The Small Flows Journal Volume 4, Issue 1, Spring 1998

N

A

C L E A R I N G H O

MALL FLOW

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A collection of

professional papers on

the study of onsite and

small community

wastewater issues

Volume 3, Issue 1, Winter 1997

Journal

N

ATIONAL SMALL FLOW

S

C L E A R I N G H O U S E

The

Flows

Smallll

Volume 4, Issue 1, Spring 1998
The Small Flows Journal Volume 4, Issue 1, Spring 1998

Contents

1

Contents

From The Editor .............................................................................................. 3

by Cathleen Falvey

RESEARCH

Effects of Length-Width Ratio and

Stress on Rock-Plant Filter Operation .................................................................. 4

by H.C. Bounds, Ph.D.,

 James Collins,

 Zhiyun Liu,

 Zhen Qin, and

 T. A. Sasek, Ph.D.

LITERATURE REVIEW

Assessing the Impact of Household Cleaning

Products on Wastewater Treatment Systems .................................................... 15

by Daniel E. Edwards, Ph.D., and

 Alvaro J. DeCarvalho

NSFC NEWS/RESOURCES

NSFC Offers Discussion Groups on the Web..........................................................28

Special Spring Offer—All NSFC Products

Half Price, June 22–23 ....................................................................................... 28

PROFESSIONAL NEWS

Group Seeks Comment on Proposed

Performance Standards.......................................................................................29

Call for Proposals—Clermont County, Ohio .........................................................30

Committee Discusses Drainfield Questions,

Identifies Topics for Further Research ............................................................... 31

Manuscript Submission Guidelines ..........................................................33

LOWS

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MALL FLOWS

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C L E A R I N G H O U S

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Printed on Recycled Paper E

NATIONAL SMALL FLOWS

CLEARINGHOUSE

The Small Flows Journal

Sponsored by:

U.S. Environmental Protection Agency

Steve Hogye, Project Officer

Municipal Support Division

Office of Wastewater Management

Washington, D.C.

National Small Flows Clearinghouse

West Virginia University

John L. Mori, Ph.D., Manager,

Environmental Services and

Training Division

 Peter Casey, P. Eng.,

Program Coordinator

Cathleen Falvey, Editor

Daniel Gloyd, Graphic Designer

Technical Advisor

Patricia Miller, Ph.D.,

Virginia Department of Health

International Standard Serial Number

1079-1531

The Small Flows Journal

National Small Flows Clearinghouse

West Virginia University

P.O. Box 6064

Morgantown, WV 26506-6064

(800) 624-8301

(304) 293-4191

http://www.nsfc.wvu.edu

Reprints

For permission to reprint information

appearing in The Small Flows Journal,

please send a letter of request to

the editor.

The Small Flows Journal is funded by

the U.S. Environmental Protection

Agency (EPA). The contents of this

journal do not necessarily reflect the

views and policies of the EPA, nor does

mention of trade names or commercial

products constitute endorsement or

recommendation for use.

The

Flows

Small

Journal
The Small Flows Journal Volume 4, Issue 1, Spring 1998

2

Terry Bounds, P.E.

Roseberg, Oregon

Steven Berkowitz, P.E.

Onsite Wastewater Section

Division of Environmental Health

North Carolina Dept. of Environment and Natural Resources

Craig Cogger, Ph.D.

Washington State University, Puyallup

Research and Extension Center

James Converse, Ph.D., P.E.

Biological Systems Engineering Dept., University of Wisconsin

Brian Cooper, C.E.T.

Simcoe Engineering Group, Ltd., Pickering, Ontario

Donald Gray, Ph.D.

Professor of Civil Engineering, West Virginia University

Mark Gross, Ph.D., P.E.

Associate Professor, Dept. of Civil Engineering

University of Arkansas

David Gustafson, P.E.

University of Minnesota Extension Service

Michael Hines, M.S., P.E.

Quantum Engineering Corporation, Knoxville, Tennessee

Anish Jantrania, Ph.D., P.E.

Technical Services Engineer, Virginia Dept. of Health

Craig Jowett, Ph.D., P. Eng.

Research Associate Professor

Waterloo Centre for Groundwater Research

University of Waterloo, Ontario

Jim Kreissl

Environmental Engineer, Center for Environmental Research

U.S. Environmental Protection Agency

George Loomis

Research Soil Scientist

Natural Resources Science Dept., University of Rhode Island

Ted L. Loudon, Ph.D., P.E.

Professor and Extension Agricultural Engineer

Michigan State University

Roger E. Machmeier, Ph.D., P.E.

Professor Emeritus, University of Minnesota

Karen Mancl, Ph.D.

Associate Professor of Agricultural Engineering

The Ohio State University

Stewart Oakley, Ph.D., P.E.

Professor, Department of Civil Engineering

California State University, Chico

Richard J. Otis, P.E.

Vice President, Ayres and Associates, Madison, Wisconsin

Michael H. Ogden, P.E.

Southwest Wetlands Group, Santa Fe, New Mexico

Mike A. Parker

i.e. Engineering Inc., Roseburg, Oregon

Frank Pearson, Ph.D., P.E.

Hercules, California

Sherwood Reed, P.E.

Consultant and Principal

Environmental Engineering Consultants, Norwich, Vermont

Will Robertson, Ph.D.

Research Assistant Professor, Dept. of Earth Sciences

University of Waterloo, Ontario

A. R. Rubin, Ph.D.

Extension Specialist and Associate Professor

North Carolina State University

William A. Sack, Ph.D., P.E.

Professor Emeritus, Civil and Environmental Engineering

West Virginia University

C. M. Sawyer, Ph.D., P.E.

Director, Municipal Wastewater Division

Virginia Dept. of Health

Robert L. Siegrist, Ph.D., P.E.

Research Associate Professor

Environmental Science & Engineering Division

Colorado School of Mines

Dennis Sievers, Ph.D.

Biological and Agricultural Engineering, University of Missouri

Steve Steinbeck, P.G.

Onsite Wastewater Section

Division of Environmental Health

North Carolina Dept. of Environment and Natural Resources

Jerry Stonebridge

President, Stonebridge Construction, Inc.

 Langley, Washington

William L. Stuth Sr.

Stuth Company Inc., Maple Valley, Washington

George Tchobanoglous, Ph.D., P.E.

Professor of Civil Engineering, University of California, Davis

Jerry Tyler, Ph.D.

Associate Professor, University of Wisconsin

A. T. Wallace, Ph.D., P.E.

Professor, Department of Civil Engineering, University of Idaho

Ted Walker, R.E.H.S.

Sonoma County Health Department, Sonoma, CA

Editorial Review Board

Editorial Review Board
The Small Flows Journal Volume 4, Issue 1, Spring 1998

From the Editor rom the Editor

3

From the Editor

A

mong the offerings in this issue of The Small Flows Journal are two

technical articles that focus on onsite systems, a subject of interest to

most readers who live in or work with small communities. The first

paper, Effects of Length-Width Ratio and Stress on Rock-Plant Filter

Operation, examines rock-plant filter performance. According to the authors,

rock-plant filters have low maintenance requirements and are a valuable

alternative technology for sites with water-saturated soils with low permeability. The second paper, Assessing the Impact of Household Cleaning Products on

Wastewater Treatment Systems, evaluates existing literature to determine

whether down-the-drain disposal of household cleaning products upsets

biological treatment processes in onsite wastewater systems.

Another interesting feature in this issue is information for readers from the

National Small Flows Clearinghouse (NSFC), publisher of The Small Flows

Journal. Internet users should refer to page 28 for information about the

NSFC’s new online discussion groups. Details about the NSFC’s annual Earth

Day special also are announced on this page. A new section, Professional News,

follows the NSFC news section on page 29. Articles describing the researchrelated activities of two groups from different organizations are featured, and

both articles outline the groups’ efforts toward the development of performance-based standards for onsite systems. Both articles request feedback from

the public and the research community.

This issue also marks another important change for the journal. Patricia Miller,

Ph.D., who left the NSFC last year to begin work with the Virginia Department

of Health, has continued to work as technical advisor for the journal on a

volunteer basis. After this issue, she will begin a different role as a member of

the journal’s editorial review board. We thank Dr. Miller, who has worked with

the journal since its inception, for being so generous with her time and for her

valuable help and guidance.

This year, with the help of our editorial review board, we plan to evaluate the

current role and format of the journal as it relates to the NSFC’s mission to

serve small communities. I would like to take this opportunity to invite readers

who have thoughts, suggestions, encouragement, or criticism concerning the

journal, to write to me at the National Small Flows Clearinghouse, West

Virginia University, P.O. Box 6064, Morgantown, WV 26506-6064, or via

e-mail to cfalvey@wvu.edu.

Sincerely,

Cathleen Falvey

Editor

The Small Flows Journal
The Small Flows Journal Volume 4, Issue 1, Spring 1998

R ock-plant filters (which are also

sometimes referred to as submerged vegetated beds) include

any system of wastewater treatment that uses a bed of gravel or rock in

combination with various semiaquatic

plants. The rocks provide a support medium

for plant growth as well as surfaces for

microbial activity (Cooper and Boon,

1987; Wolverton, 1987). The filter system

is essentially a substitute for the traditional

absorption field lines associated with

septic tank systems (Wolverton et al.,

1983; Wolverton et al., 1984).

Rock-plant filters have been shown by

several studies to be an effective means of

treating domestic wastewater (Burgan and

Sievers, 1994; Huang et al., 1994), animal

wastes (Maddox and Kingsley, 1989), and

4

Effects of Length-Width Ratio

and Stress on Rock-Plant Filter

Operation

RESEARCH

ABSTRACT: Three rock-plant filters sized to accommodate wastewater from a typical

three-bedroom home were constructed with length-width (L-W) ratios of 4:1, 10:1, and

30:1. Each filter was preceded by two 1,900-liter (L) septic tanks in series, had a surface

area of 25 m2, and a design flow of 1,514 liters per day (L/day). Standard parameters of

biochemical oxygen demand (BOD), total suspended and volatile solids (TSS, VS), as

well as ammonium and sulfide effluent levels and biofilm accumulation on the gravel

were determined over a 103-week (two-year) test period. No significant difference between

the filters due to L-W ratio was observed, except for sulfide discharge amounts. Once

plant and bacterial growth became established (approximately 6 to 8 weeks after initial

start-up), each filter produced an effluent with BOD and TSS less than 30 mg/L. Various

stress tests, such as “wash day,” “equipment/power failure,” and “10-day vacation,” as

well as unscheduled shutdowns, changing the plant species in the filters, and an extended

period of intermittent flow all failed to reduce the efficacy of the rock-plant filters.

Effects of Length-Width Ratio

and Stress on Rock-Plant Filter

Operation

industrial wastes (Litchfield and Schates,

1989). The advantages of rock-plant filters

over other methods of wastewater

treatment include low maintenance

requirements, few if any mechanical parts,

and beds that can be lined and used in

soils with low permeability.

The Louisiana Department of Environmental Quality’s Nonpoint Source

Management Plan (LDEQ, 1993) estimates that over 1.3 million people in

Louisiana treat and dispose of their

wastewater in individual septic tank

systems even though soil surveys indicate

that 87 percent of the soils in Louisiana

are considered inadequate for conventional septic systems. For example, the 25

parishes (counties) that border or lie south

of the Interstate 10-Interstate 12 corridor

by H. C. Bounds, Ph.D.

