The year is January 2017, 177 years since the end of the industrial revolution and the planet’s climate has never been harsher. Man has mined into the earth, the atmosphere and the biggest driver of this revolution, was his mind. Man mined his mind and connected into the universal ether to reveal to himself the secrets of the universe to enhance his livelihood and in the process, a lot of waste and pollution has been generated. From degradation of the forests, to the emissions damaging the ozone; from the mountain heaps of landfills of municipal waste, to the mere fact that we only use 20% of our brain capacity-even for the geniuses! I find this quite fascinating of how wasteful we have become. But my question is, why all this waste? Why can’t we use the resources bestowed upon this creation with greater responsibility and accountability? Why is post industrial revolution catalyzing the end of our planet as we know it, to the point where we are looking for another planet to rehabilitate our human species, yet this revolution is what has enabled space exploration to begin with?


Earth’s Imminent Destruction due to Pollution


The answer lies in how efficient, sustainable and effective our conversion processes are-conversion from the unusable to usable without much waste. In my opinion, energy is the next frontier of global development and especially in Africa. One Julius Robert Mayer said, energy cannot be destroyed; it can only be transformed from one form to another. So it got me thinking about the various ways we have developed to convert our waste to energy for use, through empirical processes.

Waste-to-energy (WtE) is the process of generating energy in the form of electricity and/or heat from the primary treatment of waste. WtE is a form of energy recovery or rather, waste recovery. Most WtE processes produce electricity and/or heat directly through combustion, or produce a combustible fuel commodity, such as methane, methanol, ethanol or synthetic fuels. For purposes of this post, I will review 4 main waste to energy processes adopted by the world today;

  • Gasification
  • Pyrolysis
  • Thermal depolymerization (TDP)
  • Anaerobic digestion
  1. Gasification

I thought this described the farting process but to my enlightenment, it is a process that converts organic or fossil fuel based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures (>700 °C), without combustion, with a controlled amount of oxygen and/or steam. The resulting gas mixture is called syngas (from synthesis gas or synthetic gas) or producer gas and is itself a fuel.


Simple wood gasification process illustration
Not gasification

The power derived from gasification and combustion of the resultant gas is considered to be a source of renewable energy if the gasified compounds were obtained from biomass.

Sources of these carbonaceous materials include coal, petroleum , a variety of biomass and waste-derived feedstocks can be gasified, with wood pellets and chips, waste wood, plastics and aluminium, Municipal Solid Waste (MSW), Refuse-derived fuel (RDF), agricultural and industrial wastes, sewage sludge, switch grass, discarded seed corn, corn stover and other crop residues all being used.

Waste gasification has several advantages over incineration:

  • The necessary extensive flue gas cleaning may be performed on the syngas instead of the much larger volume of flue gas after combustion.
  • Electric power may be generated in engines and gas turbines, which are much cheaper and more efficient than the steam cycle used in incineration. Even fuel cells may potentially be used, but these have rather severe requirements regarding the purity of the gas.
  • Chemical processing (Gas to liquids) of the syngas may produce other synthetic fuels instead of electricity.
  • Some gasification processes treat ash containing heavy metals at very high temperatures so that it is released in a glassy and chemically stable form.

But this process comes with its challenges which are:

  • Waste gasification processes cannot reach an acceptable electric efficiency due to the significant power consumption in the waste preprocessing and high oxygen consumption
  • Short service intervals of the plants to clean
  • Constant opposition from environmental advocates who have referred to it as “incineration in disguise” and argue that it is still dangerous to air quality and public health.
  • antigasification-campaign-in-toronto                             Anti-gasification campaign poster in Toronto, Canada

2. Pyrolysis

For those who’ve watched the Movie Suicide Squad, the character El Diablo is depicted as a pyro kinetic-meaning one who controls fire. We have half the definition of the term Pyrolysis.


El Diablo, the Pyro kinetic from Suicide Squad


The word is coined from the Greek-derived elements pyro “fire” and lysis “separating”, which is a thermochemical decomposition of organic material like wood, cloth, and paper, and also of some kinds of plastic, at elevated temperatures in the absence of oxygen (or any halogen). It involves the simultaneous change of chemical composition and physical phase, and is irreversible.

