San Francisco startup turns human poop into fertilizer

Why does Americans' poop rot in landfills when it could be fertilizing farms and parks?

By Lina Zeldovich | Published Mar 14, 2023 9:00 AM EDT

I AM STANDING in the basement of 1550 Mission Street in San Francisco—a new high-rise in the city's prime real estate location—listening to the steady hum of human grime being filtered. Above me, residents on 38 floors are showering and brushing their teeth as part of their morning routine. In front of me, a maze of pipes and tubes feeds their discarded water into a membrane bioreactor the size of a backyard hot tub. Inside, the membranes and oxygen bubbles purify the H2O and channel it back into the building instead of into sewage pipes, clean enough for flushing toilets and urinals. "We’re able to reuse about 95 percent of it," says Aaron Tartakovsky, co-founder and CEO of Epic Cleantec, the company that designed the technology. His father, Igor, the other co-founder and the chief engineer, chimes in with a twinkle in his eye and a proud smile. "It's kinda cool how it works."

The really cool stuff, however, is stationed in the nearby New Market, or NEMA, building where Aaron and Igor piloted their poop-recycling operation. Unlike the 1550 Mission setup, which recovers only grey water—from everything but toilets and kitchen sinks—NEMA's does the dirty work. Here, a silvery machine resembling a giant food processor the size of a small fridge collects people's waste, intercepting the sewage outflow. When the machine runs, the sludge splats onto its rotating mesh belt. The liquids trickle through, but the feces stay on. A wrangler squeezes out more water, producing palm-size glops of dung that plop into a bin.

When the pilot program was in operation in 2019 and 2020, Aaron or his coworkers would replace that 55-gallon bin weekly and drive it to the company's nearby poo-processing facility, Epic Hub, located in a former car dealership. There, the excrement was chucked into another apparatus that thoroughly mixed it with a disinfecting chemical blend, killing pathogens. The sterilized gunk was composted into soil, which Aaron and Igor used to turn an industrial patch of land outside Epic Hub into a blooming garden. "We call it ‘Soil by San Franciscans for San Franciscans,’" Aaron says. "We’re talking to the city about using it in parks." I share every bit of his excitement. As someone who grew up on a small farm in the former Soviet Union that my grandfather fertilized with the contents of our septic system, I believe our so-called "humanure" should nourish our crops.

The US produced 5,823,000 dry metric tons of biosolids—the end product of wastewater treatment plants—in 2018. In terms of its chemistry, the stuff is like your average dirt, albeit with a smell. In an ideal world, biosolids—potent fertilizers high in nitrogen, phosphorus, and potassium—would be returned to vegetable and dairy farms to replenish the nutrients we’ve extracted or grow the trees we cut. Scientists call this concept circular ecology, which is key to sustainable living in the 21st century. Yet at the moment, only half of our biosolids come back to farmlands. The other half rots in landfills, releasing greenhouse gases—or, worse, is shoved into incinerators that spit smoke into the air. The reasons for these wasteful approaches span from financial to logistical to the general yuck factor. New equipment for turning sludge into pathogen-free fertilizer that meets EPA standards can be expensive. If a big metropolitan area generates a few thousand metric tons of biosolids a week and doesn't have enough farmland nearby to absorb it, the city will have to truck it away using fossil fuels. Finally, people just don't love wastewater facilities, which they see as epitomes of filth.

That mindset began to change in 2011, first among tech creators and then the larger public, when the Bill and Melinda Gates Foundation issued the Reinvent the Toilet Challenge, asking experts to recover valuable resources from toilet outputs, including clean water and nutrients. Originally intended to solve sanitation challenges in poorer countries, it propelled new ideas for sewage treatment in general. California's historic drought was another big catalyst. "In 2014, our elected officials asked, ‘Why are we still using fresh water to flush toilets in San Francisco? And why can't we reuse it?’" Aaron says. "So we really focused on solving that problem."

The city wanted to encourage water reuse, particularly in big new buildings, says Paula Kehoe, director of water resources at the San Francisco Public Utilities Commission, an agency that services 2.7 million people in the San Francisco Bay Area. "We started thinking about the on-site water treatment systems as more of resource recovery facilities," Kehoe says.

