How much value is your utility getting out of sewage?
Officials at DC Water, which takes in 1,500 tons of sewage each day, see waste as “liquid gold” that can be used to pay for water infrastructure, according to Fortune.
The utility turns sewage into a soil fertilizer called “Bloom,” which it ships to nurseries and garden centers, the report said. It’s all part of an “ambitious” initiative that begins when sewage arrives at the treatment plant, the report said:
Oils, fats, sediments, and objects are screened out, and the water is disinfected. The remaining sludge then goes through a three-stage process that cooks it in high heat and pressure, sterilizing and softening it. The clean sludge is then sent to four 80-foot-tall anaerobic digesters, where giant mixers churn the liquid for two weeks while a population of microorganisms called “methanogens” eats the organic matter, producing methane gas for electricity that ultimately powers a third of the water plant’s operations. The solids then travel to a belt-filter press that squeezes out water and delivers the crumbly compost to bunkers that can hold 1,000 tons each.
The resulting Bloom can be used to fertilize gardens and trees. Bloom is in high demand, Brian Riddle of Homestead Gardens said in the report.
DC Water required upgrades before it could produce Bloom, according to a blog post by George Hawkins, head of DC Water.
“Before we built our CAMBI system, we produced Class B biosolids. Not as clean, and subject to different regulations than Class A, this type of material works great on farms. We would pay millions of dollars a year to truck it down to farmers in Virginia, who were delighted to receive it for free. In fact, we had a 2-year waiting list!” he explained.
“But that’s a lot of trucks and a lot of money. It’s also the traditional way of recycling biosolids in the United States. With Class A Bloom, we are shifting our business from waste disposal to resource recovery,” he continued.
Resource recovery is touted by environmental policymakers around the world. The United Nations made a major push this year for water managers to support the recovery of resources from sewage. The UN “Why Waste Water?” campaign is a vehicle for the organization’s sewage messaging, which highlights recycled water as an important part of making the most out of sewage.
The campaign factsheet cites St. Petersburg, FL, as an example of an effective recycled water program.
“Since 1977, in St Petersburg, Florida, USA, a parallel network of pipes, separate from potable water mains, has served a mix of residential properties, and commercial and industrial parks, enabling them to use recycled water for irrigation, laundry, vehicle and building washing, and ornamental water features,” the fact sheet says.
For more on wastewater resource recovery visit Water Online’s Sludge And Biosolids Processing Solutions Center.
Image credit:"Cherry Washington Monument," Tom Finzel © 2013, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by/2.0/