United States
Environmental Protection
Agency
Office of Water
Program Operations (WH-546) ,
Washington DC 20460 I
February 1984
Overland Flow:
A Decade of Progress
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February 1984
OVERLAND FLOW: A Decade of Progress
by
Richard E. Thonas
Municipal Technology Branch
U.S. Environmental Protection Agency
Washington, D.C. 20460
Presented at Missouri Water Pollution Control
Association, Annual Meeting, February 26-28, 1984
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This report has been reviewed by the
Environmental Protection Agency and approved for
publication. Approval does not signify that the
contents necessarily reflect the views and policies
of the Environmental Protection Agency, nor does
mention of trade names or conmerical products
constitute endorsement or recommendation for use.
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Overland Flow: A Decade of Progress
by R. E. Thomas
INTRODUCTION
*
Treatment of wastewater by allowing it to flow as a thin sheet over
gently sloping ground is cotitionly referred to as "spray runoff," "gratis
filtration" or "overland flow. " The term overland flow has been
by the United States Environmental Protection Agency (U.S. EPA) and
be used in this discussion. Overland flow is not a new technology for
disposal of wastewater. It has been in use for many decades for
disposal of industrial wastewaters and municipal wastewater on a limited
basis. Conversely, the concept of overland flow as a treatment process
is relatively new. Research to understand the removal mechanisms and
the control of these mechanisms by design and operation is a rapidly
advancing science.
Research on treating domestic wastewaters by overland flow in the
United States started about 12 years ago at the EPA research labbfStBry
in Ada, Oklahoma . Many other Federal, State and private sources Hive
contributed to the rapid development of this promising technology during
the ensuring decade. Those wishing to delve into the results Of irflisfe
research efforts should look for the proceedings of periodic workshops
such as the one held at Dallas, Texas in September 1980 . ThoSe who are
more interested in current design information should refer to a design
manual , or to project specific information available on the rapidly
increasing number of systems in design, under construction or now
operating .
Research and limited operational data available to date show
overland flow to offer an energy saving and simply operated wastewater
management concept with substantial cost saving potential for smaller
communities. Overland flow has potential to treat raw sewage without
sludge production. It can be used to upgrade existing treatment
facilities inculding primary plants, treatment ponds, and even secondary
plants. It will achieve good removal of oxygen demand (BOD) , suspended
solids (SS) , and nitrogen without energy input or chemical addition.
EPA; like others; recognizes the benefits which can be achieved if the
results demonstrated by research can be achieved routinely in actual
practice.
In this context, overland flow is an excellent example of the
innovative and alternative technology thrust of the Clean Water Act of
1977. The definition of land treatment in the Act, as extended in the
EPA operating guidance for the Construction Grants Program, includes
overland flew in the category of alternative technology which makes it
eligible for the financial incentives of this program.
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Our knowledge of overland flow technology is very dynamic. We are
at an important transition point as a decade of research results are
about to be verified and improved with performance data from operational
facilities. Any state of the art summary becomes rapidly dated in such
a period of rapid transition. I will highlight sources of past, present
and future information with the objective of guiding interested parties
to the best source of information for their needs.
RESEARCH
Research on overland flow in the United States started about
25 years ago when a slow-rate land treatment system treating food
processing wastewater was modified to become an overland flow system.
Other food processors adopted the concept and overland flow became
established as a reliable and low cost process serving many food
processing facilities in the 1960's. Research staff at the Robert S.
Kerr Environmental Research Laboratory of the EPA initiated a decade of
research on treatment of municipal wastewater in 1971. Other Federal,
State and several university teams have contributed to a substantial
body of information on design and performance. Major sources of key
research results are identified in Table 1.
A decade of work has contributed a firm understanding of the basic
concept. It is well understood that microbial populations on the soil
surface play a key role in the treatment process. I prefer to visualize
overland flow as a batch reactor. The flat reactor surface is rough and
gently sloping to produce variable liquid depth and residence time.
