In research described at the 16th annual Green Chemistry & Engineering Conference, the researchers said they have developed a sustainable way to extract and find uses for virtually every bit of the 15.6 million tons of orange and other citrus peel discarded worldwide every year.
The scientists say those uses could include biosolvents, fragrances and water purification, and that it could revolutionise what has been an unattractive process in the past.
The new process developed by Clark, Lucie Pfaltzgraff and colleagues sees the orange peels exposed to high-intensity microwaves at low temperatures that transform many components of the orange peel into liquid that can be later collected and from which useful products are obtained.
What remains is cellulose, which can be used as a food additive or a thickening agent or to be converted into a solid biofuel.
"This is a great example of what can be done with something that is produced in quantities that would astound people," said James Clark, director of the University of York's Green Chemistry Centre of Excellence.
"At the moment, orange peel has very little value and actually can have a negative effect on the environment. We believe that using the biorefinery concept in combination with the principles of green chemistry will allow us to make a whole series of products that can displace traditional, often petrochemical-based, manufacturing processes."
The project, dubbed the Orange Peel Exploitation Company (OPEC), is a partnership between researchers from the University of York, University of Sao Paulo, Brazil, and the University of Cordoba, Spain, with hopes of a prototype biorefinery up and running soon.
"We're aiming to create a zero-waste biorefinery," Clark said. "We want to use everything. We want to give value to every component of the peel."
Discarded no more
Brazil and the United States produce about 38 per cent of the world's oranges. After juicing, peel represents about 50 per cent of the orange's mass, which until now has been usually discarded, either by burning, which creates greenhouse gases, or by dumping in landfills, where oils from the rotting peels can leach into the soil and harm plant life.
In some cases, the largest juicing plants dry and detoxify orange peel so it can be used in livestock feed, said Clark.
Manufacturers also extract pectin, an ingredient used in foods, cosmetics and pharmaceuticals, from the peels. But these processes are time-consuming and costly and often require the use of acids and additional mechanical means.