Fuel from sewage is the future—and it's closer than you think

November 2, 2016 by Susan Bauer, Pacific Northwest National Laboratory
Sludge from Metro Vancouver's wastewater treatment plant has been dewatered prior to conversion to biocrude oil at Pacific Northwest National Laboratory. Credit: Courtesy of WE&RF

It may sound like science fiction, but wastewater treatment plants across the United States may one day turn ordinary sewage into biocrude oil, thanks to new research at the Department of Energy's Pacific Northwest National Laboratory.

The technology, hydrothermal liquefaction, mimics the geological conditions the Earth uses to create crude oil, using high pressure and temperature to achieve in minutes something that takes Mother Nature millions of years. The resulting material is similar to petroleum pumped out of the ground, with a small amount of water and oxygen mixed in. This biocrude can then be refined using conventional petroleum refining operations.

Wastewater treatment plants across the U.S. treat approximately 34 billion gallons of sewage every day. That amount could produce the equivalent of up to approximately 30 million barrels of oil per year. PNNL estimates that a single person could generate two to three gallons of biocrude per year.

Sewage, or more specifically , has long been viewed as a poor ingredient for producing biofuel because it's too wet. The approach being studied by PNNL eliminates the need for drying required in a majority of current thermal technologies which historically has made wastewater to fuel conversion too energy intensive and expensive. HTL may also be used to make fuel from other types of wet organic feedstock, such as agricultural waste.

Using hydrothermal liquefaction, organic matter such as human waste can be broken down to simpler chemical compounds. The material is pressurized to 3,000 pounds per square inch—nearly one hundred times that of a car tire. Pressurized sludge then goes into a reactor system operating at about 660 degrees Fahrenheit. The heat and pressure cause the cells of the waste material to break down into different fractions—biocrude and an aqueous liquid phase.

What we flush can be converted into a biocrude oil with properties very similar to fossil fuels. PNNL researchers have worked out a process that does not require that sewage be dried before transforming it under heat and pressure to biocrude. Metro Vancouver in Canada hopes to build a demonstration plant. Credit: PNNL

"There is plenty of carbon in municipal waste water sludge and interestingly, there are also fats," said Corinne Drennan, who is responsible for bioenergy technologies research at PNNL. "The fats or lipids appear to facilitate the conversion of other materials in the wastewater such as toilet paper, keep the sludge moving through the reactor, and produce a very high quality biocrude that, when refined, yields fuels such as gasoline, diesel and jet fuels."

In addition to producing useful fuel, HTL could give local governments significant cost savings by virtually eliminating the need for sewage residuals processing, transport and disposal.

Simple and efficient

"The best thing about this process is how simple it is," said Drennan. "The reactor is literally a hot, pressurized tube. We've really accelerated hydrothermal conversion technology over the last six years to create a continuous, and scalable process which allows the use of wet wastes like sewage sludge."

An independent assessment for the Water Environment & Reuse Foundation calls HTL a highly disruptive technology that has potential for treating wastewater solids. WE&RF investigators noted the process has high carbon conversion efficiency with nearly 60 percent of available carbon in primary sludge becoming bio-crude. The report calls for further demonstration, which may soon be in the works.

Biocrude oil, produced from wastewater treatment plant sludge, looks and performs virtually like fossil petroleum. Credit: WE&RF

Demonstration Facility in the Works

PNNL has licensed its HTL technology to Utah-based Genifuel Corporation, which is now working with Metro Vancouver, a partnership of 23 local authorities in British Columbia, Canada, to build a demonstration plant.

"Metro Vancouver hopes to be the first wastewater treatment utility in North America to host hydrothermal liquefaction at one of its treatment plants," said Darrell Mussatto, chair of Metro Vancouver's Utilities Committee. "The pilot project will cost between $8 to $9 million (Canadian) with Metro Vancouver providing nearly one-half of the cost directly and the remaining balance subject to external funding."

Once funding is in place, Metro Vancouver plans to move to the design phase in 2017, followed by equipment fabrication, with start-up occurring in 2018.

"If this emerging technology is a success, a future production facility could lead the way for Metro Vancouver's wastewater operation to meet its sustainability objectives of zero net energy, zero odours and zero residuals," Mussatto added.

Nothing left behind

In addition to the biocrude, the liquid phase can be treated with a catalyst to create other fuels and chemical products. A small amount of solid material is also generated, which contains important nutrients. For example, early efforts have demonstrated the ability to recover phosphorus, which can replace phosphorus ore used in fertilizer production.

