Solid Organic Waste Conversion in Small Communities
Alberta generates approximately 4 million metric tons of solid organic waste (SOW) per year, most of which is landfilled. This waste, with significant energy content, decomposes to generate leachates and methane, a potent greenhouse gas. Conversion into valuable products would reduce the amount of SOW landfilled, take advantage of its energy content, and mitigate other environmental problems. A study was conducted to identify the most promising technologies and their providers for converting 10,000 to 100,000 tonnes of SOW per year, generated by or in the vicinity of small and medium communities in Alberta.
The identification is based on Key Intelligence Parameters, reflecting desired technology and provider attributes. A numerical ranking method highlighted the most promising technologies and their providers. The driving forces influencing future developments of SOW conversion technologies were ascertained.
The identification yielded over 700 SOW conversion technologies and their providers falling into two broad categories: biological and thermochemical processes. The ranking method, combined with our expertise, led to an in-depth appraisal of three representative technologies.
While current technologies are expected to undergo further improvements resulting in reduced costs, there is an urgent need for new technologies yielding higher-value products than heat and power.
Alberta produces the highest amount of MSW per person in Canada. organizations operate 124 active landfills (86 MSW landfills and 38 industry sites, often oil and gas related) as well as 35 waste transfer stations. About 40 percent of Alberta’s current active landfills will have to close within the next 10 to 20 years due to capacity constraints. The cost for siting, constructing, and operating new landfills under current environmental regulations will be two to three times greater than existing ones. In addition, gaining social acceptance for new landfills will become increasingly difficult, due to issues such as appearance, odors, leachates, greenhouse gas (GHG) emissions, and impact on property values.
As illustrated by Figure 1, over 57 percent of MSW generated from Alberta municipalities are biodigestible materials, including compostable organics (33 percent), household hygiene products (5 percent), and papers (19 percent). These organic components are a valuable resource, rich in nutrients and energy which can potentially be recovered using biological technologies. In addition, 27 percent of plastics and noncompostable organics have significant energy and chemical values, benefits that can potentially be recovered by thermal and chemical technologies.
There has been a strong trend for diverting organic MSW components from landfills, driven by environmental concerns and underpinned by improving economics of waste treatment. However, modern waste treatment facilities have been largely limited to large urban centers. For example, the city of Edmonton will divert 90 percent of its residential waste from landfills to its waste-to-biofuels facility and a high-solid anaerobic digestion facility will be constructed in 2018. There is a great need to advance waste treatment facilities that address the needs of small and medium municipalities in Alberta and elsewhere in Canada and abroad.
The utilization of solid organic waste for value-added products (heat, electricity, syngas, biogas, digestate, biochar, etc.) will relieve the pressure on Alberta’s existing landfills, and thereby reduce the need for new ones. Additionally, it will mitigate substantial GHG emissions, while enhancing energy security, creating jobs, and supporting the development of Alberta’s rural communities.
The purpose of the present study, commissioned by Alberta Innovates and performed in partnership with Signals Analytics Inc., was to develop high-level intelligence on currently available and emerging SOW conversion technologies, together with their products and byproducts, that have the potential to function effectively under Alberta conditions. Signals provided technology data mining expertise for the study.
The study was carried out in five steps: developing a comprehensive WANT statement, conducting a computer-based key word search, identifying key intelligence parameters (KIP), ranking the technologies, and synthesizing the results. Once steps 1 to 3 were complete, data pertaining to the over 700 technologies and technology providers were tabulated as Excel spreadsheets, together with the corresponding KIP weights and scores. A total of 135 technologies and their providers were found to be in compliance with one or more of the KIPs.
The 135 technologies and technology providers identified were ranked (in descending order) by using an objective function that represented the sum of the normalized numerical products of the KIP weights and scores. The top 20 technologies and their providers were selected for further assessment based on the view that this was a sufficiently large sample to reflect the range of technologies that met the conditions of the WANT Statement. These technologies could be grouped into the following categories:
• Anaerobic Digestion2: A biochemical reaction process carried out in a number of steps, using several types of bacteria in the absence of oxygen and at temperatures typically below 60 degrees Celsius. The biodigestible materials in SOW are converted to biogas, which typically consists of 60 percent methane and 40 percent carbon dioxide (on a volumetric and dry basis), while nondigestible materials and inorganics remain as a digestate. The composition and volume of biogas are functions of the feed SOW. Biogas can be converted into electricity, heat, renewable natural gas, and (using Fischer Tropsch synthesis or other processes) into valuable chemicals, including liquid hydrocarbons.
