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Three Waste-to-Energy Solutions

RP Siegel | Monday October 15th, 2012 | 16 Comments


What is this stuff we call waste?

We all add to the waste stream every day – probably without thinking much about it. According to Webster, waste is “damaged, defective, or superfluous material,” also considered, “an unwanted by-product,” or refuse, which is defined as “a worthless or useless part of something.” In other words, it is something that was created that no longer has any use for anyone. In a given day an individual’s waste stream might include packaging from a new purchase, discarded coffee cups, take-out food containers or used up toothpaste tubes – just to name a few once-valuable items that become waste every day.

So if we have a waste problem, which we do, (Americans generate some 200 million tons of waste per year) it appears that there are two ways to address it. First, stop creating the waste in the first place, or, second, find a way to to turn that waste back into something useful. In other words, turn it into a raw material for some other process.

Janine Benyus, author of Biomimicry, explains that nature merges waste and raw materials – fallen leaves turn into fertilizer for new saplings in the forest, for example. Benyus calls this “waste equals food.” If we are to become sustainable, she suggests we need to follow nature’s lead.

I don’t expect we’ll ever find ourselves eating municipal waste, but since we also have an energy problem, converting that waste into energy would certainly be the next best thing. Besides, what is food after all, if not a source of energy?

Waste-to-energy is already happening today and there are many technologies to make the process cleaner and more efficient. Let’s have a look.

1) Waste incineration

The simplest approach is to just burn the stuff directly. These basic incinerators are in operation in over 1000 plants around the world, mostly in Europe and Asia. After some presorting, the municipal solid waste (MSW) is dumped into a bunker where it is burned. The heat is used to create steam, which generates electricity, and the exhaust is processed by an extensive air pollution control system (here’s a video).

Many waste items contain mixed materials (e.g. metal and plastic), which are difficult to separate and can’t be economically recycled. So the only disposal options for these items are incineration or landfill. At least with incineration, some value is extracted in the form of energy. However, there are questions about the resulting emissions from incineration plants. Greenpeace and other groups have long fought these plants, raising concerns over heavy metals, as well as dioxin and furans, and new pollutants formed during the incineration process. They also give off CO2 and other greenhouse gases that contribute to climate change – so emissions capture systems must be very robust.

Waste incineration also produces a waste product of its own – ash – which must be treated as hazardous waste. However, as the capture technology improves, these risks are being mitigated and managed. In super-green Denmark, incineration plants are very popular and effective – only 4 percent of all trash ends up in landfills, compared with 54 percent in the U.S.

Should waste incineration be considered a renewable energy source? While the generation of MSW seems endless, incineration is first and foremost an attempt to manage the waste problem and reduce landfills, rather than a truly renewable fuel, since it does create some waste of its own. And while these plants produce cheap energy and reduce the volume of waste sent to landfills, both good things, ultimately it would be better for society to produce less trash in the first place.

2) Landfill gas

There are low carbon alternatives to waste incineration. The first is relatively common landfill gas collection. As organic matter in landfills decomposes, it gives off several gases, primarily methane. Methane is the principal component of natural gas. It is also a potent greenhouse gas, twenty times stronger than CO2. When this gas is collected it can be used as a power source, rather than a contribution to global warming.

When methane is burned to generate electricity, the byproduct is CO2. Although CO2 has global warming impacts of its own, the conversion is actually much better than you might think. First of all, CO2 is preferable to methane because of its lower heat-trapping effect. Beyond that, if the volume of trash in the landfill is similar to the volume of food and other products that are being grown above ground (capturing carbon as they grow), the process can essentially be considered carbon neutral.

Some landfill gas projects simply siphon off the methane, others heat the waste in a pyrolysis process giving rise to syngas. This process can spin off useful byproducts and does not produce the hazardous waste associated with incinerator ash. North Carolina’s ReVenture Park is an example of such a project.  One problem facing landfill gas projects right now is that natural gas prices are at historic lows which make the financial return on investment much less attractive than it was a few years back.

3) Waste to ethanol

So far, all of these waste-to-energy concepts have led to electric generation. But there are lots of ways to make electricity renewably. What about liquid fuels to power transportation? Waste can provide an alternative to gasoline, diesel fuel and biofuels.

