Softener Discharge Versus Aerobic Wastewater Treatment Units

Flowing Issues
Softener Discharge Versus Aerobic
Wastewater Treatment Units
System Design is Key–Research Answers Questions
in the Age-Old Debate
down the solids and dissolved nutrients
he debate over whether or not
By David Averbeck, Mike Catanzaro,
in the wastewater.
water softener discharge impedes
Jason Davis and Andrew Warnes
An aerobic treatment system relies
the performance of on-site septic
upon bacteria that utilize oxygen to achieve
systems has dragged on for almost
this task, whereas, an anaerobic system (such as a conventional
30 years. The subject of the debate is critical because some
septic tank) treats wastewater by using bacteria that can function
jurisdictions (Michigan, Texas, Delaware, Connecticut and
in conditions lacking oxygen. If high doses of sodium from water
some municipalities in California) have limited or banned the
softener regeneration and other household products flow into the
discharge of brine into septic systems until conclusive scientific
tank, bacteria could be affected. If bacteria are negatively affected,
evidence is developed. Standard policy for on-site wastewater
the system might not operate at its full potential, and some solids
treatment system manufacturers is to void the warranty of their
and/or dissolved nutrients might not fully decompose.
systems if water softener brine is discharged into their products.
NSF researchers found that brine wastes had no negative
An important study undertaken by water treatment technology
effects on the bacterial population living in the aerobic treatment
manufacturer Pentair is poised to take the debate one step further
tank, even when the system was loaded with twice the normal
towards final resolution.
amount of brine. Tests determined that water softener wastes
As a publicly traded corporation with approximate annual
actually help with treatment processes.
revenue of $3.3 billion (USD), Pentair is uniquely positioned to
WQA’s final report states that the brine has “a beneficial
deliver technical expertise and support for this type of research.
influence on a septic tank system by stimulating biological
The company manufactures both ion exchange and wastewater
action in the septic tank and caused no operational problems in
treatment systems, and is widely recognized as a significant
the typical anaerobic septic tanks or the new aerobic treatment
industry participant and technical leader in these segments.
units.” In other words, the researchers in this study found that
microorganisms living and working in a home aerobic treatment
The history
system are not harmed by water softener salts.
Perhaps the best summary of prior softener discharge/onResearchers also found that the additional amount of water
site waste treatment system debates appeared in the Winter 2001
discharged to a treatment tank during the regeneration process
edition of Pipeline, the newsletter of the National Small Flows
had no negative impact. The question concerned whether the
Clearinghouse. It documented the history of the Water Quality
volume and flow rate of the regeneration brine might overload
Research Council (WQRC) and the Water Quality Association
the system and cause carryover of solids into the drainfield.
(WQA), which supported two studies in the late 1970s. One
The study found that the volume of water discharged was
was by the National Sanitation Foundation (NSF International)
comparable to or less than that from many automatic washing
in Ann Arbor, MI, and the other conducted by the Small Scale
machines and other household appliances. Researchers also found
Waste Management Project (SSWMP) at the University of Wisthat wastewater flowed into the treatment tank slowly enough
consin in Madison. Both studies compared the performance of
so that it caused minimal disturbance.
home sewage treatment systems with and without added water
The study at the University of Wisconsin-Madison examined
softener brine.
whether regeneration brine affected the soil in a septic system’s
The two studies were designed to help answer questions
drainfield. This research was prompted by the common knowlconsumers ask about their water softeners. The SSWMP reedge that sodium causes some soil particles to swell, thereby
search sought to determine if a water softener’s brine affects
reducing water’s ability to seep readily through the soil.
a drainfield’s ability to absorb wastewater. NSF investigated
Researchers found that the water softener regeneration
whether the influx of brine from a water softener’s regeneration
brine did not reduce the percolation rate of water in the absorpphase affects the processes that occur in an aerobic treatment
tion field of a normally operating septic system. This conclusion
system. Researchers also investigated whether additional water
was reached because while brine not only contains just sodium,
discharged during backwash and regeneration (up to an extra 50
it also includes significant amounts of calcium and magnesium.
gallons [189 liters]) into the septic tank interferes with the settling
The calcium in the brine acts similarly to gypsum, a calcium-rich
and floatation processes.
substance routinely used to increase the porosity of clay soils in
NSF researchers used individual aerobic wastewater
agriculture. The research report stated that calcium, therefore,
treatment units to study possible effects the brine might have
helps counteract any negative effects of the sodium. Most water
on treatment processes in the tank. The normal performance of
softener manufacturers and many industry experts agree with
both septic tanks and aerobic tanks depends on the presence of
the WQA’s position.
active bacteria living in the system. These bacteria help break
Water Conditioning & Purification
February 2010
NSF limit
NSF test results
Softener average
Efficiency brine average
Capacity brine average
Some don’t agree
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 protocol (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 or
attached aerobic bacteria that digest solids and dissolved nutrients in the wastewater. The wastewater in the tank is constantly
stirred via aeration.
