From Sewage to Fertilizer . . . This photo,
taken about 8 miles east of Helena, shows a
special truck that is used to inject sludge into
farmland soil. Sludge is a byproduct of
sewage treatment. Finished sludge can be
dried and disposed of in a landfill, or it may be
put to use. In some cases dried sludge is
burned as a fuel. Since it is rich in nitrates,
sludge from some cities is used as fertilizer.
During the summer, sludge from Helena is hauled to
this farm east of town where it is transferred
into the yellow truck shown above. The truck
is equipped with a device that injects the wet
sludge into the soil, providing nutrients for
crops to grow. During the winter it is added to composting material that the city collects. In other cities such as
Missoula and Kalispell, the sludge is sold to
companies that make compost. These
businesses mix the sludge with wood chips
and other "secret" ingredients, compost the
product, and then sell it in bulk or as individual
sacks that can be purchased in
hardware/home improvement stores.
Here's how sludge is formed. . .
When a toilet is flushed in one of Montana's
larger cities, the sewage ends up at a
wastewater treatment plant (a.k.a. sewage
treatment plant). Treatment plants use a
variety of processes to break down the
sewage. In the first step, called the
"headworks", big screens filter out sticks,
rags, and other larger objects. Gritty solids
like sand fall to the bottom. Material removed
at the headworks is taken to a landfill. Next,
the sewage sits in a tank called a "clarifier"
where the organic waste sinks to the bottom,
while oils and grease float to the top. Organic
waste is anything that comes from plants or
animals (including human waste). The stuff
that sinks to the bottom, called sludge is
removed and sent to a "digester" where
bacteria eat much of the organic waste. Air is
mixed in (aeration) to help these bacteria thrive. When
the bacteria are finished the sludge looks a lot
like mud. From the digester, sludge may go to
a lagoon; a large pond that holds sludge while
it basks in the sun until much of the water
evaporates. Or, it can be sent through a big
press that squeezes out the water.
That's not all . . . Two other important byproducts of
sewage treatment are methane gas and a clear liquid called "effluent". Methane is a gas formed when any organic material decays. Landfills, swamps, and sewage treatment facilities all release methane. It is a strong greenhouse gas, so methane is burned it as it comes out of the sewage treatment plant. Ideally it would be burned as fuel but that often is not economically feasible. Below: Methane is being burned (flaring) at Helena's Wastewater Treatment Plant near the Costco store (Scratchgravel Hills in background).
Below: Effluent is treated with UV rays to disinfect it before it empties into Prickly Pear Creek. However, like sludge, the effluent still contains plenty of nutrients, which can be problematic for streams and lakes. The nutrients cause excess algae to grow and bacteria that consume the dead algae use up dissolved oxygen in the water, making it difficult for fish and other organisms to live there. Watch the video near the bottom of this page to learn more. Helena discharges its effluent into this canal, which takes it to Prickly Pear Creek, then into Lake Helena, and onto the Missouri River (closer view).