WRRF Virtual Tour


How our Water Reclamation & Reuse Facility Works

The function of a Water Reclamation & Reuse Facility is to treat and remove impurities from the city's wastewater in order to return it to the environment with minimal impact. Wastewater is processed using naturally occurring micro-organisms combined with dissolved oxygen to remove such nutrients as nitrogen and phosphorus from the wastewater stream. The City of Moscow owns and operates a fully accredited lab for on-site wastewater analysis that performs numerous tests in accordance with EPA guidelines to ensure that treated water is suitable for the local environment.

Wastewater Influent

The City of Moscow's wastewater or sewage is from homes, businesses, and the University of Idaho through a long series of piping called a wastewater collection system. It flows either by gravity or by pumping to the Water Reclamation and Reuse Facility (WRRF) for treatment.

WWTP influent

Preliminary Treatment

Larger objects and inorganic matter are removed by a mechanical screening process. Wastes such as rocks, sand particles, coffee and cinders are also removed.

WWTP Preliminary Treatment

Primary Clarifier

A tank or basin in which wastewater is held for a set period of time to allow heavier solids to settle to the bottom and lighter materials to float to the surface.

* The City of Moscow WRRF does not utilize primary clarification. This tank is used as a catch basin for excessively high influent flows.

WWTP Primary Clarifier

Influent Pump Station

The influent pump station (IPS) is an Archimedes style positive displacement screw pump that conveys wastewater from a low point in the piping system to a higher point and into the aeration basin, allowing gravity to pull the wastewater through the remainder of the plant process.

WWTP Influent Pump Station

Aeration Basin - Anerobic Selectors

Anaerobic (without the presence of  dissolved oxygen) Selectors allow wastewater microorganisms to co-mingle with incoming wastewater to start the biological nutrient removal  process.  Phosphorus, a nutrient, is released here so the microorganisms can "consume" other nutrients.

WWTP Anaerobic Selector

Anoxic Selectors contain no dissolved oxygen, but has some chemically bound oxygen attached with nitrogen as a nitrate. The anoxic selector also releases nitrogen gas bubbles after the nitrifications process. This process is called Denitrification, or the conversion of nitrates to nitrogen gas.

WWTP Anoxic Selector

Aeration Basin - Oxidation Ditch

The oxidation ditch is at the end of the aeration basin. It contains mechanical aerators that force dissolved oxygen into the wastewater or, at this stage, called Mixed Liquor (slurry of influent and millions of microorganisms under aeration). Microorganisms convert ammonium and ammonia to nitrites then to nitrates here during a process called Nitrification.

WWTP Oxidation Ditch

Secondary Clarifiers

The Mixed Liquor flows from the Oxidation Ditch into the secondary clarifiers. The heavier material, known as sludge, contains millions of microorganisms that settle to the bottom of the tank.

A portion of this sludge is returned back the aeration basin as Return Activated Sludge (RAS) and introduced to incoming wastewater to begin the nutrient removal process all over again.

Another portion of the sludge called Waste Activated Sludge (WAS) is removed and sent to holding tanks until it is de-watered and the drier sludge is hauled away for composting.

This stage of the treatment process sees the separation of water and solids. The solids or WAS is removed and the water flows to the next component of the treatment plant.

WWTP Secondary Clarifier

Sand Filtration

The sand filter serves as a tertiary effluent polishing system. The filter is a continuous backwash sand filter that, when aluminum sulfate is mixed with the clear water from the secondary clarifiers, chemically bonds with and removes most of the remaining phosphorus.

The backwashed water is returned back to the wastewater influent for continued treatment and the clean water flows into the re-aeration basin.

WWTP Sand Filtration

Re-Aeration Basin

To help support life in the receiving water, an amount of dissolved oxygen is added to the wastewater. The re-aeration tank contains a floating mechanical aerator that cascades the wastewater into the air and mixes dissolved oxygen into the wastewater.

WWTP Re Aeration Basin

Chlorine Contact Chamber*

The wastewater must be disinfected before it is allowed to flow into the receiving water. The disinfection is accomplished by slowing the wastewater in the contact chamber to allow chlorine (CL2) to, oxidize or destroy, any pathogenic (disease causing organisms) in the wastewater.

Before it enters the receiving water as final effluent, a solution of sulfur dioxide (SO2) is added to neutralize any remaining chlorine.

* The chlorine contact chamber is covered in the summer months to reduce sunlight entering the chamber. Without sunlight, algal growth is significantly reduced.

WWTP Chlorine Contact Chamber

Final Effluent

The final effluent now flows into Paradise Creek. The effluent is closely monitored for nutrient removal and other parameters set by the Environmental Protection Agency (EPA) in the National Pollutant Discharge Elimination System (NPDES) permit.

WWTP Final Effluent

Sludge Holding Tanks

Settled Sludge from secondary clarifiers is pumped to the sludge holding tanks. To keep the sludge fresh, it is aerated until it arrives at the de-watering building. Sludge is generally kept in the holding tanks for no more than 1 - 2 days.

WWTP Anerobic Sludge Holding Tanks

De-Watering Building

Sludge is pumped from the sludge holding tanks into the de-watering building where a liquid polymer is mixed with the sludge to bond the sludge solid particles together and allow drain off. The de-watered sludge is then hauled via truck to a compost facility and is available for Moscow city residents for no charge. The water, or centrate, is returned back to the wastewater influent to be processed again.

WWTP De Watering Building

What Not to Put Down the Drain

  • Cat Litter
  • Cigarettes
  • Condoms
  • Dental Floss
  • Fats, Oils, and Grease
  • Prescriptions (medicines)*
  • Auto Fluids
  • Disposable Diapers
  • Egg Shells
  • Feminine Hygiene Products
  • Fertilizers
  • Paints, Varnish, or Paint remover
  • Paper or Plastic Trash
  • Paper Towels
  • Pesticides
  • Photographic Chemicals

Plant process microorganisms cannot breakdown, remove, or reduce these  items. In fact, some items can cause harm or death to the microorganisms. Furthermore, some of the items can clog sewer piping which can cause sewer back-ups or overflows and can cause expensive damage to wastewater pumps and treatment plant components. 

For more information about how you can help keep our sewers clear and functional, check out our page on Residential FOG.

*Unused prescriptions and medicine can be anonymously dropped off at the City of Moscow Police Department for appropriate disposal.

Schedule a tour!

Now that you know how our Water Reclamation & Reuse Facility works, come see it for yourself! 

To schedule a tour, call (208) 882-2725.