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
Would the same results have been found if a conventional
septic tank had been used? Many experts agreed that more research was needed to resolve these and other potential issues.
What’s new?
In 2009, Pentair embarked upon a detailed technical
investigation into the issues surrounding the brine versus aerobic
treatment unit (ATU) debate. In order to ensure the highest
possible standards of technical accuracy and objectivity, testing
was done at an ANSI-accredited independent laboratory. System
operation, sampling and analysis were performed by Gulf Coast
Testing LCC, located in Prairieville, LA.
The laboratory is contracted by NSF for NSF/ANSI Standards
40: Residential Wastewater Treatment Systems and 245: Wastewater
Treatment Systems – Nitrogen Reduction testing. BOD, TSS and pH
analyses were performed per APHA’s Standard Methods for the
Examination of Water and Wastewater.
The wastewater treatment system tested was a Delta Environmental ECOPOD certified to NSF/ANSI Standards 40 and
245 with a rated capacity of 500 gpd (1,892.7 L/d). It included a
500-gallon anaerobic pretreatment tank and had recently, successfully completed a six-month NSF/ANSI 245 certification test.
The water softening system utilized was a widely commercialized one-cubic-foot softener with a Fleck 2510 electronic
control valve connected to municipal feedwater. The softener
was exhausted between regeneration cycles, with the softened
water discharged to domestic sewer (not to the waste treatment
unit) to ensure that the softener waste would have the appropriate ion ’mix’.
Water Conditioning & Purification
The softener drain was introduced to
the anaerobic pretreatment tank at an inlet
NSF limit
tee, and commercially available softener
NSF test results
salt (NaCl) was used for regeneration. The
Softener average
Efficiency brine average
softener was regenerated every two days
Capacity brine average
at 2:00 a.m. with varying brine doses as
outlined in the data presented here.
Introducing the softener waste at 2:00
a.m., and directly into the pretreatment
tank, was intentional as this represents
the worst-case scenario—there is no di1
lution of the waste from other flows or
from residual water in the wastewater
piping system.
Wastewater was dosed to the system as per NSF/ANSI 40
guidelines for design loading of a 500-gpd system and baseline
data was taken before softener discharge was introduced to the
About the relevant ANSI/NSF Standards
ANSI/NSF Standard 40
Standard 40 is for residential wastewater treatment systems
having rated capacities between 400 gallons (1,514 liters) and 1,500
gallons (5,678 liters) per day. The standard is not restrictive in the
type of treatment technology. Any system can be evaluated.
The standard includes a wide range of product evaluation methods and criteria for residential treatment systems. Most notably is
the ability of the treatment system to produce an acceptable quality
of effluent.
This is demonstrated during a six-month (26-week) test where
wastewater of required strength is subjected to the system at the
rated capacity of the system as evenly dosed at periods prescribed
by the standard. Stress sequences are included to simulate wash
day, working parent, power outage and vacation conditions.
The effluent criteria required of a Class I system is based on the
US EPA secondary effluent treatment requirements for municipal
treatment facilities. Testing can be performed at several test facilities.
In addition to the effluent performance, requirements also exist
for product literature, including installation, operation and maintenance, and troubleshooting and repair manuals. The system must
also meet minimum requirements for structural integrity, leakage,
noise, electrical certification, access ports, failure sensing and signaling equipment (visual and audible alarms), flow design, data
plate and service labels.
ANSI/NSF Standard 245
This standard has been developed for residential wastewater
treatment systems designed to provide for nitrogen reduction. The
evaluation involves six months of performance testing, incorporating stress tests to simulate wash day, working parent, power outage
and vacation conditions.
ANSI/NSF Standard 245 is set up to evaluate systems having
rated capacities between 400 gallons (1,514 liters) and 1,500 gallons (5,678 liters) per day. Technologies testing against Standard
245 must either be Standard 40-certified or be evaluated against
Standard 40 at the same time an evaluation is being carried out for
Standard 245, as both tests can be run concurrently.
Throughout the testing, samples are collected during design
loading periods and evaluated against the pass/fail requirements. A
treatment system must meet the following effluent concentrations
averaged over the course of the testing period in order to meet Standard 245:
• CBOD5 - 25 mg/L • TSS - 30 mg/L
• Total nitrogen - at least a 50 percent average of influent TKN
• pH - 6.0 to 9.0 SU
February 2010
system. The softener was regenerated every two days at the two
salt-dose extremes: maximum efficiency (four lbs./cu.ft.) and
maximum capacity (15 lbs./cu.ft.). The systems were operated
for a minimum of three weeks at each dose.
To monitor whether the softener discharge disrupted solids
settling in either the anaerobic pretreatment tank or the aerobic
treatment tank the sludge blanket was monitored in both tanks
with a sludge judge. It was found that the sludge blanket was not
disrupted, the system maintained good separation of the sludge
blanket, and clear zone at both salt-dosage settings throughout
the test.
