Municipal Waste is Not Renewable Fuel
Posted October 26, 2011
Should municipal solid waste (MSW) be converted into energy? Is it a renewable fuel?
Renewable Portfolio Standards (RPS) require electric utilities to generate a certain percentage of electricity from renewable energy sources. Although there are no federal renewable energy standards, as of 2010 twenty-eight U.S states had adopted an RPS standard.
While there is near unanimity among environmentalists, policy makers, and industry officials that recycling should be given priority in how we manage our wastes, in numerous states with RPS standards municipal waste is in fact classified as a renewable fuel and strong lobbying efforts are underway working to expand the number of jurisdictions that classify municipal waste as a renewable fuel.
It would be a mistake to classify municipal solid waste as a renewable fuel without carefully examining the facts. Most of the materials found in MSW cannot be considered a renewable fuel.
Let’s start with a description of what we are dealing with.
Here is the characterization of municipal solid waste according to the EPA, for 2009, the last year for which data are available:
- Plastics: 12.3%
- Metals: 8.6%
- Glass: 4.8%
- Paper: 28.2%
- Food scraps: 14.1%
- Yard waste: 13.7%
- Wood: 6.5%
- Rubber, Textiles, Leather 8.3%
- Other: 3.5%
Each category of waste has its ecologically optimal disposal route, and both public policy and private investments should encourage the routing of materials found in the waste stream to their best use. How should each category of municipal waste be handled for best ecological result? For the reasons summarized below, most, about 75% - 80%, should be recycled.
Plastics (12.3% of MSW) are petroleum. Some are made from natural gas, and a small amount might be made from coal. Although plastics contain about 12,000 Btus/lbs, they are fossil fuels and cannot be classified as a renewable energy source. Petroleum based plastics should be recycled.
Metals (8.6% of MSW) are made from non-renewable ores and minerals. They cannot be classified as a renewable fuel. Nor are they well suited for combustion. Metals are low in Btus (300 Btus/lbs compared with 12,000 Btus/lbs for plastics) and should be recycled. It is as a secondary raw material at the manufacturing sector, not in a combustor, that metals provide the greatest energy benefit.
Glass (4.8% of MSW) is manufactured using non-renewable fossil fuels, and is made from a non-renewable, albeit currently plentiful raw material. Nor is glass ideally suited for energy recovery. It is not high in Btus, containing only 60 Btus/lbs. Glass should be recycled.
Paper, (28.2% of MSW) for many reasons other than those relating to energy calculations, should be recycled. We can debate whether all forests should be considered renewable, but certainly many that are being destroyed for paper making are ecologically rare and biologically irreplaceable. The bio-chemical processes at certain forests currently used for paper making are not always renewable. Moreover, the manufacture of paper involves the use of non-renewable energy, and pulp and paper mills are classified as a “major” source of hazardous air emissions by the EPA. Most consumers would not consider as “renewable energy” or “environmentally preferable” a fuel whose production engenders the emission hazardous air pollutants (or wipes out vast tracts of natural forests, consuming more water than virtually any other industrial process). Paper should be recycled and should not be considered a renewable fuel.
Food scraps (14.1% of MSW) that cannot be recovered for redistribution should be composted or sent to a sewage treatment plant. They are high in moisture, not particularly high in Btus, 2,000 Btus/lbs compared with 12,000 Btus/lbs for plastics, 7,200 Btus/lbs for paper, and 8,000 Btus/lbs for wood. And food waste is high in nitrogen, a GHG pollutant when emitted from waste combustors.
Yard waste (13.7% of MSW) should also be composted. Its Btu value is only 2,800 Btus/lbs, but let’s assume for argument’s sake that it is comprised entirely of woody debris at 8,000 Btus/lbs, (which it isn’t), and can be considered renewable and combusted for energy recovery.
Wood (6.5% of MSW) is generally a renewable resource (see qualification about certain ecologically rare forests referenced above) and is combustible, producing 8,000 Btus/lbs. Moreover, wood recovered from the MSW stream cannot be composted due to contaminants and should not be landfilled due to the emissions it causes. Wood recovered from MSW should be combusted for energy recovery.
Rubber, Textiles, and Leather (8.3% of MSW) are manufactured using fossil fuels and other non-renewable resources. Given the nature of their manufacture, they cannot be considered a renewable fuel despite their high Btu value, ranging from 7,500 Btus/lbs (textiles and leather) to 10,000 Btus/lbs (rubber). These materials should be recycled or composted, and the portion not recovered for recycling can be considered for combustion for energy recovery, but cannot be considered renewable fuel.
So the only portions of the municipal waste stream that can be considered a non-recyclable renewable fuel is wood and a portion of yard wastes. If we inappropriately include all yard wastes in this category and correctly include all wood, they together total 20.2% of the waste stream. That is why NRDC estimates that about 80% of the MSW stream is either recyclable, made from a non-renewable resource, or is otherwise not well suited for combustion due to low Btus (or a combination of all three).
Even if we also unrealistically added in the entire 3.5% of the non-descript “other” category of MSW as being entirely a renewable material, combustible, and not recyclable, that would still only amount to 23.7% of the waste stream as being suitable for combustion, and that includes the assumption that all yard wastes should be combusted, none composted.
Based on the above, the reader should note NRDC’s position that none of the materials in the MSW stream should be landfilled. Minimizing landfill waste by increasing recycling and reducing waste streams is a far better policy than converting trash for energy. Still, capped landfills release significant methane that can and should be captured to produce energy and reduce highly-polluting flaring.
About 12% of all MSW is currently combusted in the U.S. for energy recovery, (as of 2009). Of that amount, NRDC would estimate that more than half of all the material being sent to existing combustors is either recyclable, compostable, non-renewable, or non-combustible. These materials should be diverted away from combustors through a process we call “fuel cleaning”.
Consequently, the least-cost, the fastest, and the most ecologically sound approach to new combustion capacity dedicated to renewable waste is fuel cleaning at existing MSW combustion units.
NRDC estimates that fuel cleaning at existing waste combustors might free up about fifty percent or more of combustion capacity for energy recovery from non-recyclable, renewable, combustible materials.
Until that is done, NRDC does not see the need to discuss the development or permitting of new MSW combustion (or conversion) capacity.
Moreover, we see no basis for classifying MSW combustion as currently practiced as an energy source supplied by renewable fuel.
Wind is renewable.
Sunlight is renewable.
Water is renewable.
The non-renewable petroleum, ores, minerals and other materials that comprise MSW, and that are refined and manufactured through polluting processes that rely on the use of fossil fuels, are not renewable fuels.