1. Introduction Waste is defined as the unwanted and undesirable material produced by residential, industrial, and commercial activities (FullCycle, 2009). The substantial volume of waste created from anthropogenic activities has become a significant issue. Coupled with the current rate of population growth, amount of waste production and its management has become of paramount concern. The acquisition of new waste sites is becoming increasingly problematic, moreover, effectively dealing with waste production has also become a challenge.
A promising solution to the aforementioned issues is waste biomass, which can be used to create energy in the form of biofuel and eliminate the large amount of methane that is produced from landfill gases. An ideal method for obtaining energy from landfills is through gasification of waste (Bullis, 2007). Once municipal solid waste (MSW) is converted to feedstock for molecular breakdown via gasification, the organic components can be used to synthesize ethanol and methanol (2007). Ethanol can be used as a fuel additive or as a primary fuel for cars (Bullis, 2007). From an economic perspective, the process of gasification is considered favorable, not only because of biofuel produced, but also the diversion of a significant amount of waste from landfill sites (Bullis, 2007).
Using this technology, a landfill power plant that produces on average 3 MW of electricity can supply up to 1900 homes, eliminating up to 6000 tons of methane and 18000 tons of CO2 annually (Biofuels, 2010).
2. Waste-to-Biofuel Technology in Alberta: A Partnership between Enerkem & Edmonton Alberta is expanding its energy future towards green, sustainable alternatives, most recently including construction of a state of the art waste-to-biofuel facility, located in Edmonton, Alberta. In 2011, ground was broken to begin construction of North America’s largest industrial waste-to-biofuel facility, a joint project between the City of Edmonton and Canadian green energy company Enerkem, with the aim of increasing diverted landfill waste from 60 to 90% and producing carbon neutral methanol based biofuels (Schubert & Arguin, 2011).
Unfortunately, due to the patenting and evaluation process, it is difficult to explore in detail the technologies which are currently in use at the Edmonton Waste-to-Biofuel facility, however, there are a number of standardized processes by which waste will be converted to syngas (Figure 1). The core process of waste-to-biofuels involves gasification: in this process, municipal non-recyclable waste, termed feedstock, is heated between 530 – 1600 degrees celsius, causing vaporization or “gasification” of the components, producing carbon monoxide and hydrogen gas (Kopyscinski & Schildhauer, 2009). These gasses are then purified or separated and finally converted via catalysis to Enerkem Tailored Syngas – this syngas has a variety of derivative chemicals, including methanol based biofuels (Figure 2) (Lynch, 2011).
It is not surprising that Edmonton, with a historically high level of landfill innovation, has focussed on waste-to-biofuels as an integral element of waste management. The advantages of waste-to-biofuels are many; methanol biofuels & syngas derived chemicals may be sold for a profit, converted to electricity for use in the facility or directly use to power waste management vehicles. Current estimates predict that the Edmonton Waste-to-Biofuel facility will produce 36 million litres of methanol based biofuel per year (Lynch, 2011). A major advantage of waste-to-biofuel processes involves the diversion of waste from combustion-based incinerators, which are high CO2 producers. Gasification produces no additional CO2 beyond potential CO2 stored in syngas, allowing the City of Edmonton to reduce it’s carbon footprint and thus avoid high carbon taxes and gain carbon credits (Bellomare & Rockni, 2013).
3. Future Opportunities for Edmonton Waste-to-Biofuel: The Advanced Energy Research Facility, located at the Edmonton landfill, will explore new waste-to-biofuel opportunities by offering facilities for practical, macro experimentation & research (Lynch 2011). The opportunities for waste-to-biofuels are expanding to include new technologies for higher efficiency gasification, syngas-to-liquids conversion methods & utilization of anaerobic co-digestion byproducts, such as methane, for generation of syngas and as feed sources for gasification electricity. While there are many exciting technologies, we shall study two particularly interesting technologies, which offer greater efficiency of the waste-to-biofuel process and open up new avenues for syngas use.
3.1. Plasma Gasification: Similar to traditional gasification, plasma gasification involves vaporization of waste material into basic molecular structures (H & CO) & converting the inorganic waste into an inert vitrified glass . The advantage to a plasma reactor lies in the feedstock – plasma reactors do not require feedstock to be highly homogenous, thus removing the process of sorting feedstock & improving efficiency. Further, gas composition coming out of a plasma gasifier is lower in trace contaminants than with any kind of incinerator or other gasifier, reducing the need for energy intensive cleaning processes (Gasification Technologies Council, 2013).
3.2. Methane Reformer: A device which can produce syngas using catalyst, it uses oxygen and carbon dioxide or steam in a reaction with methane to form syngas. An exothermic process, methane becomes partially oxidized to produce H2 + CO + H2O (Dufour 2009). Landfills are high GHG methane producers, produced during the process of anaerobic digestion of MSW (Schburt & Arguin, 2011). Methane is commonly removed from landfills via combustion, however, by undergoing reformation, we produce additional syngas & remove excess methane/CO2 from the atmosphere.
4. Discussion The initial goal of waste-to-biofuel technology was to deter landfills from incinerating waste, and to reduce the amount of land sequestered to landfills, but is expanding to include mainstream applications, such as transportation.
In 2008, fossil fuels contributed a staggering 500 EJ to global fuel consumption while biofuel only contributed 50-54 EJ (Rosillo-Calle, 2012). As waste-to-biofuel technology becomes more popular we have exceedingly high expectations. It is projected that this will contribute 56 EJ annually, the equivalent of 135 billion gallons of biodiesel, by 2015, and by 2050, contribute 500 EJ to global fuel consumption (Rosillo-Calle, 2012).
4.1 Benefits In addition to the contribution of biofuels to global fuel consumption, other benefits include a reduction in CO2 emissions, a comparable energy equivalent to petroleum (95%), and their potential role as a viable alternative to petroleum fuel (Stichnothe and Azapagic, 2009). The transportation sector is responsible for almost 20% of the present global CO2 emissions. Current petroleum fuel emits 85g of CO2/MJ (Stichnothe and Azapagic, 2009). This is significantly higher than biofuel-derived waste which emits only 6.1g of CO2/MJ equivalent (Stichnothe and Azapagic, 2009). This offers a substantial reduction in CO2 emissions. As a result, biofuel-derived waste proves that it has the potential to be a competitive fuel alternative to petroleum.
4.2 Drawbacks Drawbacks must also be considered when evaluating the practicality of waste-to biofuel technology, including the ever-fluctuating volume and caloric content of waste, cost of operating landfills, minimal government support, and contradicting information on GHG emissions (Stichnothe and Azapagic, 2009, Lin et al, 2013). Several sources suggest that waste-to-biofuel technology contributes near equivalent GHG emissions due to the operation of gasification equipment, however, this problem could be eliminated by sequestering methane from the landfill and using it to operate the gasification equipment (Rosillo-Calle, 2012).
In the future, waste-to-biofuel technology hopes to gain more support from not only the government but the public and prove that the benefits of this technology significantly outweigh the drawbacks.
5. Conclusion Edmonton, Alberta is currently at the forefront of waste-to-biofuel technology. Implementation of traditional and enhanced gasification techniques, methane reform, as well as a variety of other technologies, may enable higher efficiency production and will contribute to a significant decline in landfill GHG emissions. Although there are drawbacks, we are confident that proper utilization of waste-derived biofuels will enable us to forge towards a future primarily focused on sustainable energy.