The 4 Influent Screw Pumps, each capable of pumping up to 10 million gallons of wastewater a day, sit beneath green odor control covers at the beginning of the treatment process.
These pumps, referred to as Archimedean Screw Pumps, are well-suited to applications where high capacity and non-clogging operation is required.
As a "primary" treatment step, water passes through large settling tanks (primary clarifiers) where some of the particulate and floatable pollutants are removed. Suspended and dissolved pollutants still remain.
Scraper devices that travel along the surface and floor of the tanks mechanically collect floatable and settleable material. The collected material is then pumped through a device that removes inorganic material and is subsequently pumped to the anaerobic digesters.
The 2 large "aeration basins, "each with a volume of 1,885,000
gallons, use a variety of hungry microorganisms (bacteria) to remove the
suspended and dissolved pollutants remaining from the primary treatment
step. This process, one of many, is known as "secondary treatment."
Special "zones "within these tanks encourage the growth of specific
types of microorganisms that perform specific jobs such as the removal
of ammonia nitrogen.
After "feeding," the microorganisms are settled in large tanks called "secondary clarifiers." Some of the settled microorganisms are recycled back to the aeration basins to feed again and others are removed from the system. Treated effluent (water) exits from the top of the tank, overflowing serrated plates around the circumference called weirs. Weirs ensure uniform flow distribution and prevent "short circuiting "or incomplete treatment, in the tank.
Treated effluent then flows to the disinfection station for one final treatment step before discharge.
At the disinfection station, contact with ultraviolet light destroys most of the remaining bacteria in the effluent before it is discharged to the Puyallup River.
Without the addition of any chemicals, ultraviolet light destroys bacterial DNA, thus, preventing reproduction. The device pictured contains two sets of multiple ultraviolet light bulbs through which the treated effluent must flow. The ultraviolet lights are beneath the water surface and not visible in this photograph.
A large machine, called a centrifuge, uses centrifugal force for separating substances of different densities. In this case, water is being separated from an organic solid material known as waste activated sludge. The removal of water prior to anaerobic digestion requires less tank volume and less volume to be heated. In this photo, the operator adjusts the hydraulic back-drive in order to optimize the removal efficiency.
Covered, heated and mixed tanks, referred to as anaerobic (absence of free oxygen) digesters, are used to stabilize solid organic material often referred to as sludge. The process reduces objectionable organic matter to relatively stable organic and inorganic compounds. This process utilizes anaerobic bacteria in complex biochemical reactions that, as one byproduct, produces methane gas which is used for heating the sludge.
Stabilized material from the anaerobic digestion process, now referred to as biosolids - in recognition of its potential to be "beneficially recycled," are run through a device known as a belt press. Aided by a chemical product called a polymer, large amounts of water are removed, and the material is consolidated to a thicker and dryer form. The dewatered biosolids can now be readily hauled by truck to agricultural fields where nutrients (nitrogen, phosphorous, potassium, etc.) contained in the biosolids can be recycled back into the soil. Before land application is permitted, biosolids must meet a number of quality requirements established by the U.S. Environmental Protection Agency and the Washington State Department of Ecology.
One of the most important operational necessities of a treatment facility is the ability to provide 24-hour, year-around operation. To meet this requirement, most treatment facilities are capable of generating their own electrical power. In this photograph, 1 of 3 large diesel generators capable of supplying all electrical needs for Puyallup's facility is pictured.
The device pictured here is known as a grit classifier. Grit is generally heavy mineral matter, including sand, eggshells, and cinders,
that will not decompose in the treatment process. This device uses
centrifugal velocity to create a vortex, which keeps the organic matter
in suspension and returns it to the treatment process while allowing the
heavier grit particles to pass through the bottom of the device.
Collected grit is conveyed up an inclined ramp into a garbage dumpster
that is subsequently disposed of at a sanitary landfill.
Pictured, are large, 200 horsepower blowers, which provide air for both mixing and biological oxidation in the aeration basins. Aerobic microorganisms - requiring oxygen - use organic pollutants present in the wastewater as a food source. The presence of a large population of microorganisms allows the aeration basins to achieve a high degree of treatment in a relatively short period of time.
Having demonstrated competency through examination, experience, and
ongoing training, all operations staff are licensed by the Washington
State Department of Ecology for Water Pollution Control Plant operation.