The results
The most significant pass/fail criteria of NSF/ANSI Standard
40 are those pertaining to biological oxygen demand (BOD), total
suspended solids (TSS) and pH. The test results were:
• BOD maximum allowable 30-day average = 25 mg/L
• Before softener average = 9.0 mg/L
• After softener average = 9.0 mg/L
• TSS maximum allowable 30-day average = 30 mg/L
• Before softener average = 9.0 mg/L
• After softener average = 10.3 mg/L
• pH allowable range = 6 to 9
• Before softener average = 7.4 mg/L
• After softener average = 7.4 mg/L
Performance of the Delta Environmental ECOPOD was
virtually the same with and without softener discharge and
was well below NSF/ANSI 40 limits with and without softener
discharge. Additionally, Delta Environmental’s field experience
uncovered zero instances of on-site treatment system failures
linked to softener discharge.
Upon completion of the first rounds of testing, process experts
at Delta stated: “we recognize that some advanced wastewater
treatment technologies are not compatible with water softener
discharge brine. Non-compatible technologies can cause problems
ranging from maintenance issues to catastrophic failure.
“The utilization of spray nozzles, screens, inappropriate
operating levels, media types, etc., or combinations thereof,
contribute to potential maintenance issues/failures. The Delta
ECOPOD system has no nozzles, screens or any other components
that can clog. The media in the Delta’s ECOPOD system is
completely submerged in the reactor chamber, which allows for
the maximum operation capacity of the unit.”
Delta is confident enough in the data developed to date that
it has announced it will be modifying its warranties to accept
the use of Delta-approved, demand-initiated, twin-tank water
Water Conditioning & Purification
softener systems with the Delta ECOPOD. Delta will be notifying
various third-party agencies, as well as state and local regulators,
of this significant development.
1. Alhajjar, Bashar Jamil, 1981, The Effects of Electrolyte Concentration, Cation
Adsorption Ratio, and the Septic Tank Effluent Composition on Hydraulic Properties of Natural Swelling Soil Systems, University of Wisconsin-Madison.
2. Corey, R.B., and Tyler, E.J., 1978, Potential Effects of Water Softener Use
on Septic Tank Soil Absorption On-Site Waste Water Systems, University of
3. Corey, R.B., Tyler, E.J. and Olotu, M.U., 1978. Effects of Water Softener Use
on the Permeability of Septic Tank Seepage Fields. Proceedings of the Second
National Home Sewage Treatment Symposium. ASAE, St. Joseph, MI.
4. DalTech Dalhousie University. 2001. The Effect of Softeners on Onsite
Wastewater Systems, Centre for Water Resources Studies, On-Site Applied
Research Program, Nova Scotia, Canada, 2001.
5. Deal, K, 1998. Analysis of Septic System Failure in Gallatin County Montana,
MSU Extension Service.
6. Etzel, J.E., 1978. Softener Brines Do Not Harm Household Sewage Systems,
Purdue University, West Lafayette, IN.
7. Isaacs, W.P., and Stockton, G.R., 1981. Softened Water Energy Savings
Study Controlled Experimental Testing Program on Household Water Heaters,
New Mexico State University, Las Cruces, NM.
8. Great Lakes Upper Mississippi River Board of State Sanitary Engineers,
1980. Recommended Standards for Individual Sewage Systems.
9. Renn, C.E., Effects of Salts on Waste Treatment Systems, Johns Hopkins
10. Tedrow, J.C.F., 1997. The Effect of Sodium Discharge from Water Softeners
into the Septic Fields of New Jersey, Rutgers University.
11. NSF International, 1978. The Effect of Home Water Softener Waste Regeneration Brines on Individual Aerobic Treatment Plants.
12. Michaud, C.F., 2005. “What’s the Big Stick on Septic Discharge?”,
WC&P Magazine, May 2005.
13. National Small Flows Clearinghouse, Pipeline, Winter 2001.
14. Water Quality Association. 1976. Effects of Backwash Water and Regeneration Wastes from Household Water Conditioning Equipment on Private
Sewage Disposal Systems.
15. Wood, F.O., The Results of Putting Brine Effluent Into a Septic Tank
Drainage System, Salt Institute, Alexandria, VA, 1984.
About the authors
S David Averbeck is Director of Advanced Applications, Pentair Water
and can be reached at (262) 784-9940 or
Mike Catanzaro is Director, Water Treatment Sales, Delta Environmental and can be reached at (225) 665-6162 or Jason Davis is Engineering Manager, Advanced Treatment,
Pentair Water and can be reached at (419) 281-9224 or Jason.davis@ Andrew Warnes is Senior Channel Manager, PRF (A
GE/Pentair Joint Venture) and can be reached at (847) 274-0595 or
February 2010
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