James Collins,

Zhiyun Liu,

Zhen Qin, and

T. A. Sasek, Ph.D.
The Small Flows Journal Volume 4, Issue 1, Spring 1998

5

H. C. Bounds, Ph.D., James Collins, Zhiyun Liu, Zhen Qin, and T. A. Sasek, Ph.D.

The Wastewater System

from Lake Charles to Slidell, Louisiana,

comprise roughly 25 percent of the land

area of the state and consist of mainly

water-saturated soils with low permeability. Individual residences in these parishes

not on public wastewater systems have

the potential of contaminating the bayous,

bays, and estuaries that feed into the Gulf

of Mexico. Currently, the only approved

option for new residential construction

other than a septic tank is a mechanical

aeration unit. The rock-plant filter, if

incorporated into Louisiana’s sanitary

code, could be useful in such areas and

would require only very low maintenance

for several years.

An evaluation of the experimental rockplant filter systems in use in Louisiana in

1992 showed that 30 percent (8 of 27) of

the systems considered met the U.S.

Environmental Protection Agency (EPA)

standard for BOD effluent discharge of

less than 30 mg/L, 37 percent produced

effluents with a daily maximum of less

than 45 mg/L, and 33 percent exceeded

both limits (Bounds and Denison, 1992).

There was no standardization of design

for the systems in overall capacity,

length-width (L-W) ratio, retention time,

or type of gravel medium used.

After reviewing the report, the Louisiana

Department of Health and Hospitals,

Office of Public Health (LDHH/OPH)

requested a study of the effect of L-W

ratio on a design it would adopt for a

typical three-bedroom residence. Another

objective was to determine how well the

FIGURE 1

Generalized cross-section of the

rock-plant filter bed (not to scale).

filter system could recover from various

types of stress such as might occur from

“everyday” operation by the typical

homeowner.

This report summarizes the data accumulated from three rock-plant filters, each

with a design load of 1,500 L/day, during a

103-week test period from May, 1995

through April, 1997.

Filter Bed Systems

Three rock-plant filters of equal surface

area but with L-W ratios of 4:1, 10:1, and

30:1 were constructed on the Northeast

Louisiana University campus. Each filter

bed system was preceded by two metal

500-gallon (1,893-L) septic tanks in series,

provided a surface area of approximately

25 m2, and had a design flow of 1,514

L/day. Each filter bed was filled to a depth

of 0.46 m with unwashed “oversize gravel”

(19 to 64 mm in diameter). Effluent drains

were placed to maintain a 0.3-m water

level. Assuming a 40 percent void space, the

hydraulic capacity of each filter was 3,028

L. This was the standard set forth by the

LDHH/OPH for a typical three-bedroom

home to provide for a 2.5-day retention

time in the septic tanks and 2-day retention

in the filter bed.

Overall dimensions for the three filter beds

were as follows:

a) 2.5 m wide • 10.0 m long • 0.46 m

deep (4:1 L-W ratio).

b) 1.58 m • 15.8 m • 0.46 m (10:1 L-W

ratio).

c) 0.9 m • 27.4 m • 0.46 m (30:1 L-W

ratio).

Because of the drop in elevation at the test

site, the 30:1 filter bed was divided into

three 9.14-m sections, with the second and

third sections approximately 0.15 m lower

than the first section. Drains placed at the

end of each section maintained a 0.3-m

water level throughout the filter. Figures 1

0.46m

Water Level

0.3m

Methodology
The Small Flows Journal Volume 4, Issue 1, Spring 1998

6

Effects of Length-Width Ratio and Stress on Rock-Plant Filter Operation

and 2 show a generalized cross-section of a

filter bed with the layout and sampling

points of the test facility. Photos 1 through

5 show the project site and the filter beds

at different stages of the project.

Canna lilies (Canna flaccida) and elephant

ears (Colocasia esculenta) were used in

combination as the plant species in each

bed during the first 48 weeks of operation

(year 1) and were established from bulbs

placed at the water line in the gravel beds

in mid-April, 1995. The plants were spaced

on 0.9-m centers down the middle of the

30:1 bed, but 0.9 m apart in staggered rows

in the 10:1 and 4:1 filters. During weeks

49 and 50 of the test period in late April,

1996, the plant growth was changed to

single species by removing all or part of

the canna lily-elephant ear clumps and

adding cattails (Typhia latifola) to the 30:1

filter, canna lilies only to the 4:1, and

elephant ears only to the 10:1 filter.

Raw municipal sewage for the systems

was pumped from a Monroe, Louisiana,

sewage lift station approximately 60 m

away. The sewage was pumped from the

wet well by a 1/4 hp submersible pump

and delivered to the septic tank systems via

38-mm PVC pipe. The flow rate of the

influent sewage into the septic tanks was

calculated by a timed-fill procedure,

delivering 76 L/minute during the duration

of the project.

Gravity flow from the septic tanks was

distributed into the 30:1 bed through a

standard 3-m section of 10-cm perforated

PVC pipe with an extra row of holes

drilled between the existing perforations.

Influent was distributed to the 4:1 and 10:1

filters through two 1.5-m sections of

perforated pipe connected to the septic

tank line with a “tee” and short sections of

PVC. The perforated sections were placed

approximately 0.4 m from the sides of

each filter (see figure 2).

The systems were charged in April, 1995,

and sampling began on May 22, 1995.

FIGURE 2

Plan view of experimental

facility showing sampling

ports for septic tank

effluent (not to scale).

Original site in fall,

1994, before any

excavation for rockplant filters.

30S 30-1 30-2 30-E

0.9 x 27.4 m (30:1)

4S 4-1 4-2 4E 2.5 x 10 m (4:1)

10S 10-1 10-2 10E

1.5 x 15.4 m (10:1)

RAW

SEPTIC TANKS

 PHOTO 2

Installing septic tanks

(January, 1995).

PHOTO 1
The Small Flows Journal Volume 4, Issue 1, Spring 1998

Expericmental Design and Data

7

H. C. Bounds, Ph.D., James Collins, Zhiyun Liu, Zhen Qin, and T. A. Sasek, Ph.D.

Dosing Schedule

The dosing schedule used in this project

was a modification of American National

Standard Institute (ANSI)/NSF International Standard 40 requirements for

individual aerobic wastewater treatment

plants (NSF International, 1990). The

NSF 40 schedule calls for the hydraulic

loading to be 35 percent daily flow in the

morning, 25 percent at noon, and 40 percent

in the evening. The flow into the municipal

wet well did not fit this pattern. Apparently,

most of the residents served by this lift

station followed the “working parents”

routine listed in NSF 40 as a stress test. The

“working parents” routine (40 percent daily

flow in the morning, 60 percent daily flow

in the evening) was followed when the

daily flow was 1,514 L/day. During some

winter weeks of year 1, a reduced flow

(757 L/day) was added at one dosing.

The filter beds were subjected to stress

tests by altering the normal hydraulic

loading to include “wash day,” “equipment/power failure,” and “10-day vacation” cycles as per NSF 40 guidelines.

The “wash day” cycle modified the normal

routine by adding three washer loads of

detergent to each filter system during one

5-day period with a 24-hour period between

each loading. The “equipment failure”

test required 40 percent design flow added

between 5 and 8 a.m., then no loading for

48 hours, followed by 60 percent design

flow (including one load of washing). The

“10-day vacation” cycle required 60 percent

design flow between 6 a.m. and 2 p.m. on

a Friday, followed by no influent until 5 to

8 p.m. on the second Sunday (60 percent

design flow plus three loads of washing).

An unscheduled stress test occurred when

the lift station was closed for 47 days for

structural repairs. Dosing ceased on October

9, 1995, and resumed on November 25,

1995. After week 48 (when plant species

were changed in the filter beds), intermittent flow of 1,514 L/day but dosing only

three times per week was used during

summer, 1996 to maintain plant growth.

Daily dosing was resumed at week 68 and

continued until the end of the project.

PHOTO 3

Emergence of plants from

completed beds

(May, 1995).

PHOTO 4

Plant growth at the end of the

first year (October, 1995).

PHOTO 5

Mature plant growth

in the second year

(fall, 1996). Beds

have been converted

to single species.
The Small Flows Journal Volume 4, Issue 1, Spring 1998

8

Effects of Length-Width Ratio and Stress on Rock-Plant Filter Operation

Biofilm accumulation on the gravel was

estimated by collecting 400 g of gravel

from the mid-level of the water area at

1/3- and 2/3-bed length, and effluent end

of each filter. The gravel samples were

collected with a shovel. Water was

allowed to drain from the gravel, then

individual rocks were removed with tongs

and placed in a sealable plastic bag on the

pan of a triple beam balance at the

research site. Duplicate samples were

taken from each location and the procedure repeated on three successive days.

At the lab, 200 mL of double-strength

(2X) BOD buffer solution was added to

each bag. A bag was placed in a sonicatorcleaner containing 1,000 mL of tap water

and was sonicated for three minutes. The

sonicate was decanted into a clean container

and the bag was refilled with a second

portion of 2X buffer solution. After sonicating for another three-minute cycle, the

two aliquots were combined and the TSS

of the material determined. Triplicate

determinations were made on each sample.

The results were reported as mg biofilm

(dry weight) accumulated per kg gravel.

All data accumulated during the 103-week

test were computed as per NSF standard

40 parameters of average value, standard

deviation (s.d.) from the average, minimum-maximum, median, and interquartile

range. Analysis of variance (ANOVA) was

used to determine the significance of data.

A summary of the CBOD values obtained

over the course of the study is shown in

table 1. The data are presented as year 1

and year 2 instead of an overall average

since the plant species were changed from

the combination of plants used in year 1 to

single species per bed during year 2.

While there were differences between

year 1 and 2 CBODs, the data clearly

indicate that no significant difference in

CBOD was observed between the filter

effluents due to L-W ratio.

Sampling and Testing Methods

Primary composite samples were collected from raw sewage, septic tank

effluents, and filter bed effluents daily

using Sigma 800SL automatic samplers.

Secondary samples were collected as grab

samples usually once per week from

sampling ports located at 1/3- and 2/3-

bed length in each filter. Each daily

sample was made by taking an amount

proportionate to the morning and evening

loading rate (40 percent from morning, 60

percent from evening).

The samples were held at 4oC between

collection times and processed within one

hour of the last sampling. The daily tests

consisted of biochemical oxygen demand

(BOD), total suspended solids (TSS), and

volatile solids (VS), and were performed

in accordance with Standard Methods for

the Examination of Water and Wastewater,

18th ed. (Am. Public Health Assoc., 1992).

For this report, BOD is reported as carbonaceous biochemical oxygen demand

(CBOD) as described in Standard Methods.

Temperature determinations were made on

site as samples were collected. Ammonium-N, nitrate-N, and hydrogen sulfide

determinations were made on daily

composite samples using Hach Chemical

Company (Loveland, Colorado) reagents

and test procedures. It is important to note

that hydrogen sulfide measurements were

made on the morning samples immediately upon return from the field when it

was determined that chilling lowered the

sulfide levels.

The oxidation-reduction potential (ORP)

was determined on the filter bed fluid at

1/3- and 2/3-bed length and the effluentend sampling ports of each bed with a

Corning portable oxygen sensor. Samples

were collected with a sewage sampler

designed to hold 60-mL bottles but

without the bottle. Measurements were

made on site by inserting the sensor into

the collected sample to a premarked depth

and were read when the instrument

reached equilibrium.

Results
The Small Flows Journal Volume 4, Issue 1, Spring 1998

9

H. C. Bounds, Ph.D., James Collins, Zhiyun Liu, Zhen Qin, and T. A. Sasek, Ph.D.

The interquartile range is the range of

values about the median between the upper

and lower 25 percent of all values (NSF

International, 1990). This calculation

deletes extreme lows and highs for each

sample and provides a more “normal” range

of values. Extreme low CBOD values for

raw sewage always occurred after heavy

rainfall. Apparently, surface water runoff

was infiltrating the municipal sewer. High

CBODs could be obtained routinely only by

amending the municipal sewage with 4 to 5

L of reconstituted powdered milk added to

the wet well prior to pumping into the

systems.

