How to Create Treating and Recycling Water

Treating and
Recycling Water
In the United States, each person generates almost
75,700 liters (20,000 gallons) of sewage each year.
Fruits, vegetables, grains, milk products, and meats derived
from nutrients in the soil are brought into cities,
to be later flushed out as sewage. Some communities
discharge bacteria-laden sewage into nearby lakes, rivers,
or the ocean. Most cities and towns send the sewage to
treatment plants, where the solid matter (sludge) settles
out. The remaining liquid is chlorinated to kill bacteria
and then dumped into a local waterway.
The sludge is pumped into a treatment tank, where
it ferments anaerobically (without oxygen) for several
weeks. This kills most of the disease-causing bacteria
and precipitates out most minerals. The digested
sludge is then chlorinated and pumped into the local
waterway.

Waterways can’t finish the natural cycle by returning
the nutrients back to the soil, and end up with increasing
amounts of nutrients. This nutrient-rich water
promotes the fast growth of waterweeds and algae. The
water becomes choked with plant growth, and the sun
is unable to penetrate more than a few inches below the
surface. Masses of plants die and decay, consuming
much of the oxygen in the water in the process. Without
oxygen, fish suffocate and die. The waterway itself
begins to die. Over a few decades, it becomes a swamp,
then a meadow. Meanwhile, the farmland is gradually
drained of nutrients. Farm productivity falls, and produce
quality declines. Artificial fertilizers are applied to
replace the wasted natural fertilizers.

Designers can step into this process when they make
decisions about how wastes will be generated and handled
by the buildings they design. Sewage treatment is
expensive for the community, and becomes a critical issue
for building owners where private or on-site sewage
treatment is required. In a geographically isolated community,
like Martha’s Vineyard off the Massachusetts
coast, restaurants have been forced out of business by
the high cost of pumping out their septic tanks. One local
businessman calculates that it costs him about one
dollar per toilet flush, and if his septic tank fills up, he
will have to shut down before it can be pumped. In
1997, Dee’s Harbor Café was closed after its septic system
failed, and the owner lost her life savings. Even in
less remote locations, dependence on a septic tank
often limits the size of a restaurant and prohibits
expansion.
Sewage disposal systems are designed by sanitary
engineers and must be approved and inspected by the
health department before use. The type and size of private
sewage treatment systems depend on the number
of fixtures served and the permeability of the soil as de-

Treating and
Recycling Water

RURAL SEWAGE TREATMENT
In times past, rural wastes ended up in a cesspool, a
porous underground container of stone or brick, which
allowed sewage to seep into the surrounding soil. Cesspools
did not remove disease-causing organisms. Within
a short time, the surrounding soil became clogged with
solids, and the sewage overflowed onto the surface of
the ground and backed up into fixtures inside the
building.

Cesspools have mostly been replaced by septic systems
tank, a distribution box, and a leach field of perforated
drainpipes buried in shallow, gravel-filled trenches.
Septic tanks are nonporous tanks of precast concrete,
steel, fiberglass, or polyethylene that hold sewage for a
period of days while the sewage decomposes anaerobically.
Anaerobic digestion produces methane gas and
odor.

During this time, the sewage separates into a clear,
relatively harmless effluent and a small amount of mineral
matter that settles to the bottom. Soaps and slowto-
degrade fats and oils float to the top of the tank to
form a layer of scum. Inlet and outlet baffles in the tank
prevent the surface scum from flowing out. The liquid
moves through a submerged opening in the middle of
the tank to a second chamber. Here finer solids continue
to sink, and less scum forms. This part of the process
is known as primary treatment.

When the effluent leaves the septic tank, it is about
70 percent purified. The longer sewage stays in the tank,
the less polluted is the effluent. If the building and its
occupants practice water conservation, less water and
wastes flow through the septic tank, the effluent stays
in the tank longer before being flushed out, and it
emerges cleaner. Every few years, the sludge is pumped
out of the septic tank and is hauled away and processed
to a harmless state at a remote plant. The methane gas
and sewage odor stay in the tank.
Each time sewage flows into the tank, an equal volume
of nitrate-rich water flows out and is distributed
into the leach field, which provides secondary treatment.
There the water is absorbed and evaporates. Nitratehungry
microbes in the soil consume the potentially
poisonous nitrates. In the process, plant food is manufactured
in the form of nitrogen.

