Wastewater Treatment Process
Welcome to the Logan Regional Wastewater Treatment Facility.
Headworks
At the headworks, raw wastewater flows into the Logan Regional Wastewater Treatment Facility (LRWWTF) from a collection system of underground pipes and lift stations covering Smithfield to Nibley. Here, the influent wastewater is preliminary treated through screening and grit removal. The LRWWTF is designed to receive an average 18 million gallons of wastewater per day.
Band screens with 6mm diameter holes capture and remove larger debris such as rags, disposable wipes, sticks, and many other materials that get sent down the collection system. These screenings get washed and compacted, then transported in a bagged bin to the Logan Landfill.
Following screening, the wastewater flows into circular vortex grit basins that slowly stir the wastewater with paddles to settle out sand, gravel, fingernail clippings, seeds, and other inert grit materials. Grit pumps transfer the grit from the center of the basins into grit classifiers. The classifiers dewater the grit by auguring the material up a chute into a roll-off bin that is transported to the Logan Landfill.
The influent wastewater is then transferred by four large influent pumps down a mile long pipe to the main facility site for further treatment in the bioreactors.
Bioreactors
LRWWTF has three bioreactor basins that hold two million gallons of wastewater each. LRWWTF’s bioreactor process is called a 3-Stage Bardenpho process because each bioreactor has three separate zones that encourage the growth of certain bacteria to remove organic matter and excess nutrients from the water.
The three zones are:
1. Anaerobic, an oxygen free environment perfect for preparing heterotrophic phosphorous accumulating bacteria for phosphorous uptake.
2. Anoxic, an oxygen free environment containing nitrate (NO3) envouraging heterotrophic denitrifying bacteria.
3. Aerobic, an oxygen rich environment where phosphorous uptake occurs and encourages autotrophic nitrifying bacteria.
Each of the three zones contain submerged mixers to keep the mixture of microorganisms and wastewater, called mixed liquor, suspended throughout the bioreactors.
Secondary Clarifiers
Mixed liquor from the bioreactors flows over the bioreactor effluent weirs and is gravity fed by pipes into the center of the secondary clarifiers. The purpose of the clarifiers is to separate the solids from the water by settling the solids to the bottom of the clarifier.
Two rake arms rotate along the bottom of the clarifier to scrape the solids to a center cone connected by pipe to large pumps. At this point in the process, the majority of solids in the water are suspended biological solids, namely the bacteria responsible for treating the water in the bioreactors. These biological solids get pumped back to the bioreactors so the bacteria can continue treating the water. Recycling solids back to the bioreactors is called Return Activated Sludge (RAS). A portion of these solids is also wasted each day as Waste Activated sludge (WAS) to make room for new bacteria to grow.
The water in the clarifiers is displaced by flows from the bioreactors and overflows the outer rim clarifier v-notched weirs. The displaced water flows along a weir trough into a collection box.
Overall, water spends approximately 9 hours in the facility while solids are retained 15 to 20 days.
UV Disinfection
The water that overflows the weirs in the clarifiers, gravity feeds into the UV disinfection building. Two channels, each containing three banks of twelve UV tube lamps, provide UV disinfection. UV disinfection destroys and inactivates bacteria, viruses, and other pathogens that could cause waterborne diseases. Hydraulic drives can raise and lower the UV banks at an angle in the channels to provide easy access for maintenance.
Once the water is disinfected, weir troughs and jet mixing pumps turbulate the water to add oxygen before the water is discharged back into the environment (effluent). LRWWTF’s treated effluent is discharged into irrigation canals that flow to manmade wetlands and then into Swift Slough which connects to Cutler Reservoir. From April 15th to October 1st, farmers to the west of the facility use LRWWTF’s effluent for irrigation of animal feed crops. The LRWWTF effluent is NOT suitable for drinking water or for irrigation water on crops associated with human consumption.
BioMag/RAS Building
The BioMag/RAS building houses the pumps that pump the RAS from the clarifiers back to the bioreactors. This building also houses the equipment for LRWWTF’s BioMag® system.
The BioMag® system involves adding a dense iron ore, magnetite, into the bioreactors through the RAS flow. Magnetite acts a ballast that makes the biological solids settle faster in the secondary clarifiers. Without the magnetite, LRWWTF would need at least double the amount of secondary clarifiers to provide enough solids settling time. A benefit of magnetite is its magnetic properties that make it recoverable. Magnetic recovery drums are responsible for recovering the magnetite from the portion of solids that are wasted each day (WAS). Approximately 90% of the magnetite is recovered in the process.
The recovered magnetite gets pumped back to the bioreactors with the RAS. The leftover WAS is pumped to a solids holding tank and then onto the dewatering process.
Solids Holding
The solids holding tank provides approximately seven days worth of storage for WAS. This tank is utilized so that the dewatering equipment does not need to be run constantly.
Three jet mixing pumps keep the solids holding tank mixed and aerated. Keeping the solids aerated reduces offensive odors that can occur when organic solids begin to degrade anaerobically.
Dewatering
WAS from the solids holding tank gets pumped to rotary press units where it is blended with polymer in a flocculator to thicken the solids. The press units then squeeze the water out of the solids to create a dewatered biosolid cake. Dewatered solids fall through floor chutes into carefully positioned trucks. The dewatered cake has a total solid content of 14-16%. Currently these biosolids are sent to the Logan Landfill; however, Logan City is working on constructing a composting facility that will blend the biosolids with green waste to create a nutrient rich, Class A compost. Class A compost has the strictest treatment requirements to ensure that it is safe for use by the general public, such as in household gardens.
Operations Building
The operations building houses LRWWTF employee offices. Any visitors to the facility will need to check in at the front desk in this building. For the safety of our employees and visitors, the facility is open to approved personnel only. Members of the public will need to have an appointment or a scheduled tour to visit LRWWTF and can schedule that by clicking on this link .
Sewer Lagoons
Construction of LRWWTF was officially completed in 2022. Prior to completion of the new facility, Logan City used 460 acres of lagoons and 240 acres of wetlands to treat and further polish wastewater from the region. The sewer lagoon ponds are more than 50 years old.
In 2010, the State of Utah Division of Water Quality completed a Total Maximum Daily Load (TMDL) study for Cutler Reservoir. That TMDL study resulted in stricter effluent limits on phosphorus and is the reason for construction of LRWWTF.
The future of the lagoons has not yet been decided; however, some of the ponds are currently being used to equalize LRWWTF influent flows and for storage of storm drain water from around the facility.