Complex Waste

FastOx® gasification handles the most difficult waste. Learn what these wastes are and how they are processed.


Complex waste requires a myriad rigorous disposal techniques. Many of these methods only partially dispose of these waste streams, and, typically, have a negative impact on the environment.
Sierra Energy’s FastOx gasification systems provide a simple alternative to these complex issues. Our gasification systems can accept these hazardous and complex waste streams without additional feedstock preparation and convert them into electricity and reusable inert stone.



Medical Waste

Medical waste is generated by health care facilities such as hospitals, clinics, physicians’ offices, dental practices, blood banks, veterinary centers, medical research facilities and laboratories. This waste contains hazardous biological contaminants that require stringent handling and disposal methods. Pharmaceutical industry waste also requires intensive disposal to ensure that chemicals do not leach into water and soil at the disposal site. Current disposal methods are very costly due to these high risks.

Medical and pharmaceutical waste have a moderately high carbon content but a low proportion of ash and volatile matter. The typical energy content of medical waste is 15-16 megajoules per kilogram of waste (MJ/kg) or roughly 14-15 million BTUs per metric ton of waste (MMBTU/MT).

FastOx systems can convert this energy into one of following end products from 100 metric tons per day (MTPD) of medical waste:

  • 66 megawatt-hours of electricity per day (MWhe/day)
  • 2,770 gallons of diesel per day
  • 5,000 kilograms of hydrogen gas per day


Hazardous Waste

Hazardous waste comes in many forms and includes discarded commercial products, cleaning fluids, pesticides, and manufacturing byproducts. Hazardous wastes tend to be dangerous and/or toxic and harmful to human health and the environment. The U.S. generated over 35 million tons of hazardous waste each day in 2009. Sierra Energy aims to target select areas of the hazardous waste market.

Hazardous waste is regulated into four classifications according to the EPA:

  1. Listed Wastes
  2. Characteristic Wastes
  3. Universal Wastes
  4. Mixed Wastes


Listed wastes are specific wastes that are known to be hazardous, and are classified into three categories. The “F-list” is for non-specific source wastes that are commonly produced in manufacturing/industrial processes such as cleaning solvents. They are classified as “non-specific” because they come from various sectors of industry. A list of these can be found in the Code of Federal Regulations. The “K-list” wastes are source-specific wastes coming from certain defined industries such as petroleum refining or pesticide manufacturing. These waste streams include certain sludges and wastewater. A list of these wastes can be found in this section of the Code of Federal Regulations. The “P-list” and “U-list” wastes are for specific commercial chemical products including some pesticides and pharmaceutical products. A list of these wastes can be found in Title 40 of the Code of Federal Regulations.

Characteristic wastes are wastes that are not listed wastes, but may still be considered hazardous if it exhibits one of four characteristics defined to be ignitability, corrosivity, reactivity, and toxicity.

Universal wastes are common wastes that are widely generated. Examples include batteries, some pesticides, mercury-containing equipment, and lamp bulbs. Federal regulations for what is considered Universal waste are set forth in this section of the Code of Federal Regulations. however, states have the ability to modify the universal wastes rule and add additional universal waste(s) to their regulations. Be sure to check with your state to see what applies.

Mixed wastes are wastes that contain both radioactive and hazardous waste components. The treatment and regulation of this waste type is complex regulated by the Atomic Energy Act (AEA) and the Resource Conservation and Recovery Act (RCRA). There are several classifications of Mixed waste:  low-level mixed waste (LLMW), high-level mixed waste (HLMW), and mixed transuranic waste (MTRU).




Tires are an ideal feedstock for FastOx gasification due to their high carbon content as a primary feedstock or to supplement waste streams that are low in carbon.
Tires that are recycled into shredded rubber has a limited market. Storing them is a challenge because they take up a lot of space, pose a fire hazard, and are a breeding ground for disease carrying mosquitoes if exposed to rain. Gasifying tires eliminates these environmental hazards and creates energy product.


Construction and Demolition (C&D)


Construction and demolition (C&D) waste is commonly comprised of concrete, wood, linoleum, vinyls, asphalt, gypsum, metal, bricks, paint, glass, and plastics.

FastOx gasification converts these materials into high-value end products without sorting or special pre-treatment, including linoleum and vinyls. The halogenated compounds in chlorinated vinyls (i.e. PVC piping) are converted into compounds such as hydrochloric acid (HCl) or chlorine (Cl) that are separated from syngas during gas cleaning.

Inorganic content melts and is recovered as inert, non-leaching stone for reuse as cement clinker or building aggregate.

Other construction related waste materials that FastOx gasification can readily convert include roofing shingles, carpet remnants, carpet backing, and insulation.

Industrial Waste


Industrial waste is any type of waste produced as a byproduct or result of an industrial process. There is a wide range of materials and substances that come from such practices.

