Food Waste Can Fuel its Own Collection


Is food waste-to-energy technology sustainable? There was a lot of publicity last year about ethanol requiring more energy to produce than you can get from the fuel. Is biogas from food waste a better deal for the environment? The answer is yes. It turns out that a tonne of food waste produces enough biogas to not only fuel the collection vehicle that picks it up, but also provide enough energy to power the biogas production process (one tonne of food waste = 1.1 tons). In other words, the food waste will collect itself and turn itself into clean energy. All we have to do is supply the right equipment and feedstock. Sounds sustainable to me!

Here are the numbers:

· Your average garbage truck is a real fuel hog. It gets only about 2.8 miles or 4.5 km per gallon of diesel fuel, which is the fuel that most garbage trucks use.

· On an energy content basis, one gallon of diesel fuel is equivalent to about 4 cubic meters of natural gas.

· Some biogas digesters will produce about 65 cubic meters of natural gas equivalent from each tonne of food waste. The actual biogas production is about 100 cubic meters per tonne of waste, but it’s lower in energy content than natural gas so I’ve converted it to natural gas equivalent based on its energy content. This biogas production estimate is based on data collected from European plants that have been using this technology for several years. A similar plant, to be located in Richmond, BC, near Vancouver, will be the first in North America.

· Doing the math, 65 divided by 4 times 4.5 equals 73 km per tonne of food waste, which means we can make the garbage truck go 73 km for each tonne of food waste we put into that same garbage truck.

· Since a typical planned round-trip distance for collecting food waste may be only 30 km, there is energy to spare.

You may now say, ha! You haven’t considered all of the energy needed to process the gas that comes out of that food waste and pressurize it for those high-pressure CNG tanks on that garbage truck. Well, the ever-vigilant California Air Resources Board (CARB) has considered this. In a report released last year, CARB analyzed the total energy requirements for treating and pressurizing the gas to CNG fuel-tank pressures. They found that the total energy required, including consumption of electricity and the biogas itself for gas processing and pressurization was 317,000 BTU per million BTU of CNG produced. In other words, processing and pressurizing consumed about 32% of the gas. Estimates of the energy consumption of the digester plant itself, including all heating, lighting, pumps, fans, and motors would consume another 18% (see note 1), bringing the total consumed to about half the gas produced. This means the typical garbage truck can go about 36 km for each tonne of food waste that is fed into the system. But we only need to drive it 30 km. There is still energy to spare (see note 2).

Of course, biogas also emits much less greenhouse gas than diesel fuel while powering those garbage trucks. The same CARB study cited above found that the processing and compression of biogas reduces emissions of greenhouse gases. According to CARB, each tonne of food waste processed would save 100 kg CO2e (carbon dioxide equivalent). In addition, the diesel emissions saved in that 30 km round trip will save another 67 kg of CO2e.

These calculations illustrate how biogas from food waste is renewable energy. The plant near Vancouver may produce electric power for the grid, rather than CNG. Future projects, perhaps in your community, may produce CNG for vehicle fuel, an exciting prospect for closed loop equations whereby trucks are powered by the food waste within.

NOTE 1: Most of this energy is electrical and would not actually be produced by the biogas if we are making CNG for vehicles, but it is included for comparison to other renewable energy sources. Biogas conversion efficiency assumed is typical for small gas-to-electricity projects.

NOTE 2: In fact, a typical garbage truck can carry more than our hypothetical one tonne of organic waste. Typical capacities are 4 tonnes or even more. But on most trips the typical truck is never filled to capacity. And the average load is always less than half of the full load, because the truck starts the collection trip empty. The average load probably is more than one tonne, but we’re being very careful here not to overstate our case, and using the one tonne simplifies the presentation. But some waste is likely riding for free in our example, meaning we have more energy to spare.

Article by Tom Kraemer, Vice President for Project Delivery at Harvest Power. The company develops, builds, owns and operates next-generation organics recycling facilities that harvest the renewable energy, nutrients, and organic matter from discarded organic materials using best-in-class technologies for composting, anaerobic digestion, and biomass gasification.



Have any Question or Comment?

9 comments on “Food Waste Can Fuel its Own Collection

Have you ever run a comparison of the food wastes being used as a fertilizer instead of fuel? Comparing all of the carbon footprint for a ton for ton of petroleum-based fertilizer and using the food as a replacement for fertilizer should have some interesting results.

Additionally, should the food waste be fermented (as in the EM Bokashi method), the resulting NPK in the fermented food wastes would be in bio-available forms, meaning they are non-leaching (non-polluting). Odors and vectors are taken care of in the fermentation process. In all, the process is more efficient that composting and does not produce greenhouse gases such as methane in the process.

In the USA, food wastes are being hauled much further than 30km. In many cases it is being 30 to 80 miles in one direction. Examples for this are in New York City area and San Francisco and Seattle. The conversion numbers would not work unless a new facility were put in place closer to the source. Odors alone would prevent that from happening.