Liquid depth may range from one to twenty-five millimeters while
residence time may vary by as much as plus or minus 50 percent of the
design time of about 30 to 60 minutes. Overland flow is typically
operated with feed periods of 6 to 12 hours per day for 5 to 6
consecutive days. The 12 to 18 hour daily rest periods provide time for
biooxidation of the more resistent fraction of the settled solids and
reareation of the surface reaction sites. The extended rest after 5 to
6 consective days of feed provides sufficient drying to control insect
breeding cycles as well as to return the microbial population to the
rapid growth stage. It is important to keep the active microbial
population lean, mean and hungry to get the most out of them.
Results to date show that the combination of settling, filtration,
microbial degradation and interactions with the soil combine to produce
better treatment than conventional suspended growth or fixed-film
biological treatment processes. The biochemical oxygen demand (BOD) and
total suspended solids (TSS) in overland-flow effluent usually average
10 to 20 mg/1 with maximum values seldom exceeding 30 mg/1. Nitrogen is
also removed through microbial nitrification - deritrification, crop
uptake and ammonia volatilization. Nitrification - denitrification
dominates at recommended loading rates while crop uptake will become a
major factor as the total annual nitrogen load drops toward that needed
to satisfy the crop demand. For example, nitrification - denitrifi-
cation will clearly dominate when the total annual nitrogen load is
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2,000 pounds per acre; the annual crop demand is 100 pounds per acre;
and the system is achieving 85 percent (1700 pounds) mass removal.
Conversely, crop uptake will be a major factor if the total annual
nitrogen load is 800 pounds per acre; the annual crop demand is 300
pounds per acre; and the system is achieving 90 percent (720 pounds)
mass removal. It is comparatively easy to design and operate to achieve
total nitrogen removals in the range of 70 to 90 percent based on total
mass removal. It is more meaningful to use total mass removal as
opposed to concentration reduction because there is substantial water
loss to evapotranspiration and seepage. The effluent discharged
(excluding rainfall input runoff) is usually 50 to 80 percent of the
wastewater applied to the system.
Soil interactions with the clayey soils which make the best sites
provides 40 to 60 percent phosphorus removal. The amount of removal may
decline with time in service and varies according to the properties of
the site soils. Several researchers have shown that phosphorus removal
can be improved by chemical addition. One would predict that the
accepted principals of phosphorus removal by chemical precipitation
would apply to this fixed-film batch reactor as well as any other witii
one basic difference. The precipitated phosphorus is deposited on the
soil surface to be incorporated into the soil rather than being removed
as a sludge to be further processed for disposal.
We are also at a significant transition stage in the support and
conduct of research on overland flow as a treatment technology.
Laboratory, pilot and demonstration type studies are on the decline. It
appears that we have sufficient confidence in our understanding of the
basic concept to shift our attention to the gathering of information
from full-scale operational facilities. One approach is use of "field
tests" as established by the 1981 amendments to the construction grants
provisions of the Clean Water Act. In my roles as National Coordinator
of the innovative and alternative technology program, I have initiated
an effort evaluate our current reservoir of design and operating
information and to incorporate it into a supplement to the EPA design
manual on land treatment. This effort is well underway and the
supplement to the design manual should be available in October 1984.
DESIQJ GUIDANCE
The consideration of overland flow in facility planning presents a
specific and rather unique set of circumstances. As already mentioned,
it is a developing technology and there is very little operational
experience. Because of this lack of operating experience, State
regulatory agencies may not have established criteria and guidance on
design and operation. The fact that overland flow shows excellent
capability to treat raw sewage presents a further complication.
Application of raw sewage to the land is contrary to accepted environ-
mental engineering practice. The idea of applying raw sewage to the
land conjures up the historical health incidences associated with raw
sewage farming with food crops in the 19th century. This practice of
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irrigating human food crops with raw sewage was justifiably abandoned
because of unacceptable health risks. An educational and adjustment
period is needed to provide operational experience for establishment of
State criteria and to determine an appropriate match-up of preappli-
cation treatment with the overall objective of specific projects. It is
the cannon dilemma of which comes first — the horse or the cart — and
it demands a position of flexibility for case-by-case determinations.