In contrast to most residential waste, industrial waste is usually collected and disposed of by private companies, and commonly in hazardous waste landfills. According to the EPA, American industry generates and disposes of approximately 7.6 million tons of industrial waste each year.

This broad category can be subdivided into three types of waste: medical waste, construction and demolition waste, and specialty waste. Sierra Energy specifically targets medical waste and C&D waste but can also use specialty waste in FastOx gasification. To handle a unique waste stream, Sierra Energy must perform a feasibility study to ensure that the system designs optimizes energy production for that particular industrial source.


Railroad Ties


In the U.S. close to 3,000 railroad ties are used per mile of track. Railroad ties, which are predominately constructed of wood, are carbon-rich materials. Railroad ties typically have an energy content of 18-19 megajoules per kilogram of material (MJ/kg), which is roughly 17 to 18 million BTU per metric ton (MMBTU/MT). While there may be some metals in railroad ties, they are easily recovered in FastOx systems as they collect in a molten state at the base of the gasifier.

FastOx systems can generate the following amount of valuable end products from 100 metric tons per day (MTPD) of railroad ties:

  • 109 megawatt-hours of electricity per day (MWhe/day)
  • 4,600 gallons of diesel per day
  • 8,600 kilograms of hydrogen gas per day


Toxic Waste


Toxic waste is capable of causing injury or death to live organisms. This includes explosive, poisonous, carcinogenic, mutagenic, and bioaccumulative.

Toxic waste is typically generated by industrial processes, but can also be found in household, office and commercial waste streams like batteries, pesticides, and electronic waste. Toxic waste is an acceptable feedstock for FastOx gasification. While these waste streams are not optimal, the gasification process renders the constituents of these toxins into syngas and inert stone product.

Auto Shredded Residue (ASR)

There are approximately 185-200 auto shredder residue (ASR) facilities in the U.S. These facilities process automobiles and large appliances into small, more manageable sized materials (DeGaspari, 1999). Any material remaining after the removal of reusable and recyclable parts is called “ASR” or “auto fluff.”

ASR contains metals, glass, fiber, rubber, automobile liquids, plastics, and dirt. This waste is classified as hazardous waste as it can contain lead, cadmium and rare earth metals as part of printed circuit boards. As a result, ASR generates higher-than-average tipping fees making it costly as well as difficult to dispose of.

ASR also yields high levels of energy (up to 10,500 Btu/pound). Based on these levels, one tonne of ASR could produce approximately one barrel of synthetic diesel. The U.S. generates approximately five million tons of ASR annually, the majority of which is landfilled. If this waste were gasified by Sierra Energy’s FastOx system, it could produce 5 million barrels of synthetic fuels and generate approximately $300 million in revenue (based on a $60 per barrel sale price.) Additionally, tipping fees from this waste stream would amount to $245 million in additional income (based on a national average tipping fee of $54/ton of waste.)

The ASR market is projected to increase given the growing number of cars scrapped each year and the increased use of plastics and computer chips in the production of those cars. Sierra Energy looks forward to new opportunities within the ASR industry to implement FastOx gasification as a way to reduce liabilities and improve the efficiencies of ASR processing.


Electronic Waste (e-Waste)


Electronic waste generally consists of information technology (IT) and telecommunications equipment, such as computers, monitors, televisions, mobile phones, etc.

Electronic waste commonly contains many precious metals and potentially toxic materials, like rare earth metals, lead, and mercury, that must be sequestered and treated separately. This process is costly and carries a high level of environmental risk.

FastOx gasification systems accept eWaste, converting it into energy and capturing the metals and inorganics, which can be extracted and reused.

For more information on eWaste production and current management methods, please visit the Electronics Take Back Coalition webpage.
Further reading:

– Facts and Figures on eWaste and Recycling
UNU Global eWaste Monitoring



Glass, along with other inorganic materials, melts into an inert stone. This output material is safe and can be sold as a construction material, such as cement clinker or road base. It has been tested with the US Environmental Protection Agency’s (EPA) ‘Toxicity Characteristic Leachate Procedures (TCLP)’ by outside laboratories to ensure that it is non-leaching of heavy metals and therefore salable.

With FastOx gasification, glass and other inorganic materials are quickly melted into an inert stone by hot gases rising from the tuyere zone. The inert stone is “tapped” from the existing “tapholes” on the lower side of the vessel. Inert stone products can be sold as a construction and building materials, such as cement clinker and road base. It has been proven by an independent entity to be non-leaching of heavy metals and safe for reuse.

Due to its low carbon content, glass is not recommended as a primary feedstock but is readily accepted as a supplementary feedstock for other high carbon waste streams such as municipal solid waste, biomass, tires, or railroad ties.