by Spike Carlsen
. What
happens
after the
flush
KITCHEN WASTE
WATER INLET
"Out of sight, out of
mina" is the attitude
most of us have when
it comes to flushing
the toilet, popping the
bathtub drain or run-
ning the dishwasher
But all that waste-
water goes some-
where. And that
"somewhere" is
usually a wastewater
treatment facility, or
an on-site septic
system.
Recycled/Recyclable • Printed on Recycled Paper (20% Postconsumar)
Reprinted by the U S Environmental Protection Agency with permission from THE FAMILY HANDYMAN Magazine, Home Service Publications. Inc . an
affiliate of Reader's Digest Association Inc. 7900 International Drive, suite 950. Minneapolis. MN 55425 Copynght 1997 All Rights Reserved
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INCOMING
WASTEWATER
(INFLUENT)
GRIT REMOVAL
, CHAMBER
WASTEWATER
VOLUME METER
PRIMARY
SEDIMENTATION
TANK
A T IEATMENT
PLANT runs wastewater
through a chain of basins and
tanks, progressively removing
solids, dissolved solids and
harmful pathogens By the time
the water is released, it has
spent 8 to 16 hours in the
facility and is at least as clean
as the body of water it's
released into.
AERATION
TANKS ,
s*
ACTIVATED
SLUDGE
TO-SOtJDS
NO SLUDGE
PROCESSING
7
DISINFECTION
TANK
Sanitary disposal hasn'r
alwavs been the norm, l.'p until
the rnni- LSI UK it was common
practice to simply dump chain
her pots and garbage into street-
side gutters, ditches and Ces-spl!s.
When Louis Pasteur discovered
that microorganisms in raw
sewage made people sick, cities
began developing st-wer systems
to usher wastes out or town. Still,
even MI vcars ago, it was com-
mon lor ulies even those
with a population of
more than .1 million -
todirei tivi.ru:i:m
untreated waste into
rivers and Likes I;
"wasn't until the l^~0s,
when the Clean Water
Act mandated that all
wastewaier be cleaned
before being returned to
rivers and lakes, that the United
States really began cleaning up
its act.
Here's the poop.
SEPTIC SYSTEMS
In outlying areas, where
installing sewer pipes between
distant houses and treatment
facilities are prohibitively expen-
sive, septic systems (Fig. A| are
used. About one quarter < >t the
U.S. population (up to 50 per-
cent of the population in
some states) relies on these
on-site wastewater treatment
systems
The process is quite simple.
Wastewater enters the tank,
where solids drop to the bottom
ot the tank to create sludge, and
grease and oils rise to the top :o
Create scum. The sludge and
scum should be pumped .-n;
everyone !o two \ eai
wastewater between the two la\ •
ersflows to a distribution
which sends it out to ,1 series oi
1O8 MARCH 1997 THi FAMILY
I
-------
absorption or leach trenches. From
here the wastewater is absorbed by
the surrounding gravel and soil; a
small amount is wicked up to the
surface to evaporate or be con-
sumed by vegetation.
The sludge on the tank bottom
decomposes with the help ot bacte-
ria. Lots ot'grease can slow or even
wipe out the bacterial action ot'a
septic tank, and if the grease is
allowed to flow into the leach field,
it can coat and clog the rock and
soil and prevent absorption.
Because of this, garbage disposals
are not recommended for homes
with septic tanks unless a grease
trap is incorporated into the sys-
tem. The grease trap, located
between the kitchen sink and septic
tank, has special baffles to trap
grease before it enters the septic
system. The grease in the trap must
be pumped out regularly.
Septic system owners may not
get nailed with monthly sewer
fees—but those who neglect pump-
ing their tank, or are careless with
what thev dispose of, will get nailed
with a clogged drainfield and even-
tually a bill for a new septic system.
Paints, varnishes, waste oil and pes-
ticides can destrov the bacterial
Use less water; treat less water
Regardless of whether your house is connected to a septic system
or wastewater treatment facility, the less water you use, the less
wastewater needs to be processed.
Following are a few water-saving tips:
• When it's time to remodel, install a low-flush toilet. Older toilets
use 5 gallons per flush, but those made within the past 10 years
use 3.5 gallons, and many built today use 1.6 gallons. If we all
converted to low-flush toilets, the United States would save 3 bil-
lion gallons of water PER DAY.