This position allows simultaneous development of State guidance and
adoption of developing technology as mandated by the innovative/alterna-
tive provisions of the Clean Water Act of 1977.
EPA guidance for preapplication treatment for overland flow which
will qualify a project for construction grant funding is divided into
general levels that provide this needed flexibility.
The two levels of preapplication treatment recognize proximity of
residents in an urban setting as an important factor in site selection.
The lesser level of preapplication treatment specifies simple screening
or comminution for overland flow in isolated areas without public
access. The second level specifies a sufficient level of biological
treatment to control odors and nuisance conditions in more urban
locations with closer proximity of human habitation.
This EPA decision to set screening or comminution as a minimum
level of preapplication treatment is based on results of several
research and demonstration projects. There is a substantial amount of
long term operational experience showing the excellent capability of
overland flow to treat raw wastewater. Many operating facilities
produce effluents with BOD and SS values of less than 20 mg/1 when the
applied raw wastewater has a BOD of more than 500 mg/1 and SS in excess
of 250 mg/1.
State guidance for overland flow is at an early stage of infor-
mation and varies substantially from state to state. It is only within
the last four or five years that many States have formulated a written
policy on overland flow technology. In those States, overland flow is
gaining acceptance as a practical, cost-effective and environ-
mentally-sound alternative. Other States are looking at overland flow
systems on a case-by-case basis until a larger data base is developed
from first-hand experiences with overland flew systems within the State.
It is important to be avare of the status of current state criteria when
considering overland flow in facility planning.
DESIGN, OPERATION and MAINTENANCE
Transfer of research and demonstration results to practical design,
operation and maintenance usually adds new dimensions to acceptance and
implementation of a new technology. The initial group of full-scale
systems serves as a field test to verify performance and to identify
design features that facilitate better construction and easier oper-
ation. We are at that transition stage in the long range implementation
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of overland flow technology. There are seme 35 to 50 systems in design,
under construction or already in operation. A partial list of these
systems is presented in Table 2. Systems listed were selected to show
the distribution of geographic and climatic conditions represented by
this initial group of full-scale systems.
Several of the eight systems which are listed as operational have
already been studied to evaluate actual performance in relation to that
projected at the time of design. Results from these studies are
positive. Performance is consistent with design projections and
previous research results. Reports of design features needing
improvement to facilitate better construction and easier operation are
comparatively minor and readily correctible with current knowledge. The
fact that operators are very pleased with the ease that the systems rteet
discharge criteria is also encouraging. This encouraging result is
countered by reports that systems do not discharge or discharge only
part of the year. This may be the result of overly conservative design
with the resulting high cost of excessive reserve capacity. The
information gathered to date warrants an indepth study of design,
construction and performance to ensure the appropriateness of future
designs.
SIEMRRY
My perspective for overland flow treatment of domestic wastewaters
is a position of controlled optimism. Research results and limited
operational data identify simplicity/ energy savings, and low operating
costs, as major benefits. Overland flow is a good example of a
developing technology which addresses the innovative/alternative aspects
of the Clean Water Act of 1977. EPA continues to encourage consider-
ation of overland flow in this context. Workshops such as this one and
the continued research evaluation of newly constructed facilities will
provide EPA, State agencies, and applicants up-to-date knowledge for
improved design and operational reliability. Technical assessment of
overland flow systems now operating, under construction or scheduled for
construction will assist state agencies and applicants to keep pace with
this rapidly developing tehcnology. EPA is confident that overland flow
will become a popular and reliable wastewater treatment process. It is
uniquely attractive to smaller communities who stand to benefit most
from its simplicity lower cost and energy saving features.
REFERENCES
1. Thomas, R. E., K. Jackson, and L. Penrod. Feasibility of Overland
Flow for Treatment of Raw Domestic Wastewater. Robert S. Kerr
Environmental Research Laboratory. EPA Series No. 660/2-74-087,
July 1974. 31p.
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2. National Seminar on Overland Flew Technology for Municipal
Wastewater. EPA-600/9-81-022, U.S. Environmental Protection
1 Agency, Center for Environmental Research Information,
Cincinnati, OH, 1981.
