The heat of an Alabama summer afternoon certainly wasn’t helping the aroma of several million gallons of raw and partially treated sewage. This field trip to the Auburn Wastewater Treatment Plant was always the worst one I led for my Intro to Environmental Engineering class. Fortunately, we were near the end of the process and far from the most fragrant part of the plant. At this point the wastewater had been treated by the sludge, which is a “fancy” name for the bacteria that eat the organics in the wastewater. The sludge had been separated out of the treated water, the bacteria had eaten each other, and the remainder had just been pressed to remove excess moisture.
We were standing next to a twelve-foot-tall pile of biosolids, the dewatered bacteria, when the tour guide pulled his usual stunt. He took an ungloved hand and stuck it into the pile, pulling out a handful of what appeared to be a dark, rich soil. The class reacted the way classes on these trip always react: with revulsion. That’s how people respond to things recovered from wastewater, completely unaware of how valuable they can be.
The Great Poop Train
Biosolids look like rich soil because they are rich in nitrogen and organics, which are beneficial for the growth of plants. But that doesn’t make them any more desirable to keep around, and cities often go to great lengths to dispose of them. By 1986, New York City completed its 14 wastewater treatment plants. The resulting wastewater system handled 1.3 billion gallons of wastewater produced every day, creating several thousand tons of biosolids. So the city set out to find somewhere to get rid of it. At first, it was dumped into the ocean. But in 1988, the Environmental Protection Agency told the city they had to stop dumping and find a good use for the biosolids to make amends for their previous polluting ways.
After four years of trying to unload their shit on New Jersey, Alabama, Kansas, and every state in between, the city found a home for its waste. And that’s how in the spring of 1992, seventeen train cars full of New York City poop started the 1,600 mile trip to Lamar, Colorado.
The application of treated sludge to the fields in Lamar increased wheat yields by a third for some farmers. In addition, the farmers who applied it saw aphids and groundhogs leave their fields to go pester their neighbors who did not apply sludge.
New York isn’t the only city to sell their treated sludge; 60% of the 8 million tons of biosolids produced annually in the US are used as fertilizers on crops, grasslands, and forests. The biosolids in our tour guide’s hands ended up fertilizing hay in central Alabama. Some cities even have their own brand name fertilizer, like Milwaukee’s Milorganite, which you can pick up in 36 lb. bags from Home Depot.
It turns out it makes more sense for wastewater treatment plants to sell their biosolids than to pay to landfill them. Or at least it used to; New York recently stopped sending their sludge to Lamar, as the program now costs New York too much money. New York’s sludge still ends up as fertilizer, but for golf courses, yards, and flower nurseries closer to home: nothing that gets eaten.
There’s Gold In Them Thar’ Poops
Nutrients aren’t the only thing that could be extracted from the biosolids in our tour guide’s hands. Many personal care products, like face creams, include valuable ores, like gold. Silver nanoparticles are frequently embedded in clothes for its antimicrobial properties. When you wash your face or your clothes, these metals also wash down into the sewer. A team of researchers at Arizona State University found that for every kilogram of dry sludge produced from a wastewater treatment plant, there is up to 17 milligrams of gold present. This trace amount doesn’t sound like much, but that’s a concentration gold panners used to get excited about. The Arizona researchers concluded that if we had an economic way to recover gold and silver from sludge, a city of one million people could capture about $2.6 million in revenue from precious metal annually. New York City, with its 8 million people, would have about $21 million of gold and silver in their sludge – only a few million short of the $24 million it would take to make the poop train economically feasible.
From Toilet to Beer Tap
The tour operator returned the handful of nutrients and precious metals back to the pile, and we moved on with our tour to the last stop. We walked to where the wastewater is disinfected and discharged, and rested for a few minutes under some shade to escape the blazing Alabama sun. As we stood watching the fully treated wastewater flow down some concrete steps and into the environment, the operator, as he does during every tour, dipped a beaker in and offered everyone a drink. And I did what I always did: take him up on the offer. As I would always joke to my students, it was the second freshest water in the city, after the water from the water fountain at the water treatment plant.
All of my students were appalled, which is a normal reaction to the idea of drinking treated wastewater. But at least my refreshing drink had been treated. This past summer saw an interesting new approach to handling untreated wastewater at the largest music festival in Northern Europe, Denmark’s Roskilde Festival. Festival organizers, aware of the impact of thousands of gallons of sterile urine on the local wastewater treatment plant, installed giant pee troughs for male festival goers (and females who took advantage of supplied accessories). In a project they’re calling “Piss to Pilsner,” the collected urine will be sent to a local barley farm. The barley will eventually be turned into beer, just in time for the 2017 Roskilde Festival. Organizers with the Festival and the Danish Agriculture & Food Council estimate that 25,000 liters of urine will be enough to fertilize the barley for between 140,000 and 180,000 bottles of beer. Many festival goers thought that “beercycling” was a neat idea, even if they would be disgusted by the idea of drinking urine.
Wastewater treatment facilities, including Auburn’s Wastewater Treatment Plant, are designed to eliminate wastewater pollution as with minimal environmental impact and minimal contact with the society. But this may be a mistake. Wastewater has value to the right audience. In the hands of a farmer, the nutrients in biosolids could increase crop yields by a third. In the hands of a miner, the same biosolids could be worth millions in gold, silver, and other precious metals. And in the hands of a Roskilde Festival goer, it’s a beer now and a beer in the future.