Microwaving sewage waste may make it safe to use as fertilizer on crops — The Conversation


Water purification at a modern urban wastewater treatment plant involves removing undesirable chemicals, suspended solids and gases from contaminated water.
arhendrix/Shutterstock.com

Gang Chen, FAMU-FSU College of Engineering

My team has discovered another use for microwave ovens that will surprise you.

Biosolids – primarily dead bacteria – from sewage plants are usually dumped into landfills. However, they are rich in nutrients and can potentially be used as fertilizers. But farmers can’t just replace the normal fertilizers they use on agricultural soil with these biosolids. The reason is that they are often contaminated with toxic heavy metals like arsenic, lead, mercury and cadmium from industry. But dumping them in the landfills is wasting precious resources. So, what is the solution?

I’m an environmental engineer and an expert in wastewater treatment. My colleagues and I have figured out how to treat these biosolids and remove heavy metals so that they can be safely used as a fertilizer.

How treatment plants clean wastewater

Wastewater contains organic waste such as proteins, carbohydrates, fats, oils and urea, which are derived from food and human waste we flush down in kitchen sinks and toilets. Inside treatment plants, bacteria decompose these organic materials, cleaning the water which is then discharged to rivers, lakes or oceans.

The bacteria don’t do the work for nothing. They benefit from this process by multiplying as they dine on human waste. Once water is removed from the waste, what remains is a solid lump of bacteria called biosolids.

This is complicated by the fact that wastewater treatment plants accept not only residential wastewater but also industrial wastewater, including the liquid that seeps out of solid waste in landfills – called leachate – which is contaminated with toxic metals including arsenic, lead, mercury and cadmium. During the wastewater treatment process, heavy metals are attracted to the bacteria and accumulate on their surfaces.

If farmers apply the biosolids at this stage, these metals will separate from the biosolids and contaminate the crop for human consumption. But removing heavy metals isn’t easy because the chemical bonds between heavy metals and biosolids are very strong.

Gang Chen microwaves some biosolids, separating the organic material from the toxic metals.
Gang Chen/FAMU-FSU College of Engineering, CC BY-SA

Microwaving waste releases heavy metals

Conventionally, these metals are removed from biosolids using chemical methods involving acids, but this is costly and generates more dangerous waste. This has been practiced on a small scale in some agricultural fields.

After a careful calculation of the energy requirement to release the heavy metals from the attached bacteria, I searched around for all the possible energy sources that can provide just enough to break the bonds but not too much to destroy the nutrients in the biosolids. That’s when I serendipitously noticed the microwave oven in my home kitchen and began to wonder whether microwaving was the solution.

My team and I tested whether microwaving the biosolids would break the bonds between heavy metals and the bacterial cells. We discovered it was efficient and environmentally friendly. The work has been published in the Journal of Cleaner Production. This concept can be adapted to an industrial scale by using electromagnetic waves to produce the microwaves.

This is a solution that should be beneficial for many people. For instance, managers of wastewater treatment plants could potentially earn revenue by selling the biosolids instead of paying disposal fees for the material to be dumped to the landfills.

It is a better strategy for the environment because when biosolids are deposited in landfills, the heavy metals seep into landfill leachate, which is then treated in wastewater treatment plants. The heavy metals thus move between wastewater treatment plants and landfills in an endless loop. This research breaks this cycle by separating the heavy metals from biosolids and recovering them. Farmers would also benefit from cheap organic fertilizers that could replace the chemical synthetic ones, conserving valuable resources and protecting the ecosystem.

Is this the end? Not yet. So far we can only remove 50% of heavy metals but we hope to shift this to 80% with improved experimental designs. My team is currently conducting small laboratory and field experiments to explore whether our new strategy will work on a large scale. One lesson I would like to share with everyone: Be observant. For any problem, the solution may be just around you, in your home, your office, even in the appliances you are using.

Biosolids after collection from a waste treatment facility.
Gang Chen/FAMU-FSU College of Engineering, CC BY-SA

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Gang Chen, Professor of Civil & Environmental Engineering, FAMU-FSU College of Engineering

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Pagosa Area Water & Sanitation District is working up a strategy improve odor control

Oxidizing/Polishing Dry Air Scrubber provide a two stage chemistry for the control of odors from hydrogen sulfide (H2S), mercaptans, ammonia, amines and other odors generated in wastewater collection and treatment systems. They are easy to use, effective and economic. Photo credit: Syneco Systems

From The Pagosa Sun (Randi Pierce):

At its Jan. 7 meeting, the board of the Pagosa Springs Sanitation Gen- eral Improvement District (PSSGID) again worked to deal with a stinky issue that’s plagued the district and some Archuleta County residents — odor control near the town’s two pump stations in the Timber Ridge area.

