When you throw something out, where does it go? Likely, you forget about your trash the moment you bring the garbage cans out to the street. That's not the end of your trash's journey, though. The human race is generating garbage at an alarming rate, and the world's landfills are overflowing. The United States alone produces roughly 220 million tons of waste each year, and approximately 55% of that waste ends up in landfills. As that waste decomposes, it produces methane, which is 25 times more dangerous to the atmosphere than CO2. Thankfully, there's hope for a solution, and it stems from something we've already been doing for hundreds of years: converting our waste to energy.
From Waste to Fuel: WtE Technology
Waste to Energy technology, usually referred to as WtE, is not a new concept. In its earliest beginnings, it was as simple as burning trash. These days, there are several methods for turning garbage into energy. Concerns about global waste production and energy consumption have paved the way for developing alternative energy technologies. WtE, though not as popular as other forms of alternative energy, is a viable solution to both the garbage crisis and our need for renewable resources. WtE technology is quickly evolving, and safer, more environmentally-friendly methods are under development. The market is expected to grow to an estimated $35.5 billion in 2019. In the meantime, extensive R&D is underway to identify affordable, economical ways to implement new WtE methods.
Thermal vs. Biological WtE
WtE can be broken down into two categories: thermal and biological. Thermal WtE is by far the most widely-used method, accounting for 88% of the market revenue in 2013. Traditional thermal methods include incineration, which has faced much opposition because of its high cost and harmful emissions. However, other forms of thermal WtE, like gasification, are more accepted and starting to become mainstream. Biological methods like anaerobic digestion are rapidly gaining interest as well. In fact, biological treatment can be considered the fastest growing WtE technology. The compounded annual growth rate (CAGR) is an estimated 10.9% from 2014 to 2019. Over the next several years, we can expect to see vast improvements in both thermal and biological WtE technology.
Drawbacks of Incineration
The market will continue to face challenges as it expands. Thermal WtE in particular, which makes up the majority of the market, faces a great deal of negative public perception and opposition from environmentalists. The primary concerns are the impacts incineration has on public health and the environment, due to the hazardous byproducts that are created in the process. Gasification, however, does not produce these byproducts. Though the process of gasification has been around since the 1800s, it is just now gaining popularity. Experts suggest that gasification will gain significant traction in North America over the next 5 to 10 years.
Will Gasification Replace Incineration?
The main difference between gasification and incineration is that gasification does not use combustion to produce energy. When municipal waste is incinerated using combustion, the two main byproducts are hazardous flue gasses and ash containing high levels of carbon. With gasification, partial oxidation occurs, but not enough oxygen is introduced to allow combustion. This means that the off-gases created through gasification are significantly less hazardous, as more of the main product can be recaptured. Gasification's main product is syngas, which is used in several ways:
- Can be burned to produce steam and power turbines, which generates electricity.
- Can be used as fuel in a syngas engine.
- May be processed for use in a gas turbine.
The byproduct of gasification is an inert solid waste, commonly referred to as slag. Unlike the ash produced by incineration, slag does not need to be disposed of in a dedicated facility and can even be reused. Of course, the technology has a long way before it will be perfected, but as it is, gasification already offers significant advantages over incineration. Hydrogasification and plasma gasification are exciting emerging technologies which offer better efficiency and virtually no environmental impacts.
Implementing Biological WtE
Biological WtE methods are also gaining a lot of headway. Anaerobic digestion is used to produce biogas, which can be used in the same manner as syngas. Anaerobic digestion uses microorganisms to break down organic materials, similar to the process that occurs during composting. The main advantage of anaerobic digestion is that the process doesn't necessitate the use of oxygen and is organic, meaning it does not produce any hazardous byproducts. In fact, the byproducts of anaerobic digestion can be used as fertilizer. However, this method can only be used to create biogas out of the organic components of municipal waste. Furthermore, Anaerobic digestion is a slow process and has a lower output than thermal WtE methods. A potentially effective waste management plan might incorporate both anaerobic digestion and gasification or another thermal method.
WtE processes have been around long before we ever had a name for them, but have only recently become a serious consideration in the renewable energy market. Perhaps this is due to the ever-worsening garbage crisis we are facing. Will technology catch up in time to offset our wasteful habits? Let's hope so.