In a time when we embrace locally grown food, it makes sense to process the remnants locally as well. The centralized treatment plants that most city municipalities rely on might have worked well in the 20th century, but many have now aged to the point where they’re no longer sustainable or economical. The typical wastewater pipe lasts 50 to 100 years; the average US one is about 45 years old, with some being more than a century old, which creates the risk of sewage spills and contamination. According to a 2019 estimate from the Report Card of America's Infrastructure, the nation's utilities spent more than $3 billion to replace about 4,700 miles of pipelines—only a tiny fraction of the country's total 1,300,000-mile network. A 2017 report estimates that by 2042, 56 million more people will be using these centralized treatment systems, and some $271 billion will be needed to sustain them annually.

On-site filtration and treatment could be a crucial alternative. "There are certainly advantages with a centralized wastewater system, as you get specialized knowledge and technical expertise in one place in case something goes wrong," says Bill Brower, senior biosolids engineer at Brown and Caldwell, an environmental engineering and construction firm. Yet in the era of climate change and increasing droughts, purifying the precious H2O at the source has real benefits too. "I think there's certainly a place for doing more decentralized treatment," Brower says. But before we start shutting down the sewage lines, we need to figure out where to put the "number two."

Growing up in 1960s Odessa, Ukraine, then a part of the USSR, Igor Tartakovsky aimed to be a rocket scientist. "I wanted to build planes and spaceships—that was my childhood dream," he says. Yet for a Jewish kid, it was a difficult path. The anti-Semitism in the Soviet empire was palpable: Igor graduated from high school with highest honors, but was turned down from his town's engineering schools. He didn't give up easily and was eventually accepted to study aeronautics at Electromechanical College in Novosibirsk, a snowbound Siberian city. He traded Odessa's mild climate for endless winter in a heartbeat.

When he applied for a summer job in engineering the next year, he filled out 15 forms, submitted more than a dozen photos of himself, and was still rejected. He let go of his aerospace dream and pivoted to studying refrigeration and air conditioning.

The career switch didn't help. Again, Igor graduated at the top of his class, and again, he was turned down for the jobs he applied for. He got a gig at a floating fishing factory boat that sailed in the frozen Far East for six months at a time. Besides refrigerating seafood, his engineering prowess came in handy for building a contraption to distill moonshine from fermented apple juice—a feat his crewmates loved, but Igor didn't. He felt he was wasting his life. It was clear that he didn't have a future in the Soviet Union, so his family decided to leave.

The only way to emigrate from the KGB state at the time was to receive an invitation to "reunite with the family" from a relative living abroad. Any correspondence asking for such a favor could be intercepted by the government. So Igor's kin penned a so-called "underwear letter." They wrote their names and dates of birth down on the stretched-out waistband of a pair of boxers; when the rubber shrank down, the text wasn't visible. A person leaving the country took their underwear missive with him, and after a year, the coveted invite came through. The KGB officer working on Igor's case called him "an idiot" because he "clearly had bright prospects in this country," and gave him 45 days to leave. Igor obliged. His parents and sister followed.

In San Francisco, Igor met his future wife, got a job, and had children. Later he launched his own company, designing air-conditioning systems for apartment and office buildings in the city. He never thought he’d end up making "humanure."

Throughout most of human history, our relationship with our waste has been thorny. We can't stop producing it, but we can't live with it. The undigested nutrients in our feces—proteins, lipids, sugars—breed intestinal worms and the deadly bacteria that cause scourges like dysentery, gastroenteritis, and typhoid. To avoid spreading disease, we must distance ourselves from our metabolic output as quickly and efficiently as possible.

The industrial Western sewage systems of the past 150 years perfected this process. As cities grew, so did their centralized sewage operations. The first wastewater treatment plants in America were developed in the 1850s. Today, more than 16,000 of them chug out sludge 24/7, processing what comes down municipal, home, and office pipes. Combined, the US has enough such tubing to wrap around our planet 52 times. Or reach to the moon and back almost thrice. About 62.5 billion gallons of wastewater flow through these lines daily.

