Composting Process

What’s in Oquirrh Mountain Compost?

Oquirrh Mountain Compost products are loaded with nutrients and other elements that are good for your grass and plants, all at a price that’s good for your wallet, too.  Our compost products offer you an attractive medium for your gardening needs.

Oquirrh Mountain compost is made from a blend of Central Valley Water Reclamation Facility biosolids and ground wood.  The biosolids are derived from the wastewater treatment process as explained in more detail below and on the Central Valley Water Reclamation Facility website (CVWRF.org).  The ground wood chips are produced from waste wood chips, branches and logs generated from the local tree trimming and service industry.  The chips consist of mixed hard and soft woods with small amounts of leaves, needles, and bark.  The wood waste is processed through a large industrial chipper/shredder and screening system to produce the optimum particle size mixture for compost production.

Here are just some of the benefits:

  • Compost provides plenty of macro and micro nutrients for your plants such as phosphorus, nitrogen, magnesium, potassium, iron, sulfur and zinc. A chemical fertilizer would provide some but not all of these nutrients. These nutrients are derived from the food we eat.
  • Compost is ideal in low-water landscaping conditions because it provides a complex organic carbon substrate derived from both the biosolids and decomposed wood products that conditions soil to provide more moisture holding capacity.
  • Compost has a relatively low ammonia content and a high amount of organic nitrogen that’s released slowly, so you stretch out the benefits. The slow-release feature of the organic nitrogen helps compost to last for an entire season.
  • Research shows that plants grown in biosolids compost grow taller and produce more mass than those grown in conventional green waste compost, grown without compost, or grown with chemical products (Correa, R. S., et.al., 2005, Klock-Moore, K. 1999).  Specific research conducted by Utah State University on CVWRF’s anaerobically digested biosolids used to make Oquirrh Mountain Compost shows that land application of biosolids on depleted rangeland soils significantly increases soil moisture holding capacity and forage plant quantity and quality.  Research papers from the Utah State University studies can be downloaded here:
    Biosolids Article in Biocycle
    Water Practice Article

Oquirrh Mountain Compost helps the environment and greens our community.

How Are Oquirrh Mountain Compost Products Made?

Here’s a little about how the wastewater treatment process works, and how we reuse biosolids and waste wood to make Oquirrh Mountain Compost Products.  For more information visit the Central Valley Water Reclamation Facility Website at CVWRF.org:

The Wastewater Treatment Process

Used water that goes down our sinks, tubs and toilets in our homes and businesses enters the sewer collection system and becomes wastewater. The wastewater from a large portion of Salt Lake County eventually ends up at the Central Valley Water Reclamation Facility.  At the Central Valley Water Reclamation Facility the wastewater is treated to separate and process the liquids and solids, then return them safely to the environment. Because wastewater treatment destroys disease-causing organisms that may be in the wastewater, it protects public health and safeguards water quality, preventing pollution in our lakes and rivers.

Wastewater Treatment

Once wastewater flows to the treatment facility, screens and preliminary treatment facilities remove trash and grit materials such as sticks, rags, wipes, plastics, sand and gravel that are harmful to downstream processes.  These trash materials are disposed of in the landfill.  The wastewater then slowly flows through large primary sedimentation tanks, where gravity physically separates organic solids from liquids. The partially treated water flows from the top of the tanks to a secondary treatment process and the solids that settle to the bottom are removed from the primary sedimentation tanks and enter the solids treatment process.

In secondary treatment, the water passes through trickling filters, aeration basins and secondary clarifiers where the biological action of a culture of beneficial microorganisms removes residual organic solids and dissolved organic matter. The process grows a large quantity of microorganisms, a portion of which must be continuously removed from the system.  The waste microorganisms that are removed from the secondary process also enter the solids treatment process.

Finally, the clean water flows through a disinfection process where high intensity UV light is used to inactivate harmful bacteria and other microorganisms before the water is released to the environment.  The water is now ready to safely return to Mill Creek and the Jordan River or be treated further for reuse to irrigate the Central Valley Golf Course.

Solids Treatment

The Central Valley Water Reclamation Facility uses anaerobic digestion and in-vessel aerated static pile (IASP) composting to ensure our composted biosoids is what’s called Class A – Exceptional Quality, EPA’s highest rating, so that our products are completely pathogen free.  By using the IASP process, we make sure that our biosolids products are safe, and what’s more, it helps us produce a product that consumers want to use in their yards and gardens.

First, in our two stage anaerobic digestion process, a culture of beneficial microorganisms decompose – or digest – the waste primary and secondary solids at mesophilic temperatures of 98 degrees F. The solids are held in the digestion tanks for approximately 30 days under conditions that exclude all air and oxygen while mixing continuously to promote thorough anaerobic decomposition.  This biological stabilization process reduces the solids mass by approximately 50 percent by turning the solid material into methane gas.  The methane is collected and burned in large engine generators to produce electricity that powers the wastewater treatment process and heat to warm the digestion process.  The anaerobic digestion process also significantly reduces the potentially harmful microorganisms contained in the solids and reduces odors. The anaerobic digestion process is classified in Federal Regulation 40 CFR 503 as a Process to Significantly Reduce Pathogens (PSRP).

