KEAAU, Hawaii — The trucks roll in and out of the plant at a business park nestled near papaya farms and a forest preserve on the Big Island here, an operation that transforms waste cooking oils, animal fats, fruit and seeds into biodiesel fuel, nearly 13,000 gallons a day.
Owned by Pacific Biodiesel, an industry pioneer, the plant was designed with an eye toward conserving water and energy and avoiding environmental harm.
But after about $20 million and four years of operation, a central question about the plant, and the industry as a whole, has persisted: Do biofuels ultimately reduce carbon emissions?
“We’re worried that the efforts to ramp up our use of biofuels are actually doing a lot of damage and digging the climate hole deeper,” said Jonathan Lewis, a lawyer focused on climate change at the Clean Air Task Force.
Now, the biodiesel industry’s backers say they have an answer, at least for this modest plant. The Sustainable Biodiesel Alliance, a nonprofit industry group, commissioned an audit of the plant’s sustainability by an independent company, and the result was yes. It was the first United States-based certification of sustainability granted for a biodiesel plant, according to the alliance.
For biofuels, the environmental benefits of which have fallen under increasing scrutiny in recent years, that differentiation is ever more important, executives and advocates say.
Credit Kent Nishimura for The New York Times
“There are lots of different ways of making biodiesel — lots of different feedstocks — and some have been more sustainable than others,” said Jeff Plowman, chairman of the alliance’s certification committee. “Much like the organic labeling or non-G.M.O. labeling, it gives consumers some information to make a choice,” a reference to nongenetically modified organisms.
A decade or so ago, biofuels seemed to have great potential to help wean the country off fossil fuels to reduce greenhouse gas emissions. Plants absorb carbon dioxide as they grow, making them essentially carbon-neutral if used for fuel, the thinking went.
Starting in 2005, the federal government approved requiring biofuels to be blended into the gasoline supply at increasing volumes, a move that, with generous grants and subsidies, helped spur their production.
But much of that was ethanol from food crops like corn and sugar cane, which led to criticisms. Using those crops for fuel can drive up the price of food and animal feed and release more carbon dioxide into the atmosphere as farmers clear land, including rain forests, to grow more of those crops to meet the increasing demand. And although biodiesel differs from ethanol — it derives from oils rather than sugars and works in conventional diesel engines — it, too, can fall into a similar cycle.
“It’s a bunch of small economic steps, but if the end result is deforestation of a tropical forest, there’s a massive carbon pulse when you do that,” Mr. Lewis, the Clean Air Task Force lawyer, said.
As a result, producers have been migrating toward so-called advanced biofuels, which are generally made from plant or animal feedstocks that do not compete with food uses, but they have proved difficult and expensive to produce, and because petroleum prices are so low, they have become less attractive.
In addition, climate change specialists say, there may simply not be enough agricultural waste to produce significant quantities of biofuel without causing other environmental problems, and it is important to account for what would have happened to the waste material had it not been funneled into fuel.
“You can’t just automatically make assumptions that, say, waste-based fuel is O.K.,” said John M. DeCicco, a research professor at the University of Michigan Energy Institute. “If you have a waste that was otherwise not going to decay, then that carbon is already being kept out of the air with respect to the atmosphere, and at that point you’re as ahead of the game as you’re ever going to be.”
At the same time, debate over the usefulness of biofuels, especially corn ethanol, in reducing greenhouse gas emissions has intensified, with studies drawing conflicting conclusions.
But here in Hawaii, where leaders have pushed aggressively to embrace renewable energy sources, the Pacific Biodiesel plant avoids many of these problems, climate specialists say.
The company makes its fuel from local waste products, including restaurant cooking oils and grease and agricultural products like macadamia nuts — turned into oil — considered unsuitable for market.
Here at the refinery, the oils move through a series of stainless steel tanks and columns as they are processed and distilled into fuel. Methanol, a chemical used in the refining, is recycled, and the company is trying to develop local markets for byproducts like glycerin and potassium salts, which can be used as fertilizer.
As for the biodiesel itself, it does not travel very far: The company sells almost all of it to customers in Hawaii, rather than shipping it long distances.
The company is working to develop new feedstocks, and it is experimenting with safflower, sunflower and jatropha plants. But it also focuses on materials that can have nonenergy uses, such as its project that grows algae from waste papayas for use as fertilizer or feed for fish farms, or the cattle operations that sprawl across the Big Island’s center.
“As we’re growing energy crops, we’re bringing the cattle industry with us because we need them to take all of this protein meal,” said Robert King, who founded the company, which has headquarters in Maui, in 1995 with his wife, Kelly. She, along with Willie Nelson and his wife, Annie, and Daryl Hannah, are co-founders of the Sustainable Biodiesel Alliance.