solar, nuclear, wind, geothermal and waste-to-energy systems.

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