Water Softener Use Raises
Questions for Septic System Owners
(from
Pipeline, a newsletter of the National Small Flows Clearinghouse, Winter, 2001)
·
What makes water hard?
And how does it become soft?
o
Water Softeners Make Water
Work Better
o
Reducing regeneration brine
flow
·
Researchers Look for Answers on
effects of Softeners on Septic Systems
·
Contacts
Parts of the U.S. have what is
commonly referred to as “hard water,” and people who live in these areas battle
the problems that hard water creates. The most common defense against hard
water, which is a nuisance but not a health hazard, is to install a home water
softener.
Water softening involves
exchanging calcium and magnesium minerals present in the water-which cause the
hardness-with sodium. As the water softener processes gallon after gallon of
hard water on a daily basis, the treatment capability of the softener becomes
depleted and must be recharged or regenerated.
Regenerating the unit uses a
large quantity of sodium-rich water, called “brine,” that must be disposed of.
In homes with onsite septic systems, this brine flows into the septic tank and eventually
makes its way to the system’s drainfield.
People using home water softeners often wonder whether these units might
cause problems for their onsite septic systems. Some common questions consumers
ask are:
- Do water softeners hurt the
bacteria that work in a septic tank?
- Does the additional amount
of water from water softener regeneration affect a septic system’s
performance?
- Does the concentrated salt
water used in regeneration decrease the drainfield’s ability to absorb
wastewater?
Unfortunately, experts don’t all
agree on the answers to these questions. Research has been done that resulted
in acceptable conclusions to many people in the industry, but some authorities
believe that more studies are needed to determine what impact, if any, brine
has in a septic system.
Because of these differences of
opinion, this Pipeline issue is unlike most others. Ordinarily we offer
information that gives readers concrete answers. But because water softener brine
disposal remains somewhat controversial, Pipeline will provide opinions on the
research that has been done to date. We
know people want information about this subject. At this point, our mission is
to help readers become better-educated consumers so that they can make informed
decisions when trying to resolve their hard water problems. Some steps that
homeowners can take to minimize their concerns about the safe operation of
their onsite sewage systems are included.
Readers are encouraged to reprint
this issue or any Pipeline articles in flyers, newspapers, newsletters, or
educational presentations. Please include the name and phone number of the
National Small Flows Clearinghouse (NSFC) on the reprinted information and send
us a copy for our files. If you have
questions about reprinting articles or about the topics discussed in the
newsletter, please contact the NSFC at (800) 624-8301 or (304) 293-4191.
Home septic systems
Knowing how a septic system works
helps homeowners understand why adding something like water softener
regeneration brine may cause problems.
A conventional septic system consists of a septic tank, a distribution
box, and a drainfield, all connected by pipes. When wastewater flows from the house,
it is temporarily held in the septic tank where heavy solids (sludge) settle to
the bottom. Lighter materials float on the surface of the water in the tank and
are called the scum layer. This separation is known as primary treatment.
The solids that collect in the
bottom of the tank and the materials that float in the scum layer are partially
decomposed with the help of bacteria that occur naturally in human waste. The
liquid between the solids and the scum flows out of the tank through a baffle
(or a tee) and into a distribution.
Important note : As sludge
accumulates in the bottom of the tank and its level rises, new wastewater
coming from the house has less time for suspended particles to settle into the
sludge layer.These suspended particles can flow into the absorption field. The septic tank must be pumped out
periodically to remove the accumulated sludge and scum and to prevent clogging
the drainfield box. The distribution box evenly separates the flow into a
network of drainfield pipes. Each pipe has holes in its underside that allow
the water to drain into gravel-filled trenches. The water slowly seeps into the
soil beneath the trenches where it is further treated. This process is called
secondary treatment.
What makes water hard? And how does it become soft?
As water flows through layers of
rock underground, it picks up loose particles and dissolves minerals from its
surroundings. Because of this characteristic and the kind of rock common in
many aquifers, calcium and magnesium minerals are frequently found in household
water. Water with substantial amounts of calcium and magnesium is referred to
as “hard water.”
Hard water minerals reduce
water’s ability to function effectively in our homes. For instance, bath soap
combines with the minerals and forms a pasty scum that accumulates on bathtubs
and sinks. Homeowners must use more soap and detergent in washing, so expense for
these products increases. These
minerals also combine with soap in the laundry, and the residue doesn’t rinse
well from fabric, leaving clothes dull. Hard water spots appear on everything
that is washed in and around the home — from dishes and silverware to the
family car.
Hard water not only affects
household cleaning, but the minerals also can build up on the inside of pipes
in the plumbing system. And in water heaters, the minerals settle on the
heating element, the walls of the tank, in the hot water pipes, and in faucets
where they produce a scale (similar to the original rock) that reduces the
efficiency and life of the hot water system.
Water
Softeners Make Water Work Better
Water softeners combat this
nuisance by eliminating the minerals that cause hard water. The most common
kind of water softener is a mechanical appliance plumbed directly into the
home’s water supply intake. (See figure 1) The water softener exchanges calcium
and magnesium with sodium in a process called ion exchange.
