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In King County, Washington, Human Waste Is a Climate Solution

Climate
In King County, Washington, Human Waste Is a Climate Solution
Biosolids are applied to fallow wheat fields to build healthy soils at Boulder Park, Washington. King County

By Sarah Wesseler

Talk of natural climate solutions typically conjures up images of lush forests or pristine wetlands. But in King County, Washington, one important natural solution comes from a less Instagram-worthy source: the toilets of Seattle.


After human waste gets flushed out of sight, it's routed to a wastewater treatment plant (or, in many rural areas, to a septic tank ). At the publicly owned treatment plants, it's put through a series of mechanical, biological and/or chemical processes that separate water from the solid matter suspended within. The water then is released back into the environment. The solids left behind can be dealt with in one of three ways: incineration, burial in a landfill, or application on the land, typically in the form of agricultural fertilizer.

The first two options are extremely expensive in many parts of the country. They also have a number of drawbacks from a climate perspective: landfilled solids release methane, while incineration releases another powerful greenhouse gas, nitrous oxide. Land application, however, tends to be less of a burden on public finances, and has a number of mitigation and adaptation benefits.

In King County, treated human waste, also known as biosolids, plays an important part in the county's efforts to combat global warming. "Every year we provide the equivalent of taking about 8,000 cars off the road," said Cat Gowan, a biosolids project manager in the county's wastewater treatment division.

A manure spreader applies Loop to a farm field. King County

Robust Communications and Partnerships

King County is far from alone in sending its biosolids to farms; about 55% of all treated human waste in the U.S. is added to soils. But the Seattle-area program, which began in the 1970s, is one of the nation's most ambitious. It includes research partnerships with several universities, along with robust communications efforts: the county branded its biosolids as Loop and created a standalone website that provides in-depth information about the program.

Each day, a dozen 31-ton Loop-branded trucks deliver biosolids to farmers throughout the region. According to Doug Poole, who uses it on his crop fields, Loop costs about one-half to one-third less than chemical fertilizer.

Consisting of about 80% water, Loop is applied in a thin layer with a manure spreader. Fields typically receive applications once every few years.

Poole took over his farm from his father, who was one of the first growers to use King County biosolids; the program's longest-running research plots are located on the family's land. Poole credits Loop for raising his crop yields between 10 and 40%.

Andy Bary, a soil scientist at Washington State University, has been studying Poole's farm since 1994. His research demonstrates that yields on plots that use biosolids are consistently equal to or higher than those using synthetic fertilizers.

Comparison of wheat root systems grown with conventional fertilizer, left, and Loop, right. King County

The reason? Bary says biosolids provide a broader range of plant-beneficial nutrients than farmers can typically provide through synthetic fertilizers alone. "When you're using biosolids, you're not just putting down nitrogen, which is pretty typical," he said. "You get a broad range of nutrients, the full meal deal – you're getting nitrogen, you get phosphorus, you get sulfur, you get a whole raft of micronutrients." Replicating this cocktail with chemical inputs is prohibitively expensive for most farmers, he said.

Mitigation, Adaptation Benefits

Biosolids-based yield gains have important ramifications for climate mitigation and for adaptation. Producing and applying chemical fertilizers releases carbon dioxide, methane and nitrous oxide. Preventing these emissions without jeopardizing food supplies represents a significant achievement.

Biosolids also help sequester carbon in the soil, something that's increasingly seen as a promising way to reduce atmospheric greenhouse gas levels. In a 20-year study on Poole's farm, Bary found a significant increase in soil organic carbon in fields where Loop had been applied compared to those where commercial fertilizer, or none at all, was used.

Soils treated with biosolids also retain more moisture, which, on the mitigation side, can reduce the need for energy-intensive irrigation and pesticides. It's another important adaptation benefit, helping farms become more resistant to drought.

Documentation of rainfall infiltration and soil moisture retention in agricultural fields treated with Loop, conventional fertilizer, and no fertilizer. More infiltration and moisture retention, as seen in the Loop-treated field, has a variety of benefits, including helping plants resist drought – important from a climate adaptation perspective. King County

Biosolids currently are applied to only about 1% of America's agricultural lands. According to Ned Beecher, a longtime biosolids advocate at the North East Biosolids & Residuals Association, there's simply not enough raw material available to dramatically scale up use. Nonetheless, he estimates that if all solids produced in U.S. wastewater treatment plants were applied to land rather than burned or sent to landfills, approximately 7 million tons of greenhouse gas emissions would be prevented each year. In addition, he wrote in an email, "recycling to soils benefits local economies, improves soils, reduces irrigation needs, etc. – and puts to use a material that has to be managed somehow (biosolids are not optional)."

Not All Are Fans of Biosolids on Farmlands

Still, it's no surprise that not everyone is a fan of using treated human waste on farms. The USDA's organic standards prohibit the practice, as does Switzerland. Anti-biosolids activists cite several reports of health impacts to humans and livestock, accusing EPA and other organizations of cover-ups, conspiracies and lax oversight. Detractors often describe foul odors. Some scientific studies raise concerns that land application of biosolids may spread contaminants.

In response, proponents point to what they see as decades of successful use on farms like Poole's, and to a substantial volume of studies concluding that biosolids pose little threat. "Early on, there was a lot of concern about pathogens and metal contents," said Andy Bary. But now, "through research from various universities across the nation, there's a huge amount of research showing that if you meet the pathogen reduction guidelines and the trace element reduction numbers, biosolids are very safe, if not beneficial."

In a recent podcast produced by the nonprofit Water Environment Federation, Sally Brown, a soil scientist at the University of Washington, said that it's important to consider questions of origin and scale when discussing biosolids contamination. The chemicals most often cited as concerns – e.g., PFAS "forever chemicals" – enter the sewer from homes, where they're present in much higher concentrations than are found in biosolids, she said.

There's also a big difference between identifying a contaminant in treated waste and finding enough of it to cause harm. In one recent study, Brown's team sought to understand how much exposure to biosolids an individual would need in order to absorb one dose of pain relief medication. The result: "You would basically have to eat about 30 wet tons of biosolids to get the equivalent of two tablets," she said.

Willing to Engage With Those Skeptical

According to Cat Gowan, a willingness to engage with people who are uneasy about biosolids has helped the Loop program flourish. "Our agricultural project manager, if somebody has a concern about biosolids being applied near their home, he calls them and talks them through it, and they work out a solution," she said.

But Gowan and her colleagues put most of their outreach efforts into educating the general public, most of whom have never heard of using treated sewage as fertilizer, let alone formed strong opinions on the subject. Local gardeners who use the county's biosolids compost product, which receives an extra layer of treatment to make it safe for use in backyards and community gardens, have become particularly enthusiastic brand ambassadors.

"People are not as against it as you'd think once you explain to them how it's made," said Ashley Mihle, another King County biosolids project manager. "It's a natural process with microorganisms. It produces this thing that's so great for the soil and helps your plants grow. And if they use it, then they're sold forever."

Reposted with permission from Yale Climate Connections.

A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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