Vincent Morris of D.C. Water examines Bloom, a new soil conditioner made from sewage biosolids, at the Blue Plains treatment plant in Southwest Washington. (Adrian Higgins/The Washington Post)
Gardening columnist

By the middle of the 19th century, life in the big city had become hazardous to your health.

The air was fouled by coal smoke, the graveyards were brimming with the urban dead, and the rivers were open sewers. Literally tons of horse manure coated the streets.

Cesspits contaminated streams and wells, leading to outbreaks of typhoid fever. One of the most unpleasant occupations of the day, of which there were many, was that of the night soil man. Working in teams, the night soil men emptied privies after sundown and carted away the contents, some of it to farms for use as a fertilizer.

Some medical experts believe that the ninth president, William Henry Harrison, did not die of pneumonia caused by an interminable inauguration speech but by ingesting contaminated water. The spring that supplied the White House was close to a depository for night soil. This was in 1841, before they drained the swamp.

One blessing of modern life is that the technology of sanitation has come a long way. Washington has one of the world’s largest advanced wastewater treatment plants at Blue Plains, a 157-acre complex across the Potomac River from Alexandria.

The steel reactors cook the sludge under pressure. Behind is one of the four digester tanks. (Adrian Higgins/The Washington Post)

Night soil of a sort is still spread on farm fields, except it is the treated sewage sludge or “biosolids” that is separated from wastewater. Traditionally, sanitation engineers mixed the sludge with high quantities of lime, which killed most of the pathogens. It was then hauled off to landfills or spread on farmers’ fields after a period of decomposition.

Blue Plains used to process about 1,100 pounds of biosolids daily, but since 2015 it has cut the amount by more than half thanks to the installation of a $470 million Norwegian thermal hydrolysis system. The lime is gone, instead processed sludge is sent to silo-like pressure cookers, which destroy bacteria, and is then piped to four colossal concrete tanks where microbes are added to digest the material. This produces methane gas used to fuel an adjoining electricity generating plant. The digested wastewater is pressed into a product that functions as a soil amendment and fertilizer.

The utility that runs Blue Plains, D.C. Water, is still developing a distribution stream for its product, Bloom. Most of the material is what it calls Fresh Bloom, meaning it hasn’t been dried and has a gummy consistency. Cured Bloom has been sun-dried and turned, reducing its moisture content and making it more soil-like.

The availability of Bloom recalls a biosolid named ComPRO that was used enthusiastically by D.C. area gardeners until Montgomery County closed the composting facility in 1999 because of persistent odor problems for neighbors.

The widespread use of sewage sludge in agriculture remains controversial: Environmental groups say it causes an odor and health problems for farm workers and surrounding residents and fear it is poisoning the soil. They point out that sewage sludge is not allowed on farms designated organic by the U.S. Agriculture Department.

Among the concerns: The Environmental Protection Agency is using outdated science in regulating biosolids, which may contain pollutants not considered decades ago.

D.C. Water delivers Bloom in bulk to commercial users and is working toward streamlining delivery of a drier version to homeowners. (D.C. Water)

“This is Flint, Michigan, happening everywhere in the country in slow motion,” said Lidia Epp, a biologist and critic of agricultural sludge use who lives in rural New Kent, Va.

Bill Brower, Blue Plains’ manager for resource recovery, said independent scientists “have looked at all the literature, and if biosolids are applied correctly there’s no significant risk to human health or the environment.” He said at Blue Plains — which serves the District, Montgomery and Prince George’s counties in Maryland and Fairfax and Loudoun counties in Virginia — industrial users account for a fraction of the incoming wastewater. And they are monitored to prevent pollutant discharges into the sewers, he said. Brower added that the levels of metals in Bloom are well below permitted EPA levels. The utility has posted soil test results at its website for Fresh Bloom and Cured Bloom.

The utility has begun to make it available in bulk to landscapers, tree growers, community gardens, school gardens, soil blenders and others, as well as to farmers through its biosolid contractor. The stuff is inexpensive — $5 a cubic yard for Cured Bloom — but the utility’s delivery system is aimed at bulk users. Residents can arrange to visit Blue Plains to pick up the material. Brower said plans are in the works to improve the production and availability of Cured Bloom for consumer use.

How does it perform in the garden? I haven’t tried it myself, but I found a couple of ringing endorsements.

Nadia Mercer, program director of the one-acre Washington Youth Garden at the National Arboretum, said she tested the product by comparing two beds containing cabbage and celery, one with the garden’s usual compost-amended soil and the other with Bloom incorporated. With the biosolids, “they grew a lot more rapidly, they were bigger and healthier in general,” she said. “I was really surprised with the difference.”

It clearly drove leaf growth but not so much the development of fruits such as eggplants and tomatoes, or in root vegetables such as carrots. “So it’s great for leafy things,” she said.

She said she feels comfortable using it on edible plants because “I trust D.C. Water is doing all the tests necessary to make sure it a very safe product.”

Frank Gouin, a retired horticultural scientist and orchardist in Deale, Md., said he has been testing it in hanging baskets planted in the spring — adding half a cup or a cup, depending on the size of the basket. “All they have had is water since then, and they have not stopped growing or blooming,” he said.

He likes it for such technical aspects as a low carbon-to-nitrogen ratio, high mineral content and its high cation exchange capacity, which is a measure of the availability of nutrients to plants. As a soil dressing, he recommends a rate of two cubic yards per 1,000 square feet, and half that for lawns.

As a planting and potting mix, he blends peat with compost and then adds Bloom, but no more than 20 percent by volume. The compost brings the beneficial microbes, the Bloom the nutrients. “I’ve spent 30 years working in compost research,” said Gouin. “I’ve never had these results."

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