Pyrolysis is most commonly observed in organic materials exposed to high temperatures. It is one of the processes involved in charring wood, starting at 200–300 °C. In general, pyrolysis of organic substances produces gas and liquid products and leaves a solid residue richer in carbon content, char.

Pyrolysis is used in the following ways for energy sustenance:

  • Making simple fires whereby, in a wood fire, the visible flames are not due to combustion of the wood itself, but rather of the gases released by its pyrolysis, whereas the flame-less burning of a solid, called smouldering, is the combustion of the solid residue (char or charcoal) left behind by pyrolysis. Thus, the pyrolysis of common materials like wood, plastic, and clothing is extremely important for fire safety and firefighting


Wood Camp fire


  • Making charcoal, whereby Charcoal is obtained by heating wood until its complete pyrolysis (carbonization) occurs, leaving only carbon and inorganic ash. In many parts of the world, charcoal is still produced semi-industrially, by burning a pile of wood that has been mostly covered with mud or bricks. The heat generated by burning part of the wood and the volatile byproducts pyrolyzes the rest of the pile. The limited supply of oxygen prevents the charcoal from burning. A more modern alternative is to heat the wood in an airtight metal vessel, which is much less polluting and allows the volatile products to be condensed.
  • Making of biochar whereby Residues of incomplete organic pyrolysis, e.g., from cooking fires, are thought to be the key component of the terra preta soils associated with ancient indigenous communities of the great Amazon through the pyrolysis of various materials, mostly organic waste. Biochar improves the soil texture and ecology, increasing its ability to retain fertilizers and release them slowly. It naturally contains many of the micronutrients needed by plants, such as selenium. It is also safer than other “natural” fertilizers such as animal manure, since it has been disinfected at high temperature. And, since it releases its nutrients at a slow rate, it greatly reduces the risk of water table contamination


Terra Preta soil of the Amazon


  • Assisting in the disposal of plastic waste whereby Anhydrous pyrolysis can be used to produce liquid fuel similar to diesel from plastic waste, with a higher cetane value and lower sulphur content than traditional diesel. Using pyrolysis to extract fuel from end-of-life plastic is a second-best option after recycling, is environmentally preferable to landfill, and can help reduce dependency on foreign fossil fuels and geo-extraction. A local renewable energy university lecturer developed a prototype pyrolytic plant for a demonstration at ASK show 2012.


Courtesy of Agritech News


  • Production of biofuel whereby Pyrolysis is the basis of several methods that are being developed for producing fuel from biomass, which may include either crops grown for the purpose or biological waste products from other industries. Crops studied as biomass feedstock for pyrolysis include native North American prairie grasses such as switchgrass and bred versions of other grasses such as Miscantheus giganteus. Crops and plant material wastes provide biomass feedstock on the basis of their lignocellulose portions. Fuel bio-oil can also be produced by hydrous pyrolysis from many kinds of feedstock, including waste from pig and turkey farming, by a process called thermal depolymerization(which may, however, include other reactions besides pyrolysis).
  • Assisting in waste tire disposal whereby Pyrolysis of scrap or waste tires provides an attractive alternative to disposal in landfills, allowing the high energy content of the tire to be recovered as fuel. Using tires as fuel produce equal energy as burning oil and 25% more energy than burning coal. An average saloon car tire is made up of 50-60% hydrocarbons, resulting in a yield of 38-56% oil, 10-30% gas and 14-56% char. The oil produced is largely composed of benzene, diesel, kerosene, fuel oil and heavy fuel oil, which can be separated by fractional distillation, while the produced gas has a similar composition to natural gas. Other products from car tire pyrolysis include steel wires, carbon black and bitumen.


Waste Tyres Pyrolysis process


The challenges with this process for fuel production include:

  • High sulfur content in oil produced through pyrolysis
  • Little profit margins in the oil processing. To date, there is no known commercially profitable standalone pyrolysis plant specialized in oil production
  • Inconsistent feedstock

3.  Thermal depolymerisation (TDP)

We will recall our Chemistry 101 in understanding this definition. This is a depolymerization process using hydrous pyrolysis for the reduction of complex organic materials (usually waste products of various sorts, often biomass and plastic) into light crude oil. It mimics the natural geological processes in the earth’s crust thought to be involved in the production of fossil fuels.

