Technology converts human waste into bio-based fuel
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 sewage sludge, 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.
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.
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.
“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.
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.
First evidence for new molecular structure could open doors to chemical solutions for environmental problems
Indiana University researchers have reported the first definitive evidence for a new molecular structure with potential applications to the safe storage of nuclear waste and reduction of chemicals that contaminate water and trigger large fish kills.
The study, which was published online Oct. 6 in the German scientific journal Angewandte Chemie International Edition, provides experimental proof for the existence of a chemical bond between two negatively charged molecules of bisulfate, or HSO4.
The existence of this structure — a “supramolecule” with two negatively charged ions — was once regarded as impossible since it appears to defy a nearly 250-year-old chemical law that has recently come under new scrutiny.
“An anion-anion dimerization of bisulfate goes against simple expectations of Coulomb’s law,” said IU professor Amar Flood, who is the senior author on the study. “But the structural evidence we present in this paper shows two hydroxy anions can in fact be chemically bonded. We believe the long-range repulsions between these anions are offset by short-range attractions.”
Flood is a professor in the IU Bloomington College of Arts and Sciences’ Department of Chemistry. The first author on the study is Elisabeth Fatila, a postdoctoral researcher in Flood’s lab.
In molecular chemistry, two monomer molecules connected by a strong covalent bond are called a “dimer.” (A polymer is a chain of many monomers.) In supramolecular chemistry, the dimers are connected by many weak non-covalent bonds. A negatively charged particle is an anion.
A key part of Coulomb’s law is the idea that two molecules with the same charge create a repellent force that prevents chemical bonding — like two magnets with the same end put into close contact. But recently, experts have begun to argue that negatively charged molecules with hydrogen atoms, such as a bisulfate — composed of hydrogen, sulfur and oxygen – can also form viable chemical bonds.
“Although supramolecular chemistry started out as an effort to create new molecular hosts that hold on to complementary molecular guests through non-covalent bonds, the field has recently branched out to explore non-covalent interactions between the guests in order to create new ‘chemical species,'” Fatila said. The negatively charged bisulfate dimer in the IU study employs a self-complementary, anti-electrostatic hydrogen bond.
The molecule’s existence is made possible through encapsulation inside a pair of cyanostar macrocycles, a molecule previously developed by Flood’s lab at IU. Fatila and colleagues were trying to bind a single bisulfate molecule inside the cyanostar; the presence of two negatively charged bisulfate ions was a surprise.
“This paper is inspirational because it may launch a new approach to supramolecular ion recognition,” said Jonathan Sessler, a professor of chemistry at the University of Texas at Austin who was not involved in the study. “I expect this will be the start of something new and important in the field.”
The ability to produce a negatively charged bisulfate dimer might also advance the search for chemical solutions to several environmental challenges. Due to their ion-extraction properties, the molecules could potentially be used to remove sulfate ions from the process used to transform nuclear waste into storable solids — a method called vitrification, which is harmed by these ions — as well as to extract harmful phosphate ions from the environment.
“The eutrophication of lakes is just one example of the serious threat to the environment caused by the runoff of phosphates from fertilizers,” Flood said, referring to uncontrolled plant growth that results from excess phosphate nutrients running into lakes and ocean. When these chemicals get into the water supply as runoff from fertilizer — produced by dairy farms and used to increase crop yields — they can trigger massive algae blooms that poison water supplies and kill fish in large numbers.
In August, Flood was also named the principal investigator on a new, separate grant from the National Science Foundation to specifically focus on removing these substances from the environment. The three-year, $600,000 award is a collaboration with Heather Allen, a professor at The Ohio State University, which is near a part of the country that has recently experienced large algae blooms due to agricultural runoff into Lake Erie.