While the terms “renewable energy” and “clean energy” are often substitutable, they don’t necessarily mean the same thing. Energy sources such as wind, water, and sunlight are “renewable” because they do not get exhausted. Unlike fossil fuels, such as oil, natural gas and coal, which do not get replaced, renewable energy regenerates naturally relatively quickly.
Clean energy, on the other hand, refers to any source of power that does not pollute or harm the environment and focuses on reducing carbon emissions as a method of counteracting “dirty energy.” The burning of fossil fuels such as coal generates dirty energy, and as a result, releases carbon pollution which warms the atmosphere and alters the global climate.
The Thin Line Between Clean and Renewable
So, are there clean energy sources that are not renewable? Yes. Nuclear energy often falls in this category because it does not create carbon emissions. However, classifying nuclear energy as clean is relative because it generates radioactive waste. This waste has to be cooled and stored safely to prevent the escape of radiation into the environment.
Conversely, not all renewable energy is clean. For example, some geothermal energy processes can be harmful to the environment. Also, biofuels are controversial because land that could grow food ends up growing feedstock plants for ethanol or biodiesel. Biofuel demand can also lead to deforestation.
These exceptions notwithstanding, clean and renewable energy are the same in most cases. For instance, Solar systems capture the sun’s energy and convert it into electricity to heat or cool buildings, heat water, or power devices. Solar is clean because it does not emit any greenhouse gases, and it is renewable because it will exist until the life of the sun ends in a supernova. Other examples of clean and renewable energy include wind, hydro, and tidal.
Waste-to-Energy Conversion Pathways
Waste to Energy (WtE) is a process where the primary treatment of waste generates electricity and heat. It is also the processing of waste into a fuel source. Waste generation rates are affected by socio-economic development, degree of industrialisation, and climate. Generally, the amount of solid waste produced in an area is proportional to the urban population’s economic prosperity and percentage.
A host of technologies are available for realising the potential of waste as an energy source, ranging from simple systems for disposing of dry waste, to more complex technologies capable of dealing with large amounts of industrial waste.
Read Also: Experts raise flag over neglect of renewables
The three main pathways for converting organic waste material to energy are thermochemical, biochemical and physicochemical.
• Thermochemical Conversion: For many years, combustion has reduced waste volume and neutralised some potentially harmful elements. Combustion can create an energy source only with the inclusion of heat recovery. Thermochemical conversion processes include incineration, pyrolysis and gasification.
• Biochemical Conversion: The biochemical conversion processes work well for wastes having a high percentage of biodegradable organic matter and high moisture content. Anaerobic digestion is a reliable technology for the treatment of wet, organic waste.
• Physico-chemical Conversion: The physico-chemical technology involves various processes to improve physical and chemical properties of solid waste. The combustible fraction of the waste gets converted into high-energy fuel pellets for steam generation.
The United States as a Case study
In some states in the US, WtE plants qualify as renewable energy by law, and some proponents say the US should build more, as Europe already has. Even though these WtE facilities require a significant capital investment, they are typically the cornerstone of municipal infrastructure in the communities in which they are located. In addition to managing post-recycled waste, these facilities provide excellent economic benefits to communities. Governmental Advisory Associates’ research highlights that the waste-to-energy industry supports more than 14,000 well-paying jobs with nearly $890 million in total compensation.
Today throughout the US, 75 plants allow municipalities to reduce their greenhouse gas emissions and the amount of waste sent to landfills, while also financially benefitting the communities they serve. Unfortunately, despite their economic and environmental benefits, they cannot compete favourably with low electricity prices. The US Waste to Power industry’s economic constraints are compounded by regulatory demands and community opposition to the technologies.
Looking at the Nigerian Waste-to-Energy Context
Over the past two decades, the pursuit for reliable and sufficient power supply in Nigeria has brought about a surge of interest in renewable energy generation, particularly from wind, solar, hydro and biomass resources including municipal solid waste (MSW). According to a study published in the Journal for Cleaner Production, waste-derived energy raises unique interest because of the magnitude of benefits to environmental protection and socio-economic advancement. Their findings show that the electricity generation potential for the different states in Nigeria varied from 31 – 205 megawatts (MW), depending on the state’s waste generation capacity. Findings in the journal estimated the country’s annual electricity generation potential from MSW to be 26,744 gigawatt-hours (GWh) per year, with 89% of the states having sufficient generation capacity at minimum regulatory electricity generation requirement of 50 MW. However, based on current realities such as poor waste collection efficiencies, Nigeria’s exploitable WtE capacity from MSW was below 3800 GWh/year, with all the states having less than 50 MW capacity.
Nigeria has a few WtE facilities across the country. One of these is the food-waste-fed Ketu Ikosi Biogas Project in Lagos. Lafarge Africa also launched its waste management brand, Geocycle in Nigeria in 2018 to manage waste through a co-processing technology that enables the recovery of energy and recycling materials. The few other existing waste-to-energy plants are small scale and mostly connected to agricultural communities. One of these is the 20kW Ajima Farms Waste-to-Watt project. The plant serves Rije Area in Kuje, a community within the Federal Capital Territory. The plant requires 1,2 tonnes of organic waste daily to produce 20kW-hr of electricity.
Nigeria currently has no MSW-fed WtE plant. To date, only one WtE developer of note has successfully constructed and started operating a major waste-fed power project in Africa – the $120m Reppie plant in Ethiopia.
Is Waste Energy Clean or Renewable?
When it concerns energy-from-waste, defining what qualifies as renewable energy can be a difficult exercise. Some argue that renewables are restricted to energy from natural resources, while others believe that renewable means any resource replaced as it is being used. For example, some do not consider landfill gas to be renewable because it lasts only about 20 to 30 years, depending on the site. In the purest form of definition, this resource is not renewable. But looking at the larger picture, waste will always be generated in some form globally. Since energy can be generated from this waste when concentrated in landfills, it can be classified as renewable.
According to the Alternative Energy Group, the enormous increase in the quantum and diversity of waste materials generated by human activity. This enormous increase and their potentially harmful effects on the general environment and public health have led to growing awareness about an urgent need to adopt scientific methods for safe disposal of wastes. While there is an obvious need to minimise waste generation and reuse and recycle them, the technologies for recovery of energy from waste can play a vital role in mitigating the problems. Besides recovery of substantial energy, these technologies can lead to a substantial reduction in the overall waste quantities requiring final disposal, which can be better managed for safe disposal in a controlled manner while meeting the pollution control standards.
Research has also shown that WTE facilities produce clean, renewable energy while reducing waste volume by 90 percent, making them a great option for communities seeking the most advanced technology to manage their post-recycled waste. Waste-to-energy is a reliable and renewable form of energy that has become the basis for many successful solid waste management systems in developed countries. It is also a worthwhile option to supplement energy in countries where the energy produced is inadequate, or the energy costs are high. Recycling and reducing excessive consumption should be our priorities. But as long as people keep producing waste, generating energy should be an important part of any waste management strategy.