The water softening system
consists of a mineral tank and a brine tank. The water supply pipe is connected
to the mineral tank so that water coming into the house must pass through the
tank before it can be used.
The mineral tank holds small
beads (also known as resin) that carry a negative electrical charge. The positively
charged calcium and magnesium (called ions) are attracted to the negatively
charged beads. This attraction makes the minerals stick to the beads as the
hard water passes through the mineral tank. (See figure 3.) Eventually the surfaces of
the beads in the mineral tank become coated with the calcium and magnesium
minerals. To clean the beads, a strong sodium (salt) solution held in the
brine tank is flushed through the mineral tank. Sodium ions also have a
positive electrical charge, just not quite as strong as that of calcium and
magnesium. This large volume of sodium ions overpowers the calcium and
magnesium ions and drives them off of the beads and into the solution. The
sodium solution carrying the minerals is then drained out of the unit. Some
sodium ions remain in the tank attached to the surfaces of the beads.
The normal water softening cycle
operates like this: Hard water enters
the mineral tank. Inside the tank, the calcium and magnesium ions carried in
the water attach themselves to the beads. The surfaces of the beads eventually
hold their limit of calcium and magnesium and can’t remove any more from the
water. At this point the water softener must be "regenerated". (See
figure 2.) The three-step regeneration cycle can be scheduled according to a
timer or by a flow detection meter.
The first step, called the
backwash phase, reverses the water’s flow and flushes any accumulated dirt
particles out of the tank and down the drain. Next, in the regeneration or
recharge phase, the sodium rich brine solution flows from the brine tank into
and through the mineral tank. The brine washes the calcium and magnesium off
the beads. In the final phase, the mineral tank is flushed of the excess brine,
which now also holds the calcium and magnesium, and the solution is disposed of
down the drain.
Sodium ions from the previous
regeneration cycle cling to the beads. Now when the hard water flows into the
mineral tank, the calcium and magnesium ions change places with the sodium ions
on the resin. The displaced sodium ions remain dissolved in the water.
Reducing regeneration brine flow
- Install a water softener
whose backwash/regeneration cycle is based on need, not on a timer. A
water softener operated by a time clock regenerates the mineral tank on a
regular schedule, regardless of how much water has been used. A softening
unit that is regulated by a flow detection meter measures the amount of
water that has been used and regenerates the water softener accordingly.
These units can cost $100 to $450 more than timer-regulated water
softeners.
- Buy a water softener with a
large mineral tank. The larger tank may cost more initially, but it will
not have to be recharged as frequently as a smaller tank.
- Be more conservative with
household water use. Less water used in the home means that less water
will be measured going through the softener process; therefore, a unit
with a flow detection meter won’t have to regenerate as often.
Researchers Look for Answers
The Water Quality Research
Council and the Water Quality Association (WQA) supported two studies in the
late 1970s: one by the National Sanitation Foundation (NSF International) in
Ann Arbor, Michigan, and the other conducted by the Small Scale Waste
Management Project (SSWMP) at the University of Wisconsin in Madison. Both
studies compared the performance of home sewage treatment systems with and
without added water softener brine.
The two studies were designed to
help answer questions consumers ask about their water softeners. The SSWMP
research sought to determine if a water softener’s brine affects a drainfield’s
ability to absorb wastewater. NSF investigated whether the influx of brine from
a water softener’s regeneration phase affects the processes that occur in a
sewage treatment tank. Researchers also wanted to find out if the additional
water discharged during backwash and regeneration (up to an extra 50 gallons)
plus that water’s flow rate into the septic tank interfere with the settling
and floatation processes.
NSF’s researchers used individual
aerobic wastewater treatment units to study possible effects the brine might
have on treatment processes in the tank. (See the Winter 1996 Pipeline for
details about aerobic treatment units.) The normal performance of both septic
tanks and aerobic tanks depends on the presence of active bacteria living in
the system. These bacteria help break down the solids in the wastewater.
An aerobic treatment system uses bacteria that require oxygen to live; whereas,
an anaerobic system, such as a conventional septic tank, treats wastewater by
using bacteria that thrive in conditions lacking air. If high doses of
sodium from water softener regeneration and other household products flow into
the tank, the bacteria could be affected. If the bacteria are negatively
affected, the system might not operate at its full potential, and some of the
solids might not fully decompose.
Researchers from NSF found that brine
wastes had no negative effects on the bacterial population living in the
aerobic treatment tank, even when the system was loaded with twice the normal
amount of brine. The tests determined that water softener wastes actually help
with treatment processes. WQA’s final report states that the wastewater has “a
beneficial influence on a septic tank system by stimulating biological action
in the septic tank and caused no operational problems in the typical anaerobic
or the new aerobic septic tanks.” In other words, the researchers in this
study found that microorganisms living and working in a home aerobic treatment
system are not harmed by water softener salts.
Researchers also found that the
additional amount of water discharged to a treatment tank during the
regeneration process had no negative impact. The question concerned whether the
volume and flow rate of the regeneration brine might overload the system and
cause carry over of solids into the drainfield. The study found that the volume
of water discharged was comparable to or less than that from many automatic
washing machines and other household appliances. Researchers also found that
the wastewater flowed into the treatment tank slowly enough so that it caused
minimal disturbance.