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19 comments

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Scottingham
not rated yet Nov 02, 2016
That's some hot shit!
aksdad
3 / 5 (1) Nov 02, 2016
The technology, thermal depolymerization, has been around for awhile. Changing World Technologies proved the concept with a pilot plant in Carthage, Missouri. It ran for years on turkey waste products from a nearby ConAgra turkey processing plant. Initially it was profitable, but it turns out turkey waste isn't just a cheap throwaway anymore so the feedstock costs reduced the profitability of the plant. The fact that what was once considered waste is now a commodity is a good sign. It means that waste products are more likely to be recycled.

It's hard to imagine human waste becoming a commodity anytime soon, but maybe after a pilot plant is built it will become one. Whether the outcome is oil or some other useful product, it's a good sign when waste becomes valuable.
ab3a
not rated yet Nov 02, 2016
I wonder what smelly byproducts come from this process. I've seen many other waste-water projects get shut down because the new neighbors who bought cheap land then turn around and complain about the smell.
david_king
1 / 5 (1) Nov 03, 2016

It's hard to imagine human waste becoming a commodity anytime soon,


The way politicians have been slinging it around this year you have to wonder how much they'd be willing to pay for it.
rrrander
1 / 5 (1) Nov 03, 2016
Since the envirocranks and the Club of Rome were wrong, we didn't hit peak oil in 1980, there is enough oil for 1000 years thanks to expanded exploration and fracking. No need for hyper-expensive nonsense.
antialias_physorg
not rated yet Nov 03, 2016
It's hard to imagine human waste becoming a commodity anytime soon

I think this depends on whether the trend to reduce waste continues. With less demand (as energy/automotive sectors switch to renewables and EVs) the price of oil will also drop - so this could very well become unprofitable both ways in the long run:
- less resource availability
- less profit per gallon
Eikka
not rated yet Nov 03, 2016
The fact that what was once considered waste is now a commodity is a good sign. It means that waste products are more likely to be recycled.


The rule of thumb about almost all recycling is, if your waste is actually recyclable, someone will pay you money for it.

If they make you pay for the recycling, for instance by baking in some sort of recycling fee to the purchase price of a product, then it's not really recycling because the output is worth less than the cost of the process and they're making you pay the difference to make it happen.

With less demand


Oil/petroleum has thousands of applications besides fuel. Gasoline started out as an unwanted byproduct that was initially used to ward off lice and moths from clothes.
humy
not rated yet Nov 03, 2016
The material is pressurized to 3,000 pounds per square inch .... ...at about 660 degrees Fahrenheit.

Why the hell is the stupid obsolete empirical measurements stated here rather than the metric measurements used in all modern science?
This link stupidly didn't even bother to mention the metric conversion.
I, like most scientists, want to know what that is in METRIC.
PLEASE PLEASE stick to metric.
humy
5 / 5 (2) Nov 03, 2016
Since the envirocranks and the Club of Rome were wrong, we didn't hit peak oil in 1980, there is enough oil for 1000 years thanks to expanded exploration and fracking. No need for hyper-expensive nonsense.

you are delusional. If you were in charge, our children's children will have a bad future.
skystare
1 / 5 (1) Nov 03, 2016
As aksdad said, this tech has been around for a bit. It was even proposed to use pig sewage (even wetter, thus less profitable) as feedstock. Any organic material will do, though, including plastics, logging slash, wood construction waste, scrap roofing, tires, most municipal trash, and almost any sort of toxic or hazardous (but without heavy metals/radioactives) stuff like PCBs, pesticides, Freon, etc, (This last group has active negative value; owners will pay you to take them away, governments will pay you to destroy them.)
In the longer run this could be the source of green (aboveground carbon) fuel for aviation. Surface transport can easily run on electricity or methanol, but aircraft really need the energy density of kerosene/gasoline.
enteroctopus
4 / 5 (4) Nov 03, 2016
Since the envirocranks and the Club of Rome were wrong, we didn't hit peak oil in 1980, there is enough oil for 1000 years thanks to expanded exploration and fracking. No need for hyper-expensive nonsense.

