January 20, 2007

The Benefits of Conversion Technologies

The Los Angeles City Council hired URS Corporation to make a study, HEALTH IMPACTS OF CONVERSION TECHNOLOGIES IN CALIFORNIA, to identify technologies that would help it reach its landfill diversion goals through conversion technologies. That study was released late last year.

A followup story written by Mr. Predpall has appeared in a recent issue of MSW Management magazine. Within its content is a well-written summary of the benefits of CTs (see below). I have also included his identification of the California opposition to them - which concurs with mine. I highly recommend reading the entire article.


The Time Has Come for Conversion Technologies
by Dan Predpall, V.P. of URS Corp.

The benefits offered by CTs have not been publicized well. The benefits of CTs will be brought into public awareness as entities such as the city of Los Angeles and the county of Los Angeles continue to pursue development of CTs as a way to manage disposal of their residual MSW streams.

The key benefits of CTs are:

Increased Recycling. This benefit is not well recognized. The CTs under development today are being designed to process residuals from materials recovery facilities (MRFs) or trash (residuals after source separation).

These residuals still contain considerable amounts of recyclable materials that can be recovered in pre-processing. In addition, materials produced by the conversion units, such as slag and bottom ash, can be recycled. Some question why the operator would want to remove the recyclables from the input stream. The answer is simple: The facility will earn greater revenues by recycling additional metals, glass, and paper than it will by processing this material in the conversion unit, typically with a loss in overall efficiency. Further, “unrecyclable” plastics that would otherwise go to a landfill are excellent feedstocks for CTs.

Generation Of Renewable Energy. Processing MSW residuals to generate energy or green fuels qualifies in most states as a source of renewable energy. In addition, processing MSW to energy qualifies as a renewable energy under Renewable Portfolio Standards and can be used to create renewable energy credits in some states. If about one-third of the residential MSW collected annually in the city of Los Angeles were processed by CTs, about 50 MW of renewable energy could be produced.

Reduced Landfill Impacts. The byproducts created by CTs are typically very small in quantity, and inert. Therefore, the material that cannot be recycled in a CT and must be sent to a landfill will not result in impacts to the environment. The situation is quite different when MSW (or MSW residuals) are landfilled. Even modern landfills impact the environment via release of methane (a greenhouse gas) not captured by landfill gas collection, air emissions from equipment operating the landfill, and leakage through failures of landfill liners.

Offsets To Fossil Fuel Usage. CTs can generate electricity or green fuels by processing MSW. This in turn reduces the amount of fossil fuels needed to supply the energy requirement of a region. Energy savings result when the entire life cycle of the MSW collection and processing system is evaluated, and all of the energy usage and energy production and recycling benefits are considered.

The energy savings can be significant. For example, according to the California Integrated Waste Management BoardÂ’s (CIWMB) CT report to the legislature, energy savings in the Los Angeles region could be equivalent to a 150 MW power plant (this assumes treating about one-third of the total residential MSW collected annually in the City of Los Angeles).

Lower Air Emissions. The use of CTs can result in reductions in emissions of NOx, SOx, and particulates. For example, NOx emissions, which are precursors of smog, acid deposition, and reduced visibility, are primarily the result of fuel combustion processes. Through the use of CTs, NOx emissions can be avoided by displacing combustion activities and electricity production and increasing the recycling of materials.

Using similar data and assumptions as noted above, the NOx emissions avoided by building CTs in Los Angeles would be equivalent to those emitted from a 1,000-MW, gas-fired power plant.

Reduced Carbon Emissions. Carbon emissions contribute to the greenhouse effect, and, therefore, can lead to climate change. Carbon emissions result from the combustion of fossil fuels and the degradation of organics. Methane emissions from landfills represent a significant source of carbon emissions, since methane has a global warming potential about 21 times that of CO2. The use of CTs can create offsets for carbon emissions through increased recycling, diversion of organics from landfills, and displacement of fossil fuels.

Based upon data in the CIWMB report to the legislature, processing about one-third of the residential MSW collected annually in Los Angeles would reduce carbon emissions by about 1,000,000 metric tons per year.

The overall benefit of CTs is that of increased environmental sustainability. In general, environmental sustainability involves a number of issues, including:

• Reliance on renewable energy
• Improving environmental quality
• Reducing waste
• Conserving natural resources
• Responsible consumption
• Long-term focus

Therefore, the use of CTs closely complies with the goals of environmental sustainability.


As more CT projects are being proposed, opposition from specific groups is growing. One is the global environmental organization that opposes mass-burn incineration. This group has typically opposed CT implementation on the grounds that CTs are actually “incinerators in disguise”. This is untrue; in fact, there are many significant technological differences between CTs and mass-burn incinerators. Another opposition group is the recycling industry. This industry sees CTs as a threat to its business because it claims that CTs will process all MSW, including recyclables. As mentioned above, this is unlikely because, A.) projects under development are using MSW residuals, and B.) the value of residuals as a recycled material is higher than its value for CT processing.


The Los Angeles Bureau of Sanitation just released a detailed assessment of conversion technologies, which can be found at Evaluation of Alternative Solid Waste Processing Technologies .

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AJITH GOPI said...

Very interesting Article!. It will be great if you could give some information about Plasma Gasification Technology for the conversion of MSW (Municipal Solid Wastes). Which wil be the most economical process for these types of conversions? In India wastes are generally dumbed into a suburban location which is creating environmental hazards. We are working for some economical solutions.


Ajith Gopi
View my Renewable Energy Blog at:

C. Scott Miller said...

Plasma Gasification systems are not cheap and really just emerging.

Vinod Khosla has one of the better efforts in the works. I wrote a story about a wood chip conversion facility being planned in Georgia by his venture, RangeFuels (see BIOstock Blog). This technology is very close to what can be done with rural and urban waste.

also has a process for converting syngas to ethanol while co-generating electricity.

Have you looked into anaerobic digestion?