Amending the sewage during some weeks

and not in others accounts for the large

standard deviation for raw sewage and

septic tank effluents (STE) as seen in table 1.

For example, even though the milk was

diluted in the wet well approximately 1:250,

the average weekly CBOD of amended

sewage was 184 mg/L. Non-amended

sewage CBOD (weeks 77 to 78, 89 to 90,

and 102 to 103) averaged only 71 mg/L

(data not shown).

Ambient temperature extremes during the

103-week test resulted in weekly averages

of 27 to 28oC for the STE during the

summer months and 10 to 14oC during

winter operation (data not shown). The filter

bed effluents (4E, 10E, 30E) had weekly

averages ranging from highs of 28 to 31oC

to a low of 6oC during one winter period.

Table 2 shows that cold temperature in

weeks 31 to 48 did increase the percent of

noncompliant samples; i.e., samples that

exceed the EPA standard of less than 30 mg/

L BOD. Reducing the hydraulic loading

(increasing retention time) to 757 L/day

allowed each filter bed to produce acceptable effluents. However, temperature

extremes did not reduce filter efficiency

during weeks 68 to 103, and no adjustments

to the loading rate were made in year 2.

Table 2 also illustrates that while temperature had little or no effect on the overall

operation of the filter systems, aging of the

filter beds did result in increased filter

efficiency. In the first six weeks of operation, 87 to 92 percent of all effluent

TABLE 1

Summary of carbonaceous

biological oxygen demand (CBOD).

TABLE 2

Effect of filter aging on the

percentage of noncompliant

effluent samples.

 CBOD, mg/L

 year 1 a year 2 b

 sample avg. (s.d.)* range c avg. (s.d.)* range

raw 142 (26) 109–181 163 (58 ) 119–217

STE d 98 (28) 73–123 68 (23) 48–104

4E e 29 (16) 19–31 14 (6) 9–20

10E 27 (16) 17–29 12 (5) 8–19

30E 23 (15) 15–25 8 (4) 4–19

a Year 1 = weeks 1–48; plant species identical in each filter.

b Year 2 = weeks 68–103; plant species changed to canna lilies (4:1);

 elephant ears (10:1); cattails (30:1).

c Interquartile range = range about the median between the upper

 and lower 25% of all values.

d STE = septic tank effluent.

e 4E, 10E, 30E = effluent samples from 4:1, 10:1, and 30:1 filters.

* s.d. = standard deviation

 percent samples CBOD >30 mg/L

week # sampling days 4:1 10:1 30:1

 1–6 38 92 92 87

 7–30 72 24 22 11

31–48 a

 @ 1,514 L/day 34 50 48 29

 @ 757 L/day 20 0 0 0

49–67 b - - - -

68–103 115 2 0 0

a Weeks 31–48 includes winter months, 1995–1996.

b Intermittent dosing at 1,514 L/day, three times per

 week during summer, 1996.
The Small Flows Journal Volume 4, Issue 1, Spring 1998

10

Effects of Length-Width Ratio and Stress on Rock-Plant Filter Operation

samples, regardless of L-W ratio, exceeded the 30 mg/L standard. CBOD

dropped to 11 to 24 percent during the

next 24 weeks and was reduced to only

two percent noncompliant effluent

samples collected from the 4:1 filter in

weeks 68 through 103.

Stress tests, as defined by NSF Standard

40 (NSF International, 1990), had little or

no effect on the rock-plant filters in this

study. Table 3 shows that none of the

stress tests resulted in weekly CBOD

values greater than 30 mg/L. The “10-day

vacation” and the “unscheduled repairs”

stress tests did produce some increase in

the effluent CBODs from the previous

week. The “vacation” test was conducted

during the hottest part of late August and

early September, 1995. Evapotranspiration

lowered the water level in the filters 4 to 6

cm. Cooler weather and rainfall during the

47-day shutdown maintained the normal

water level in each filter bed. Disturbing

the beds by removing and replacing all or

part of the plants had no effect on filter

operation, even after 19 weeks of intermittent dosing.

The percent of CBOD removal within

each filter bed was essentially the same

during the first year of operation regardless of the L-W ratio (see table 4). Grab

samples collected from specified sampling

ports in the beds showed that each filter

removed 54 to 60 percent of the raw

sewage CBOD within the first third of its

length, 70 to 74 percent at 2/3-bed length,

and 80 to 84 percent at the effluent end of

the bed. Occasional sampling during year

2 exhibited the same trend, except the

overall effluent efficiency increased to 91

to 95 percent removal, irrespective of LW ratio or plant species used (year 2 data

not shown).

Removal of TSS and VS by the septic

tank-filter bed systems closely followed

that of CBOD removal. Table 5 demonstrates this quite well. The septic tanks

routinely removed 50 to 70 percent of the

TSS load and the filter beds removed 70

to 80 percent of what was left. Again, no

TABLE 4 

CBOD removal within

rock-plant filters.

 average % removal a

sampling site 4:1 10:1 30:1

1/3-bed length 54 54 60

2/3-bed length 70 71 74

effluent end 80 81 84

a Removal of CBOD from raw sewage; average

 of 20 samples.

TABLE 3 

Effect of stress tests on

rock-plant filters.

 weekly CBOD, mg/L

stress 4:1 10:1 30:1

“wash day” a

week before 27 28 22

week after 8 7 5

“power failure” b

week before 58 31 20

week after 16 17 12

“10-day vacation” c

week before 17 16 16

week after 28 25 17

unscheduled repairs d

week before 8 8 7

week after 19 16 6

change plants;

Intermittent flow e

weeks 47-48 27 26 25

weeks 68-69 7 6 5

a Normal cycle modified by adding three washer loads of detergent to each

 filter system during one, 5-day period with a 24 hour period between each

 loading.

b 40% of design flow added between 5–8 a.m., then no loading for 48 hours,

 followed by 60% of design flow including one load of washing.

c Vacation cycle requires 60% design flow between 6 a.m. – 2 p.m. on a

 Friday, followed by no influent until 5–8 p.m. on the second Sunday (60%

 desing flow plus three washings).

d Lift station closed for repairs from 10/16/95 to 11/20/95.

e Intermittent flow of 1,514 L/day.
The Small Flows Journal Volume 4, Issue 1, Spring 1998

significant difference was observed among

the filters due to L-W ratio. The pattern for

VS was similar to TSS (the VS data are

not shown), but VS accounted for approximately one-third of the total TSS load.

Attempts to measure dissolved oxygen in

the fluid in the sample port at the effluent

end of each filter (rather than from

collected samples) were abandoned early

in the study. Sulfide in the effluent would

contaminate the membrane of the oxygen

probe. The sulfide, however, did not affect

ORP determinations made on site with a

portable meter. Table 6 shows that while

there was no difference between the filter

beds in regard to CBOD, TSS, or VS

removal, there was a highly significant

difference between the filters in ORP at

the effluent ends. Normally, the 30:1 bed

had a less anaerobic (less negative) ORP

than the other two filters. This was characteristic of the bed in both years 1 and 2

even though the plant species were changed.

The 4:1 and 10:1 filters had the same ORP

throughout their respective bed lengths.

Hydrogen sulfide removal by the filter

flora correlates quite well with the ORP

data (see table 7). The 4:1 and 10:1 filters

did reduce the sulfide level of STE by 52

to 60 percent in year 1 and 68 to 71

percent during year 2, but the 30:1 flora

consistently released only 5 to 15 percent

of the STE sulfide (85 to 95 percent

removal). The increase in percent reduction during year 2 probably is due to filter

aging rather than plant species since all

three filters showed an increase.

On the other hand, ammonium concentrations in the effluents responded more to

plant species than to bed aging as seen in

table 8. During year 1 (when filters had

identical plant flora), each filter removed

only 18 to 26 percent of the NH4+-N

released by the septic tanks. The 4:1 and

10:1 filter flora uptake during year 2 was

only 25 to 28 percent. The cattails used in

the 30:1 filter utilized this form of nitrogen

to a greater extent, resulting in a 67 to 68

percent reduction.

11

TABLE 5 

Summary of analytical results for

total suspended solids (TSS).

TABLE 6 

Oxidation reduction potentials

within the filter beds.

TABLE 7 

Effluent sulfide levels.

H. C. Bounds, Ph.D., James Collins, Zhiyun Liu, Zhen Qin, and T. A. Sasek, Ph.D.

 TSS, mg/L

 year 1 year 2

sample avg. (s.d.)* range avg. (s.d.)* range

raw 90 (51) 60–100 50 (20) 31–67

STE 27 (10) 15–30 24 (11) 18–31

4E 6 (3) 4–8 6 (3) 4–9

10E 7 (3) 5–9 5 (3) 4–9

30E 8 (5) 5–9 13 (5) 6–25

* s.d. = standard deviation

 average ORP, millivolts

sample site 4:1 10:1 30:1

1/3-bed length -206 -206 -194

2/3-bed length -201 -201 -149

effluent end -195 -194 -94*

TABLE 8 

Effluent ammonium concentration.

 NH4+-N, mg/L

sample year 1 (% reduction) year 2 (% reduction)

raw 20.3 16.7

STE 23.6 20.8

4E 18.0 (23.7) 15.5 (25.5)

10E 19.3 (18.2) 14.9 (28.4)

30E 17.3 (26.7) 6.7* (67.8)

* significant at P>0.01

*

average sulfide, mg/L

sample year 1 (% reduction) year 2 (% reduction)

raw 0.15 0.38

STE 2.0 2.12

4E 0.95 (52.5) 0.66 (68.8)

10E 0.80 (60.0) 0.61 (71.2)

30E 0.30 (85.5)* 0.09 (95.8)*

* significant at P>0.01

 significant at P>0.01
The Small Flows Journal Volume 4, Issue 1, Spring 1998

The amount of biofilm accumulated on

gravel surfaces was determined after the

48th and 103rd week of filter operation.

Gravel samples collected from between

clumps of plants were used to exclude as

much visible root material as possible.

Table 9 shows the results of the two

biofilm determinations. There appears to

be no consistent pattern other than a

general increase in the amount of biofilm

on the gravel in the second year.

No explanation can be given for the large

increase in biofilm at the 1/3-bed length

location of the 10:1 filter in year 2.

Throughout the study, no attempt was

made to restrict researchers from walking

on the gravel beds. This may have accounted for some settling of the bed and gravel

at this location.

The three rock-plant filters used in this

study proved to be efficient, easily

maintainable alternatives for individual

residence wastewater treatment. Once the

plant and microbial populations became

established, the filters consistently

produced effluents below the EPA limit of

less than 30 mg/L for BOD/TSS.

It is recognized that the hydraulic loading

used for these filters was well below the

maximum for the gravel medium. It was

not our intent to determine the best design

for rock-plant filters but simply to test

variations of a design recommended to us

by the LDHH/OPH. In our hands, the

length-width ratio proved to be not as

critical as previously reported (Wolverton,

1986) in regard to BOD, TSS, or VS

reduction. In fact, the most striking

similarity between the rock filters was that

each reduced the BOD load 54 to 60

percent within the first third of the bed

and 70 to 74 percent after passage through

two-thirds of the filter length.

Rock-plant filters respond well to stress.

A “48-hour power failure,” a “10-day

vacation” period, and three washer loads

of detergent (“wash day”) are recognized

by NSF International as stress parameters

for evaluating mechanical aeration units.

