Smithsonian National Zoological Park l Friends of the National Zoo



Facilities Fact Sheet

The Smithsonian’s National Zoo strives to be a conservation leader in everyday Zoo operations and new facilities, including: employing recycling technologies; using alternative energy; and establishing environmentally sound materials and practices.

How are sustainable practices (green design) incorporated into American Trail?

  • The updated facility reused an existing site (formerly Beaver Valley)
  • Low-impact construction methods include retaining walls that reduced the disturbance of soils, vegetation and tree roots and also minimized the impact on upslope trees
  • Rain-garden drainage zones were built next to the retaining walls to assist in storm water management. There is also a large underground sand filtration unit in front of the Life Support System building to improve storm water management along the trail.
  • The Zoo replaced aquatic life support systems and equipment, enabling staff to better control water chemistry and quality
  • The Zoo was able to save more than 85 percent in water consumption and energy use (compared to standard design models)
  • Expanded backwash systems will conserve water by efficiently disinfecting and polishing the water
  • Shading over the pools reduces water evaporation and heat gained from the sun. They are adjustable to respond to weather and seasonal variations
  • An ozone disinfectant system reduces dependence on chlorine as a water disinfectant
  • Low emitting materials, certified wood, materials with recycled content, and regional materials were used to meet Leadership in Energy and Environmental Design (LEED) standards
  • Full cut-off light fixtures limit light pollution
  • Heating, ventilation, and cooling of people and animal spaces (10 percent of the building area) is controlled individually in each space. This reduces energy use when those spaces are not being used

What is the new Life Support System (LSS)?

The Life Support System building and holding areas are located adjacent to the Seal and Sea Lion exhibit pools and beaches. The building is a water-processing plant and uses various primary and secondary water filtration and treatment operations. It houses staff, animals, and equipment areas that support animal care, water quality monitoring and exhibit support equipment. It encompasses:

  • One sea lion exhibit pool (300,000 gal)
  • Two sea lion holding pools (10,000 gal each)
  • One seal exhibit pool (125,000 gal)
  • Two seal holding pools (10,000 gal each totaling Serving 465,000 gallons)

How are sustainable practices (Green Design) incorporated into the Life Support System Building?

  • Low emitting materials, certified wood, materials with recycled content, and regional materials were used to meet Leadership in Energy and Environmental Design (LEED) standards.
  • The existing 5,705 square foot structure was reused. Additions at the southern and eastern sides of the building total another 5,454 square feet.
  • The new life support systems were designed to conserve both water and energy. Much of the water used for the Seal and Sea Lion exhibit is 'process water' (like water in an industrial facility, it keeps the facility running). The Zoo was able to demonstrate over 85 percent reduction in water consumption (compared to standard design models).
  • The Life Support System features provide a more adaptable and robust means to maintain water quality. Water quality monitoring systems are fully computerized and automated, conserving staff time and providing valuable feedback on water quality issues as they arise.
  • Expanded backwash systems will conserve water.
  • Shading over the pools reduces water evaporation and heat gained from the sun.
  • Heating, ventilation, and cooling of people and animal spaces (10% of the building area) is controlled individually in each space. This reduces energy use when those spaces are not being used.

Details about the Filtration Systems

Mechanical filtration:

  • The skimmers draw water from the surface of the pools to filtration.
  • Bottom sumps draw water from the bottom of the pool to filtration.
  • Specially designed basket strainers collect the large debris (leaves) and small debris (stones, twigs, etc.) at a central location, making removal easy. This also protects the pumps from damage.
  • The primary horizontal pressure sand filters (for the exhibit pools) and bead filters (for the holding pools) remove fine particles from the water. This primary mechanical filter system recycles all the pool water in 50 to 70 minutes.

Chemical filtration and disinfection:

  • Secondary carbon filtration removes trace contaminants and color.
  • Ozone gas is the intended primary disinfectant and is generated on-site. Excess ozone flows to an ozone destruct unit before entering the atmosphere.
  • “Fractionation” separates and removes dissolved wastes, such as proteins, in specialized foaming chambers.
  • A chlorination system is available as a back-up disinfectant.

Biological treatment:

  • Urea and degrading uneaten food wastes are consumed by beneficial bacteria
  • Salt water can be produced from a brine tank.

Temperature control:

  • All pool water can be cooled through heat exchangers and air-cooled chillers. Water temperature will change with the season.

Filtration Process (see diagram)

  • Water is drawn off of the surface of the pools by skimmers (1). Leaves and debris are captured in baskets within the return sump before the water returns to the pumps.
  • The sump at the bottom of the pool (2) returns water to the pumps.
  • Water then goes through the first cleaning pass to the pumps where it goes through a finer mesh in-line basket strainer before going through the pump (B2 level) so as to prevent damage to the pumps.
  • Water then travels up through a bank of eight horizontal sand filters (3) to filter fine sediment from the water. The sand filters also provide biological filtration.
  • The majority of water is then returned to the tank at this point (4) through a dozen jets situated at various levels of the pool to stir up debris and sediment for capture by the filters.
  • A portion of the main water stream is pulled out as a side stream flow (5) through a carbon filter which takes out the organic color in the water and produces the crystal clear water seen in the pool.
  • Another side-stream of water goes through a heat exchanger (HX) which allows chilled glycol at 44 degrees F from the self contained chiller unit (6) on the roof to cool the pool water through a metal plate transfer.
  • The side stream then goes through chlorination (7) where calcium hypochlorite in a dry brick form is dissolved in the water to a very exacting concentration.
  • Another side stream is pumped upwards to the foam fractionators (8) through a venture creating a foam of water and ozone gas. The dissolved organic molecules (animal urine) are suspended in the water by an electrostatic charge which attracts the organic proteins removed as a thick brown liquid. The brown foamy slurry created (much like the foam you often see at the high water mark along the shore) overflows at the top of the fractionators and is caught and removed in sanitary waste. This hydrostatic process works best in cold salt water.
  • The ozone generator (9) injects ozone gas into the fractionators, and the contact solution chamber (10) allows the water to slow and provide time for the ozone exposure to disinfect the water. The water then moves to the Degas chamber (11) before water goes back to the pool through a gravity feed. Excess ozone is off-gassed to the ozone destruct chamber (12) where it is broken down and destroyed.
  • The efficiency of this system allows for very little water loss during the process. One hundred percent of the water will be recycled. The largest loss of water will be due to evaporation directly from the pool surface.


There are four Variable Frequency Drive (VFD) pumps supporting the sea lion pools and two VFD pumps supporting the seal pools. This allows the entire system to be monitored electronically through a computer control program that adjusts the water treatment and flow rates accordingly. If, for example, there is a fluctuation in the bio-load on the pools (such as trees losing their leaves) the pumps can be adjusted accordingly. This system provides tremendous energy efficiency by using no more electric energy than necessary.


  • Filters that become dirty are cleaned by backwashing. Individual filters can be isolated and backwashed individually.
  • Clean water for backwashing is drawn for the clean backwash recovery tank (1).
  • Dirty water from the pool filter is pumped to the dirty backwash recovery tank (2).
  • A special pump (3) and filter (4) clean the dirty water as it is returned to the clean backwash recovery tank. This filter discharges the concentrated effluent to the sanitary sewer. As such, there is a significant recovery of water.

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