The stabilized solids from the digestion process are now called biosolids and are mostly highly degraded organic matter, rich in essential plant nutrients such as phosphorus and nitrogen. We can return biosolids in de-watered form directly to the environment by applying them on agricultural land as a Class B product or use them to produce a higher quality Class A compost product for use by the general public in landscaping and gardening.

To produce the Class A compost, we use a technology called the in-vessel aerated static pile (IASP) method.  This composting method is classified in Federal Regulation 40 CFR 503 as a Process to Further Reduce Pathogens (PFRP). For this method, we mix the dewatered biosolids with ground wood chips and place the mixture in large covered windrow piles.  Photographs of the composting process and sequence are provided below.  The windrows piles are built on a concrete pad that contains an air plenum under the pile.  Once built, the windrows are covered with a special tarp containing a breathable membrane laminated between two layers of polyester fabric. 

The breathable membrane provides a barrier that most long chain molecules, fatty acids, sulfur compounds and other odorous and volatile organic compounds cannot penetrate while air and water vapor can pass through.  The tarps and some of the other specialized equipment used in the composting process are supplied by Managed Organic Recycling, Inc. (MOR). More information about the IASP composting process and equipment used can be found on MOR’s website.

The tarp is sealed against the concrete surface and then air is blown into the air plenum and through the pile to provide oxygen to the composting process.  The membrane tarp allows the air to pass through but retains moisture, heat, and odorous compounds which are broken down over time.  The temperature of the pile is measured continuously and the air flow adjusted to provide optimum composting conditions.  Sufficient heat is produced and retained within the pile by the biological process to heat the pile to greater than 131 degrees F. and kill pathogenic organisms.

compost diagram.fw
Schematic of In-vessel Aerated Static Pile Composting (provided courtesy of Managed Organic Recycling, Inc.)

  1. Air is provided throughout the windrow pile continuously along the length using air diffusion plenums in the concrete slab below the pile. This pumps necessary oxygen to the microorganisms that perform the aerobic decomposition process.
  2. Oxygen is released through the pile and membrane.
  3. Liquid moisture is condensed and contained while water vapor is released.
  4. Carbon Dioxide molecules escape.
  5. Odorous compounds are contained and decomposed.
  6. Heat that is self-generated within the pile by decomposition is trapped.
  7. Micro-organisms accelerate decomposition.
  8. Volatile organic compounds are contained and degraded.
  9. Nitrogen gas is released

After approximately 4 weeks the cover is removed, the pile is mixed with a large piece of equipment called a windrow turner, the cover is replaced and the composting is resumed for another 4 weeks.  Finally, the cover is removed, the pile is mixed again and then allowed to cure for 2 to 4 weeks.

After curing, the compost is tested and is ready to be released to consumers.  For finer compost products such as premium screened compost and for composted wood chips, the compost is screened in a large drum screen to separate the larger chips from the finer material.

 

   

   

 

 

   

   

 

 

   

 

wood chips into rotomix sludge into rotomix
rotomix blades rotomix mix
  1. Wood chips are loaded into the large bin on the back of the rotomix truck
  2. Biosolids are placed on top of the chips in the rotomix truck
  3. Large mixers in the bin are used to thoroughly blend the biosolids and wood chips
  4. The blended mixture in the bin prior to placement in the compost windrow pile
 

   

   

 

 

   

 

chip bed rotomix at the pile
  1. A bed of chips is placed on the concrete pad over the air plenum where the windrow will be made
  2. The conveyor on the rotomix truck places the biosolids/chip mixture on the chip bed
 

   

   

 

 

   

 

tarp winder 1 tarp 1
  1. A large membrane tarp is placed over the windrow pile
  2. The tarp is fastened to the concrete with special brackets

   

 

   

   

 

 

   

 

scarab start of pile covered and uncovered
  1. A windrow turner is used to mix the pile after 4 weeks when the tarp is removed
  2. A covered pile actively composting (left) and an uncovered pile curing (right).  The flags are attached to temperature probes used to control the air flow and composting temperature
 

   

   

 

 

   

 

sampling 2 sampling 1
11 and 12.  Samples of the final compost product are collected for laboratory analysis
   
 

   

   

 

 

   

 

Screener bagged
  1. The product is screened to separate composted chips from premium screened compost
  2. A portion of the premium screened compost is bagged for retail sale while the remainder is sold as bulk product

   

References:
Correa, R. S., et.al., 2005.  “Biosolids Effectiveness to Yield Ryegrass Based on Their Nitrogen Content”. Sci. Agric., Vol. 62 No. 3.
Klock-Moore, K. 1999.  “Bedding Plant Growth in Greenhouse Waste and Biosolids Compost”. Hortechnology, April-June, 9(2).