This story starts with a flush, not here in Colorado, but all the way across the country — in New York City sometime in early 1992: The flush that changed history.



Picture it — well, OK, don’t exactly picture it. But imagine the network of subterranean sewer pipes through which the flush travels to reach a wastewater-treatment plant, where it is swirled, settled and separated, the cleaned water being discharged into the Hudson River and the solid remains being packed onto a train car that rumbles west across the Great Plains and finally stops in sun-bleached Lamar, where its contents are destined for the fields of a wheat-farmer-turned-jurist whose interest in the cargo is the subject of such local skepticism and snickering that he soon earns the nickname “The Sludge Judge,” but whose decision to spread what are more officially known as “biosolids” on his fields marks a new phase in the marriage of agricultural fertilization and human-waste management.



Yes, this is a story about where feces go in Colorado once they bid you adieu — the secret afterlife of poop. It’s a lot more lively than you’d think.



“At first,” the judge, Douglas Tallman, told The New York Times in 1993, “people wanted to flee that land when they found out New York’s sewage was on the way. But if there was ever a true sister city for New York, it’s Lamar. Your waste comes out here and fertilizes our wheatfields. That helps make some of the bread that finds its way back to your tables.”



Tallman wasn’t the first in Colorado to apply biosolids to his land. And the New York City poop train doesn’t roll into Colorado anymore — it was last spotted this summer stuck in a small town in Alabama, where New York sends its waste to landfills because the shorter trip is cheaper.



But the widespread interest that those maiden journeys generated among farmers, combined with a long-running research project at Colorado State University, helped create the dominant system for disposing of human waste in Colorado: Treat it, dry it and use it as farm fertilizer.



That — at least from a storage-capacity standpoint — makes wastewater managers probably the least-stressed-out people in the broader waste industry even as Colorado’s population continues to boom. Despite more and more poop coming down the pipes, Colorado has lots of farmland and a waitlist of farmers wanting to apply biosolids.



“We’re not even close (to capacity),” said Jim Ippolito, a professor in the soil and crop sciences department at CSU who has spent most of his career studying the efficacy and safety of using biosolids as fertilizer.



In a follow-up email, Ippolito estimated that perhaps one of every 200 acres of farmland in the state has biosolids applied to it.



“We have no problem with land,” he said.

And Colorado — specifically, the Denver metro area — has no shortage of poop. The city is the largest producer of biosolids between Chicago and Los Angeles, Ippolito said.



That waste flows not directly into the South Platte River but into what could be considered one of the South Platte’s major tributaries: the plumbing connected to metro-area homes.



Those pipes eventually lead to a wastewater-treatment plant — for most of the metro area, the plant is the Metro Wastewater Reclamation District’s enormous Robert W. Hite Treatment Facility, near East 64th Avenue and York Street in Adams County. The facility, which serves an estimated 2 million people, treats 130 million gallons of wastewater a day and discharges a roughly equal amount of water back into the South Platte. A new Metro Wastewater plant that just opened near Brighton has the ability to treat another 24 million gallons a day, with the space to add more capacity as needed.

Treated water spills out of the Metro Wastewater Reclamation District’s massive Robert W. Hite Treatment Facility in Adams County, on Sept. 19, 2018. The plant treats and discharges 130 million gallons of wastewater a day. (John Ingold, The Colorado Sun)

At times during the year, as much as 85 percent of the flow of the South Platte downstream from the plants can be made up of treated water, said Jim McQuarrie, the district’s director of strategy and innovation. On Tuesday, for instance, a U.S. Geological Survey gauge just above the Hite plant’s discharge point measured the South Platte moving at nearly 30 cubic feet per second. Twelve miles downstream, in Henderson, a gauge operated by the state measured the river moving at nearly 170 cubic feet per second.



The process to separate waste and water is generally low-tech. Heavy screens block the biggest items in the flow. Metro Wastewater workers have pulled out bricks, 2x4s, money, eyeglasses, dentures and any number of other things that somehow made it into sewer pipes. One worker — McQuarrie swears this is true — once rescued a live, exotic snake from the intake screens and now keeps it as a pet.



Inside the plant, solids settle out in large, round “clarifier” tanks, while microorganisms work to chew up other waste in the water. Both the solids and the microorganisms are eventually routed to large “digester” tanks for further munching before going through a drying and testing process and being loaded onto trucks. (The water, meanwhile, goes through additional processes to disinfect and remove chemicals before being discharged into the river.)