Rock-plant filters are not mechanical

aerators, but they should recover from

such stress equally as well as any aeration

unit. Our systems were constantly under

stress (by NSF definition) since the “working parents” dosing schedule was used.

One proposed use for rock-plant filters,

especially in Louisiana, would be for

vacation homes or hunting/fishing camps

in which the occupants are away for

extended periods of time. In this study,

extended periods of no dosing, intermittent dosing, and disruption of the filter

medium failed to cause an increase in

effluent BODs above the EPA limit.

Rock-plant filters appear to be well-suited

for such conditions.

The one significant difference between

the three filters was the ORP at the

effluent end. The 30:1 filter was always

less anaerobic than the other two units, if

not aerobic. This was observed repeatedly

during both years of operation regardless

of the plant species used. The result was

a lower sulfide concentration in the 30:1

effluent than either the 4:1 or the 10:1.

On the other hand, selection of plant species

for the filter bed can have an effect on

ammonium released in the effluent water.

Cattails used during the second year in the

30:1 filter proved to be much more

effective in utilizing the ammonium in the

12

TABLE 9 

Biofilm accumulation with

rock-plant filters

Effects of Length-Width Ratio and Stress on Rock-Plant Filter Operation

Discussion

 biofilm, mg/kg gravel

 4:1 10:1 30:1

sample site year 1 year 2 year 1 year 2 year 1 year 2

1/3-bed length 640 513 593 1,593 441 657

2/3-bed length 612 978 534 713 544 670

effluent end 759 615 457 778 703 950

bed average 670 702 528 1,028 563 759
The Small Flows Journal Volume 4, Issue 1, Spring 1998

wastewater than did either the canna lilies

or the elephant ears. The cattails grew so

well, in fact, that the homeowner would

probably need to remove excess growth

routinely from the bed to prevent clogging

by roots. The removal should have no

adverse effect on the system.

In conclusion, rock-plant filters can be

used for residential wastewater treatment

in any length-width ratio that fits the

homeowner’s grounds provided the septic

tank-filter system has the hydraulic

capacity for at least 4.5- to 5-day retention

of the wastewater.

Devel

This project was funded by Louisiana

Department of Environmental Quality

Interagency Agreements #24400-94-29

and #24400-96-60 as part of a block grant

from the U.S. Environmental Protection

Agency for education and demonstration

projects. We also express our sincere

appreciation to the staff of the Monroe,

Louisiana, Water and Pollution Control

Center, especially Mr. Nathaniel Smith,

without whose cooperation we could

never have undertaken this project.

oDevl

American Public Health Association.

1992. Standard methods for the

examination of water and wastewater.

18th ed., Washington, D.C.

Bounds, H. C. and J. F. Denison. 1992.

Evaluation of rock-plant filters as an

alternative wastewater treatment system

for individual residences. Report to

Louisiana Dept. of Health and Hospitals,

Office of Public Health. New Orleans.

Burgan, M. A. and D. M. Sievers. 1994.

On-site treatment of household sewage

via septic tankand two-stage submerged bed wetland. In On-site

wastewater treatment. Proceedings of

the Seventh International Symposium

on Individual and Small Community

Sewage Systems. St. Joseph, Mich:

American Society of Agricultural

Engineers (ASAE).

Cooper, P. F. and A. G. Boon. 1987. The

use of phragmites for wastewater by

the root zone method: The UK

approach. In Aquatic plants for water

treatment and resource recovery.

Orlando, Fla: Magnolia Publishing.

153–174.

Huang, J., R. B. Reneau Jr., and C.

Hagedorn. 1994. Constructed wetlands

for domestic wastewater treatment.

On-site wastewater treatment. Proceedings of the Seventh International

Symposium on Individual and Small

Community Sewage Systems. St.

Joseph, Mich: ASAE.

Litchfield, D. K. and D. D. Schates. 1989.

Constructed wetlands for wastewater

treatment at Amoco Oil Company’s

Mandan, ND, refinery. In Constructed

wetlands for wastewater treatment:

municipal, industrial, and agricultural.

Chelsea, Mich: Lewis Publishing.

Louisiana Department of Environmental

Quality. 1993. LDEQ Nonpoint source

management plan. Lousiana Dept.

Environ. Quality. Baton Rouge, La.

Maddox, J. J. and J. B. Kingsley. 1989.

Waste treatment for confined swine

with an integrated wetland and

agriculture system. In Constructed

wetlands for wastewater treatment:

municipal, industrial, and agricultural.

Chelsea, Mich: Lewis Publishing.

NSF International. 1990. Individual

aerobic wastewater treatment plants.

American National Standard Institute/

NSF International Standard (ANSI/

NSF) 40-1990. Ann Arbor, Mich: NSF

 International.

Wolverton, B. C. 1986. Artificial marsh

(wetland) wastewater treatment systems

for small communities. Presented at

Small Community Wastewater Management Seminar. Baton Rouge, La.

Wolverton, B. C. 1987. Artificial marshes

for wastewater treatment. Aquatic

plants for water treatment and

resource recovery. Orlando, Fla:

Magnolia Publishing.

13

H. C. Bounds, Ph.D., James Collins, Zhiyun Liu, Zhen Qin, and T. A. Sasek, Ph.D.

Acknowledgments

References
The Small Flows Journal Volume 4, Issue 1, Spring 1998

Wolverton, B. C., R. C. McDonald,

and W. R. Duffer. 1983.

Microorgainsms and higher

plants for wastewater

treatment. Journal of Environmental Quality 12:236-

242.

Wolverton, B. C., C. C. Myrick,

and K. M. Johnson. 1984.

Upgrading septic tanks using

microbial/plant filters.

Journal of the Mississippi

Academy of Sciences 29:19-

25.

14

Effects of Length-Width Ratio and Stress on Rock-Plant Filter Operation

LOWS

ARINGHOUSE

SMALL FLOWS

INGHOUSE

NAL SMALL FLOWS

NATIONAL SMA

CLEARINGH

NATIONAL SM

CLEARING

 H. C. Bounds, Ph.D.

Harold C. Bounds, Ph.D., is a

professor of biology at Northeast

Louisiana University and a

researcher on two previous

rock-plant filter projects.

James Collins

James Collins is employed by

Great Bend Packing Company,

Great Bend, Kansas, and was a

graduate student during the first

year of the project.

. If you would like more information about

this project, write to H. C. Bounds, Ph.D.,

Department of Biology, Northeast

Louisiana University, Monroe, Louisiana

71209-0520.

T. A. Sasek, Ph.D.

T. A. Sasek is an assosciate

professor and a physiological

plant ecologist with the department of biology at Northeast

Louisiana University.

Zhiyun Liu

Zhiyun Liu is employed by

Louisiana State University

Medical Center, New Orleans,

Louisiana, and was a graduate

student during the first year of

the project.

Zhen Qin

Zhen Qin is employed by the

University of Mississippi Medical

Center, Jackson, Mississippi,

and was a graduate student during the first year of the project.
The Small Flows Journal Volume 4, Issue 1, Spring 1998

Healthy microorganisms are critical

to the efficiency of biological

wastewater treatment processes.

Optimization of environmental

conditions for wastewater treatment

microorganisms results in a robust living

system and promotes efficient waste

removal. Biologically adverse environmental conditions can result in the

inhibition of microorganisms, possibly

causing interference or failure of wastewater treatment processes.

Adverse conditions in wastewater treatment systems can result from exposure to

toxic concentrations of chemicals in

influent wastewater or chronic exposure

to low concentrations of certain substances. In either case, the wastewater

treatment efficiency of systems can be

compromised for a period of time. In

severe cases of biological system disruption, the wastewater treatment units may

need to be restarted with new inoculum,

or the microorganisms may require a

15

ABSTRACT: The concern has been expressed that disposal of unused household

cleaning products can disrupt microbial wastewater treatment processes. This paper

reviews the techniques used to evaluate the toxicity of cleaning products to residential

wastewater treatment processes and examines examples of available data concerning

common products under the most probable worst-case scenario—single-residence septic

tanks. Microbial toxicity tests most commonly examine consumption of oxygen by microorganisms, production of anaerobic gases, or removal of a reference compound. If the

concentration of the test substance is maintained below the “no-observed effect concentration” (NOEC) in these conservative tests, it is presumed that no toxicity will occur in

the wastewater treatment process. The four case studies reviewed support the conclusion

that disposal of whole-package quantities of typical household cleaning products results

in little or no observed effect on septic tank function.

. significant period of recovery to rebuild a

healthy population.

The majority of failures in publicly owned

treatment works (POTWs) are caused by

mechanical failures, hydraulic deficiencies, lack of maintenance, and interference

by undesired microorganisms. When

disruptions are caused by toxicity, the

origin is usually large slug-doses of

chemicals from industrial sources (Hänel,

1988). However, concern has been raised

that microbial toxicity of household

cleaning product ingredients may cause

upsets in POTWs and household septic

tanks, especially when whole containers of

product are disposed of down the drain.

The purpose of this literature review is to

evaluate the impact of down-the-drain

disposal of cleaning products on wastewater treatment processes. Patterns of cleaning

product disposal will be discussed, particularly in terms of dilution, to identify the

wastewater treatment process most likely

by Daniel E. Edwards, Ph.D.

and Alvaro J. DeCarvalho

Assessing the Impact of Household

Cleaning Products on Wastewater

Treatment Systems

Assessing the Impact of Household

Cleaning Products on Wastewater

Treatment Systems

LITERATURE REVIEW
The Small Flows Journal Volume 4, Issue 1, Spring 1998

16

Assessing the Impact of Household Cleaning Products on Wastewater Treatment Systems

to be impacted by cleaning product

disposal. Finally, case studies using worstcase assumptions will be reviewed to

determine whether disposal of cleaning

products has been found to upset biological wastewater treatment processes.

mponeDlv

As of 1992, 75.5 percent of the U.S.

population was connected to POTWs

(U.S. Bureau of the Census, 1993). The

remaining population uses onsite treatment, predominantly in the form of septic

tanks. The majority of onsite wastewater

treatment systems are septic tank systems

(EPA, 1987). In contrast to POTWs, most

septic tank systems serve single-family

residences, although some are designed

for multiple dwellings and commercial

businesses.

Septic tank systems gained widespread

use in the U.S. during the 1940s and

1950s in both rural and suburban settings.

Their design and construction is regulated

according to individual state specifications (see table 1). Twenty-eight states

require the minimum usable septic tank

volume to be in the range of 750 to 900

gallons (2,839 to 3,407 L), 18 states require

a minimum of 1,000 gallons (3,785 L),

three states are regulated on a county or

district basis, and one state (Louisiana)

allows a minimum 500-gallon (1,893-L)

septic tank for one-bedroom dwellings. In

Louisiana, the typical septic tank would

be expected to be larger because the primary

design criterion for septic tank volume is

2.5 times the estimated daily flow.

