AskNature: How do you manage waste?

The following is adapted from the Biomimicry Institute's Ask Nature Collections of strategies and products, inspired by nature, to address the 21st century's greatest design challenges. Find the full collections here.

It’s not pretty, but waste is an inevitable byproduct of life. Every action has an equal and opposite reaction, and sometimes the outcome is waste. Developments we’re making in health, technology, engineering and practically every other industry have enabled our societies to advance exponentially.

While this has led to incredible discoveries, many parts of the world have been left with the brunt of these innovations, crippled by overburdened waste streams and rampant environmental pollution. As some facets of our society evolve, others are falling further behind.

How, then, do we address this inequity? How do we make strides in industry while also being conscious of the waste we leave behind? As always, nature’s ideas could be just the ticket. This collection explores the ways that nature manages, reduces and reuses waste.

How does nature put energy-efficient chemical or physical processes to work to manage waste? How do species dispose of waste in more efficient ways or reduce the volume produced in the first place? Is one species’ trash another one’s treasure? Nature has developed incredible systems for managing waste, leading to healthier and more efficient ecosystems. Emulating nature’s strategies in human designs could uncover new solutions to our challenges with waste.

Nephrons separate and recycle resources: Human kidney

Industrial chemical processes often involve resource intensive separation steps. While most biochemical synthetic methods themselves do not need separation steps, other physiological processes do.

One example is the filtering of blood which removes potentially harmful organic and inorganic materials. Water, as well as useful minerals, glucose and proteins are separated from the harmful materials and recycled back into the blood stream. If the water and useful compounds were excreted along with the harmful compounds, the organism would have to consume gallons of water and many grams of minerals on a constant, daily basis to recover the loss. 

The filtration aspect of the kidney can be thought of as a collection of hundreds of thousands to over a million independent assembly lines carrying out the same intricate task. The assembly line here is the nephron, a tubular structure with specialized regions along its length.

The great quantity of useful water that is excreted is reabsorbed back into the blood as the nephron first descends into the deeper tissues of the kidney. This part of the nephron is the descending limb of its "loop of Henle." The cells lining the descending limb are permeable to water and impermeable to ions. As the limb descends through progressively saltier (hypertonic) regions of the kidney, water in the relatively un-salty (hypotonic) filtrate passively flows out of the nephron's lumen (interior space) and into the surrounding salty tissues via osmosis.

The concentrated filtrate then travels up the ascending limb of the loop of Henle, which ascends back towards the surface of the kidney through progressively less salty (increasingly hypotonic) interstitial regions. In contrast with the descending limb, the cells that line the lumen of the ascending limb are permeable to ions and impermeable to water. Useful ions in the filtrate are reabsorbed as they flow down their concentration gradient into the surrounding kidney tissues through protein channels, while water is excluded. 

Further along the nephron, protein pumps actively transport useful ions and substances between the lumen and the kidney cells and vice versa. Active transport requires an energy input by depleting ATP molecules. More water is also absorbed, so that by the time the filtrate reaches the bladder as fully formed urine, it contains only 1 percent of the volume of the early filtrate. 

Bioinspired products and application ideas

Application Ideas: Improve the efficiency of chemical separations in both chemical manufacturing and formulating processes. Recycle useful constituents in waste streams back into the head of the process or store for later use.

Industrial sector(s) interested in this strategy: Waste management

Detoxifying ozone inside leaves: plants

The chemical processes that take place within plants are among the most complex and efficient chemical processes known. A plant's ability to transform toxic substances into benign products or useful nutrients can give great insight into helping pollution problems encountered in today's world.

Ozone (O3) is a substance that collects in the troposphere (the lowest part of the earth's atmosphere) when nitrogen oxide and volatile organic compounds in polluted air interact with photons and break down in a process called photolysis. The presence of excess ozone remains a great threat to various plants and other organisms, as it can cause oxidative damage when it reacts with molecules in living tissues. 

Current research evidence shows, however, that many plants have a way to combat ozone's toxicity using an antioxidant compound known as ascorbate (ASC), or vitamin C. ASC molecules are found within plant apoplasts, the internal aqueous space of the cell wall. Research suggests that when ozone passes into the cell wall on the leaf, some of it oxidizes ASC.

This reaction produces non-toxic products that then can be managed by the plant cell. This way, ASC in the cell wall is part of a first line of defense against ozone, before the ozone can oxidize and damage sensitive molecules in the plant cell's underlying plasma membrane. Experimental studies have found that higher concentrations of ASC are associated with higher resistance to oxidative stress.

Bioinspired products and application ideas
Application Ideas: Understanding the mechanism by which plants create ASC and the chemical process by which it breaks down ozone may provide insight into how manufacturers can produce better air filters capable of not only preventing further pollution but also reducing existing pollution.

Industrial sector(s) interested in this strategy: Air purification, pollution management

Enzymes break down pesticides: Honey bee

Honey bees contribute an estimated $15 billion to the U.S. economy per year in the form of supplementary agricultural services (such as pollinating). However, honey bee colony health can be adversely affected by many pesticides currently in use and mite infections in the colony.

Of particular interest is a pyrethroid pesticide called tau-fluvalinate, relatively non-toxic to honey bees yet still potent against many other insects, such as the parasitic varroa mites that commonly infect honey bee colonies. Honey bees' resistance to tau-fluvalinate is derived from their unique enzymes that catalyze the breakdown of aromatic rings, a particular chemical compound that occurs on molecules of tau-fluvalinate more than on other kinds of pyrethroids.

Bioinspired products and application ideas

Application Ideas: New pyrethroid pesticides could be developed and mixed with P450 inhibitors so as to be effective against insects that have evolved resistance; alternatively, the natural resistance that bees have could be considered when developing new pyrethroid miticides, which are more harmful against mites and less harmful against bees.

Industrial sector(s) interested in this strategy: Apiculture, agriculture, bioremediation