The odor issues in the area began when the town started using a force main to move its collected waste- water to the Pagosa Area Water and Sanitation District campus for treat- ment. Construction of the pipeline was completed in 2016.

“The odor results from naturally high sulfur in the area, in waste, and the long detention times in the wet well and the force main,” an agenda brief prepared by Public Works Di- rector Martin Schmidt explains.

The PSSGID previously piloted an odor control project with little success, with Schmidt’s document stating, “it did not get close to the levels of H2S [hydrogen sulfide] that were stipulated in the contract.”

PSSGID staff, with engineering support, then brought back information on several options for the board to consider on Jan. 7, along with a recommendation to pair two of the technologies to best control odor and eliminate corrosion.

The four options brought to the board were an oxygen injection system, an aeration system with added ozone (the same technology as the pilot project), chemical dosing, an air scrubber system and an air-injector system that builds dissolved oxygen in the water to eliminate anaerobic bacteria.

Schmidt and Utilities Supervisor Gene Tautges recommended that the board combine the final two options.

The air scrubber system, manufactured by Syneco Systems Inc., has a small blower that creates a negative pressure in the wet well, the agenda brief explains.

“The removed air is scrubbed of H2S by a proprietary media that converts 100% of the H2S into a non-toxic polymer,” the document explains.
Schmidt noted the blower is not much larger than a bathroom fan, with Schmidt and Tautges indicat- ing it operates at a low decibel level, around 55 decibels.

Loveland celebrates $41.2 million in improvements to wastewater treatment plant

Photo credit: City of Loveland

From The Loveland Reporter-Herald (Max Levy):

Many may not care to think about what goes on in the Loveland Wastewater Treatment Plant, but the facility had plenty to brag about Tuesday, as officials showed off the fruits of a $41.02 million improvement project that wrapped up this fall.

The plant is responsible for reclaiming and returning the water used by Loveland residents to the Big Thompson River, while disposing of other waste.

Water and Power Director Joe Bernosky, who delivered one of the speeches at Tuesday’s “grand opening” and ribbon-cutting ceremony, described the plant as a crucial link in the water cycle that all of Loveland participates in.

“Water is a cycle — it’s not created, it’s recycled,” he said. “What this is doing is not necessarily treating wastewater. It’s reclaiming the water we’ve used.”

The improvements allowed the plant to be rerated to handle 12 million gallons of wastewater per day, an increase of 2 million gallons. Staff hope that increase will allow the plant to keep up with growth for an additional 10-15 years.

Bernosky added that the city’s partnership with Garney Construction was one of the most significant in Loveland’s history. Construction of the improvements alone cost $35.06 million, and the project finished under budget…

Improvements made to the facility include:

  • Installation of a new and reconfigured sewer collection system at the head of the plant.
  • Screening improvements with the addition of step screen technology, to remove pieces of trash such as wet wipes and hygiene products from the wastewater.
  • Mixing and aeration improvements to all six existing aeration basins.
  • A new and upsized digester facility.
  • The addition of a new return activated sludge anoxic tank.
  • Replacing pumps at the return activated sludge pump station.
  • Ultraviolet disinfection hydraulic improvements.
  • A new, 2,000 square foot maintenance building.
  • […]

    Project design began in March 2015 and construction started in April 2017. According to a city factsheet, over 2 million working hours were spent on the project.

    Southern Utes approve hefty rate increase for water, wastewater users — The Durango Herald

    Photo credit: Ute Camp in Garden of the Gods – Library of Congress

    From The Durango Herald (Shannon Mullane):

    The Southern Ute Indian Tribe Utilities Division will raise water and wastewater rates by more than 90% and 50%, respectively, starting Oct. 1.

    The Southern Ute Utilities Division, administered by the Southern Ute Growth Fund, provides both treated drinking water and wastewater treatment for the tribal campus, local tribal members living near Ignacio and the town of Ignacio. Discussions of rates have caused a rift between the town and the tribe, said Mark Garcia, interim town manager. While the town and the tribe analyze their agreement, ratepayers are stuck paying ever-increasing water and wastewater utility rates.

    “Wastewater and water rates are based on usage, and they’re going up,” Garcia said. Utility customers will be hit with the increase at different times, based on their level of use for water and/or wastewater. But for overall water and wastewater rates, “all levels of users will see probably an increase in their rates starting in 2020,” he said.