Concentrations of Product Ingredients

in Wastewater

Consumer products are not composed of

single chemicals. Household cleaning

products are generally formulations of

active ingredients, a carrier (such as

water), and additives that improve mixing

and application or otherwise enhance

state minimum volume b additional volume

gallons gallons/bedroom

Alabama 750 250

Alaska 1,000 250

Arizona 960 300

Arkansas 750 250

California c — —

Colorado 750 250

Connecticut 1,000 250

Delaware 1,000 250

Florida 900 Add 1.5 X estimated additional daily flow

Georgia c — —

Hawaii 750 250

Idaho 900 250

Illinois 750 250

Indiana 750 250

Iowa 750 250

Kansas 750 250

Kentucky 750 250

Louisiana d 500 2.5 X estimated total daily flow

Maine 750 250

Maryland 750 250

Massachusetts 1,000 1.5 X estimated total daily flow

Michigan c — —

Minnesota 750 250

Mississippi 750 250

Missouri 1,000 250

Montana 750 250

Nebraska 1,000 250

Nevada 1,000 250

New Hampshire 1,000 250

New Jersey 1,000 250

New Mexico 750 250

New York 1,000 250

North Carolina 900 250

North Dakota 1,000 200-300

Ohio 1,000 250-300

Oklahoma 1,000 250

Oregon 1,000 250

Pennsylvania 900 Add 3.5 X estimated additional daily flow

Rhode Island 1,000 250

South Carolina 890 250

South Dakota 1,000 250

Tennessee 750 250

Texas 750 250

Utah 750 250

Vermont 1,000 1.5 X estimated total daily flow

Virginia 750 200-300

Washington 750 250

West Virginia 750 250

Wisconsin 750 225

Wyoming 1,000 250

a State regulations compiled by the National Small Flows Clearinghouse (1994).

b Minimum volumes may be based on 1, 1–2, 1–3, or 1–4 bedroom dwellings

 before additional volume is triggered, depending on the state.

c Regulations are based on a county-by-county or district-by-district basis.

d Minimum volume of 500 gallons (1,893 L) in Louisiana is for a 1-bedroom

 dwelling only. The primary design factor is 2.5 times the estimated daily flow.

TABLE 1

Summary of state regulations on minimum septic tank capacities. a

Wastewater Treatment Systems
The Small Flows Journal Volume 4, Issue 1, Spring 1998

17

product performance. Following disposal,

each component of these mixtures meets

its individual fate in the environment.

Because certain household cleaning

products are designed to have antimicrobial properties, the active ingredients

providing these properties could logically

represent the greatest potential of reaching

concentrations that could inhibit biological wastewater treatment processes in

residential systems.

The microbial toxicity of cleaning product

ingredients should be evaluated in the

context of typical and worst-case exposure

concentrations under normal use and

disposal practices. Some cleaning products,

such as hand dishwashing detergents, will

enter the disposal system on a daily basis

in small quantities. Others will follow

disposal of washwaters on a weekly basis.

Pouring an entire package of a cleaning

product down the drain represents the

worst-case scenario.

In the case of POTWs, overall fluctuations

in concentrations as a result of routine

household use and disposal would be

expected to be dampened by the presence

of many POTW users. Because of the

dampening effect that occurs in POTWs,

the disposal of a single container of household cleaning product under a worst-case

scenario would not impact the operation

of the treatment works.

A simple mathematical method to predict

the wastewater concentrations of consumer product ingredients in POTWs was

developed by Holman (1981). This method

uses general assumptions about per capita

product and water use to provide an

estimate of average product ingredient

concentration in wastewater. This estimate

is considered to be conservative because it

assumes that all of the product is disposed

of down the drain, and none is consumed

during use or disposed of through other

routes. The concentration of a product

ingredient in municipal wastewater can be

estimated by the following equation:

where:

Cmw = concentration of product

ingredient in municipal wastewater

(mg/L).

X = quantity of product marketed

(mg/day).

P = ingredient fraction in product

(percent by weight/100).

Y = population of market area (number

of people).

Q = per capita wastewater flow rate

(L/day).

The quantities X and P are available to the

manufacturers of the products, and Y is

available through census data. The quantity

Q is variable according to geographic

region and water use patterns. For estimation purposes, the per capita flow of 400

L/day is generally used for U.S. estimates

(Cowen et al., 1992). More precise flow

data may be obtained for specific wastewater treatment plants by consulting their

records.

The general product ingredient category

of surfactants may be used as an example

to illustrate the application of equation 1.

Surfactants are key ingredients in almost

all cleaning product applications, including laundry detergents, dishwashing

detergents, drying and antispotting

products, and hard surface cleaners. More

than one billion kilograms (9.8 million

tons) of total nonsoap surfactants were

sold in the U.S. for use in household

cleaning product formulations in 1992

(U.S. International Trade Commission,

1994). No other single group of cleaning

product ingredients would be expected to

exceed the concentration of surfactants in

average household wastewater.

Assuming the 1992 U.S. population of

260 million people produces wastewater

at a rate of 400 L/day per capita, the

average concentration of total surfactants

calculated by equation 1 is 26 mg surfactant per liter of wastewater. This is a

conservative calculation because some

surfactants may biodegrade in sewers, and

some are used in products that are not

typically disposed of down the drain, such

as automotive or agricultural cleaning

Daniel E. Edwards, Ph.D., and Alvaro J. DeCarvalho

X • P

Y • Q

Cmw = (1)
The Small Flows Journal Volume 4, Issue 1, Spring 1998

18

Assessing the Impact of Household Cleaning Products on Wastewater Treatment Systems

products. The result of this calculation is

consistent with the high-end of the ranges

of surfactant concentration in residential

community wastewater reported in reviews

by Swisher (1987) and Srinivasarao et al.

(1992).

In cases of onsite wastewater treatment,

such as septic tanks, the lack of dilution

from other households precludes dampening of high concentrations during periods

of peak usage or disposal events. The

dampening in this case is only a result of

the wastewater coming from other uses in

the household. Maximum ingredient

concentrations resulting from disposal of

unused product into septic tanks can be

more directly calculated.

For example, if a liquid cleaning product

contains 10 percent (weight/volume) of an

ingredient, disposal of one gallon (3.785 L)

into a 1,000-gallon (3,785-L) septic tank

would lead to a maximum concentration

of the ingredient of 100 mg/L in the

aqueous phase, assuming the septic tank is

completely mixed. Subsequent household

water use would dilute and flush out this

material, creating lower concentrations.

This type of disposal into a septic tank

can reasonably be expected to represent

the worst-case scenario in terms of

concentrations of cleaning product ingredients in a wastewater treatment system.

Patterns of Product Disposal

In order to understand the frequency of

this worst-case scenario, the question

remains: how often are cleaning products

disposed of unused? In order to answer

this question, The Soap and Detergent

Association (SDA) commissioned a

market research group (NPD Group, Inc.)

to survey 20,000 randomly selected U.S.

households. The following points from the

summary of findings of the study are

relevant to this report:

Of the 13,697 returned surveys (a 68.5

percent response),

• eight percent reported disposing of at

least one unused cleaning product

within the past three months,

• twenty-three percent reported using

septic systems, and

• there was no difference in disposal

patterns between those who used septic

systems and those who used sewer

systems.

Among the eight percent who reported

disposing of unused products,

• the average number of products

disposed of over the three-month

period was 2.43,

• most of the product (67 percent) was

disposed of by leaving it in the container and placing it in the trash, and

• ten percent was poured down the drain

(no other single disposal pathway

accounted for more than one percent of

disposal).

The survey did not attempt to estimate the

percent of the product remaining in the

discarded container, but it does point out

that down-the-drain disposal is performed

infrequently. This is particularly true for

higher volume products, which tend to get

used up rather than dumped out (NPD

Group, Inc., 1995). Because cleaning

products are occasionally poured down

the drain, manufacturers routinely address

the impact of cleaning products on wastewater treatment systems.

The objective of wastewater treatment

microbial toxicity tests is to determine the

concentration at which a compound

impairs the ability of the microorganisms

to treat wastewater. If this concentration is

greater than the expected exposure

concentrations, then the compound is not

expected to have a negative impact on the

activity of wastewater treatment microorganisms. In general, there are three major

categories of testing approaches: effects

on respiration (or gas production from

microorganisms), effects on removal of

other compounds, and effects on performance during wastewater treatment

Measuring Product Toxicity
The Small Flows Journal Volume 4, Issue 1, Spring 1998

19

Daniel E. Edwards, Ph.D., and Alvaro J. DeCarvalho

simulations. These effects can be examined in both aerobic and anaerobic systems.

Oxygen Consumption

The major test currently addressing

aerobic wastewater treatment microorganism toxicity in U.S. or European regulatory guidelines is Organization for

Economic Cooperation and Development

procedure number 209 (OECD 209):

Activated Sludge, Respiration Inhibition

Test (OECD, 1993a). This test is designed

as a simple screening tool to assess the

impact of a chemical on the overall

respiration rate of activated sludge.

A solution containing an excess of nutrients

is added to a beaker with microbial inoculum (seed) and various volumes of test

substance stock solution. The microbial

inoculum is activated sludge from a

municipal facility treating primarily

domestic wastewater. Controls without

test substance are used in the test design

to measure the background activity of the

sludge. An inhibitor of respiration

(3,5-dichlorophenol) is included as a

negative control to assess sludge sensitivity to chemical inhibition. The 50 percent

inhibition concentration of the standard

inhibitor must be within a specified range

in order for the test to be considered valid.

Each mixture of sludge, nutrient solution,

test solution, and dilution water is aerated

for a set period of time (usually three

hours), following which the rate of

dissolved oxygen (DO) consumption is

measured. The “inhibitory effect” is

defined by comparison to duplicate

controls using the following equation:

where:

Rs = oxygen consumption rate (mg/

O2/L/hour) at tested concentration of

test substance,

Rc1 = oxygen consumption rate (mg/

O2/L/hour), control 1, and

Rc2 = oxygen consumption rate (mg/

O2/L/hour), control 2.

The percent inhibition is plotted as a function of the test substance concentration.

The 50 percent inhibition concentration is

determined from the resulting graph.

OECD 209 provides a measure of the

overall impact of a chemical on a highstrength inoculum such as would be

encountered in activated sludge-mixed

liquor. This high concentration of sludge

could buffer toxicity by adsorption of the

test compound onto sludge solids. The

high overall respiration rate of a variety of

species consuming the abundant carbon

also could mask some toxicity to individual species. The inhibition that is

masked in this test could potentially

become important in biodegradation tests

using more dilute inoculum.

A test somewhat similar to the OECD test

has been presented by Marks (1973). This

test is a variation of the classic biological

oxygen demand (BOD) test and is known

as the BOD microbial toxicity test or

BODm. In the BODm test a relatively

dilute seed is prepared from domestic

activated sludge. The seed is defined as 5

mL of a sludge culture that is fed daily

with domestic sewage and whose “oxygen

consumption rate is in the range of 1 to 3

mg/L/hour.”

The seed is combined with a series of

volumes of a test substance stock solution

(or mixed waste stream of interest) in

standard BOD bottles with a single

concentration of a reference compound

(glucose). The remaining volume in the

BOD bottles is filled with dilution water

and aerated to saturate the water with

oxygen. The concentration of glucose is

designed to be sufficient for the microorganisms to deplete one-half of the

dissolved oxygen (DO) present in the

mixture if no inhibition is encountered.

Each BOD bottle is incubated at 20oC for

three days without further aeration. The

1 -

2Rs

Rc1 + Rc2

• 100 (2)
The Small Flows Journal Volume 4, Issue 1, Spring 1998

20

Assessing the Impact of Household Cleaning Products on Wastewater Treatment Systems

DO is then measured in each bottle and

plotted as a function of test substance

concentration. The lowest concentration

of test substance that causes a reduction in

the oxygen consumption rate compared to

a control is defined as the “threshold

inhibition level.” Concentrations of the

test substance below the threshold are

considered to be acceptable for wastewater treatment systems. The length of

incubation can be shortened to less than

three days if a higher concentration of

sludge is used.

Numerous variations on methods measuring the impacts of chemicals on oxygen

consumption have been published as

biodegradation tests (Swisher, 1987).

