Activities at Facility
The City of Santa Fe Paseo Real Wastewater Treatment Plant (WWTP) is located at 73 Paseo Real, Santa Fe, New Mexico 87507. The WWTP practices a conventional treatment process and has a design flow of 13 million gallons per day (MGD). Santa Fe is a high desert community located at the foothills of the Sangre de Cristo mountains in north central New Mexico. The WWTP serves a population of over 65,000 residents, but the city of Santa Fe is also a tourist destination, and the WWTP handles the increased flows generated by the numerous visitors.
Wastewater Management Division Administration Building
The WWTP is composed of process units, all of which work together to produce an effluent which meets and exceeds all federal and state discharge requirements.
The headworks is comprised of various components used to remove larger debris from raw sewage entering the plant.
The bar screen is a fine screen type that can be flow actuated or run by a timer. Rocks fall into a rock collector ahead of the barscreen. The purpose of the barscreen is removal of cans, plastic products, paper, rags, and other things that are too large to pass through the screen.
These items fall into the rag press where de-watering occurs by compression.
After de-watering, the materials are discharged to the hoppers or dumpsters that
are placed below the chutes.
The influent that passes through the barscreen is allowed to continue in the waste-
water flow, passing through the parshall flume where the flow is metered and the flow
of wastewater goes into two wet wells.
The wastewater from the wet wells is pumped by one or two of four influent pumps
into the grit tanks.
The wastewater flows through one of two grit tanks. The flow of wastewater is aerated in the grit tanks just enough to allow inorganic waste (sand, glass, eggshell, etc.) to settle while allowing organics (corn, lettuce leaves, etc.) to float and go over the weirs and flow to the primary splitter box.
The heavier particles that settle to the bottom of the tank are pumped by the Grit Centrifugal Pumps back to the Grit Cyclone Separator and washed to remove the organic matter that was attached to the grit.
With the help of an auger, the grit is dropped onto a conveyor belt. The conveyor carries and drops the grit into a portable dumpster, which is picked up by the landfill and disposed in a special area at the landfill after passing a paint filter test conducted by the Laboratory.
The Wastewater Treatment Plant has two 580,600 gallon clarifiers and is fed from the splitter box wet well. The primary clarifiers are used as sedimentation tanks which allows the wastewater velocity to be reduced enough so that the heavy material (organic) settles to the bottom of the clarifier and is removed via a scrapper, to a hopper at the bottom clarifier, and pumped to the digesters. The lighter materials float to the top and is removed via a skimmer, into the primary scum pit.
The settled sludge is pumped from the bottom of the primary clarifiers by one
or two of the three positive displacement progressive cavity pumps.
The rapid mix tank is a small basin where all the returned flows from several process areas are returned and mixed together before entering the Bio-selector for further treatment.
Effluent from the primary clarifiers goes to the rapid mix tank next to the DAF (Dissolved Air Flotation) Building where various recycle flows and the RAS (Return Activated Sludge) are mixed with the primary effluent and mixed liquor. The Bio-selectors are four 325,000 gallon basins that can be aerobic, anaerobic, or a combination of both. At present, the WWTP uses a low D.O. (Dissolved Oxygen) system in combination with mixed liquor pumps to recycle mixed liquor back through the system to reduce the nitrates, utilize soluble COD (Chemical Oxygen Demand), and inhibit the growth of filamentous bacteria.
Air to the Bio-selectors is provided by one or more of the three Hoffman Blowers or
by a small Sutor-bilt or small Hoffman Blower.
Chlorinator and Chlorine Detector Room
The WWTP still uses chlorine gas to help in the destruction of the filamentous bacteria. The chlorine is introduced through the chlorinators to the Return Activated Sludge (RAS) wet well and helps out when the plant experiences foaming problems.
The mixed liquor pumps return flow to the bio-selectors from the aeration
basins at a rate of 100% (but have the capacity for up to 500%).