Nothing that can kill bacteria should ever be flushed
down the drain into a septic system. Paints, varnishes,
thinners, waste oil, photographic solutions, and pesti-
cides can disrupt the anaerobic digestion. Coffee grounds,
dental floss, disposable diapers, cat litter, sanitary napkins
and tampons, cigarette butts, condoms, gauze bandages,
paper towels, and fat and grease add to the sludge
layer in the bottom of the tank. Some systems include a
grease trap in the line between the house and the septic
tank, which should be cleaned out twice a year.
Trained professionals must clean the tank at regular
intervals. As the sludge and scum accumulate, there
is less room for the bacteria that do their work, and the
system becomes less effective. If the scum escapes
through the outlet baffle into the leach field, it clogs the
earthen walls of the trenches and decreases the necessary
absorption. Most tanks are cleaned every two to
four years.

Most septic systems eventually fail, usually in the
secondary treatment phase. If the septic tank or the soil
in the leaching field is not porous enough, or if the system
is installed too near a well or body of water, or beside
a steep slope, the system can malfunction and contaminate
water or soil. Most communities have strict
regulations requiring soil testing and construction and
design techniques for installing septic tanks. If the site
can’t support the septic tank, the building can’t be built.
Aerobic (with oxygen) treatment units (ATUs) can
replace septic tanks in troubled systems. By rejuvenating
existing drainfields, they can extend the system’s life.
Air is bubbled through the sewage or the sewage is
stirred, facilitating aerobic digestion. After about one
day, the effluent moves to the settling chamber where
the remaining solids settle and are filtered out. Because
aerobic digestion is faster than anaerobic digestion, the
tank can be smaller. However, the process is energy intensive
and requires more maintenance. The effluent
then moves on to secondary treatment.

Secondary treatment can use a number of different
techniques, with varying impact on the building site.
Disposal fields are relatively inexpensive, and do not require
that the soil be very porous or that the water table
be very deep below the surface. Drainlines of perforated
pipe or agricultural tile separated by small openings are
located in shallow trenches on a bed of gravel and covered
with more gravel. The effluent runs out of these
lines and through the gravel, until it seeps into the earth.
The gravel’s spaces hold the liquid until it is absorbed.
Buried sand filters that use sand, crushed glass, mineral
tailings, or bottom ash are also used for secondary
treatment. They are applied where the groundwater level
is high, or in areas of exposed bedrock or poor soil. A
large site area is required, but the ground surface can
become a lawn or other nonpaved surface. Buried sand
filters can be a remedy for failed disposal fields.
Seepage pits are a form of secondary treatment appropriate
for very porous soil and a low water table only.
Seepage pits can also be used as dry wells to distribute
runoff from pavement gradually.

MUNICIPAL SEWAGE
TREATMENT PLANTS
Larger scale sewage treatment plants continue to improve
the efficiency of their processes, and municipalities
are active in reducing the amount of sewage they
process. Larger plants use aerobic digestion plus chemical
treatment and filtration, and can produce effluent
suitable for drinking. Clean effluent is pumped into the
ground to replenish depleted groundwater. Digested
sludge is dried, bagged, and sold for fertilizer. Some
plants spray processed sewage directly on forests or cropland
for irrigation or fertilizer.

ON-SITE LARGE-SCALE
TREATMENT SYSTEMS
After years of sending sewage to distant treatment plants,
it is becoming more common for groups of buildings
to treat their wastes on site. The advantages include savings
to the community, reusable treated water for landscaping
and other purposes, and even pleasant and
attractive outdoor or indoor environments. In some
campus-type industrial, educational, or military facilities,
septic tanks are installed at each building, and the
outflow is combined for the secondary treatment process.
Use of sand filters for secondary treatment offers
simple maintenance, very low energy use, and greater
available usable land area.

Constructed Wetlands
By constructing an environment that filters and purifies
used water and recycles it for additional use, we can reduce
municipal sewage treatment costs and support local
plant and animal life. Free-surface (open) wetlands
use effluents to nourish vegetation growing in soil. Human
contact with these secondary treatment areas must
be controlled.
The Campus Center for Appropriate Technology at
Humboldt State University in Arcata, California, uses a
graywater treatment marsh that consists of an open

channel of water with a gravel-filled channel planted
with vegetation. A primary treatment tank filters out
large particles such as hair, grease, and food scraps.
Water then penetrates down through the gravel in the
channel. Once it reaches the end of the channel, the
water is removed from the bottom of the marsh by a
perforated pipe. This pipe then conveys water to the next
gravel marsh box, a process that supplies it with oxygen.
After treatment in the graywater marsh, water from
the sinks and shower is reused on the lawns and ornamental
plants. Except for periodic maintenance, very little
energy is used.

