Wastewater Treatment
Once the wastewater has arrived at the wastewater reclamation facility,
the first step in the treatment process is called Preliminary Treatment.
During this phase, the flow is measured and sampled, and objects like
sticks, rags, toys, rocks, coffee grinds, egg shells and sand/rocks are
removed. The first preliminary treatment process that the wastewater
passes through is called screening. It is designed to remove the larger
items (sticks, roots, rags, toys) while at the same time allowing the
wastewater and small items to pass through onto the next process. The
second step in the preliminary treatment phase is grit removal. In this
process, the wastewater is slowed slightly, to a velocity that allows gravity to work removing
coffee grinds, egg shells and other similar materials. The settled
material is pumped, dewatered and sent to the landfill for final
disposal while once again allowing the wastewater and organic material
to move onto the next phase called Primary Treatment.
Primary treatment uses sedimentation tanks also known as clarifiers
allowing settle-able solids to fall to the bottom of the tank and
lighter material to float to the water surface. This is accomplished by
slowing the wastewater velocity to 0.03 feet per second. In other words,
it takes approximately two hours for a gallon of wastewater to move
through the clarifier and on to the next treatment process. We
continuously pump the settled solids from the bottom of the tank to the
solids handling process for additional treatment along with skimming the
floating material off the surface of the water. The skimmed material is
also pumped to the solids handling process for additional treatment. The
water, however, continues to move through the treatment steps and on to
the process called Secondary or Biological treatment.
Secondary treatment means that the wastewater is exposed to living
organisms that eat the dissolved and nonsettle-able organic material
remaining in the wastewater as their food source. The Broomfield
Wastewater Reclamation Facility uses a process known as Integrated Fixed
Film Activated Sludge, or IFFAS for short. Broomfield was the first
plant in the United States to use this type of process where we combine
a moving bed plastic carrier element with our existing aerobic basins to
help grow the biomass and to maintain nitrification during year round
operation. The key to successful operations is the management of the
bacteria to ensure we have the right amount of bacteria available for
the concentration of wastes coming into the treatment plant. Again, we
slow the wastewater down to allow the bacteria enough time to work. For
this treatment process, it takes approximately four hours for a gallon of
wastewater to move through the treatment process. By now the bacteria
are full, fat and happy, ready to settle out. The blend of wastewater
and bacteria flow to the secondary sedimentation tanks/clarifiers and
once again, using gravity and a reduction in the water velocity, the now
heavier organisms settled to the bottom and are either pumped to the
digestion step or returned to eat some more. The now-clean water flows
on to be disinfected by ultra-violent (UV) light.
Disinfection is defined as a process designed to kill or inactivate
pathogenic organisms. UV disinfection is highly effective.
The Broomfield facility was one of the first in Colorado to switch from
chlorine gas, a highly toxic chemical, to UV disinfection back in 1996.
In short, UV disinfection works by exposing the wastewater to a
specified wavelength and intensity for a specified contact period. The
minimum exposure time is approximately 10 seconds. At this point, the
water is treated to the point where it is either safely discharged to Big
Dry Creek or diverted to the wastewater reclaimed treatment process.
In either case, this water is highly regulated and must meet all federal
and state regulations to avoid costly penalties.
Reuse or reclaimed water is wastewater that has received additional
treatment making it suitable for irrigation purposes. For us, the
disinfected wastewater is pumped through sand filters similar to
drinking water filters prior to pumping the water into the reclaimed
water reuse system. This is an important part of managing and conserving
our limited supply of water. It reduces the demands on the drinking
water system and postpones costly investments for development of new
water source.
Meanwhile, the solids that have been removed from both the primary and
secondary clarifiers are being treated in digesters that work very
similar to our bodies. The treatment units are kept at 98 degrees F for
approximately 20 days during which time the bacteria continue to break
down the waste by-product into a stable and beneficial organic material
called biosolids. Biosolids are a nutrient-rich fertilizer and soil
amendment that is used on farm ground. In addition, during the digestion
process, the bacteria produce a gas made up of mostly methane gas. The
methane gas is captured and reused as an energy source in the boilers
used for heating the digesters.
The advancement of wastewater treatment has been a key player in the
reduction and control of such epidemic diseases such as cholera,
typhoid, dysentery, polio and hepatitis that has killed hundreds of
thousands of people through history because of the lack of clean water.
This is not a glamorous job by any standard, but it has its rewards.
Knowing that we are protecting future generations and the world they
will inherit is a reward in itself.
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