3. Process Design Manual for Land Treatment of Municipal Wastewater.
EPA-625/1-81-013, U.S. Environmental Protection Agency, Center for
Environmental Research Information, Cincinnati, OH, 1981.
4. Innovative and Alternative Technology Projects: A Progress Report.
U.S. Environmental Protection Agency, Office of Water Program
Operations, Washington, D.C., 1983.
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Table 1: A Synopsis of Major Research Efforts
Project Study
Location/Scale Team
Wastewater
Source
Principal Findings and Garments
Ada, OK
Laboratory and
field plot
Hanover, NH
laboratory and
field plot
EPA-RSKEKL
P.O. Box 1198
Ada, OK 74820
raw
primary
secondary
OOE-CKREL
72 Lyme Road
Hanover, NH 03755
promary
secondary
Vicksburg, MS
and Utica, MS
laboratory at
WES and field
plot at Utica, MS
COE-WES
P.O. Box 631
Vicksburg, MS 39180
secondary
effluent
and lagoon
effluent
Overland Flow is a dependable technology
to provide low-cost advanced treatment.
Excellent removal of BOD, TSS and nitrogen.
Moderate removal of phosphorus easily improved
with chemical addition. Best results when
applying raw wastwater. SS as algae is most
difficult to remove. Bacterial indicators are
reduced by 90 to 99% by overland flow.
Comment; Up to 12 years of continuous use for
some plots through sequential studies.
Two years of study with erophasis on hydraulic
detention time were used to advance a design
theory. The theory represents other published
data well. Study also provided good infor-
mation regarding low temperature reduction
of BOD removal under severe winter conditions.
Also includes sane initial information on
removal of trace organics. Favorable removals
were observed for a number of organics.
Laboratory studies at the Waterways Experiment
Station addressed removal mechanisms for laboratory at
nitrogen, phosphorus and selected metals using
amended secondary effluent from a package plant.
Field plot studies with lagoon effluent at the
Utica, MS site demonstrated that slopes ranging
from 2 to 8% had little effect on treatment. SS
as algae cells was effectively rerooved by using
lower instanteous application rates. Reported
80 to 90% removals for cadmium, nickel, copper
and zinc at these slower rates.
i
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Table 1: A Synposis of Major Research Efforts
Project
Location/Scale
Study
Source
Wastewater
Principal Findings and Comments
Easley, SC
Field Demonstration
and full-scale
Davis, CA
indoor piolt
studies and field
demonstration
Moodna Basin
Hariman, NY
field plots
SC-DHEC and Environ-
mental Systems
Engineering Depart-
ment
Clemson University
Clemson, SC, 29631
Department of Civil
Engineering
University of
California, Davis
Davis, CA,
Phillip J. Clark
Engineers and
Consultants, PC
New York, NY, 12205
Raw Demonstrated overland flow for treatment of raw
lagoon caiminuted sewage (25,000 gpd) and lagoon effluent
Effluent (75,000 gpd). Both systems met or exceeded
typical secondary systems with consistent quality
of effluent. Best removals when raw sewage was
the source and removal of algae SS was most
difficult.
Comment; The system is scheduled to continue as
a full-scale operational system treating
lagoon effluent.
synthetic Semicontrolled pilot studies in the laboratory
primary were coupled with a follow up field demonstration
secondary to develop design theory and verify design for the
full-scale facility to treat 5 mgd. Design theory
is based primarily on detention time as influenced
by slope dimensions and application procedures.
primary A facility plan pilot test to verify design of
secondary overland flow as one of the alternatives under
consideration for an expansion and upgrade of
existing facilities. Fifteen months of data on
BOD, SS, nitrogen and bacteria in a cold climate
including winter operation led to conclusion that
overland flow could be operated successfully to
meet secondary in winter and achieve tertiary in
sunnier.
o
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Table 1: A Synposis of Major Research Efforts
Project Study
Location/Scale Team
Wastewater
Source
Principal Findings and Contents
Carbondale, XL
full-scale for
trailer park
Pauls Valley, OK
Field demon-
stration
Baton Rouge,
laboratory
LA
School of lagoon
Engineering and effluent
Technology
University of
Southern Illinois
Carbondale, IL, 62901
raw and pond
effluent
State Health
Department
Oklahoma City,
OK 73152
and Health Sciences
Center
University of Oklahoma
Oklahoma City, OK 73190
Center for Wetland simulated
Resources
Louisiana State
University
Baton Rouge,
LA 70803
Studies assessing the effects of high hydraulic
loading and slope lengths showed 60 to 85 percent
removal of BOD after 60 to 100 minutes of
retention time.
