Redirecting the Waste Stream: Using waste vegetable oil as fuel

NWF   |   August 7, 2008

As petroleum products become more expensive and concern over greenhouse gases rises, biofuel is the word on everyone’s lips. So far, two primary sources are in production. Ethanol, which is produced from sugar cane and corn, is already mixed with gasoline in gas stations across the nation. However, it is falling out of favor due to concerns that vast amounts of forests and wetlands, which provide important wildlife habitats and sequester carbon when left in their natural state, would need to be clearcut and replanted with sugarcane or corn to produce the fuel in sufficient quantities. Recent studies also suggest that diverting food crops for fuel usage will cause global food shortages and price hikes, which are expected to hit the developing world particularly hard. The second source, biodiesel from oils such as canola and sunflower seeds, raises similar land use and food supply issues. However, a kind of biodiesel made from waste vegetable oil already used in cooking is gaining traction for its clean-burning properties, reuse philosophy, and ease of conversion.

Because vegetable oils generate fewer ozone-producing unburned hydrocarbons, no sulfur, and less carbon monoxide than diesel fuel, biodiesel is considered a much cleaner alternative to conventional petroleum-based diesel. Using oil that has already been used once for deep-frying also neatly skirts the food vs. fuel question so hotly contested in biofuel debates. Websites with recipes for home-brewed biodiesel abound, and every now and then, in biofuel-friendly states such as California, drivers may notice the distinctive scent of French fries wafting from a passing truck. One innovative project in Scotland even solicits waste cooking oil from riders in exchange for bus fare discounts.

Vegetable oil requires a small conversion in order to be used in a #2 diesel engine, as the viscosity is too high to allow it to atomize when cold. To create a usable fuel, methanol is mixed with lye (sodium hydroxide) and then added to the vegetable oil in a process called transesterification. Once the mixture has had time to settle, the product separates into glycerin and biodiesel, which can be fed directly into diesel engines. Oil that is being reused, usually called waste vegetable oil, also contains water as a result of having foods fried in it, and therefore requires an extra step to strain out the water and leftover food particles before the conversion process can take place.

Universities are experimenting with this process in exciting ways. Mount Vernon Nazarene University in Ohio has had success producing its own biodiesel at a cost of about $1/gallon, while conventional diesel is listed at $3.96/gallon as of March 31st, 2008. MVNU has also saved the fees it used to pay for removal of its own waste vegetable oil. The initial investment of a $4,100 transesterification machine was originally intended to pay itself back within two years, but now that fuel prices have jumped, payback may come quicker, especially as managers are now researching local sources for more waste oil. The machine can produce up to 90 gallons of biodiesel in a batch, and is already fueling a bus, a dump truck, all campus lawn and snow removal equipment, and diesel generators.

Still in the planning stage, Indiana’s Goshen College is on track to convert about 12 gallons a week from the school’s cafeteria for use in the school’s generator, which runs during blackouts and at peak usage times. Professor Doug Schirch, who spearheads the project with the help of four graduate students, plans to have the operation running by semester’s end, just in time for summer and a high air-conditioning bill. By using a fuel that is recycled, biodegradable, and clean-burning, Goshen (which has signed the American College and University President’s Climate Commitment) hopes to move the campus one small step closer to carbon neutrality. Once the funding is secured, the set-up will cost $6,000, and is expected to replace up to 624 gallons of conventional diesel yearly. Schirch plans to dispose of the excess glycerin (about 8-10% of the original vegetable oil) by offering it to local farmers for fertilizer use.

Another approach to biodiesel eliminates this conversion step entirely. Because the high viscosity of cold vegetable oil is the main deterrent to using it, some engineers have added a preheating tank to engines rather than using transesterification. The engine uses conventional diesel to start, pre-heating the adjacent vegetable oil tank until the oil attains the proper viscosity for fuel lines. While this procedure eliminates the need for batching with harsh chemicals and doesn’t create any byproducts, it does require petro-diesel at the beginning and the end of each use in order to keep the engine from clogging. Bowdoin College in Maine takes this approach by adding about 1000 gallons per year of waste cooking oil from dining services directly to #2 diesel fuel used in the campus steam plant for winter heating. For this to work, generators must be in a warm location that ensures there is no chance of the oil getting cold, which could shut down the entire system just when the campus needs it most. If that requirement is planned for, then this is a very low-investment process for reusing waste vegetable oil.

Using waste vegetable oil as fuel is not only a possible replacement for conventional fuel, but is also favored for repurposing a product otherwise headed for the waste stream. However, while many restaurants will sell or even give away their used cooking oil, federal laws require a permit to transport waste materials, which makes this fuel source difficult to acquire and transport in large quantities. Campuses can use their own waste oil, but only in limited amounts. As Goshen’s Doug Schirch notes, “We couldn’t run the whole college on this unless the students ate French fries four times a day.”

In fact, the US produces about 11 billion liters of this oil yearly from fast food restaurants and snack food manufacturers, which could only offset about 1% of US fuel consumption, even if all waste oil currently used in other applications – primarily soap production and animal feed – was redirected for fuel. The excess glycerin byproduct can also be difficult to sell or otherwise dispose of (there have been cases of illegal dumping in the Midwest recently), although most producers end up using it as a fertilizer component once traces of methanol are safely removed.

Finally, federal laws require that vehicles on public roads use fuel that has been taxed, so campuses that create their own biodiesel are restricted to using it in generators for electricity demands or lawnmowers and shuttles that don’t leave campus grounds.

It’s been proven many times that there is no “silver bullet” for carbon neutrality, and that includes biodiesel from waste vegetable oil, which has its share of hurdles and is not a replacement for conservation measures. However, taken with other efforts and adapted to a specific college or university’s needs, using waste vegetable oil as a fuel source is already showing reduced costs, a more efficient closed-loop system, and definite potential as part of a concerted renewable energy effort.