To my grandfather, none of this made economic or environmental sense, especially the part about tossing dung along with trash. "You have to feed the earth the way you feed people," he used to say as he filled up his compost pits with the brown goo from our septic tank every fall. He then closed them up and let Mother Nature do her job. When he dug them up again three years later, the pits would be full of fluffy black dirt so nutrient-rich that our plants managed to bear fruit despite the short, cold, and rainy Russian summers.

Spending billions on purifying wastewater to release into rivers and streams, only to pump it back into water mains and clean it again for human consumption, doesn't make sense either. "In 2015 it became a mandatory requirement for any new building in San Francisco over 250,000 square feet to install an on-site water treatment system for their toilet and irrigation needs," says Kehoe. "And in 2021 it became a requirement for any new building over 100,000 square feet."

For Igor and Aaron, his third and youngest son, who studied political science but ended up following in his father's engineering footsteps, the move was a serendipitous one. They’d just gotten their toes wet in sewage and were pumped to dive in.

In 2013, a client asked Igor to find a building-wide sewage recycling system for their space in the Bay Area. He couldn't find a single model on the market. Some months later, at a tech conference, Igor watched someone sterilize dog poop by whipping it in a food processor with potassium permanganate. He knew the chemical from his childhood: Called margantsovka, it was a common disinfectant. When his aquarium fish would start getting sick, he would add a few drops, he recalls. "The bacteria would die, and the fish would swim in a rosy water for a little while because potassium permanganate is also a colorant." The compound (chemical formula KMnO4) causes an oxidizing reaction that kills microorganisms, including the pathogenic ones that commonly afflict humans. "It's been widely used to wash wounds or disinfect a glass that someone drank from," says Govind Rao, professor of biochemical engineering at the University of Maryland, Baltimore County. "It's a very powerful oxidant, but it works best when pathogen loads are low." Disinfecting typical sewage would require tons of KMnO4, but the Tartakovskys found a workaround—just do it at the source. Most people don't carry large amounts of dangerous pathogens in their intestines (otherwise they’d be very sick), so what they flush isn't usually festering with germs. It is after sludge floats through the miles of pipes for days that it becomes colonized with all sorts of bugs that naturally dwell there, growing and multiplying. "When sewage swirls down the pipes for days and weeks, its pathogen load is huge," Aaron explains. "But if you get it right after someone flushed the toilet, the pathogen load is much lower."

Igor and Aaron started by whipping their family dogs’ droppings in a food processor, too. For better sterilization, they added other chemicals, coming up with their company's proprietary microbe-busting mix. Now they needed to scale up, so they convinced an Italian company that built industrial-size mixers to let them try their neutralizing method on septic sludge at a wastewater treatment plant near Florence. In March 2015, they flew in for a test. As they experimented with the settings on a machine the size of a backyard grill, the reaction released too much heat. The mixer's top blew off, painting the ceiling with sanitized yet still stinky slime—a historic incident Aaron caught on video. But that taught the father and son the parameters for an industrial processor. Once back home, they formed Epic Cleantec, a water recycling solution company, and focused on building their own mixer.

They hired an engineering company in Minnesota to build one. Testing it in the Land of 10,000 Lakes proved messy too. Aaron was filling up a bucket of fecal goo when the pressurized slush hit the bottom so hard, it splashed him from head to toe. "I almost lost my lunch that day," he recalls. Later, the muck partially froze in the frigid Midwestern winter, rattling around the mixer. They never considered giving up. "I learned early on that failure was not an option," Igor says. Aaron draws his inspiration from his family history. "My grandparents were Holocaust survivors," he says. "Considering what they went through, I can deal with sewage."

The Minnesota exercise gave them exact mixer dimensions—length, diameter, blade size. But the final version was built by a company in Los Angeles. Driving down to give it a whirl, Aaron called every kennel in the area to ask for dog poop. Most laughed and thought it was a prank, but five dished some out. More came from the SPCA, which became Epic's first official poop supplier.