Many oxygen consumption tests use

respirometers. A respirometer is a device

that continuously monitors oxygen

consumption and/or carbon dioxide

generation in a test vessel. Respirometers

can be used to measure real-time effects

of substances on biological respiration in

a continuously aerated system (Eckenfelder,

1980). Unfortunately, respirometric tests

use apparatus that is relatively expensive

and requires significant skill on the part of

the analyst. However, recent technical

advances in respirometer design and

computerization are leading to wider use

of these instruments (Mahendraker and

Viraraghavan, 1995).

Anaerobic Gas Production

Anaerobic biological treatment is a major

wastewater treatment process used

throughout the world, primarily in the

form of sludge digesters and household

septic tanks. Because appreciable quantities of oxygen are not present in anaerobic

systems, respiration tests based on

dissolved oxygen are not applicable. In

the place of oxygen consumption, gas

production is the most common measurement of anaerobic activity.

The validity of gas production as an

indicator of anaerobic activity is contingent on the presence of an active methane-producing (methanogenic) consortium

of bacteria. The test system must be

completely protected from exposure to

oxygen, which is toxic to methanogens.

Oxygen contamination in the test system

can also lead to negative gas pressure as a

result of absorption of oxygen into the test

liquid. Examples of procedures used to

evaluate anaerobic gas production are

provided later in case studies reported by

Yang et al. (1979) and Vaishnav and

McCabe (1996).

Reference Compound Removal

An alternative to respiration measurements is measuring the effect of a chemical on the removal of a reference compound. The matrix containing the test

chemical and a microbial seed (usually

activated sludge or an anaerobic inoculum

such as septage) is analyzed for the

reference compound after a defined exposure period. This technique is regarded to

be a conservative estimate of microbial

inhibition because it measures a specific

activity and not necessarily lethality.

A general test for inhibition of activated

sludge using removal of 14C-glucose has

been described by Larson and Schaeffer

(1982). In the aerobic version, sludge is

obtained from a POTW receiving primarily domestic wastewater, aerated, and

used within 2 hours of collection.

Aliquots of the sludge are placed in open

beakers on a rotary shaking table with

various concentrations of test substance

stock solutions. After a five-minute

equilibration period, an aliquot of 14Cglucose solution is added to each mixture.

Equilibration is continued for an additional 15 minutes, then terminated by the

addition of hydrochloric acid. Samples of

each mixture are filtered and assayed for

14C activity by liquid scintillation

counting (LSC), and the percent removal

of the 14C-glucose is calculated. The

concentration of chemical inhibiting

glucose removal by 50 percent (IC50) is
The Small Flows Journal Volume 4, Issue 1, Spring 1998

21

Daniel E. Edwards, Ph.D., and Alvaro J. DeCarvalho

calculated and normalized to the control

response by using an empirical nonlinear

regression model. The anaerobic version

of this test is identical except that it uses

septage as the test matrix, and the

incubation is performed in an anaerobic

chamber.

Wastewater Treatment Simulations

Laboratory-scale wastewater treatment

simulations performed to determine the

treatability of a test substance can also

provide important information on the

longer-term impact of chemicals in

wastewater treatment. Simulation tests

such as continuous activated sludge

(CAS), porous pot (American Society for

Testing and Materials [ASTM], draft

method), and coupled units (OECD

procedure number 303A) (OECD, 1993b)

can provide insight into potential problems that can occur at wastewater

treatment facilities. Simulation tests

assessing the impact of cleaning product

ingredients on septic tanks have been

reported in literature (Pearson et al., 1991;

Holman and Hopping, 1980; Truesdale

and Mann, 1968).

It is generally recognized that normal use

levels of household cleaning agents and

disinfectants do not impair septic tank

function (Gross, 1987; Truesdale and

Mann, 1968). There have been few studies

in the published research literature

specifically examining the impact of

disposing of larger quantities of household

chemicals on wastewater treatment

systems, although the procedures listed

earlier in this article are commonly

conducted by manufacturers to provide

data for safety assurance on new or

reformulated products.

Toxicity of Chemicals

In a report entitled Recovery of Anaerobic

Digestion after Exposure to Toxicants,

Yang et al. (1979) provide a detailed

literature review on previously published

data relating toxicity of various chemicals

to anaerobic wastewater treatment microorganisms. The authors also performed

their own experiments, examining the

toxicity of more than 30 chemicals

representing heavy metals, inorganics,

various organic chemicals common to

industry, and antibiotics.

This study was undertaken to test the

previously widely held perception that

methane fermentation cannot tolerate

chronic or slug doses of toxicants. Two

types of assays were used: an “anaerobic

toxicity assay (ATA)” and an anaerobic

filter assay. The ATA was designed as a

short-term test to determine the impact of

single doses of chemical into an unacclimated system. The anaerobic filter assay

was used in a continuous flow mode that

allowed long-term operation and acclimation by microorganisms. Gas production

and COD removal were measured over

time from each filter unit.

Under an ATA test using unacclimated

sludge (figure 1), 25 mg/L of an anionic

surfactant (tradename “WXN,” produced

Relevant Case Studies

FIGURE 1 

Response of unacclimated

methanogens to an anionic

surfactant (source: Yang et

al., 1979).
The Small Flows Journal Volume 4, Issue 1, Spring 1998

The vessel was sealed, and the headspace

was connected by tubing to a second

vessel containing water. Water displacement into a third vessel was measured and

used as an indicator of anaerobic respiration. The concentration of test substance

inhibiting anaerobic respiration by 50

percent over a 96-hour exposure period

(EC50) was calculated, along with the noobserved effect concentration (NOEC).

Sodium chloride was used as a reference

compound.

Using the NOEC value derived from these

test procedures and worst-case scenario of

disposing of an entire container-full of a

granular all-fabric bleach and a general

purpose cleaner (trade names withheld at

manufacturer’s request) directly into a

750-gallon (2,839-L) septic tank, Vaishnav

and McCabe calculated whether the

product concentration in the septic tank

would exceed the NOEC.

As table 2 describes, the worst-case

predicted septic tank concentrations for

22

Assessing the Impact of Household Cleaning Products on Wastewater Treatment Systems

by American Cyanamid Corporation)

reduced gas production to about 80

percent of the control. At 50 mg/L, the gas

production rate gradually declined for the

first 10 days then subsequently increased.

At 100 mg/L, the initial gas production

rate was about 20 percent of the control.

Subsequently, it decreased and later

showed acclimation after 20 days. Gas

production ceased after 10 days at 12

percent of the control volume in the system

with 250 mg/L of anionic surfactant.

Note that in this ATA system, the mixed

liquor suspended solids (MLSS) were

measured at 600 mg/L, significantly lower

than typical anaerobic digesters where

solids typically range from one to five

percent (weight/volume), which is

equivalent to 10,000 to 50,000 mg/L.

Thus, the low MLSS level could have

exhibited toxicity at lower chemical

concentrations than would be seen in

actual systems.

In the anaerobic filter system, continuous

additions of 15 and 30 mg/L of the

anionic surfactant did not produce

sustained inhibition; however, 60 mg/L

for 28 days produced a gradual decrease

in gas production until the surfactant

additions were stopped (figure 2). Gas

production remained about 50 to 60

percent of the earlier maximum levels

until beginning to improve approximately

30 days after the last surfactant addition.

The study was terminated before complete

recovery was evident.

Cleaning Product Safety

Inhibition of anaerobic gas production

from cellulose degradation was used by

Vaishnav and McCabe (1996) to assess

safety of cleaning products to anaerobic

microorganisms. In this procedure,

various concentrations of the test compound were added to incubation vessels

(250-mL flasks) containing constant

amounts of anaerobic digester sludge,

cellulose, and a synthetic sewage feed

mixture.

FIGURE 2 

Response of anaerobic filter

to an anionic surfactant

(source: Yang et al., 1979).
The Small Flows Journal Volume 4, Issue 1, Spring 1998

23

Daniel E. Edwards, Ph.D., and Alvaro J. DeCarvalho

either product did not exceed the NOEC.

Therefore, it is unlikely that disposing of

an entire container of either product will

cause harm to septic tank microbes.

Impact to Septic Tanks

In a report presenting data on the impact of

the disposal of household cleaning

products on septic tanks, Gross (1987)

examined chlorine bleach and Lysol® (a

disinfectant). Gross suspected these

common household products had the

potential to harm septic tank operation

because of their antimicrobial properties.

The first step in this study was to establish

the concentration of each product required

to “kill all of the bacteria.” One-liter samples

of septic tank effluent were subjected to

interaction with various concentrations of

the chemicals. They were allowed to interact

for about one hour and then analyzed for

total coliforms following standard procedures. The concentrations required to

eliminate coliforms in effluent samples

were 1.85 mL/L for chlorine bleach and 5

mL/L for Lysol.

Four septic tanks were used in a field study

to assess the impact of these coliforminhibiting levels of the products on septic

tank operation. The volumes of these tanks

were 400 gallons (1,514 L) for septic tank

C and 375 gallons (1,420 L) for septic tank

D. Prior to the field test, the tanks were

pumped out and then operated for two

weeks to allow return to normal operation.

The cleaning products were injected into

the tanks by flushing them down a toilet.

Samples of liquid were taken from the

septic tanks periodically and tested for

coliforms until the coliform population

was found to reach predosing levels.

When the concentrations of bleach and

Lysol, equivalent to those determined in

the first part of the experiment, were

flushed into tanks C and D, coliform

populations were temporarily reduced but

returned to approximate predosing levels

within 60 hours (table 3). The pH, BOD5,

and total suspended solids of septic tank

products NOEC worst-case concentration

granular all-fabric bleach b 625 mg/L 356 mg/L

general purpose cleaner c 10,000 mg/L 750 mg/L

a source: Vaishnav and McCabe, 1996.

b assumes 64-oz. container (1.89 L).

c assumes 1-gallon container (3.785 L).

TABLE 2 

Impact of two cleaning products

on gas production by anaerobic

sludge. a

 400 gallons (1,514 L) 375 gallons (1,420 L)

recovery recovery

time coliforms time coliforms

product dose (hours) (colonies/100 mL) (hours) (colonies 100 mL)

liquid 0 68E5 0 48E5

bleach 4 0 4 0

 8 0 8 0

11 19E0 11 6E1

22 32E2 22 43E2

26 86E2 26 92E2

31 29E3 31 18E3

43 99E4 43 19E5

48 26E5 48 31E5

52 42E5 52 42E5

Lysol® 0 6.7E5 0 3.8E5

 4 0 5 <10,000

12 1E2 24 <10,000

26 1.6E3 290.8E5

32 2.9E3 483.2E5

39 2.1E4

50 2.3E5

56 3.8E5

a source: Gross, 1987. 2 gallons (7.57 L) 2 gallons

TABLE 3 

Results of a field study on the

impact of cleaning products on

septic tank coliforms. a

Septic Tank C Septic Tank D
The Small Flows Journal Volume 4, Issue 1, Spring 1998

24

Assessing the Impact of Household Cleaning Products on Wastewater Treatment Systems

Conclusions

Acknowledgments

effluents were not impacted by the

chemical treatments.

Glucose Removal Method

Bookland et al. (1992) tested four

materials using the glucose

removal method in septage

collected from a functioning

septic tank. These four chemicals were chosen as representative of ingredients in cleaning

products that could exhibit

antibacterial properties: linear

alkylbenzene sulfonate (LAS, an

anionic surfactant), ethanol (an

organic solvent), sodium

hypochlorite (a bleach), and dioctyl di-methyl ammonium chloride

(DODMAC, a cationic surfactant). The

results of this study are reported in table 4

as HA50 (heterotrophic activity reduced

by 50 percent as measured by reduction in

glucose uptake) and as the NOEC

(concentration having no effect on

glucose uptake).

