Generating Electricity from Municipal Solid Waste

We live in a throwaway society that accumulates vast quantities of waste every day. While this comes with pressing challenges, there are also opportunities for professionals including electrical engineers to process at least some of the waste to produce much-needed renewable energy.

According to the U.S. Energy Information Administration (EIA), in 2018 a total of 68 U.S. power plants generated around 14 billion kilowatt-hours of electricity from 29.5 million tons of combustible municipal solid waste (MSW). Biomass, which comes from plants and animals and is a source of renewable energy, was responsible for more than half (about 51%) of the electricity generated from waste. It also accounted for about 64% of the weight of the MSW used. The rest of the waste used was from other combustible materials including synthetic materials made from petroleum and plastics. Glass and metal are generally not noncombustible.

WTE_Plant_Belgium

Waste-to-Energy is now widely accepted as a part of sustainable waste management strategy.

Municipal Solid Waste in the U.S.

Burning MSW is not only a sustainable way to produce electricity, it also reduces the volume of waste that would inevitably end up in landfills. Instead, the EIA estimates that burning MSW effectively reduces waste volumes by about 87%.

But, while more than 268 million tons of MSW are generated in the United States every year, in 2017, only 12.7% of it was burned to recover energy. More than half (52.1%) went to landfill, about a quarter (25.1%) was recycled, and the rest (10.1%) was used to generate compost.

According to a U.S. Environmental Protection Agency (EPA) fact sheet on sustainable materials management published in November 2019, the total MSW generated in 2017 by material, comprised:

  • Paper and paperboard, primarily containers and packaging 25%
  • Food 15.2% (see below)
  • Plastics 13.2% (19.2% of the total materials that ended up in landfill were plastics)
  • Yard trimmings 13.1% (most of this type of waste is composted)
  • Rubber, leather and textiles 9.7%
  • Metals 9.4%
  • Wood 6.7%
  • Glass 4.2%
  • Other 3.5%

Indicating tremendous human waste in its worst form, 22% of the material that ended up in landfill was classified as food. Trashed food was also the product category with the highest landfill rate, at an alarming 75.3%. Nearly a quarter (22%) of materials that were combusted with energy recovery were food, and overall, food was also the highest product category to recover energy, with a rate of 18.4%.

The total MSW combusted to generate energy was made up of the following materials:

  • Food 22%
  • Plastics 16.4%
  • Rubber, leather, and textiles 16.1%
  • Paper and paperboard 13.2%
  • Wood 8.4%
  • Metals 8.6%
  • Yard trimmings 6.2%
  • Glass 4.3%
  • Other 4.3%

Generating Electricity from MSW

There are a variety of technologies for generating electricity from municipal solid waste, but in the US the most common system involves mass burning of MSW in a large incinerator that has a boiler that produces steam, and a generator that produces electricity. Another entails processing MSW into fuel pellets for use in smaller power plants.

Waste materials destined to be processed to generate electricity

Generating electricity in mass-burn WTE plants is remarkably straightforward and follows seven basic steps:

  1. The MSW is dumped out of garbage trucks into a large pit.
  2. A crane with a giant claw attachment is used to grab the waste and dump it into a combustion chamber.
  3. The waste, which now becomes the fuel, starts to burn, releasing heat.
  4. The heat that is released turns water in the boiler into high-pressure steam.
  5. The steam turns the turbine generator’s blades and produces electricity.
  6. The mass-burn plant incorporates an control system to prevent air pollution by removing pollutants from the combustion gas before it is released through a smoke-stack.
  7. Ash is inevitably produced in the boiler and the air pollution control system, and this has to be removed before another load of waste can be burned.

While the volumes burned as fuel in different plants vary, for every 100 pounds of MSW produced in the US, potentially, more than 85 pounds could be burned to generate electricity.

Of course, the USA isn’t the only country that uses waste-to-energy plants to generate electricity from MSW. And in fact, when compared to a lot of other countries, the percentage of MSW burned with energy recovery in the U.S. is minimal. At least nine countries are named by the EIA as bigger producers of electricity from municipal waste. In Japan and some European countries, for instance, there are fewer energy resources and not much open space available for landfills. So generating electricity from MSW is an obvious opportunity.

The four leading nations identified by the EIA as burning the most MSW with energy recovery are:

  • Japan 68%
  • Norway 54%
  • Switzerland 48%
  • France 35%
  • The United Kingdom 34%

One thing’s for certain, the percentages are all set to continue increases globally as the move towards sustainability gains momentum. And U.S. percentages are going to increase too.

Obstacles in Implementation of Waste-to-Energy

The biggest obstacle to the implementation of Waste-to-Energy lies not in the technology itself but in the acceptance of citizens. Citizens who are environmentally minded but lack awareness of the current status of MSW-to-energy bring up concerns of environmental justice and organize around this. They view WTE as ‘dumping’ of pollutants on lower strata of society and their emotional critique rooted in the hope for environmental justice tends to move democracy.

Spittelau-Incinceration-Plant

An advocate of public understanding of science, Shawn Lawrence Otto regrets that the facts are not able to hold the same sway. Some US liberal groups such as the Center for American Progress are beginning to realize that the times and science have changed. It will take more consensus on the science and the go ahead from environmental groups before the conversation moves forward, seemingly improbable but not without precedent.

Spittelau Waste-to-Energy Plant

The Spittelau waste-to-energy plant is an example of opposition coming together in consensus over WTE. It was built in Vienna in 1971 with the purpose of addressing district heating and waste management issues. Much later awareness of the risks of dioxins emitted by such plants grew and the people’s faith in the technology was called into question.

It also became a political issue whereby opposition parties challenged the mayor on the suitability of the plant. The economic interests of landfill owners also lay in the shutting down of the WTE facility. The alternative was to retrofit the same plant with advanced technology that would remove the dioxins through Selective Catalytic Reduction (SCR).

Through public discussions it appeared that the majority of the people were against the plant altogether though thorough studies by informed researchers showed that the science backs WTE. The mayor, Helmut Zilk eventually consulted Green Party members on how to make this technology better perceived in the eyes of the people, and asked the famous Austrian artist Freidensreich Hundertwasser, who was a green party member to design the look of the plant.

Freidensreich Hundertwasser after carefully studying the subject wrote a letter of support, stating his belief as to why WTE was needed and accepted Mayor Helmut Zilk’s request. Later public opinion polls showed that there were a majority of people who were either in favor of or not opinionated about the plant, with only 3% in outright opposition of the plant.

Polarized Discussion

Waste-to-Energy or recycling has kept public discourse from questioning whether there may not be intermediate or case specific solutions. This polarization serves to move the conversation nowhere. For now it can be agreed that landfills are devastating in their contribution to Climate Change and must be done away with. The choice then, of treatment processes for municipal solid waste are plentiful. If after recovery of recyclable materials there remains a sizeable waste stream the option of waste-to-energy can be explored.

Primary Considerations

  • Environmental implications (i.e. CO2 emissions vis-à-vis the next best fuel source) given the composition of the local waste stream. If the waste stream consists of a high percentage of recyclables the more sustainable waste strategy would be to ramp up recycling efforts rather than to adopt WTE,
  • Likely composition and variation of the waste stream and the feasibility of the technology to handle such a waste stream,
  • Financial considerations with regards to the revenue stream from the WTE facility and its long term viability,
  • Efforts at making citizens aware of the high standards achieved by this technology in order to secure their approval.

Note: This excerpt is being published with the permission of our collaborative partner Be Waste Wise. The original excerpt and its video recording can be found at this link