Imagine you are a smoker. You know it's going to kill you eventually and that it's terribly expensive. Your doctor warns you that your breathing sounds suspiciously like you have advanced lung cancer and she urges you to have an MRI at once. The MRI comes back clean! You recover from bronchitis two weeks later and you're cancer free. Does that mean it's time to light up a cigarette and celebrate?

No, it's time to take the hint and quit. Regardless of any "good news" on fossil fuel production, or even if someone found climate change predictions were far too dire and we'd have 1000 years more to burn the shit it would still be in our best interest to quit.
Eikka
not rated yet Nov 06, 2016
stuff like PCBs, pesticides, Freon, etc


You don't want to liquefy anything which contains chlorine, sulfur or fluorine, because the resulting oil will be unfit for use.

That means no old car tires (vulcanized), or plastics including PVC and PTFE, or PCBs, PBBs, CFCs etc.

All sorts of random paper scrap, plastics, also contain minerals due to additives, such as clay, which interfere with the process and the equipment. The method is basically mostly suited for biomass and biowaste.
TheGhostofOtto1923
5 / 5 (2) Nov 07, 2016
They do burn them.

"Tire-derived fuel (TDF) is composed of shredded scrap tires. Tires may be mixed with coal or other fuels, such as wood or chemical wastes, to be burned in concrete kilns, power plants, or paper mills. An EPA test program concluded that, with the exception of zinc emissions, potential emissions from TDF are not expected to be very much different from other conventional fossil fuels, as long as combustion occurs in a well-designed, well-operated and well-maintained combustion device."

-So I don't see what the difference would be, other than to be able to remove contaminants during the liquefaction process.
skystare
1 / 5 (1) Nov 07, 2016
Eikka . . . Special models of the machine would have to be designed to distill or otherwise separate such contaminants, certainly increasing running cost, however even the slimmest of profit margins would be justified by the ability to safely destroy toxic wastes.
Eikka
not rated yet Nov 07, 2016
Eikka . . . Special models of the machine would have to be designed to distill or otherwise separate such contaminants, certainly increasing running cost, however even the slimmest of profit margins would be justified by the ability to safely destroy toxic wastes.


As far as I know, the same wastes are normally incinerated directly, which is much much cheaper.

There's no real reason to put S-Cl-F or wastes rich in heavy metals etc. in the oil press, because it just generates more trouble down the line. The viability of the system is in comparison to the price of naturally occurring oil, so any cost-increase would delay adoption of such systems and defeat the point of handling toxic wastes in that way.

-So I don't see what the difference would be, other than to be able to remove contaminants during the liquefaction process.


The contaminants remain in the oil until the refining step, and they complicate the process.
Eikka
not rated yet Nov 07, 2016
Basically, if you liquefy a bunch of old car tires, you get oil that is equivalent to dirty bunker oil with high sulfur content. Of course if you dilute it with enough other stuff, you may pass it through under the limits, and the sulfur is then someone else's problem.

The problem comes from things like old computer cases which are full of fire retardants (bromine) and fillers (clay/chalk) which interfere with the process.

Ordinary plastics such as shopping bags and milk cartons however are perfectly fine.
skystare
1 / 5 (1) Nov 07, 2016
Actually, another down side to plastics as fuel feedstock is that they are mostly made from petroleum in the first place and are thus not aboveground carbon.
TheGhostofOtto1923
5 / 5 (2) Nov 08, 2016
The contaminants remain in the oil until the refining step, and they complicate the process... Basically, if you liquefy a bunch of old car tires, you get oil that is equivalent to dirty bunker oil with high sulfur
-which has nothing to do with:
You don't want to liquefy anything which contains chlorine, sulfur or fluorine, because the resulting oil will be unfit for use.

That means no old car tires (vulcanized), or plastics including PVC and PTFE, or PCBs, PBBs, CFCs etc
-because if burning the tires for fuel is OK then turning them into oil and burning it will also be OK. And of course
The problem comes from things like old computer cases which are full of fire retardants (bromine) and fillers (clay/chalk) which interfere with the process
-has nothing to do with burning tires or oil made from them.

You're ad libbing again.
Dark_Solar
1 / 5 (1) Dec 22, 2016
Ok, here's something I've been wondering about ever since I first learned of biocrude: if the feed stock is not dry going in, will it contribute to the formation of lighter hydrocarbons like acetone, ethers, propane rather than heavier hydrocarbons such as diesel, gasoline, paraffin, etc?

More to the point, is it a manipulable process or is it strictly X goes in, Y comes out, period?

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