These data were used to calculate the

maximum ingredient concentration

(ICmax) that can be disposed of into a

septic system without causing an adverse

effect in a 750-gallon (2,839-L) septic

tank:

ICmax = NOEC (mg/L) • 3.785 L/gallon •

750 gallons per tank.

The maximum amount of product (Pmax)

that can be safely disposed of is calculated

by:

Pmax = ICmax/PICmax (mg/L),

where PICmax is the maximum product

ingredient concentration.

For example, if ethanol is used in cleaning

products at a maximum concentration of

five percent NOEC (weight/weight), its

NOEC would be converted to a Pmax as

follows:

ICmax = 10,000 mg/L ethanol (NOEC) •

3.785 L/gallon • 750 gallons/tank = 28.4

kilograms (kg) ethanol/tank.

Pmax = 28,388 g/tank • 100 mL product/

5 g ethanol • 1 L/1000 mL • 1 gallon/

3.785 L = 150 gallons.

Therefore, up to 150 gallons (568 L) of

product containing five percent ethanol

can be added to a 750-gallon (2,839-L)

septic tank without adversely affecting

heterotrophic activity.

Similar calculations illustrate that up to

4.5 gallons (17 L) of product containing

30 percent anionic surfactant linear

alkylbenzene sulfonate (LAS), 4.3 gallons

(16.28 L) of bleach containing 5 percent

sodium hypochlorite, and 2.5 gallons

(9.46 L) of product containing 30 percent

cationic surfactant DODMAC can be

added to a 750-gallon (2,839-L) septic

tank without adversely affecting heterotrophic activity (table 4).

TABLE 4 

Summary of septic tank safety

data based on glucose

removal. a

NOEC equivalent

amount of product

in 750-gallon (2,839 L)

test material HA50 (mg/L) NOEC (mg/L) septic tank (Pmax)

sodium hypochlorite 475 288 4.3 gallons (16.28 L) b

LAS 6,750 1,820 4.5 gallons (17 L) c

ethanol 80,000 10,000 150 gallons (568 L) d

DODMAC >1,000 >1,000 2.5 gallons (9.46 L) e

a source: Bookland et al., 1992.

b assumes 5% sodium hypochlorite.

c assumes 30% LAS.

d assumes 5% ethanol.

e assumes 30% DODMAC.
The Small Flows Journal Volume 4, Issue 1, Spring 1998

25

Daniel E. Edwards, Ph.D., and Alvaro J. DeCarvalho

References

These case studies support several

statements related to down-the-drain

disposal of cleaning products in septic

systems:

• Septic tanks are robust in tolerating

chemical exposures resulting from

disposal of household cleaning

products, even those designed as

disinfectants.

• Rapid hydraulic turnover minimizes

the exposure of microorganisms to

high concentrations of chemicals

resulting from one-time slug loads.

This aids in the rapid recovery of

microorganisms even if temporary

adverse biological conditions are

experienced in the tank.

• Quantities of cleaning products

required to inhibit septic tank activity

are larger than single packages,

sometimes much larger. This is

observed even when using conservative “no effect” indices of glucose

uptake or toxicity to coliforms in

septic effluent.

Because of the amount of dilution that

occurs in POTWs, disposing of single

household quantities of cleaning products

that are normally mixed with water will

not impact their concentration in POTW

influent. In these community-level

wastewater treatment systems, products

can be regarded as safe for disposal if

found to be nontoxic to waste treatment

microorganisms at the average predicted

concentration (plus a reasonable safety

factor). Approximately 25 percent of the

households in the U.S., however, use

single residence onsite wastewater

treatment, most commonly configured as

septic tank/absorption field systems. For

these systems, dilution is limited to the

volume of the septic tank and subsequent

household water use.

It is generally accepted that normal-use

concentrations of unused cleaning products

do not create problems in septic tanks, but

it is possible to temporarily elevate product

concentrations in a septic tank by pouring

an entire package down the drain. A recent

survey shows that disposing of unused

household cleaning products down the

drain is an infrequent practice. The worstcase scenario of product disposal in

wastewater treatment is the disposal of a

completely unused package of product in

a minimum size septic tank. If a product

does not impact waste treatment under

this scenario, it may be assumed to be safe

for other common use and disposal

scenarios.

Available data indicate that disposal of

household quantities of cleaning products,

such as bleach and detergents, do not

cause long-term septic tank upset. Screening tests indicate that disposal of whole

packages of these products results in

maximum concentrations in septic tanks

that are within the no-effect concentrations

for gas production and glucose uptake.

Support for this work was provided by

The Soap and Detergent Association

(SDA) and by Roy F. Weston, Inc. The

authors gratefully acknowledge efforts of

The SDA Product Disposal Task Force in

providing technical review, in particular

James McCabe of The Clorox Company

and Celeste Kuta of The Procter & Gamble

Company. Additionally, the editorial

assistance of Pat Sobota (Roy F. Weston,

Inc.) is also gratefully acknowledged.

Summary

Conclusion

Acknowledgments
The Small Flows Journal Volume 4, Issue 1, Spring 1998

26

Assessing the Impact of Household Cleaning Products on Wastewater Treatment Systems

Bookland, E. A., D. C. McAvoy, D. L.

Wilke, R. T. Williams, and E. C.

Schaeffer. 1992. Screening level tests

for determining effects on septic tank

functions. Paper presented at 13th

Annual Meeting of the Society of

Environmental Toxicology and

Chemistry (November 8–12). Cincinnati, Ohio.

Cowen, C. E., T. M. Rothgeb, R. J.

Larson, W. I. Fanta, B. E. Domeyer,

and T. C. J. Feijel. 1992. Environmental risk assessment of perfume raw

materials in aquatic and terrestrial

environments. Proceedings from the

Sixth International Information

Exchange. Princeton, N.J: Research

Institute for Fragrance Materials, Inc.

Eckenfelder, W. W. 1980. Principles of

water quality management. Boston:

CBI Publishing Company, Inc.

Gross, M. A. 1987. Assessment of the

effects of household chemicals upon

individual septic tank performances.

Technical Completion Report Project

G-1212-07. Water Resources Research

Center. University of Arkansas,

Fayetteville.

Hänel, K. 1988. Biological treatment of

sewage by the activated sludge process. New York: John Wiley & Sons.

Holman, W. F. 1981. Estimating the

environmental concentrations of

consumer product components. In

Aquatic toxicology and hazard assessment: Fourth Conference. Philadelphia:

American Society for Testing and

Materials. ASTM STP 737. 159–182.

Holman, W. F. and W. D. Hopping. 1980.

Treatability of type A zeolite in

wastewater-Part II. Journal WCPF

52:2887–2905.

Larson, R. J. and S. L. Schaeffer. 1982. A

rapid method for determining the

toxicity of chemicals to activated

sludge. Water Research 16: 675–680.

Mahendraker, V. and T. Viraraghavan.

1995. Respirometry in environmental

engineering. Journal of Environmental

Science and Health A30:713–734.

Marks, P. J. 1973. Microbiological

inhibition testing procedure in Biological Methods for the Assessment of

Water Quality. Philadelphia: American

Society for Testing and Materials.

ASTM STP 528. 221–226

National Small Flows Clearinghouse.

1994. Septic tanks from the state

regulations. Morgantown, WVa.

WWBKRG25.

NPD Group, Inc. 1995. Consumer

disposal of household cleaning

products. Report prepared for the Soap

and Detergent Association. New York.

OECD. 1993a. Activated sludge, respiration inhibition test. Test method 209.

OECD guidelines for testing of

chemicals, 7th ed. Paris, France:

Organization for Economic cooperation and Development.

_____. 1993b. Simulation test-aerobic

sewage treatment: coupled units test.

Test method 303A. OECD guidelines

for testing of chemicals, 7th ed. Paris,

France: Organization for Economic

Cooperation and Development.

Pearson, F. H., H. R. McLean, and S. A.

Klein. 1991. Pilot-scale septic tank

treatment of preservative-laden waste.

Res. J. Water Pollut. Control Fed.

63:999–1011.

Rittman, B. R. 1987. Aerobic biological

treatment. Environ. Sci. Technol.

21:128–136.

Srinivasariao, C., S. K. Dentel, and H. E.

Allen. 1992. Impacts of surfactants on

sludge management processes.

Presented before the Division of

Environmental Chemistry, American

Chemical Society. San Francisco, Ca.

April 5–10.

Swisher, R. D. 1987. Surfactant Biodegradation. 2nd. ed. New York: Marcel

Dekker, Inc.

Truesdale, G. A. and H. T. Mann. 1968.

Synthetic detergents and septic tanks.

The Surveyor and Municipal Engineer

131: 28–33.

U.S. Bureau of the Census. 1993. Statistical abstract of the United States. 113th

ed. Washington, D.C.

U.S. Environmental Protection Agency

(EPA). 1987. Statistical abstract of the

 References
The Small Flows Journal Volume 4, Issue 1, Spring 1998

27

NAT

CLEARIN

AL SMALL F

EARINGHOU

ATIONAL SMA

Alvaro J. DeCarvalho

Alvaro DeCarvalho is the director of

environmental safety for The Soap

and Detergent Association. He

attended Wairarapa College in

Masterton, New Zealand, and has an

A.S. in Liberal Arts from Massasoit

Community College (Brockton,

Massachusetts) and a B.S. in

Environmental Engineering from

Rensselaer Polytechnic Institute.

Daniel E. Edwards, Ph.D.

From 1992 to 1997, Daniel Edwards

was a principal project scientist at the

Environmental Fate and Effects Laboratory at Roy F. Weston, Inc. He has an

M.S. in Agronomy from Penn State

University and a Ph.D. in soil microbiology from the University of Missouri.

Since 1997, he has been a senior regulatory analyst for Amway Corporation.

Daniel E. Edwards, Ph.D., and Alvaro J. DeCarvalho

unsewered U.S. population (based on

1980 census). PB88-113352.

U.S. International Trade Commission.

1994. Synthetic Organic Chemicals:

United States Production and Sales,

1992. USITC Publication 2720.

Washington, D.C.

Vaishnav, D. D. and J. W. McCabe. 1996.

Development of an anaerobic sludge

respiration inhibition test and its use to

assess septic tank safety of consumer

products. Environ. Tox. Chem. 15:663–

669.

Yang, J., G. F. Parkin, and R. E. Speece.

1979. Recovery of anaerobic digestion

after exposure to toxicants. Final

Report. U.S. Department of Energy

Report No. DOE/CS/40049-1. Reproduced by National Technical Information Service, U.S. Department of

Commerce. Springfield, Va.

For more information about this paper,

contact Alvaro J. DeCarvalho,

The Soap and Detergent Association,

475 Park Avenue South, New York, NY, 10016,

e-mail: adecarvalho@sdahq.org.
The Small Flows Journal Volume 4, Issue 1, Spring 1998

NSFC News / Resources NSFC News / Resources

28

Special Spring Offer—All

NSFC Products Half Price

June 22–23

In celebration of Earth Day, the National

Small Flows Clearinghouse (NSFC) is

offering 50 percent off the regular price

of all products for orders placed by phone,

fax, or e-mail June 22 and 23, 1998.

Phone orders must be placed between 8

a.m. and 5 p.m. Eastern Time. Orders

placed by fax or e-mail will be accepted

until midnight, Tuesday, June 23.

The NSFC maintains an inventory of

more than 250 educational products

about wastewater treatment technologies

and issues for small communities.