• Gasification3: A thermochemical process, operating at elevated temperatures (less than 900 degrees C), with a controlled amount of sub-stoichiometric oxygen and/or steam, yielding syngas consisting primarily of CO, CO2, CH4, and H2. Upon clean-up, the syngas can yield value added products, including heat, electricity, and chemicals. The inorganic materials in the SOW feed are converted to ash.
• Pyrolysis: A thermochemical process conducted at intermediate temperatures (400 to 750 degrees C) in the absence of oxygen. Pyrolysis is based on the well-established process of charcoal production and involves reaction times ranging from minutes to hours. Principal products are syngas and various types of bio-oils and biochars. The bio-oils and biochar can further be processed into value-added products.
• Torrefaction: A thermochemical process, similar to pyrolysis, but carried out at lower temperatures (typically in the range of 200 to 320 degrees C) and in the absence of oxygen. The process alters the chemical composition of SOW and leads to a major reduction in moisture content. The release of water vapor and lighter materials (volatile components) result in a biomass product with a higher calorific value than the SOW feed. The solid product is typically a dry, blackened material called torrefied biomass or bio-coal. The volatile components can be used for generating the energy required to run the torrefaction process. The process is particularly well-suited for SOW with low moisture contents.
• Hydrothermal Carbonation4: A thermochemical process for converting organic materials at intermediate temperatures and elevated pressures in the presence of liquid water. The resulting product is a coal-water-slurry. The coal fraction can be separated and differs significantly in chemical and physical properties from the SOW feed. The solid product has a similar calorific value to fossil fuels, such as coal. The produced water may be used for other purposes, such as processing wet (high moisture content) organic waste.
The effectiveness of the initial literature review was constrained by the availability of data in the public domain. To improve the information and to mitigate data gaps, technology providers were sent a questionnaire and, in some cases, contacted by telephone. Examples of important data gaps that needed to be addressed included mass and energy balances of the technologies identified, as well as capital and operating costs. After the completion of the in-depth analysis of the top 20 technologies and their providers, three were selected for further study: Bekon Energy Technologies (anaerobic digestion), Chinook Sciences (gasification and pyrolysis), and Ensyn (circulating fluid bed gasification).
Overview of Technology Landscape
Figure 3 presents the current SOW technology landscape. Some 135 technologies met the desired KIP values to at least some extent; 61 percent and 39 percent of these technologies are based on thermal and biological processes, respectively. Furthermore, 78 percent of the technologies are commercially deployed or deployable, while 22 percent are still in the prototype/precommercial stage. Additionally, 72 percent of the thermal conversion processes are commercial, while the remaining 28 percent are in the prototype/precommercial phase. In the case of biological technologies, the share of commercial and prototype technologies is 86 percent and 14 percent, respectively.
The majority of the technologies identified have large production capacities—42 percent have capacities greater than 100,000 tons per year (TPY) and therefore exceed the needs of small and medium Alberta communities. These larger plants are dominated by the thermochemical conversion technologies, which are more cost competitive due to economies of scale. Only 35 percent of the technologies/technology providers identified fall into the desired capacity range (10,000 to 100,000 TPY) of primary interest to the majority of Alberta’s municipalities. A lack of data availability was evident regarding plant scale—23 percent of the technologies shortlisted had unknown or unspecified capacities. A reason for this is that many of these technologies are in the prototype/commercial stage, and therefore do not report design capacities in the open literature.
It is important to note that the findings of this work are constrained by the availability of data in the public domain, and the degree to which technology providers were willing to share proprietary information. Additionally, the evolving nature of technological innovation presents another caveat to the present findings because the intelligence gathering process focused on technologies available at the time the study was initiated. It does not account for subsequent innovation and new market entrants.
The primary technologies suitable for converting SOW, which consists of 80 percent of MSW, in small and medium Alberta communities, are biological and thermochemical processes. Anaerobic digestion is one of the most promising technologies to convert SOW with high biodigestible content and high water content into valuable products, while preserving plant nutrients. A representative biogas technology provider is BEKON Energy Technology. Thermochemical technologies, represented by gasification and pyrolysis, are particularly suitable for converting dry SOW, such as paper, plastics, and wood waste into syngas and bio-oil. Representative thermochemical technology providers are Chinook Sciences and Ensyn Technologies. All technologies identified through this study require presorting of wastes.