The study at the University of
Wisconsin-Madison examined whether regeneration brine affected the soil in a
septic system’s drain field. This research was prompted by the common knowledge
that sodium causes some soil particles to swell, thereby reducing water's
ability to seep readily through the soil. Researchers found that the water
softener regeneration brine did not reduce the percolation rate of water in the
absorption field of a normally operating septic system. This conclusion was
reached because the brine contains sodium, but it also includes significant
amounts of calcium and magnesium. The calcium in the brine acts similarly to
gypsum, a calcium rich substance routinely used to increase the porosity of
clay soils in agriculture. The research report stated that calcium, therefore,
helps counteract any negative effects of the sodium.
Most manufacturers and many
industry experts agree with the WQA ’s position.
As with most scientific research,
these two studies answered each of the proposed questions under the specific
conditions of the research project. Because other variables exist that weren’t
part of the study’s setup (e.g., problems that might occur because of a poorly
functioning home water softening unit) some people feel that more research
needs to be done to completely resolve the disputed issues.
The NSF study, for example, used
an aerobic treatment tank rather than an anaerobic tank (a conventional septic
tank). Conventional septic systems are much more common than aerobic treatment
units. An aerobic system often has a pretreatment tank to settle out much of
the solids. Aerobic systems require air to be injected into the tank to
support the growth of the suspended aerobic bacteria that digest solids in the
wastewater.The wastewater in the tank is constantly stirred to mix in the air.
On the other hand, a conventional
septic tank separates solids from wastewater by settling. In a properly
functioning conventional system, most of the solids sink to the bottom of
the tank leaving the liquid portion relatively clear. The anaerobic bacteria do
their work without the wastewater in the tank being agitated. Would the same results have been found if a
conventional septic tank had been used? National Small Flows Clearinghouse
Senior Engineering Scientist David Pask remains skeptical. He tells of
residential drainfield failures that he has seen where the distribution pipes
were plugged with "a noxious fibrous mass" that, under microscopic
inspection, appeared to be made up of grease and cellulose fibers identical to
fibers from toilet paper.
Pask said the homes all had ion
exchange water softeners connected to their water supplies, and softener brine
discharged into each home’s septic system. His discussion of the situation with
colleagues led him to question if the sodium in the "plug flow" of
brine might cause metabolic shock to the bacteria in the septic tank. This
shock could cause the bacteria to be less able to digest the cellulose fibers,
which then might be carried over into a septic system’s drainfield.
"I still believe that the
case for discharge of softener wash to the septic tank is unproven and that
some research is justified," Pask said. "As for research needs ...I
would add to the list the effects of plug flow of brine on the digestion of
cellulose and scum components in a standard septic tank."
Terry Bounds, an engineer and
respected expert in the wastewater industry, also would like to see more
research done before any conclusive statements are made about the effects of
water softener regeneration brines in septic systems. In the summer 1994 issue
of Small Flows (the precursor of the Small Flows Quarterly magazine) Bounds
stated that in his work he has seen noticeable differences between septic tanks
with and without water softener brine discharges in septic tank effluent pump
(STEP) systems (an alternative wastewater collection and treatment method) and
in conventional systems. Bounds said that in the tanks with added water
softener discharge, he saw reduced scum layer development, carryover of solids
and grease to the pressure sewer collection system, and a less distinguishable
"clear zone" that might mean solids remain suspended instead of
settling in the tank.
Today, Bounds contends that
research has focused on water softener discharge of regeneration brine under
ideal conditions. Water softeners that malfunction or are not used correctly
(i.e., timed to regenerate too frequently) may cause septic system
problems. "Our experience with
regard to the operation and maintenance of systems that discharge water
softener backwash to septic tanks is that it has a detrimental effect on the
effluent that is discharged," Bounds said. "As a researcher, I
believe that when "all" the variables and processes are evaluated and
monitored, measured performance and science will share close results. So
far, I have seen no research that compares to typical environmental engineering
sciences in anaerobic digesters. Most of the reports that I’ve seen suggest
that this research still needs to be done."
Contacts
National Small Flows
Clearinghouse (NSFC)
The NSFC offers a variety of technical assistance and free and low-cost
information and materials about wastewater technologies for small communities.
Just a few of the NSFC’s many resources and services are mentioned in this
newsletter. Call the NSFC at (800) 624-8301 or (304) 293-4191 or visit our Web
site at http://www.nsfc.wvu.edu/ for
more information.
Water Quality Association
The Water Quality Association (WQA) is the international trade association
representing the household, commercial, industrial, and small community water
treatment industry. WQA is a resource of information, product testing, and
professional certification for all water users. Contact the WQA at (630)
505-0160 or visit their Web site at http://www.wqa.org/.
NSF International
(formerly called the National Sanitation Foundation)
NSF International is a private, nonprofit organization devoted to research,
education, service, and training. NSF tests and publishes standards for
products related to public health and the environment.Contact them at (800)
673- 6275 or visit their Web site at http://www.nsf.org/.