Current Treatment Processes

The Truckee Meadows Water Reclamation Facility is permitted as a 44 Million Gallon per Day (MGD) wastewater treatment facility. Current treatment is carried out with the following unit operations:

• Preliminary Treatment - Initial Screening
  • Headworks Bar Screens: These are bars that are placed 1.2" apart and are meant to catch any large debris that enters the facility. 
  • Grit Removal: Two sets of tanks that are designed slow down the flow of water to a speed where heavy, inorganic material (i.e. sand) is able to fall to the bottom and be removed. 
• Primary Treatment - Gravity Separation
  • Primary Clarification Tanks: These 7 tanks slow the flow of water even more than in the grit removal facility. Water spends between 2-4 hours in these tanks. During that time, heavy, settleable organic pollutants are able to fall to the bottom of the tanks where they are collected and sent on to solids handling.
• Secondary Treatment - Biological Treatment
  • Aeration Tanks: These tanks facilitate a process known as Activated Sludge, where a population of microorganisms is introduced that will consume the remaining organic matter that couldn't be settled out in the previous step. TMWRF employs a type of activated sludge process known as Enhanced Biological Phosphorus Removal (EBPR) where these tanks are configured so that phosphorus accumulating organisms (PAOs) are preferentially grown. This EBPR process is carried out by having an anerobic/oxic tank configuration where the first section is not provided any air, followed by air provided the rest of the tank volume. This anaerobic period enables PAOs to have a competitive advantage because they can utilize their stored phosphorus in this portion of the basin and continue to consume resources. 
  • Secondary Sedimentation Tanks: These tanks slow the water down just as in the primary clarifiers. The dissolved and suspended organic matter that had been present in the facility influent gets assimilated into the cell mass of the microorganisms in the aeration process and effectively gets converted into a settleable solid. These solids are settled out in the tanks where they are removed and either returned to the aeration process to continue carrying out the process of pollutant removal, or sent on to solids handling. 
• Tertiary Treatment - Advanced Nutrient Removal
  • Nitrifying Trickling Filters: There are 6 nitrifying trickling filters that each contain 8,300,000 square feet of plastic media surface area that promote the growth of nitrifying biomass. An arm rotates at the top of the cylindrical towers, distributing water across the surface area and fans provide forced ventilation through the bottom. The biomass utilizes this oxygen and converts ammonia into nitrate.
  • Denitrifying Fluidized Bed Reactors: There are 4 fluidized bed reactors, each containing 200 tons of sand. Flow is routed through the bottom which suspends/fluidizes the sand and promotes the growth of biomass uniformly on each sand particle. These reactors are anoxic, meaning with freely dissolved oxygen but containing chemically bound oxygen in the form of nitrate. The organisms on the sand particles utilize this form of oxygen for cellular respiration essentially breathing in nitrate and breathing out nitrogen gas which bubbles out of the reactors and joins the atmospheric nitrogen. 
  • Dual Media Filtration: Twelve dual media gravity filters are used to remove suspended solids from the FBR effluent prior to disinfection. Each filter has 4 inches of gravel, 12 inches of sand, and 2 ft of anthracite media. The sand and anthracite layers perform the filtration of the flow by reducing TSS and turbidity. In addition, if alum is added upstream, the filters will capture phosphorus precipitates and direct them back to the headworks through the backwash recovery tank. The layer of gravel does not provide additional filtration and is there to provide space for an underdrain and hold the filtration media in place.  
• Disinfection System:
  • Disinfection: 12.5% Sodium Hypochlorite (bleach) is injected into the head of contact tank where the water spends between 60-75 minutes inactivating pathogenic organisms prior to discharge. 
  • Dechlorination: Given that chlorine is a marine pollutant, sodium bisulfite is used to quench the chlorine residual after disinfection is complete. This helps protect fish and wildlife from the harmful impacts of chlorine. 
• Outfall:
  • Main Effluent; Finally treated, the water flows into Steamboat Creek and ultimately is returned to the Truckee River. 
  • Reuse: The effluent of the treatment plant is also used in a variety of beneficial ways such as irrigating local parks and golf courses and for dust abatement. 
• Solids Handling: 
  • Primary Sludge: Sludge from the primaries is thickened in one of two gravity thickeners where it is thickened to 3.5% solids and sent to the digestion process.   
  • Secondary Sludge: wasted activated sludge is sent to one of two dissolved air flotation thickeners where it is thickened to 5% solids and sent to the digestion process. 
  • Digestion: The facility has a two phase digestion, acid phase where the complex organics are broken down into volatile fatty acids. These are further broken down and stabilized in a series of methane phase digesters where volatile fatty acids are converted to carbon dioxide and methane.
  • Dewatering: After stabilization in the digestion process, water is removed from the solids with centrifuges and the dewatered biosolids are returned to the landfill. 
  • Biogas: The methane gas produced in the digesters is captured and refined through a gas conditioning system to remove gaseous pollutants such as hydrogen sulfide and siloxanes. This gas is then burned in boilers to heat the buildings at the facility as well as in a 988 kW engine to produce approximately 1/3 of the power of the facility.