Igor and Aaron were also working on assembling the apparatus that managed the sewage flow, which would put sludge through the rotating mesh belt and then a wrangler to compact it into the palm-size glops that would be fed into the disinfecting mixer. Stringing the mesh belt and wrangler together was reasonably straightforward, but the father and son needed large quantities of sewage to test the process from end to end. In 2017, Epic began buying sludge from Stanford University's Codiga Resource Recovery Center, which had a miniature sewage station, to continue calibrating their system. "It cost 40 cents per pound," recalls Sebastien Tilmans, Codiga's executive director.

When even that stream proved insignificant, Epic began chugging sludge by the truckload—literally. By then, Epic Hub was located in a former car dealership, so the sewage trucks that were emptying some of the Bay Area septic systems would roll in to dish out their cargo. "We would stretch a hose from the truck into our system and let it run, end to end," Aaron says. "Some of these trucks carried sewage from a Facebook cafeteria bathroom," he explains. "Some of our soil is Facebook-made."

Once they tested the mixer-processor in their Epic Hub, the Tartakovskys approached the owners of NEMA (whom Igor knew) about testing it in real life. Building engineer Derwin Narvaez's first reaction was one of sheer disgust. "You’re going to do what?" he remembers asking. Seeing the tech in action won him over. "The end product is just black dirt!"

Standing next to the custom mixer, which resembles a giant meat grinder, Aaron demonstrates how that black dirt was produced during the pilot. The glops of excrement picked up from the sludge squeezer in the NEMA basement were shaken in from the collecting bin—and the machine would chew through them with Epic's disinfecting blends for about 20 minutes. Then Aaron would put the freshly made earth through a battery of tests, checking for pathogens and heavy metals, before letting it dry outside near the Epic Hub garden. "I always wondered what people in nearby skyscrapers thought we were doing," he says. "But no one complained," given there was no stink.

"My grandparents were holocaust survivors. considering what they went through, I can deal with sewage."

He scrapes some of the dirt residue from the mixer's innards and offers it to me. After some hesitation, I hold the powdery black substance in my hand and give it a timid sniff. It looks and smells just like the garden dirt from my grandfather's pits. But while his backyard-farm approach worked on a small scale, Epic's might change how we process sewage in entire high-rises, which is crucial, because two out of every three people worldwide will likely be living in urban areas by 2050.

Other companies are redesigning our relationship with excrement in their own unique ways. A group of pee-cyclers in Vermont founded Rich Earth Institute, a nonprofit that gathers urine from residents in containers and distributes it to farmers, but for many that manual process is a downside. Israel-based startup HomeBiogas pioneered a toilet that helps produce fertilizer and methane, the latter to be used for cooking fuel—a self-sustaining approach that works for private homes and small buildings, but not high-rises. South African company LiquidGold Africa developed a way to extract fertilizing compounds from urine, which can be collected en masse from plumbing in buildings, but it doesn't yet recycle solids. In Portland, Oregon, a large apartment complex, Hassalo on Eighth, built an entire outdoor wastewater treatment facility, but that requires a lot of surrounding space. Australia-based company Aquacell operates several building-level water recycling systems in the Bay Area; according to Kehoe, a few more are in the works, but Aquacell doesn't dig into the solids business. By comparison, Epic's end-to-end tech is particularly well suited for offices and dwellings in densely populated cities, the number of which will keep growing. "This firm seems to have a solid, innovative technology," says William Toffey, sustainability strategist at BlueTech Research, a company that specializes in water solutions. "The 1550 residence in San Francisco is its shiniest example."

Will more skyscrapers join in? Narvaez, who is now an ardent supporter, thinks so. "Rather than rationing water, buildings should adopt this approach," he says. "To me, it's the future of all new buildings. The buildings will save a lot, and so will society. It's a win-win situation."

In the coming years, Epic's next-generation OneWater system will be installed in four other buildings in San Diego and San Jose, where it will function as a full-blown mini-treatment plant. The mesh belt processor will squeeze water out of the sludge. The membrane bioreactor will clean it and put it back in circulation. And the mixer will turn the gunk into garden topsoil, eventually feeding the cities’ parks, the Tartakovskys hope. "We’ll use the same motto," Aaron says. "‘The soil by San Diegans for San Diegans.’ And so on."