McQuarrie said the Hite plant produces 10,000 to 12,000 wet tons of biosolids a month (or about 2,200 to 2,600 dry tons), and there’s a waitlist of farmers who want to buy them. Biosolids are priced based on their nitrogen content — more nitrogen, which plants need to grow, means a higher price. To ensure there’s always somewhere to take their product even if other farmers lose interest, Metro Wastewater owns a 52,000-acre farm east of Denver where it grows wheat, corn and other crops.



All told, farmers spread nearly 53,000 dry metric tons of biosolids on Colorado fields last year, according to statistics from the Colorado Department of Public Health and Environment.



“The alternative,” said McQuarrie, “is chemical fertilizers.”

A wheat field at Metrogro Farm near Deer Trail, photographed on Sept. 19, 2018. The 52,000-acre farm, which grows wheat, corn and sorghum, is owned by the Metro Wastewater Reclamation District and uses biosolids — sewage sludge treated at a Metro Wastewater plant — as fertilizer. (John Ingold, The Colorado Sun)

But is it actually safe to use human waste as fertilizer? Is it good for the plants?



CSU’s Ippolito has spent the past 27 years trying to answer those questions, beginning as a graduate student and working on study plots in eastern Colorado fertilized by biosolids from Englewood and Littleton. The studies, begun by a since-retired professor, now comprise the longest-running research project for the soil and crop sciences department.



Ippolito has found that nitrogen-rich biosolids release their nutrient cache more slowly than chemical fertilizers, providing longer-lasting benefit to crops. They improve water retention in the soil. More grain is produced by wheat grown in test plots where biosolids are applied.



Two USGS monitoring studies at Metro Wastewater’s farm have found that use of biosolids didn’t significantly change groundwater quality or result in heavy metal uptake in plants.



“When I started working in this field 27 years ago, there was a lot of skepticism, a lot of eyebrows raised,” Ippolito said. “Over the years, our program has proven that’s it’s relatively safe. There’s hardly any questions anymore that come our way, to be honest with you.”



That view isn’t shared universally, though. A vocal community nationwide has argued against using biosolids as fertilizer. Their concerns center around other chemicals — from pharmaceuticals, for instance — that may not be removed during the treatment process and that they fear concentrate in biosolids.



“Biosolids generated in our large industrialized urban centers — and 84 percent of land-applied sludge originates in those centers — is very likely the most pollutant-rich waste mixture of the 21st century,” Caroline Snyder, a retired university professor who founded the group Citizens for Sludge-Free Land, wrote to a Pennsylvania legislative committee in 2016.



CSU colleagues of Ippolito’s have documented that rainfall in the weeks after biosolids are applied can cause runoff of steroid hormones. And Metro Wastewater’s McQuarrie said wastewater managers across the country are monitoring new research coming out about pharmaceutical byproducts and about chemicals that can mess with the endocrine systems of humans or wildlife to figure out how to better treat both water and sludge.



But, meanwhile, Metro Wastewater is pressing ahead with a new use for sewage. In the next two years, it expects to have a system in place that pulls phosphorous out of sludge for use as a separate fertilizer. McQuarrie said it could be helpful to farmers growing flowers or for lawn care.



“We’re one of the first in the country to evaluate it,” he said.



Which, in a kind of fitting, circular way, brings Colorado back to where we started this story — at the forefront of poop innovation, where solutions often come from within.

The unflushables:



For the most part, what makes it into sewer pipes from your toilet or kitchen sink moves swimmingly along to the wastewater treatment plant. But wastewater experts have a couple of pet peeves about stuff that ends up in the sewers all the time and can really gum up the works: grease and so-called “flushable” wipes.



The former — which includes bacon grease and other fats from meat but also can include cooking oils — often congeals in the cold of the sewer system. The latter may be able to be flushed but they shouldn’t because the wipes don’t break down the way toilet paper does.



Combined, the two can meld together into something out of a nightmare: an ever-growing “fatberg” that blocks sewer lines dozens of feet underground and bedevils public-works crews. One such fatberg formed in Denver’s sewer’s in 2013.



“We have to physically go down there and collect all the wipes and bring them up and get rid of them through the trash system,” Denver Wastewater Management’s Lupe Martinez told Fox31 at the time.



So, please, flush responsibly.

This story was updated at 2:45 p.m. on Sept. 20, 2018, to clarify the amount of biosolids produced every month at Metro Wastewater’s Hite plant.