Most commercial technologies identified in this study are designed for large SOW feed rates, typically greater than 100,000 TPY. These plants are dominated by thermochemical conversion technologies. Less than 35 percent of the technologies/technology providers identified fall within the desired capacity range applicable to the majority of Alberta’s small and medium municipalities, i.e. generating 10,000 to 100,000 TPY.
Prospective Technology Intelligence
The aforementioned information and intelligence is evidence-based, and therefore inherently retrospective. It does not address the important question: What will be required of SOW conversion technologies in the future? Responding to this future-oriented question is the purpose of prospective technology intelligence. This question is important because future technologies may not only reflect incremental improvements in current proven technologies, but may also include quite different technologies. Future technologies may also have to reflect changing expectations of society and regulatory agencies.
There is no hard data or information on the long-term future and extrapolation of current trends is of limited value. Insights therefore depend on understanding the forces and their interactions that drive the development, deployment, and commercialization of SOW conversion technologies. The consequences of key forces impacting the future of SOW conversion technologies:
• No single technology will provide a feasible alternative to divert MSW from landfills. Both biological and thermochemical technologies are required to convert all organic constituents of MSW.
• Public awareness of the benefits of source separation of organics and other constituents in wastes will simplify pre-sorting.
• SOW characteristics will increasingly determine the choice of conversion technologies, with:
a. biological processes being favored when the SOW moisture content is high and nutrient preservation or formation is important. Combining anaerobic digestion and composting is a necessary course of treatment.
b. thermochemical processes being favored when the SOW moisture content is low and the production of syngas, petroleum-type liquids and biosolids is desired.
4. The ability of microorganisms to convert all SOW constituents (including specified risk materials, emerging pollutants, such as personal care products, pharmaceuticals, and endocrine disruptors) will be challenging and hard to prove, especially because new products are continuously introduced into the marketplace and become part of SOW.
5. SOW conversion rates by microorganisms are low compared with therm-chemical rates, resulting in comparatively high process residence times and high space requirements. This favors their application in locations where land is readily available and feed rates are comparatively low. However, biological processes are relatively simple and can preserve plant nutrients in organic wastes. Biological conversion technologies therefore have considerable potential for small communities, especially for converting wet-digestible SOW.
6. Thermochemical SOW conversion technologies have the potential of converting a wide range of SOW constituents at high rates. Elevated pressure operations will likely emerge since they have increased conversion rates and hence reduced space requirements. Due to their favorable economies of scale, thermochemical SOW conversion technologies hold particular promise for larger cities.
7. High capital and operating costs, corrosion and materials problems will remain major concerns for both biological and thermochemical conversion processes. The current capital cost for anaerobic digestion is about $260 per metric ton (MT) to $790/MT, and operating cost is approximately $30/MT under Alberta condition, where the electric power market is less than 5 cents per kilowatt-hour.
8. The range of products resulting from SOW conversion will increase. While this can be achieved by Fischer-Tropsch synthesis or similar conversion of syngas and biogas, more direct conversion routes that require less purification and chemical balancing of syngas will likely emerge.
9. Plasma technology, a specific example of thermochemical SOW conversion technologies with high conversion rates and efficiencies, holds considerable promise. At present, it is best-suited for high feed rates that exceed the requirements of most Alberta municipalities. Scaling-down and process complexity issues remain to be resolved.
Reference in this report to any specific commercial product, process or service by trade name, trademark, manufacturer or otherwise does not constitute or imply its endorsement, recommendation or favoring by AI. The views and opinions of the authors expressed in this report do not reflect those of AI.
Author: Babatunde Olateju, Xiaomei Li and Axel Meisen
Alberta Innovates-Energy and Environment Solutions
1 Babatunde, O, X. Li and A. Meisen, 2016, Available Technologies for Converting Solid Organic Waste into Value Added Product in Small Communities – Technology Intelligence.
2 Rogoff, M. J. and F. Screve, 2011. Waste-to-Energy: Technologies and Project Implementation. Elsevier. New York. ISBN 978-1-4377-7871-7.
3 Basu, P., 2011. Biomass Gasification, Pyrolysis and Torrefaction – Practical Design and Theory. 2nd edition. Elsevier. New York. ISBN 978-0-12-396488-5.
4 Antaco Biomass to Energy, Hydrothermal Carbonisation (HTC). http://www.antaco.co.uk/technology/hydrothermal-carbonisation-htc