Pulped cellulose material

But wait, couldn’t waste be a biofuel? Well, it turns out that municipal solid waste contains roughly 18 percent food and 40 percent organic matter. So maybe that’s not such a crazy idea. Craig Stuart-Paul, CEO of Fiberight, located in Catonsville, Maryland, certainly doesn’t think so. Several years back they developed a method to separate organic from inorganic waste.  Working with Novozymes, they came up with a way to break down organic pulp from packaging materials such as cardboard into cellulosic ethanol. Considering that cardboard will sit untouched in a landfill for many years without breaking down, the fact that Fiberight can convert it into cellulosic ethanol in just a few days is quite impressive.

Once they receive the municipal waste, they separate the organic from the inorganic waste. Then they remove the recyclables. Finally, they extract the organic pulp from the liquid. The liquid is used to produce compressed natural gas (CNG), which many garbage trucks are beginning to use as fuel. This means the trucks can fuel up when they come to dump the trash. In the future, the CNG will also be used to power the plant itself. But the real novelty is in the final step where the remaining pulp is converted, using their proprietary process, into cellulosic ethanol. All told, 80 to 85 percent of everything that comes in is put to some use and thus avoids the landfill. The process is quite unique. According to Stuart-Paul, “We can take a [disposable] diaper, strip off the plastic, and recover the cellulose and the poo that’s in it,” converting the one to ethanol and the other to biogas.

Conversion process

This is already happening in a “pre-commercial reference plant” in Lawrenceville, Virgina, with an annual capacity of one million gallons of ethanol. This process will move to a full-scale plant in Blairstown, Iowa, next year, which, serving 225,000 people living in the three surrounding communities, can produce 6 million gallons of ethanol plus an additional 4.5 million (diesel equivalent) gallons of CNG.

Suddenly, our municipal material recovery facilities (MRF), which used to handle only recyclables, can begin to handle all waste, in what is called a “dirty MRF,”  and our waste stream begins to resemble something that you might expect to find on a forest floor where trash equals food and nothing is wasted.

Images Courtesy of Fiberight

RP Siegel, PE, is an inventor, consultant and author. He co-wrote the eco-thriller Vapor Trails, the first in a series covering the human side of various sustainability issues including energy, food, and water in an exciting and entertaining format. Now available on Kindle.

Follow RP Siegel on Twitter.


▼▼▼      16 Comments     ▼▼▼

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  • Dave Shires

    The waste to ethanol idea sounds incredible. Is it actually profitable though? ie – can if be sold at a price competitive with other fuels? or, better yet, can a city/municipality save tax money by letting a company come in and handle their waste for this purpose?

    • RPSiegel

      The business model seems very sound to me. First, the municipalities pay them to accept the trash. Second, they sell CNG to the garbage trucks that fill up right there. Then they sell the ethanol, plus any other material of value that they can extract. Of course, fuel prices are unpredictable. But he said that they are pushing their productivity to the point where they could make money even if they had to pay for the raw material.

  • Ghuerta

    One thing you didn’t mention directly but alluded to is anaerobic digestion. The methane collected during the process is converted into biogas which then can be used as electric power or further processed to make biodiesel or biofuel as well.

  • Horsey

    I’m surprised this isn’t already much more common. I guess it’s a matter of the inertia from gasoline still being relatively cheap (at least in the US).

  • ZagoZana

    Please contact Jerry Horton, previous owner of “Sweetwater” at; JWHorton@frontiernet.net
    He would like to see what you are doing because he is expanding into new areas that may interest you.
    Read up on him and give him a call.
    He’s very approachable.

  • http://twitter.com/Tia_t Maynex

    Maynex has a nice waste to energy system that is small enough to fit in most vehicles. It’s the H2-Flex, and it will turn your waste pee and aluminum foil into very clean hydrogen gas.

  • Doug Anderson

    The more we can recycle or reuse, the less we have to rely on virgin resources and all the energy required to prepare these raw materials for manufacturing. Waste to energy and many other waste technologies fail to account for the fact that this energy is largely lost when a product is burnt, digested or whatever. Agressive recycling is the only technology that preserves this energy and is hence the most efficient. San Francisco recently achieved 80% recycling and other communities are close behind. Companies trying to sell fancy waste technology prefer to view garbage as a useless amorphous mass but in fact everything in the garbage stream is recyclable and all of it is being recycled somewhere.

  • http://www.facebook.com/shlomo.dowen Shlomo Dowen

    Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, waves and geothermal heat, which are renewable (naturally replenished). I don’t see garbage on the list…

    • Darius

      But why shouldn’t garbage be on the list? As long as we’re generating waste, or to be correct, compost and other, ahem, material, that we currently flush, doesn’t it make perfect sense to use it?