Subsurface flow wetlands consist of a basin lined
with large gravel or crushed rock, and a layer of soil with
plants above. Plants encourage the growth of microorganisms,
both anaerobic and aerobic, and bring air
underwater through their roots. The effluent is then filtered
through sand and disinfected. It is then safe to use
for many purposes, including landscape watering. This
secondary treatment option is safer for human contact,
and also attracts birds. The master plan for the Coffee
Creek Center southeast of Chicago features constructed
wetlands for on-site treatment of wastewater from
homes and businesses.

Pasveer Oxidation System
The Pasveer oxidation sewage treatment system was used
by the New York Institute of Technology in Old Westbury
on Long Island in New York. Purified effluent returns
to the ground through 48 leaching wells under the
school’s athletic field. The sludge is processed using a
mechanical aerator for aerobic digestion. There is no
compressor, only the noise of splashing water. The process
has a low profile and is screened by trees.

Greenhouse Ecosystems
Greenhouse ecosystems (Fig. 11-2) are secondary sewage
treatment systems that are constructed wetlands moved
indoors. Marine biologist John Todd developed Living
Machines at Ocean Arks International. They consist of a
series of tanks, each with its own particular ecosystem.
The first is a stream, and the second is an indoor marsh
that provides a high degree of tertiary wastewater treatment.
The system costs less to construct and about the
same to maintain as a conventional sewage treatment
system. It uses less energy, depending upon solar energy
for photosynthesis and on gravity flow. There is no need
for a final, environmentally harmful chlorine treatment.
The system produces one-quarter of the sludge of other
systems.
These greenhouse environments are pleasant to
look at and smell like commercial greenhouses. They
are welcome in the neighborhoods they serve, and can
save huge costs in sewer lines that would otherwise run
to distant plants. Greenhouse ecosystems offer an opportunity
to enrich the experience of an interior environment
while solving a serious ecological problem.

Within the greenhouse ecosystems, aerobic bacteria
eat suspended organic matter and convert ammonia to
nitrates, producing nitrites. Algae and duckweed eat the
products of the bacteria. Snails and zooplankton then
eat the algae. The floating duckweed creates shade that
discourages algae growth in the later stages of production.
Finally, fish eat the zooplankton and snails. The
systems support water hyacinth and papyrus, canna
lilies, bald cypress, willows, and eucalyptus, which remove
phosphorus and heavy metals during the lives of
the plants, returning them to the earth when the plants
die. Small fish (shiners) are sold as bait, and dead plants
and fish are composted.
On-site wastewater treatment has a significant impact
on the design of the building’s site. Interiors are
also affected, as the system may use special types of
plumbing fixtures and may include indoor greenhouse
filtration systems.

RECYCLED WATER
Water is categorized by its purity. Potable water has usually
been treated to be safe for drinking. Rainwater offers
a sporadic supply of pure water that can be used for
bathing, laundry, toilet flushing, irrigation, or evaporative
cooling with little or no treatment. Graywater is
wastewater that is not from toilets or urinals. It comes
from sinks, baths, and showers. Blackwater is water with
toilet or urinal waste.
Graywater may contain soap, hair, or human waste
from dirty diapers and other laundry. It can be treated
and recycled for uses like toilet flushing and filtered drip
irrigation. Dark graywater comes from washing machines
with dirty diaper loads, kitchen sinks, and dishwashers,
and is usually prohibited by codes from being
reused. If graywater contains kitchen wastes, grease and
food solids are a problem. Currently, few communities
allow the reuse of graywater; and those that do tend to
restrict its use to underground landscape irrigation for
single-family houses. New York-based architect William
McDonough has used gray and blackwater in designs
for Eurosud-Calvission, a software research and development
facility in southern France.

Future water conservation measures may include
the use of water from bathing for flushing toilets,
which would save 21 gallons per person each day. The
14-gallons per person used daily for laundry can help
with irrigation, preferably through underground distribution
systems that limit contact with people.
The Aquasaver Company in England has developed
a system that diverts and cleans water from lavatories,
baths, and showers for flushing toilets, washing clothes,
washing cars, and irrigation. A low-pressure system installed
behind panels in the bathroom pumps graywater
through a series of filters, removing soaps, detergents,
and other impurities. The water then goes to a storage
tank in the attic or above points of use. The system uses
nonhazardous cleaning agents and a network of carbon
filters.

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