The Bio-selector Effluent flows to the aeration basins.
The aeration basins (also known as the AB’s) are where the majority of the Activated Sludge biological process takes place. The bacteria/microorganisms reproduce and grow in the AB’s, digesting the sludge and reducing the contaminants in the wastewater. Nitrification and then denitrification take place to remove ammonia and nitrates. Thenitrification process utilizes dissolved oxygen that is fed through fine bubble diffusers in order to change ammonium to nitrite. Ammonia can be stripped off with increased air or converted from ammonia to nitrites by bacteria/microorganisms called Nitrosomonas. The nitrite continues through the basin to the anoxic zone and is broken down from nitrite to nitrate by the bacteria called Nitrobacter and then Heterotrophic bacteria convert nitrates to nitrogen gas, nitrous oxide, carbon dioxide (CO2), and water.
Air is supplied to the bacteria/microorganisms in the AB’s by three Turblex Blowers.
The mixed liquor flows into four 460,000 gallon secondary clarifiers to allow solids to settle to the bottom of the tank. The effluent water flows over the weirs and out of the tanks. The bacteria/microorganisms that have settled are pulled from the bottom of the clarifier, via suction pickup tubes, on the traveling bridges called Clarivacs into RAS (Return Activated Sludge) Channels.
These solids (.5 % solids) in liquid form, enter two common channels and flow into the RAS (Return Activated Sludge) and WAS (Waste Activated Sludge) wet well on the west side of the DAF (Dissolved Air Flotation) building. This wet well supplies the DAF in order to thicken some sludge and pump it to the digesters as TWAS (Thickened Waste Activated Sludge). Most of the bacteria/microorganisms (sludge), otherwise known as RAS (Return Activated Sludge), is sent back to the Bio-selector for further treatment.
Solids Handling Building, DAF (Dissolved Air Flotation)
The operators run various in-house process control tests in the DAF (Dissolved
DAF - The city of Santa Fe uses Dissolved Air Flotation (DAF) in order to thicken bio-solids (sludge). The DAF operates by pressurizing water above atmospheric pressure in a pressure tank, (Hydrostatic Tank).
The pressurized water is introduced to a header along with pumped sludge and a thickening agent, (polymer). The sludge, pressurized water, and polymer enter into the actual DAF tanks, which are at atmospheric pressure. The difference in pressures causes air to come out of solution as fine bubbles, which rise to the surface of the DAF tank. The sludge attaches to the fine bubbles and floats to the surface where it is concentrated, thickened.
Polymer is used as an aid in thickening.
The equipment that makes up the DAF is two 32,300 gallon DAF (Dissolved
Air Flotation) tanks.
There are two hydrostatic tanks, each of which is supplied air by its own air
compressor. Each hydrostatic tank has its own control unit and is regulated
to 40 psi by the operation of a motorized valve, (motor control unit).
There are four positive displacement progressive cavity pumps, three that
pump the Waste Activated Sludge (WAS) to the DAF Units and one that
pumps the Thickened Waste Activated Sludge (TWAS) to the digesters.
There are three centrifugal pumps for the RAS (Return Activated Sludge).
The thickened bio-solids are then handled in either one of two ways:
Anaerobic Sludge Digestion or Lime Stabilization.
Anaerobic Sludge Digestion - The anaerobic digesters at the city of Santa Fe have a wide and varied history. In the past, they have served as sludge storage tanks and currently serve as digesters. A major modification and replacement project was to use existing tankage, with a new addition for the pumping and heating equipment, and use them as anaerobic digesters. The digesters further reduce the volatile sludge solids to methane (CH4), carbon dioxide (CO2) and water (H2O). The SRT (Sludge Retention Time) is well over the 15 days. Fifty percent of volatile solids reduction by the digesters is a norm. The digesters are composed of a fixed cover digester with a capacity of 462,000 gallons and a floating cover digester with a capacity of 453,000 gallons, each having three gas mixing guns.