    Starting Oct. 1, ratepayers will pay higher base rates for fewer correlating gallons of water. Water rates will increase from $32.80 per 8,000 gallons to $47.80 per 6,000 gallons, a 94% increase. The rates will jump again Oct. 1, 2020, to $62.80 per 6,000 gallons, a 156% increase over current rates, according to a July letter to Garcia from the tribe.

    The town charges customers additional fees for billing, repairs and collections. Garcia said the town’s water fees will increase from $24.60 to $26.48 a month starting Jan. 1, 2020, a 6.4% increase.

    Wastewater rates will also increase. Service users currently pay $72.09 per ERT, or Equivalent Residential Tap, per month. One ERT allows for 7,500 gallons of usage.

    That billing system will change. The tribal utility will charge the town based on winter usage, not ERT. This shift will also make ratepayers pay more for fewer gallons. On Oct. 1, the rate will increase to $87.09 per 6,000 gallons, a 51% increase over current rates. Wastewater rates will jump again in 2020. Users will be charged $102.09 per 6,000 gallons, a 77% increase over current rates.

    The town charges an additional $9.88 base rate to users for billing, repairs and collections.

    According to Garcia, the average town customer uses 4,000 gallons of wastewater per month, so ratepayers are paying for more wastewater than they are using.

    “With the new rates and winter flow basis, the rates that the tribe charges the town as a bulk customer will actually go down from the current bulk rate charged,” the tribe wrote in a June news release.

    Cortez: Six-month project to repair sanitation infrastructure on the north side to turn dirt July 1, 2019

    Cortez early 1900s via Crow Canyon Archaeological Center

    From The Cortez Journal:

    The Cortez Sanitation District contracted with Four Corners Materials for the construction, which will include replacing 1 mile of sanitary sewer line and manholes along with reconnecting sewer services between North Ridge Drive, North Market Street and West Empire Street.

    Greeley Water Pollution Control Facility awarded a National Association of Clean Water Agencies (NACWA) Peak Performance Platinum 8 Award

    Photo credit: Greeley.gov

    From The Greeley Tribune (Tamara Markard):

    NACWA recognizes wastewater plants that achieve 100% compliance with the National Pollutant Discharge Elimination System (NPDES) over a consecutive five-year period.

    The Greeley wastewater plant discharges more than 7 million gallons of treated water back into the Poudre River daily. Compliance with permitted requirements ensures that water is safe for downstream users, aquatic habitats, and the environment, according to a Greeley news release…

    The wastewater plant maintains compliance through the operation and support of various systems that remove pollutants from the wastewater. Samples of the water are then tested and analyzed to ensure that the proper treatment has been performed…

    or more information on the plant, water and sewer utilities, or to inquire about a tour, call (970) 350-9360 or visit http://www.greeleygov.com/water.

    The Metro Wastewater Reclamation District honored 19 metro area organizations for perfect compliance with their industrial wastewater discharge permits on May 8, 2019

    Here’s the release from the Metro Wastewater Reclamation District (Kelly Merritt):

    The Metro Wastewater Reclamation District (Metro District) honored 19 metro area organizations for perfect compliance with their industrial wastewater discharge permits on May 8, 2019. Water Remediation Technology, LLC, received a Platinum Award for perfect compliance for five consecutive years (2014 through 2018).

    The following were recognized with Gold Awards for perfect compliance from January through December 2018:

     Acme Manufacturing Company, Inc.
     Advanced Circuits, Inc.
     Ball Metal Beverage Container Corp.
     CoorsTek, Inc.
     CW Elaborations, Inc.
     Denver Metal Finishing
     G & K Services, A Division of Cintas
     Industrialex Manufacturing Corp.
     Majestic Metals, LLC
     Packaging Corporation of America
     Pepsi Beverages Company
     RMO, Inc.
     Rocky Mountain Bottle Company, LLC
     Safeway, Inc., Denver Beverage Plant
     Swire Coca-Cola, USA
     United States Mint
     Upsher-Smith Laboratories, LLC
     Wanco, Inc.

    The federal Pretreatment Regulations under the Clean Water Act require the Metro District to have an Industrial Pretreatment Program to control the discharge of industrial wastes to the sanitary sewer system. One of the ways that the Metro District controls these discharges is through issuance of industrial wastewater discharge permits.

    Metropolitan Wastewater Reclamation District Hite plant outfall via South Platte Coalition for Urban River Evaluation