Depending on lifestyle and consumption patterns, each person on the planet can generate tons of waste over the course of his or her life. The total amount of trash skyrockets with the farm, mine, and industrial wastes generated during the production of food, power, and consumer items.
“Working with Waste,” the 10 August special issue of Science, highlights the fact that trash can often be turned into treasure—a feedstock that the human race can’t afford to overlook as a burgeoning world population tries to use (and reuse) its resources more efficiently.
Over the years, working with human waste has become an increasingly complex challenge. A clever mix of science, practical policy, and appropriate technology will be needed to minimize the amount of waste generated and to wring the most value out of the trash created, according to experts. Luckily, a growing number of researchers seem to be interested in getting their hands dirty.
“Waste is far from a glamorous subject, but it can’t be avoided,” said Nick Wigginton, an associate editor for Science, during a 8 August press telephone conference about the special issue. “The problems of waste are by-products of our own development…and the Reviews and Perspectives in this issue cover broad topics, such as making wastewater a more efficient source of freshwater, electricity and harvestable chemicals, the economic and technical challenges associated with recycling metals, and getting more value from food and agricultural waste through green chemistry.”
An editorial by Janet Hering, director of the Swiss Federal Institute of Aquatic Science and Technology in Dübendorf, Switzerland, and professor at the Swiss Federal Institutes of Technology in Zürich and Lausanne, as well as a Review article by Stanley Grant from the University of California in Irvine and colleagues, tackles the issue of wastewater management.
According to the authors, more than 4 billion people live in parts of the world where the scarcity of fresh water directly threatens water security and biodiversity. However, the reuse and recycling of low-quality water has the potential to meet dire needs in these water-stressed regions. The challenge will be altering the ways in which fresh water is sourced, used, managed, and priced, they say, so that new sources can be delivered to water-starved areas of the world and water can be used more productively elsewhere.
“The options that we have for addressing the water needs of populations really are dwindling,” said Grant. “Historically, we’ve focused on augmenting water supply by doing things like building dams or pipelines for transferring water between water basins, building aqueducts, and that sort of thing… but there are a number of problems with those approaches.”
“In many cases, the rivers that we’ve been tapping are simply dry,” he said. “Many of the world’s largest and most important rivers—like the Nile, for example, or the Colorado River in the U.S.—are not reaching their deltas many years, which obviously has very significant implications not only for human water security but also for ecosystem sustainability.”
Grant argues that the only real alternative to such approaches is to improve water productivity, or the value of goods and services that are achieved with a given unit of water. In other words, the world simply has to do more with less.
According to Grant, there are three basic concepts that may allow this: substitution, or the use of lower-quality water where higher-quality water is not needed; regeneration, or the conversion of wastewater into high-quality, potable water; and reduction, or using less water with technologies such as dual flush toilets.
Another Review article in the special issue highlights some different ways of turning waste into useful chemicals and electricity. Bruce Logan from the Pennsylvania State University and Korneel Rabaey from Ghent University in Belgium explain how certain microorganisms might be used to convert waste biomass into energy during the wastewater treatment process. Such biomass is a cheap and abundant source of electrons. Certain developing technologies like microbial fuel cells, they say, could enable electrochemical microbes to generate biofuels, hydrogen gas, methane, or other valuable chemical compounds.
“I’d like you to think about the movie, ‘The Matrix,’ in which machines hook people up to devices to obtain electricity,” Logan said during the teleconference. “We describe a process that is somewhat like that, except we use certain microorganisms that can be connected to devices to directly generate an electrical current, which can then be used to make electrical power.”
“The property of these microbes to release electrons to electrodes has created a whole new field of science called electromicrobiology,” he explained. “And we’re using these microbes to develop many different technologies—we call them microbial electrochemical technologies—like microbial fuel cells, which can be used to treat wastewater and generate electricity at the same time. So, this could effectively turn a wastewater treatment plant into a power plant.”
Another Review article by Barbara Reck and Tom Graedel from Yale University delves into the challenges involved with metal recycling. In principle, metals are infinitely recyclable, they say. But in practice, social behavior, product designs, and recycling technologies often can render metal recycling inefficient or completely nonexistent.
The authors explain that today, virtually every stable element on the periodic table has been embraced by industry to take full advantage of their unique physical and chemical properties. As a result, most products on the market are more functional and more reliable than ever before. However, more complicated and challenging methods of recycling are needed now to make the most out of those resources.
The authors divided all of the metals on the periodic table up into three groups—common metals, precious metals, and specialty metals—and then determined the average recycling rate for each type. Common metals, which include iron, aluminum, copper, and zinc, as well as precious metals, such as gold, silver, and platinum, are recycled at rates between 50% and 70%. Specialty metals like indium, gallium, and germanium, which are key to the operation of many advanced electronic devices including cell phones and batteries, are not recycled at all.
“The reason for this is that they are typically used in only very small amounts that provide little or no economic incentive for recyclers,” said Reck. “Also, the processing technologies that would be required to recycle those metals are often very complex or simply not yet developed.”
There’s plenty of money to be earned for people working with waste in the right ways, according to Roger Sheldon from Delft University of Technology in the Netherlands. In a Review article appearing in the special issue, he and lead author Christopher Tuck from the University of Nottingham in the U.K. focus on ways to get more value out of the waste that humans produce—particularly through conversion into chemicals.
They say that the rising cost and dwindling supply of the world’s oil, which drives the production of most carbon-based compounds in the chemical industry today, has highlighted the need to develop alternative routes to chemicals, fuels, and solvents that rely upon biomass instead.
“What is needed here is more out-of-the-box thinking and close partnerships between chemists and chemical engineers to develop processes to get the maximum value out of our waste,” Sheldon suggested during the teleconference.
“As we say in England: ‘Where there’s muck, there’s brass.’”
Read “More Treasure Than Trash,” an introduction to the Science special issue by Nick Wigginton, Jake Yeston, and David Malakoff.
Check out an infographic related to the “Working with Waste” special issue (available free to the public for one month).
Listen to a 8 August teleconference with the Science authors.