  • http://www.facebook.com/alan.watson.902266 Alan Watson

    Why can’t we follow nature’s lead with “waste equals food”? Plastics, which are oil based and non-renewable, are essentially the only part of the waste stream which can be incinerated but can’t be composted or digested – and burning plastics in inefficient and expensive incinerators simply doesn’t make environmental or economic sense.

  • Dorothy

    Its not renewable energy – they need to burn ‘calorific’ wastes ie plastics, as there is not enough calorific material in the residual waste so they need to bolster it. Burning plastics is not renewable energy. The public has never been informed of this or about waste contracts which are cunningly written -( thats in our waste contract here in Derby which no-one really knows about) Sometimes, its called residual waste incineration, yet the plastics they need to burn will be those which can be recycled instead. Burning plastics – which RRS/Shanks also admitted to at the inquiry – of course produces dioxin which we are to be reducing production of, not increasing, (Persistent Organic POllutants Treaty signed by UK amongst other countries) and supposed to be teaching women and children about it. Then theres the 172,000 tonnes of CO2 to be produced each year from the incineration plant, as well as nitrogen dioxide worsening the AQMAs, interfering with recycling, creating fewer jobs (59-112 recycling jobs per 10,000 tonnes of waste resources as opposed to 10 incinerator jobs – DEMOS) plus exposing incinerator workers to DNA damge, elevated levels of mercury…..it never rains, but…………………

  • Bharati Chaturvedi

    Let me share the story from the developing world. I work in India. Incinerators, and now, waste to energy plants are displacing hundreds of the most poor urban dwellers, who salvage and recycle our plastics, glass and metals, out of work, and forcing their children back to work, out of school. Plus, dioxins are a huge threat here as everywhere. It makes no sense to set up plants like this, the human and societal cost is massive and irreversible. It increases poverty.

  • Mariel Vilella

    Successful examples of Zero Waste projects around the world (Hernani – Spain, San Francisco, TaiWan, Capannori – Italy, Flandes – Belgium…) have achieved 80-90% diversion rates from landfills – no incinerator will run with 10-20% of MSW, and it’d be just too expensive to make it worth it. The business model will only work if the incinerator burns recyclable materials, which will essentially be a waste-of-energy. For the residual waste – let’s engage in ecodesign, extended producer responsibility, boycott products campaigns…whatever it takes not to produce anything that cannot be reused or recycled. And, by the way…considering energy from incinerators as renewable energy is already a pretty old greenwash fallacy that is no longer credible amongst responsible waste and energy experts. Cheers.

  • Josh Schlossberg

    Any form of incineration and/or combustion releases toxic air pollution.

    If you think trash incineration is green, I urge you to look at the science: http://energyjustice.net/incineration

    Clean energy doesn’t come out of a smokestack.

  • Rene D. Pineda, Jr.

    Renewable energy can never come from burning domestic waste because these resources won’t self-replenish. It’s simply unsustainable and will hasten de-energizing our planet because more energy is required to produce goods from non-renewable resources than what can be recovered by incinerating the waste therefrom.

    Simply put, incinerating waste disguised as a purportedly sustainable energy recovery is an indictment to human insensitivity and indifference to the welfare of the next generations. It perpetuates avarice with complete disregard to humanity’s challenge how not to waste.

  • Corey Johnson

    All of these are waste disposal methodologies which produce energy as a beneficial side-product, not the other way around. They are waste treatment systems, not power plants. Power just happens to be a by-product of treating waste. Incineration is the only practical player here, the only one that’s stood the test of time as many fly-by-night firms have tried over the years to treat waste and extract energy using all kinds of Rube Goldberg machines, most of which result in the waste being taken through the exact same chemical reactions as it would in incineration.

    The European Union approach of disincentivizing landfill is the way to go here. In cases like India, it allows waste pickers to continue working. It allows recycling, incineration, composting, and other treatment technologies to compete. You’ll find that recycling works best for some things, incineration best for some, and composting best for others. Incentivizing WTE based on energy production will ensure that waste will be inappropriately treated and resources will be wasted as people try to cash in on the energy subsidies.

    Landfill gas systems serve only to mitigate some of the problems of landfilling. It is not a treatment technology and should not be incentivized in any way other than to mitigate the methane emissions from existing landfills.