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Recycling Agricultural Waste

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Recycling means more than separating trash into two containers at the curb. In principle, whatever we discard can become a resource instead of a waste. That includes post-consumer, post-industrial, and agricultural wastes. Technological difficulties and economic issues make it hard to recycle certain wastes. Here are some uses for agricultural waste and problems they encounter.

Making Ethanol from Cellulose

President George W. Bush proclaimed America’s addiction to oil. He championed making ethanol from cellulose. Most of the ethanol we use now comes from corn. Corn used to make ethanol cannot feed either people or cattle. Consider the process of growing, fertilizing, and harvesting corn. Corn-based ethanol requires more energy to produce than burning it provides. So why not use non-food feedstock instead?

Ethanol comes from fermenting glucose, a monosaccharide (simple sugar). Corn and other plant foods contain disaccharides. The sugar called sucrose connects one glucose molecule to one fructose molecule.

Starches and fiber are polysaccharides. They comprise ten or more simple sugars. Making ethanol from cellulose first requires breaking more complex sugars down to get glucose. The longer the molecular chain, the more expensive it is to break out the glucose.

Getting a source of cellulose is easy. After a corn harvest, stalks remain in the field. Other crops leave behind similar farm waste. It’s rich in cellulose. Farmers can also grow non-food crops like switchgrass for cellulose. They grow in soil too poor to support food crops. Unfortunately, its weight makes it uneconomical to ship it more than about 50 miles. Today’s industry depends on large factories. A network of small refineries, each within 50 miles of the most distant farm, does not fit current economic models.

Cellulosic ethanol, then, faces two problems. Scientists looking for ways to simplify the process of refining it to get glucose. It also needs a way to make more decentralized economic models attractive to venture capitalists.

The Success and Failure of One Pioneer in Cellulosic Ethanol

Nevertheless, the Italian chemical conglomerate Mossi & Ghisolfi decided to add cellulosic ethanol to its product line. It formed one subsidiary, Chemtex International, to operate a plant in Crescentino, Italy, and another one, Beta Renewables, to license its technology. The plant opened in 2012.

A company in Brazil, GranBio, licensed technology from Beta Renewables. It opened a plant in São Miguel dos Campos in 2014. A competitor, Raizen, opened its cellulosic ethanol plant using different technology.

Mossi & Ghisolfi also built a plant to make resins from recycled PET bottles in Texas. Delays and cost overruns pushed the conglomerate into bankruptcy in October 2017. Hurricane Harvey caused many of them. The Crescentino plant had to close after five years of successful operation. The two Brazilian plants and a few others have proved profitable, but not yet very efficient. However, some experts believe cellulosic ethanol can become economically viable within the next decade.

Another Use for Cellulose

Electronic gadgets require a dizzying array of metals. Then they go obsolete in the blink of an eye. Junk electronics become hazardous wastes, but what if we could recover all the different metals and reuse them? It requires another complicated and expensive process called hydrometallurgy.

Hydrometallurgy uses a liquid to extract metals from whatever substance contains them. Chemically, it doesn’t matter whether it is an ore or an old television. Hydrometallurgy normally uses sulfuric acid or other hazardous material. The Idaho National Laboratory and collaborators have looked for alternatives. They work with a bacterium called Gluconobacter oxydans, one that causes fruit to rot. It produces a chemical soup of organic acids, including gluconic acid. This mixture extracts metals better than sulfuric acid. It also has less serious environmental consequences.

But like any other living being, Gluconobacter oxydans must eat. Buying glucose for it from a supplier could make up as much as 44% of the cost of the experiments. So the scientists turned to agricultural waste. Using cellulose might be an expensive way to make commercially viable quantities of ethanol. But it makes a cheap source of glucose for research on biohydrometallurgy.


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Making Asphalt from Hog Manure

Americans eat a lot of pork, which means farms grow a lot of hogs. Hog manure makes a good fertilizer, but hog farms produce too much to safely apply to crops. They push most of it into smelly, unhealthy lagoons. In the summer of 2018, farmers in eastern North Carolina are facing lawsuits as environmental nuisances.

Several years earlier, Dr. Elham Fini of North Carolina A&T University discovered a way to use hog manure to make a superior asphalt adhesive. The asphalt used to pave our highways comprises 95% crushed rock and 5% adhesive, mostly from petrochemicals. Refiners can make more profit from other products, so they limit the amount of adhesive they make.