Comment? The results of this study show the same
comparatively broad peak of good
performance at loadings of 10 to
50 inches per week as others observed at
loadings as low as 2 inches per week.
Treatment of raw wastewater demonstrated the
ability to achieve BOD and SS removals better than
conventional secondary under winter and summer
operation. Temperature was shown to have a direct
effect on removal efficiency. Treatment of the
lagoon effluent provided limited benefits as an
advanced treatment process. There was 100% virus
removal for the raw system. Airborne bacteria
were greater in downwind samples but no viruses
were isolated in air samples.
These carefully controlled studies showed that
ammonia volatization was a minor mechanism in
nitrogen removal as it accounted for about 5% of
the removal. Nitrification - denitrification and
crop uptake could dominate depending on the total
nitrogen load to the system.
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Table 1: A Synposis of Major Research Efforts
Project Study
Location/Scale Team
Wastewater
Source
Principal Findings and Ccnments
Logan, UT
field plots
Laramie, WY
field plots
Paw Paw, ME
field test and
full-scale
Utah Water 'Research
Laboratory
Utah State University
Logan, UT, 84322
Department of
Agricultural
Engineering
University of Wyoming
Laramie, WY, 82070
William & Works
P.O. Box 6510
Grand Rapids,
MI, 49506
lagoon
effluent
lagoon This brief three month study on newly established
effluent plots during the fall season showed no BCD or SS
removal at loading rates of 2 to 6 inches per
Comment; Work at other locations has demonstrated
the need for several months of system
conditioning to ensure stable conditions
for evaluating performance.
Preliminary results from the first year of study
support previous work which had projected that
start up and operation in cold climate winter
conditions could present formidable design
challenges.
Field site for study has been prepared and is
being conditioned with wastewater applications.
applications. Spring of 1984 will initiate
period of wastewater application under
stabilizing conditions for evaluation of
performance.
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raw
pond effluent
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Table 2: A Selected List of Overland Flow Systems
Conrnmity, State
Alma, AR
* Alpine, AZ
Arcadia, IA
Castor, IA
Cleveland, MS
Corsicana, IX
*Davis, CA
*Easley, SC
Esterwood, LA
*Falkner, MS
Forrest Hill, IA
Franklinton, IA
Hall Summit, IA
Heavener, OK
Kenbridge, VA
*Lamar, AR
Morse, LA
*Mt. Olive, NJ
*Newrnan, CA
Norwalk, IA
Norwood, LA
Oppelo, AR
*Santa-Fernwood, ID
Vinton, IA
Wabbaseka, AR
Design
Flow
(MGD)
1.27
0.515
0.03
3.0
,0
.0
1.
5.
0.1
0.018
0.04
0.06
0.74
0.056
0.45
0.3
0.11
0.09
0.02
0.6
0.035
0.12
0.1
1.0
0.104
Design
Consulting Firm
Ellis, Murphy & Holgate
Ralar and Assoc.
S.M. Cothren
Clark Dietz Engineers
Gilbreth & Assoc.
Brown & Caldwell
Alex Iheriot, Jr. & Assoc.
Alex Theriot, Jr. & Assoc.
N-Y & Assoc.
Alex Teriot, Jr. & Assoc.
Alford Engineering Co.
Environmental Technology Consultants, Inc.
Burrough, Verling, Braswell, Inc.
Alex Theriot, Jr. & Assoc.
Brown & Caldwell
US Environmental Planners
Affiliated Engineers
J-U-B-Engineers
Roy F. Weston
Affiliated Engineers
u>
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* systems reported to be operational
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