Wading Through the Waste Stream: Turning Solid Waste into Energy and Fertilizer

fertilizer from sewage waste at Orem Wastewater Treatment facility
fertilizer from sewage waste at Orem Wastewater Treatment facility

-By Elisabeth Luntz

Editorial note: This is the second of a two-part series focused on waste treatment and public policy amidst Utah’s explosive growth. Part I was published in November and can be found here.

Just west of the Utah Valley University West campus, a couple hundred yards off Geneva Road at 1000 South, is Orem City’s sewage treatment plant, servicing 297 miles of sewer line for both Orem and neighboring Lindon.  Across the street is a park with a children’s  playground, residential neighborhoods, and nearby are two high schools for at-risk kids, including pregnant teenagers. Most visitors wouldn’t realize that the city’s 297 miles of sewer line converge at this one facility.  The purification process is fairly simple, and the odor is, for the most part, contained.

Incoming wastewater is screened at the headworks when it enters the facility.  Two cubic yards a week of screenings are buried in a landfill, the remaining wastewater flows through bioreactors where organic contaminants and nutrients are stabilized by microorganisms.  Suspended solids settle to the bottom of clarifiers and clear water flows out over the top. It then proceeds to the biological nutrient removal process where high levels of nitrogen and phosphorous are broken down in the absence of oxygen. This is a critical step in the process to reduce nutrients that contribute to the toxic algae blooms that are forcing marina closures across the state. The water is then disinfected by ultraviolet light and released into Utah Lake and surrounding wetlands.

In addition to the eight million gallons of water a day that the facility treats, they convert 30 tons of biosolids into fertilizer and generate 120 cubic feet per minute of methane daily. The biosolids are funneled through five hundred feet of heated pipe in the thermophilic digester where temperatures are maintained at 125-130 degrees. The temperatures are then lowered to 95-100 degrees for further pathogen reduction in the mesophilic digester.

There are two sources for the digesters; raw solids from the primary clarifiers and processed aerobic biosolid waste. Prior to the implementation of the Clean Water Act in 1972, water quality standards were low and anaerobic treatment was the cheapest.  

Subsequent to the Act, an aerobic treatment system was developed which requires more energy but produces a higher quality fertilizer.  After the aerobic process, approximately 150 gallons a minute of biosolids are pumped over to the anaerobic cycle.  When the sludge reaches full treatment it is transferred to aluminum covered holding tanks and then it goes through belt presses to remove more water.  The result is a high-quality fertilizer that is trucked to local farms and given away at no cost. Lawrence Burton, Reclamation Manager at the Orem facility explains the benefits of giving this product away are both environmental and cost effective, “It costs a minimum of $20 a ton to dispose of this in a landfill, a farmer will take it off our hands for free. Hauling is the only disposal cost.”  This keeps costs down for both the city and the farmers.  Burton added, “It also yields a better product for the environment than commercial fertilizers that are loaded with phosphorous and nitrogen.”

unused methane gas burning off on site at Orem wastewater facility
Unused methane gas burning off on-site at Orem Wastewater Treatment facility. photo credit Elisabeth Luntz

The methane that is a byproduct of the anaerobic digesters, is captured and about 50%-70% of it is used to fire the boilers that heat the thermophilic digesters, the rest of the methane is burned off, on-site in a manner similar to natural gas flaring and is a source of public concern during Utah’s notorious winter inversions.

The majority of lower atmospheric ozone formation occurs when nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOC’s), react in the atmosphere in the presence of sunlight. NOx, CO, and VOC’s are called ozone precursors.

VOC’s are a large group of carbon-based chemicals that easily evaporate at room temperature and, while most people can smell high levels of some VOCs, others have no odor. Sources of VOCs are both biological, as with plants, and also man-made, such as from paints, fossil fuels, formaldehyde, and methane gas.

Compared to other hydrocarbon gasses, methane produces less carbon dioxide but current research shows that these VOC sources react with other chemicals in the atmosphere to form ozone. Ozone can cause the muscles in the airways to constrict, leading to wheezing and shortness of breath. According to the Environmental Protection Agency, “Recent studies consistently report associations between short-term ozone exposures and total non-accidental mortality, which includes deaths from respiratory causes.”  The Orem treatment facility is located on land zoned “Controlled Manufacturing” (CM), as are the adjacent high schools, according to Orem city’s Long Range Planner, Christian Kirkham.

accumulation of suspected insulation material from illegal disposal
Accumulation of suspected insulation material from illegal disposal.  Photo credit, Lawrence Burton

As for the mysterious contaminate that has been a costly and time-consuming menace to the plant for the last 6 months, Burton says, “We have narrowed down what it is and where we think it is coming from. I went to Home Depot and purchased a bag of ground cellulose insulation material and we looked at it under a microscope comparing it to catch samples we collected and they were identical.”  Because the material was non-toxic and did not create any environmental concerns in state waters, the city is responsible for enforcement or punishment.  Fines and punishments vary.  Burton estimated, “It can start with thousands of dollars per episode if our legal team can prove it is the same person each time. It can get more severe from there, depending on whether it was a malicious act or an innocent discharge without knowledge.”

Converting waste to energy in treatment plants and producing a useful commodity like soil enrichments are becoming critical conservation practices as the city continues to grow along with all of Utah. Increasing the efficiency and applications of the methane capture process will reduce the ozone impacts throughout the valley and also reduces energy costs and other social impacts associated with developing new fossil fuels.

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