• Fix drippy faucets. A faucet dripping twice a second wastes 50
gallons of water—and treatment—per week.
• Don't leave the water running. Keep a jug of water in the fridge
so you don't have to run water to get a cold drink. Turn off the
water when it's not needed while shaving, brushing your teeth or
washing your car.
action of a system. These chemicals
may also migrate into the drinking
water supply if there's a well on the
property. Likewise, plastics, diapers,
condoms, coffee grounds, tampons
and cai litter can contribute to the
premature demise of a septic-
system.
Septic systems and drainage
tields are carefully designed, based
on soil conditions and the number
of people living in a house. Life-
spans of 20 years or more are tradi-
tionally projected, but with careful
planning and maintenance, systems
can last indefinitely.
WASTEWATER
TREATMENT FACILITIES
Wastewater treatment simulates
nature's purification process—but
at a much accelerated pace. While-
water released from a treatment
facility isn't "drinking water" clean,
it is likely to match or exceed the
purity of the body of water it's
INCINERATOR
SOLIDS
COMPOSTING
FIG. C SLUDGE, produced at the annual rate of about 500 Ibs. per household, is disposed of in increasingly
environmentally sound ways After it's dewatered, it can be burned for heat, composted to create soil amendments, even
incinerated and the ash turned into building materials.
11O MARCH 1997 THE FAMILY HANDYMAN
-------
released into.
Treatment if\g. B) can be
broken down into five basic
steps, though processes may be
combined and vary greatly
from plant to plant.
In preliminary treatment,
wastewater is delivered to the
facility via sewer pipes, some as
large as 12 ft. in diameter. At
this stage, less than 0.5 percent
of the wastewater is solids; the
rest is water and dissolved mat-
ter. The wastewater flows
through bar screens to remove
trash and debris, then slowly
moves through a grit tank
where sand and heavy particles
settle and are removed.
During primary treatment,
water moves on to sedimenta-
tion tanks where it's undis-
turbed tor a few hours. Solids
that sink are scraped from the
bottom of the tank and
removed. Grease and oils that
float to the top are removed
with large rotating skimmers.
About 15 percent of U.S. treat-
ment plants discharge water
after this stage.
Secondary treatment begins
with the wastewater wending its
way through a chain of concrete
basins. The water is mixed and
oxygen is introduced, to begin
the aeration process. This sets
up an environment where the
active bacteria, called activated
sludge, feed on the incoming
waste solids and dissolved
organic matter, thus speeding
up the treatment process. The
water then flows into clarifying
tanks where the heavy, activat-
ed sludge microorganisms set-
tie out. As odd as it seems, some
of this sludge is recirculated
back into the aeration tanks to
provide active microorganisms
to keep the bacterial treatment
process alive.
During disinfection, harm-
ful bacteria and other microor-
ganisms in the water are killed
by adding chlorine, or running
the water past banks of high-
intensity ultraviolet lights. This
is to prevent the discharge of
harmful organisms or
pathogens into the receiving
body of water. At this point the
wastewater has been in the
plant for 8 to 16 hours,
In some plants, water moves
on to advanced treatment, most
often to remove phosphorus
and nitrogen, which stimulate
algae growth and eventually
deplete the oxygen levels of
lakes or rivers. Some forms of
advanced treatment are so
thorough, the water is used to
water yards and parks. In most
cases though, it's discharged
into streams, rivers, lakes or
oceans.
Each household generates
about 500 Ibs. per year of the
solids or sludge removed dur-
ing treatment (Fig. C). Often
the sludge is simply buried, but
increasingly it's being recycled.
In some cases the sludge is
dewatered and then combined
with other ingredients to create
fertilizers and soil amend-
ments. Sludge may also be
incinerated, and the ashes used
as a soil conditioner or in con-
struction materials. Sludge can
also be composted or
processed to produce methane
gas, which can in turn be
burned to supply heat for a
portion of the facility. 0
An Direction • MIKE SMITH
llluiirationi • DON MANNES
Contultinl • DENNIS LINDEKE.
METROPOLITAN COUNCIL.
ENVIRONMENTAL SERVICES
THE FAMILY HANDYMAN MARCH 1997 113
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