In areas where the round-trip distance is 30km or less, this sounds like a good conversion. However, the numbers still only work for the waste side of the food, not the energy that goes into the production of the foods in the first place.

Nice calculation on food to fuel, Tom! RT @CleanTechies Food Waste Can Fuel its Own Collection | CleanTechies Blog http://bit.ly/ckCbpi

This comment was originally posted on Twitter

Tom Ward

Great work, but overly cautious regarding the truck trip miles and carrying capacity. Being conservative is well and good, but regarding Note 2, the cautiousness leads to an error.

First, I’ll assume that the trucks 4.5km/gal fuel economy is for average, typical duty. That is, this includes empty outbound, sitting idle, power needed to lift loads and compress them, and driving around with the load that varies and increases during the route, then returning to the start point.

Back to Note 2.

What is relevant here is the amount of food waste in the truck at the end of its route, NOT the average load during the route. For example, if the truck would typically return with 3.0 tonnes, then we travel 30km/3.0t = 10km/t. At 4.5km/gal that means (10km/t)/(4.5km/gal) = 2.22gal/t. Multiplying by 4 m^3 nat. gas equivalent (nge) per gal diesel we get 8.9m^3/t. Thus, each tonne of collected and delivered food waste would consume 8.9m^3 nge of biogass.

Comparing the net gas production per tonne of food waste with the simple trip distance is apples to oranges. Better to put the logic above / Note 2 into the body of the article and compare apples to apples IMO.

For example, the article indicates 65m^3 nge / tonne on a gross basis. Multiplying by 50% (100% – 32% – 18%) gets 32.5m^3 nge / tonne on a net gas basis. Subtracting 8.9m^3 nge consumed by the truck gets net production of 23.6m^3 nge / tonne.

Tom Kraemer

Mr. Ward, You are quite right! It is not the average load during the trip that counts, it is the total tons delivered. Thank you for reading the article so carefully and pointing out this error. It only affects the footnote, however, and makes the analysis in the article, where only one ton delivered was assumed, even more conservative. There is energy to spare. And I agree your approach to calculating it is a better way to compare it “apples to apples,” or in this case apple cores to apple cores.

Just one comment on calling the excess energy “net production”: I consider the fuel used to power the hauling truck to be part of net production. This food waste needs to be picked up and hauled away from homes and businesses, and by using biogas we are displacing diesel fuel.

Mr. Lancaster, you are also right that this analysis addresses only the waste side of food, not the energy to produce them. But we have other reasons for producing food than just managing the resulting waste! Hopefully we can help set an example here of using renewable energy and ingenuity to get away from fossil fuels.

You are also correct that in some locations food wastes are being hauled much farther that assumed in my article, which is based on a project my company plans in the greater Vancouver, BC area. In fact, I’m aware that some food wastes from the Portland, OR area are hauled north of Seattle for processing, a distance of over 300 km! This isn’t sustainable.

Finally, with regard to comparing the use of food waste for energy vs. fertilers, there is no conflict! When we digest the wastes we aren’t removing or degrading their fertilizer value. Our digester in Vancouver will be built as a kind of “front-end” processor at an existing compost operation. The fertilzer value in the form of nitrogen, phosphorus and potassium, will be incorporated into the compost made from the solid residuals. You get both energy and fertilizer.

And to iknowtrash: Muchas Gracias.

Andrew Cox

I suggest readers have a look at the technology developed by St1 Biofuels in Finland – see: http://www.st1.fi

The company has commercialised the production of ethanol from the waste streams at several food production plants and breweries – using the Etanolix technology.

If it is kept separated and uncontaminated, food waste could be transported to a decentralsed Etanolix plant and converted into ethanol – which could power the waste collection vehicles. The solid residue left over from the process is used as animal feedstock.

Check out the process.

Soy beans make a great feedstock for biofuels, as the food portion as used for food, and the left over waste oil is used in biofuel blend.

Good work! I’m glad that I’ve found this blog post. I really learned many things in reading your post. Amazing. Good work!

Andrew Cox

Tom – I recommend you check out the Finnish company St1 Biofuels

See video and technical information at http://www.st1.fi

They have fully commercialised a process to turn food and other organic waste into ethanol – called Etanolix.

In November 2009 I visited a small plant operating adjacent to a bread plant in a suburb of Helsinki.

This technology ought to be adopted by breweries, food plants and other facilities which are in reasonable proximity of a refinery – so the ethanol can be dried and then blended with petrol.

Give this process a mention in your blog sometime.

gremlin

using the sewer system any food waste could be sent to sewage plants. all you would need is a good grinder to make it fine. keep it simple. no trucks needed to transport the waste food any ware just running water. flushing water for the sewage system could be the prossed water from the sewage system.

but then using the sewage system to make methane would be a smart ideal any way. having every one in the city use, garbage disposals in there houses and any place that uses food and has waste would be a boon to the city’s methane production.

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