Categories of NSFC products include

• case studies,

• computer searches and software,

NSFC Offers Discussion

Groups on the Web

The National Small Flows Clearinghouse

(NSFC) is pleased to announce its new

online discussion groups—the most

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offers to Internet users.

Some of the topics currently posted for

discussion in the NSFC group include

septic tanks and grease, odors and house

vents, soils evaluation versus percolation

tests, and antibacterial cleansers. There are

numerous others, and anyone is welcome

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small community wastewater issues.

Internet users also can participate in a

National Onsite Demonstration Project

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Information about other NSFC services

also can be found at the site, as well as

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the National Environmental Training

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• design manuals/modules,

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The NSFC products guide also can be

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Earth Day 1998

NSFC News/Resources
The Small Flows Journal Volume 4, Issue 1, Spring 1998

Professional News

29

Professional News

Group Seeks Comment on

Proposed Performance

Standards

A group of researchers and ASAE members (formerly the American Society of

Agricultural Engineers) have developed a

series of seven proposed performancebased standards for onsite wastewater

systems, which are summarized in the

table below. The proposed voluntary

national standards could be used to either

augment or replace prescriptive onsite

system codes currently used by many

towns, counties, and states, and they can

be applied either to the performance of

specific pretreatment units or to receiving

environments.

The proposal, titled “Performance Standards for On-Site Wastewater Treatment

Systems,” by Michael T. Hoover, Dennis

Sievers, and David Gustafson, was first

presented in March in Orlando, Florida, at

ASAE’s Eighth National Symposium on

Individual and Small Community Sewage

Systems and is included in the symposium

proceedings available from ASAE (see the

ordering information on page 30).

The ASAE SW-262 Committee (Countryside Engineering Committee) is formally

leading the effort to develop these standards and is seeking public comment and

review of the standards until July 1, 1998.

Afterwards, the ASAE SW-262 Standards

Subcommittee led by David Gustafson of

the University of Minnesota will compile

the written comments and develop a

formal draft. The subcommittee will

establish an expert panel to work with

other industry groups interested in

developing performance-based standards,

such as the National Onsite Wastewater

Recycling Association (NOWRA), the

American Society for Testing and Materials (ASTM), NSF International, and the

National Small Flows Clearinghouse.

Performance-based standards have been

advocated by many in the onsite profession as a more flexible water quality- and

continued on page 30

standard BOD TSS PO4-P NH4-N NO3-N total fecal coliform

nitrogen colony densities

mg/L % removed a no./100mL

TS1 - primary treatment

 TS1u - unfiltered 300 300 15 80 NA NA 10,000,000

 TS1f - filtered 200 80 15 80 NA NA 10,000,000

TS2 - secondary treatment 30 30 15 10 NA NA 50,000

TS3 - tertiary treatment 10 10 15 10 NA NA 10,000

TS4 - nutrient reduction

 TS4n - nitrogen reduction 10 10 15 5 NA 50% 10,000

 TS4p - phosphorus reduction 10 10 2 10 NA 25% 10,000

 TS4np - nitrogen &

 phosphorus reduction 10 10 2 5 NA 50% 10,000

TS5 - bodily contact disinfection 10 10 15 10 NA 25% 200

TS6 - wastewater reuse 5 5 15 5 NA 50% 14

TS7 - near drinking water 5 5 1 5 10 75% <1b

a minimum % reduction of total nitrogen (as nitrate-nitrogen plus ammonium-nitrogen) concentration in the raw untreated

wastewater

b total coliform colony densities <50/100 mL

source: Hoover, M. T., D. Sievers, and D. Gustafson. 1998. Perfomance standards for on-site wastewater treatment systems.

In On-site wastewater treatment: Proceedings of the eighth national symposium on individual and small community sewage

systems. St Joseph, Mich: ASAE.

constituent concentrations

Professional News
The Small Flows Journal Volume 4, Issue 1, Spring 1998

risk-based alternative to the current

variety of prescriptive codes used in most

jurisdictions. The authors also argue that

the lack of performance standards and

code uniformity has inhibited the influx of

venture capital into onsite system research

and development, limiting manufacturers’

capabilities to provide new, cost-effective

onsite technologies.

A complete discussion of the proposed

standards is published in ASAE publication number P0398, On-Site Wastewater

Treatment: Proceedings of the Eighth

National Symposium on Individual and

Small Community Sewage Systems. To

purchase a copy, contact ASAE at (616)

428-6324, fax (616) 429-3852, or write to

ASAE, Dept. 1677, 2950 Niles Road, St.

Joseph, MI 49085-9659. The price is

$49.00 for ASAE members and $59.00 for

nonmembers plus $4.25 for postage and

handling.

To comment on the proposed standards,

please write directly to David Gustafson,

Agricultural Engineering Specialist,

University of Minnesota, 1390 Eckles

Ave., St. Paul, MN 55108, or via e-mail at

gusta002@tc.umn.edu.

30

CLERMONT COUNTY GENERAL HEALTH DISTRICT

The Clermont County General Health

District is seeking proposals for field

demonstration of innovative technology for

household onsite wastewater systems in

Clermont Silt Loam, a soil that is severely

limited by wetness. Clermont County is

located in the Illinoian Till Plain of southwest Ohio. Clermont Silt Loam is a widely

distributed soil that does not perform well as

a treatment medium. Some of the factors

that contribute to its unsuitability are a

seasonal high water table, slow internal

drainage, limited response to subsurface

drains, poor surface drainage, and a humid

climate with an average of 42 inches of

rainfall per year.

Proposals will be evaluated on the following

criteria:

a) reliability and cost of components with

 estimated service life,

b) time required for installation,

c) ability to monitor and achieve perfor-

 mance criteria,

d) ease of maintenance and service, and

e) safety and site aesthetics.

This call is part of a USEPA 319 Project titled

“Reduction of Nonpoint Source Pollution from

Onsite Sewage Systems in Clermont County,

Ohio.” The project sponsor, the Clermont

County General Health District, will select two

types of innovative, nonproven systems that

demonstrate potential for providing onsite

wastewater renovation on the county’s most

severe wet soils. One of each type of system

will be installed in 1999. A second system of

each type, with possible modifications, will

be installed in the year 2000. The systems

will be evaluated for at least five years.

Information packages should be requested

from Ralph Benson by phone at (513) 732-

7603 or fax at (513) 732-7936.

Proposals must be received before July 1,

1998.

Call for Proposals

Innovative Onsite Wastewater

Demonstration Project For Very Poorly Drained Soils

Professional News
The Small Flows Journal Volume 4, Issue 1, Spring 1998

Committee Discusses

Drainfield Questions,

Identifies Topics for

Further Research

As part of a continuing effort to develop

scientifically-based performance standards for the onsite industry and to

provide direction for future research, The

National Onsite Wastewater Recycling

Association (NOWRA)’s Technical

Practice Committee is examining, in

detail, various onsite system components

and unit processes. The committee met in

October, 1997, at NOWRA’s annual

meeting in Texas to discuss “drainfield

dynamics.”

“The goal of the meeting was to consider

two questions, which may seem simple at

first: how do drainfields work and how

long do they last?” explains Bob Mayer,

P.E., committee chair. “We hoped this

topic would generate considerable

discussion, and we weren’t disappointed.”

After hearing presentations from individuals familiar with different aspects of the

onsite profession, the group discussed the

following items with the goal of reaching

some consensus:

• The committee agreed that total

suspended solids (TSS) impact

drainfield operation and that enhanced solids removal is available via

various pretreatment devices (such as

effluent filters); however, more needs

to be known about exactly how much

TSS removal is really practical and

necessary for any given soil type or

flow volume.

• The committee agreed that although it

is known that effluent with high

levels of biological oxygen demand

(BOD), such as commercial wastewaters containing fats, oils, and greases,

can limit the life of drainfields, many

states either ignore or don’t pay

enough attention to high-strength

waste characteristics in their regulations or practices.

• The committee questioned whether

treating effluent to drinking water

quality guarantees a permanent onsite

installation, or whether saving money

by treating only to moderate levels

can still ensure long-term service

from a system.

• The committee agreed that hydraulic

overloading leads to system failures;

however, predicting soil capacity with

the variety of wastewater characteristics that exist is still not a defined

science.

• The committee also agreed that

nitrogen and pathogens are parameters that should be addressed in any

analyses of drainfield performance

because of their potential to impact

public health and the environment.

The group questioned, however,

whether the national standard for

nitrate (the 10 mg/L drinking water

standard) is a realistic number, and

where the samples should be taken

for monitoring nutrients.

• The committee agreed that oxygen,

temperature, and soil depth affect

drainfield dynamics and that soil depth

is not only a function of oxygen and

temperature, but also of the living organisms present in shallow soils that

are beneficial to system operation.

• The committee questioned the exact

meaning of long-term acceptance rate

(LTAR). Is LTAR a loading rate

determined for the total size of the

system that will help extend the life

of the drainfield, or is it the rate at

which effluent will pass through a

mature anaerobic mat? No agreement

was reached on this point.

continued on page 32

31

Professional News
The Small Flows Journal Volume 4, Issue 1, Spring 1998

In addition, the group agreed on the

following list of ten general subjects or

questions that warrant further examination

before definitive design criteria and

ensuing performance standards for

drainfields are developed.

1. Should there be one loading rate for

all soils? Should all anaerobic

drainfields have the same domestic

strength application rate as defined by

gallons per day per square foot and

pounds of BOD per square foot per

day? Are there two or more loading

rates? Should load be determined

from a design curve that assumes the

less permeable the soil the lighter the

load? Or should all drainfields be

designed to be aerobic?

2. What is the role of microbes, worms,

and other biota in shallow soils? It is

known that the bioactive shallow soil

is beneficial to treatment and disposal

processes, but exactly how does it

apply to drainfields?

3. Is pressure dosing superior to gravity

distribution because of the increased

amount of oxygen in contact with the

wastewater in the systems using

pressure dosing?

4. What is the role of synthetic fibers,

such as lint and laundry fibers, in a

system? How much of this material

will clog piping or form mats in

absorption trenches?

5. How do water softeners affect

systems? Should the backwash from

water softeners be disposed of in

systems? If the backwash is not

recombined with the softened water

in systems, will a chemical imbalance

result in the effluent that could be

detrimental to the system?

6. Should sand-lined trenches be used in

drainfields? Is the additional sand

beneficial, harmful, or of little use to

drainfield performance?

7. What is the effect of sodium on

systems? How much sodium is too

much for a given soil type?

8. How do we predict the life of a

system?

9. Is effluent ponding in the drainfield

good or bad? (This question also

relates to item 3.) Is oxygen at the soil

interface of the drainfield necessary

for achieving a permanent system?

Do anaerobic processes in ponded

systems doom them to finite lifespans?

10. Is drainfield shape critical to its

operation? Although it is known that

drainfield length, width, and depth

help define the type of processes that

result when effluent is applied,

questions concerning drainfield shape

should be left open until agreement is

reached concerning exactly what the

relevant processes are.

While some of these issues may seem

simple or obvious to experienced onsite

system designers, some generallyaccepted answers may be based mostly on

anecdotal evidence. There is a need for

scientifically proven design standards

based on scientifically collected data and

studies with reproducible results. The

committee is questioning whether drainfield science has definitive answers to all

of these questions and is encouraging

input from the research community on

these topics.

If you have input or questions concerning

the Technical Practices Committee or

NOWRA’s performance-based standards

initiative, contact Bob Mayer at (800)

345-3132, ext. 103, or by e-mail at

topvacat@aol.com.

32

Professional News
The Small Flows Journal Volume 4, Issue 1, Spring 1998

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