The contents of the digesters are heated by two hot water boilers.
The hot water is circulated with primary and secondary hot water pumps
to the heat exchangers.
The heat is transferred by the use of spiral heat exchangers. The digester
boilers have the ability to be fueled by either natural or digester gas.
The digester contents are re-circulated by the Rotary Lobe pumps and are also mixed by the use of digester gas, which is compressed and introduced into the mixing guns.
Excess digester gas (Methane) is burned off using a waste gas burner.
The second method used at the city of Santa Fe for bio-solids treatment is Lime Stabilization. Lime stabilization is a simple, batch process, where bio-solids are pumped into a holding tank and lime is added to raise the pH. The pH is raised to 12.0 and above and must remain at 12.0 and above for two hours. In addition, the pH must not drop lower than 11.5 after another twenty-two hours has passed. Using an existing tank, the city converted a septage-receiving ramp into a holding tank. A wall was built and a pump and mixer were placed into service. Bio-solids and scum are pumped into the holding tank over a period of hours, days, and/or months. At a fixed level, the bio-solids and scum are stabilized. The city uses a lime slurry because of safety concerns with dry lime and also because of the ease to use a liquid form of lime. Lime is shipped by truck to a portable lime slacking unit, (Porta-Batch) where it is mixed into a slurry and used.
Sludge Storage Tanks - After the bio-solids have been treated, the city
has the capability to store the bio-solids before disposing of them.
The sludge in the storage tanks is pumped by two positive displacement progressive cavity pumps to the Sludge Injection Field.
The Sludge Injection Field (100 acres) is divided into four areas in which sludge
can be injected.
The city uses sub-surface sludge injection for sludge disposal. At times, the
snow from the winter months melts and saturates the ground making sludge
injection difficult.The city is therefore able to store the bio-solids for later disposal
during warmer weather or surface spread during cold winter months when the
The #1 sludge storage tank has a storage capacity of 660,000 gallons and
is located adjacent to the lime stabilization ramp.
The #2 sludge storage tank is much larger with a capacity of 1,618,000 gallons.
The effluent flow from the secondary clarifiers enters the influent channel on the east side of the sand filters tanks. A bypass valve on the east side is for emergencies to send the flow directly to the UV system, bypassing all of the filters.
The flow continues through the channel to the south side where gates allow the flow to enter five 119,725 gallon sand filters. Each filter has the ability to handle 5.4 MG at peak flow. The sand filters by use of head differential and can monitor its own need for back washing by a traveling bridge back washing system. The filtered effluent goes over the weirs of the effluent channel of the sand filters to the influent channel to the UV building.
Ultra Violet Disinfection
The UV system disinfects the effluent prior to discharge. The radiation disinfects by causing the bacteria and virus to mutate, rendering them unable to reproduce. The system can operate manually or automatically by monitoring the flows. Operators monitor UV intensity (brightness of the lights) and clean the lamps crystal sleeves by placing the UV banks in one of two acid baths when they become cloudy or dirty (lowering the intensity). When the cleaning is completed the intensity increases.
A small air blower in the effluent channel is used to ensure permit compliance
for dissolved oxygen. This blower runs 24 hours a day and is monitored to
ensure that it is always in operation.
The plant effluent flows through the parshall flume where it is metered before l
eaving the plant and makes its way to the Santa Fe River.
The effluent from the Wastewater Treatment Plant meets all the New
Mexico Environment Department requirements to be classified as Class 1A.
The non-potable water pump(s) system draws filtered disinfected water
from the effluent channel to supply clean water for re-use as seal water
for various pieces of equipment.
This effluent water is also sold at the standpipe to contractors for use in construction, dust control and compaction.
The non-potable re-use pump houses, pump the filtered/disinfected non-potable water to various golf courses and sports fields.
The WWTP accepts Septic Sludge up stream from the treatment plant.