Carnegie Museum of Natural History’s
Powdermill Nature Reserve
The Marsh Machine
Wastewater Treatment at Powdermill
Purifying wastewater in a clean and environmentally friendly manner is a top priority for the wastewater
management system at the nature center. Public sewage treatment is not available, and other traditional septic
systems could contaminate groundwater and, possibly, Powdermill Run stream. No chemicals are used in the
Marsh Machine-just small pumps and gravity for moving water through the system, and natural sunlight for
growing the plants and warming the greenhouse.
Clean groundwater under the reserve is utilized in the nature center’s shower, sinks, and drinking fountains. The
wastewater is naturally purified in the Marsh Machine and stored in the clean water storage tank. Some of the
water is then recycled to flush the nature center’s toilets, while some is diverted to the Living Stream exhibition to
demonstrate the purity of the water. Excess purified water is drip-irrigated onto the forest floor.
What is Wastewater?
Wastewater is any water–from toilets, dishwashers, and washing machines-that goes down the
drains in our homes, schools, and businesses. To be usable again by people, plants, and animals
alike, this water must be treated.
Wastewater consists of 97% water and 3% solids. Solids come from a variety of sources…
32% debris from sinks (hair soap, cleansers, fabric, dirt)
20% urine
18% food
16% feces
8% toilet paper
6% miscellaneous
How it Works
Outside the Marsh Machine
Tank 3: Equalization tank , 2000 gallon capacity
As wastewater leaves the building, it is sent into a
series of three precast concrete holding tanks buried
underground.
The septic effluent (fluid mixture) then
flows into an equalization, or “surge” tank,
designed to hold excess flow from peak
usage times, before being transported
through a pair of submersible pumps into the
greenhouse and into Marsh 1.
Tanks 1 and 2: 1,500 gallon capacity each
Solid materials settle at the bottom of the tanks, and
grease and soap scum collect near the top. Then
anaerobic bacteria (oxygen-poor) break down the
carbon-containing solids and nitrogen-containing
liquid and solids, converting organic nitrogen to
ammonia.
Inside the Greenhouse
The outlet of the second septic tank is equipped with
a septic solids retainer, a filter that minimizes the
solids being dumped into the third tank. The second
septic tank serves to trap non-biodegradable material
including grit, rags, and grease, with some anaerobic
decomposition.
Marsh 1:
Water is now pumped into Ma
both aerobic (oxygen-rich) an
poor) bacterial environments
with four feet of gravel, and w
Canna and Papyrus grow up t
Concrete Holding Tanks
Tank
1
Tank
2
These deep-rooted wetland p
small amount of oxygen belo
and act as a host for aerobic
bacteria convert carbon comp
(“floc,” or amassed bacteria
also convert nitrogen (in the
to nitrate. (Ammonia is first c
which is then quickly convert
presence of oxygen).
Tank 3
Surge
Tank
UV Light
Restrooms, Kitchen,
Shower, Sinks
1
Marsh 1
Clean Water
Tank
Aquaculture
Tanks
2
3
Marsh 2
A recirculating pump under th
the marsh water from bottom
dissolved oxygen, help water
stimulate nitrification and ox
The plants in the marsh utiliz
Some is also denitrified and t
gas by anaerobic bacteria loc
water-saturated gravel benea
nitrogen gas is then expelled
Phosphate from the watewat
positively charged sites on th
consumed by the wetland pla
Living Stream Exhibition
Photos by Carnegie Museum of Natural History staff
arsh 1 which contains
nd anaerobic (oxygens. Marsh 1 is filled
wetland plants such as
through the marsh.
plants transport a
ow the gravel surface
bacteria. These
pounds into biomass
cells). The bacteria
form of ammonia)
converted to nitrite,
ted to nitrate in the
he gravel moves
m to top to increase
r the plants, and
xidation.
ze some of the nitrate.
turned into nitrogen
cated in the
ath the roots. The
d from the wetland.
ter attaches to
he gravel and is also
ants.
Initial planting of the Marsh
Machine Winter 2007
The remaining carbon compounds, ammonia,
nitrate, phosphate, and bacterial biomass are
carried into the three Aquaculture Tanks.
Aquaculture Tanks:
These three white tanks hold 550 gallons of
water each and are highly aerobic environments,
promoting bacterial floc formation and
nitrification. The majority of the carbon is
converted into bacterial biomass and the
majority of the ammonia is converted to nitrate,
some of which is consumed by the plants and
algae. Plants and algae also consume small
amounts of phosphate. Living inside the tanks
are hundreds of small aquatic snails which
consume some algal and bacteria biomass. The
biomass settles to the bottom of the tanks.
After the purified water flows through all three
tanks, it drains into the final marsh.
Marsh 2:
The same reactions occur as in Marsh 1, but this
marsh is more anaerobic due to lack of
recirculating pumps. The higher water level does
not stimulate deep root growth, which would
add oxygen to the marsh. This encourages
anaerobic bacteria to consume any
remaining organic material using the oxygen
of the nitrate molecule to produce nitrogen
gas, which diffuses into the atmosphere. After
spending time in Marsh 2, the water is pumped
through an Ultraviolet Light Unit.
Ultraviolet Unit:
As water passes through
the UV light tube, UV
radiation de-activates
the DNA of bacteria,
viruses, algae and other
pathogens,
eliminating their ability
to reproduce. The water
is no longer a health hazard. From here it is sent
into the clean water tank
for holding.
Clean Water Holding
Tank:
This 850-gallon
tank will hold the
purified water to be
used as clean flush
water in the
restrooms. When
this tank overfills,
the excess water
flows through the
Living Stream
exhibition to
demonstrate that
the water is healthy
enough for aquatic
organisms such as
brook trout,
stoneflies, and
mayflies to live in.
Plants of the Marsh Machine
The plant life of the Marsh Machine is essential to the success of the system. The roots provide attachment surfaces
for the growth of microbial populations, which are responsible for 95% of the work in ecological wastewater
treatment systems. The plants also serve as habitat for beneficial insects and organisms that utilize the bacterial
biomass. If plants are dying or become unhealthy, they are not able to house as many organisms, nor are they able
to fully participate in the nutrient cycles. The continued success of the wastewater treatment system is based on
thriving and healthy plant life.
Papyrus
Elephant Ear
Canna
The Living Stream Exhibition
The Living Stream is a thousand-gallon exhibition
that flows through the visitor center. It is continuously
supplied with purified water from the Marsh
Machine. It is home to many species of aquatic
macroinvertebrate insects, as well as native species of
fish. Organisms like those found in the Living Stream
can be important indicators of water quality. Many are
sensitive to changes in the environment caused by
pollution, habitat impact, or severe natural events like
droughts and flooding. Because of these sensitivities
and their basic role in the food web, invertebrates
indicate the health of a stream or river (or, in this case,
the purified marsh water). As the water flows out of the
Living Stream, some is recycled back into the Marsh
Machine, and some is drip-irrigated onto the forest
floor to help replenish the groundwater supply.
1847 Route 381
Rector, PA 15677
WWW.POWDERMILL.ORG
724.593.6105
Publication of this brochure was made possible by
a grant from The Garden Club of Allegheny County,
a member of The Garden Club of America.
Printed on 100% recycled paper