To be sustainable, a biological alternative would have to use raw materials not suitable for food. And it could not require a lot of water to make it. Shortly after joining the NCAT faculty, Fini investigated hog manure. Its high water content makes it an ideal raw material for a biological asphalt adhesive. Her process extracts the carbon from it to make the adhesive. The remaining nitrogen, potassium, and phosphorous still make excellent non-hazardous fertilizer.

The environmentally friendly adhesive can become much less expensive than petrochemical adhesives. It is also more durable in cold weather, an important consideration in pothole country.

As is the case with cellulosic ethanol, making asphalt adhesive from hog manure faces economic hurdles. Fini worked with the university’s technology transfer office. They founded a company called Bio-Adhesive Alliance to market the adhesive. The company has two employees and operates out of an office on campus.

This project, like so any others, also faces another problem – marketing. Scientists at less-known universities like NCAT produce excellent research; much of which can help solve environmental problems. Unfortunately, the universities themselves often don’t publicize it effectively.

In this case, a university in central North Carolina produced a process that can help hog farmers. However, hog farmers in eastern North Carolina may not even have heard of it. Laboratory research finds ideas. It doesn’t make new products from them. That requires venture capital and marketing skills. Professors with heavy teaching loads can’t do that kind of work, often leaving too many great ideas hidden in academia.

Making Fabric from Milk Waste

You can drink milk, cook with it—wear it?

People have worn protein fibers for millennia. Think wool. Milk contains protein, especially one called casein. Excess casein from milk production becomes an agricultural waste.

In 1904, German chemist Frederick Todtenhaupt began to explore making a silk substitute from milk byproducts. He gave up five years later, but his work attracted the attention of Italian futurists. By 1920, the “Manifesto of Futurist Women’s Fashion” added milk to a list of “new revolutionary materials” for clothing.

A Futurist political party merged with Benito Mussolini’s Italian Fascist Party. Mussolini wanted Italian industry to become self-sufficient. By 1929, Italian company SNIA Viscosa became a world leader in manufacturing rayon. When Italian engineer Antonio Ferretti succeeded in making fiber from milk, the company added it to its product line under the name lanital in 1935. Two years later it produced 10 million pounds of it.

With enthusiastic support from the government, the company sold its patents around the world. In the US, Atlantic Research Associates began to produce a milk fabric it called aralac.

Unfortunately, Ferretti’s process produced a weak fiber that broke easily, especially when ironed. Worse, when it got damp, it smelled like sour milk. Cheaper and better synthetic fabrics from petroleum soon drove milk fabric from the market.

In 2011, German microbiologist and fashion designer Anke Domaske introduced a new milk fabric. She called it QMilch—Q for quality and Milch, the German word for milk. Her process uses fewer chemicals and much less water than Ferretti’s. The breakthrough—and Domaske’s odd combination of careers—caused an immediate flurry of news stories.

Very expensive at first, the cost of QMilch has come down a lot. According to the company’s website, it has expanded its product line. Besides fashionable clothing, it makes toilet paper and other wipes. Its biopolymers can complete with some applications for plastics.

Will QMilch outlast lanital? Time will tell. If not, the other products look promising.

Making Waste into a Resource

We can’t eat every part of the plants and animals we use for food. If we regard the inedible parts as waste, we have a disposal problem. If we regard them as a resource, we can use them to solve other problems.

Humans have long used leather and wool. Now, science has begun to find new uses for agricultural wastes. Many still require technological advances before they can succeed. All need comparable imagination in marketing and manufacturing. In principle, we can recycle anything. We just need to build successful pilot projects up to commercial scale.

Editor’s Note: This article was contributed by David Guion. David Guion served for three years on a university sustainability committee. He writes the acclaimed blog Sustaining Our World.

Featured Image Credit: Image courtesy of Idaho National Laboratory (INL) Bioenergy Program via FlickrSome rights reserved.

Recycling Agricultural Waste
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Article by: Megan Ray Nichols

Megan Ray Nichols is a freelance science writer and science enthusiast. Her favorite subjects include astronomy and the environment. Megan is also a regular contributor to The Naked Scientists, Thomas Insights, and Real Clear Science. When she isn't writing, Megan loves watching movies, hiking, and stargazing.