Fossil Fuel Formation in the Earth illustration

Under pressure and heat, long chain polymers of hydrogen, oxygen, and carbon decompose into short-chain petroleum hydrocarbons with a maximum length of around 18 carbons. The table below illustrates the output ratios of various waste products:

Feedstock Oils Gases Solids (mostly carbon based) Water (Steam)
Plastic bottles 70% 16% 6% 8%
Medical waste 65% 10% 5% 20%
Tires 44% 10% 42% 4%
Turkey offal 39% 6% 5% 50%
Sewage sludge 26% 9% 8% 57%
Paper (cellulose) 8% 48% 24% 20%


4. Anaerobic digestion

Leave the chemistry class and enter the biology lecture room. This is a collection of processes by which microorganisms break down biodegradable/organic material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste and/or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion. The three principal products of anaerobic digestion are biogas, digestate, and water.

Using anaerobic digestion technologies can be used as an energy source and help to reduce the emission of greenhouse gases in a number of key ways:

  • Reducing or eliminating the energy footprint of waste treatment plants. This is achieved because anaerobic digestion is particularly suited to organic material, and is commonly used for industrial effluent, wastewater and sewage sludge treatment. This simple process, can greatly reduce the amount of organic matter which might otherwise be destined to be dumped at sea, dumped in landfills, or burnt in incinerators.

Pressure from environmentally related legislation on solid waste disposal methods in developed countries has increased the application of anaerobic digestion as a process for reducing waste volumes and generating useful byproducts. If the waste processed in anaerobic digesters were disposed of in a landfill, it would break down naturally and often anaerobically. In this case, the gas will eventually escape into the atmosphere. As methane is about 20 times more potent as a greenhouse gas than carbon dioxide!


Landfill dumpsite in  Dandora, Nairobi


  • Generation of power whereby Methane and power produced in anaerobic digestion facilities can be used to replace energy derived from fossil fuels, and hence reduce emissions of greenhouse gases. Biogas from sewage works is sometimes used to run a gas engine to produce electrical power, some or all of which can be used to run the sewage works. Some waste heat from the engine is then used to heat the digester. The scope for biogas generation from non-sewage waste biological matter – energy crops like sugar cane, food waste, abattoir waste, etc. – is much higher. A vegetable farm in Naivasha, Kenya is using waste vegetables to generate power of up to 2.4 MW of electricity through this process. Incredible!


  • Alternative for vehicle fuel whereby after upgrading with the gas production technologies, the biogas (transformed into biomethane) can be used as vehicle fuel in adapted vehicles. A famous reference is the city of Linköping in Sweden where 100% of public transport uses biomethane and 60% of the vehicle gas is biomethane generated in anaerobic digestion plants…and the other 40%? I have a hunch: Reminds me of the flatula car video; hilarious at the same time mind-blowing. Check the video of the Flatula Car


Public Bus that runs on biomethane in Sweden


  • Making cooking gas whereby by using a bio-digester, which produces the bacteria required for decomposing, cooking gas (biogas) is generated. The organic garbage like fallen leaves, kitchen waste, food waste etc. are fed into a crusher unit, where the mixture is conflated with a small amount of water. The mixture is then fed into the bio-digester, where the bacteria decomposes it to produce cooking gas. This gas is piped to kitchen stove.
Simple Biogas Digester setup

A 2 cubic meter bio-digester can produce 2 cubic meter of cooking gas. This is equivalent to 1 kg of LPG. The notable advantage of using a bio-digester is the sludge/digestate which is a rich organic manure. The use of human waste is applicable but this is a story for another day with all the politics and myths surrounding this concept demystified.

In conclusion, the industrial revolution has given birth to a new man-made resource for our current and future needs; waste. Countries like Sweden have overused and over recycled their primary waste i.e. plastics and have even embarked on an importing spree for waste material. It is my hope that with this knowledge, the capacity of our useful brain will reduce from 80%. I challenge you my reader, to choose a waste problem of your choice in your country and a feasible process to convert it to energy and consequently, to convert this waste to wealth.


“On This Day in Engineering History: 13/1/1942 Henry Ford patented a Soybean car (a plastic car) which was 30% lighter than regular cars. Henry Ford came up with a unique tubular steel framework which he could bolt his plastic panels on. It is believed the plastic was made from Soybean, so that car was also called Soybean car.”


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