EPA-600/2-76-131
June 1976
OVERLAND FLOW TREATMENT OF RAW WASTEWATER
WITH ENHANCED PHOSPHORUS REMOVAL
R. E. Thomas, B. Bledsoe, and K. Jackson
Wastewater Management Branch
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
ADA. OKLAHOMA 74820
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DISCLAIMER
This report has been reviewed by the Robert S. Kerr Environmental
Research Laboratory, U.S. Environmental Protection Agency, and
approved for publication. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
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ABSTRACT
A 36-month pilot study was conducted to evaluate the capability of overland flow to
provide complete treatment of raw comminuted wastewater on a year-round basis in
mild climates. This second report in a series covers 36 months of performance at a
loading of 10 cm/week and a special 15-month adjunct on phosphorus removal by
chemical precipitation with aluminum sulfate. Data for 15 parameters are included,
and data for suspended solids, biochemical oxygen demand, chemical oxygen demand,
total organic carbon, nitrogen, and phosphorus are covered in detail. Data collected
over the 36-month period show overland flow to be a simple and reliable treatment
process. Pilot studies are continuing at this laboratory, and field projects are
underway in two states.
This report was submitted as an in-house project by the Wastewater Management
Branch, Robert S. Kerr Environmental Research Laboratory, of the Environmental
Protection Agency. Work was completed as of December 1974.
111
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CONTENTS
Page
Abstract iii
List of Figures vi
List of Tables vii
I Introduction 1
II Summary 2
III Conclusions 3
IV Recommendations 4
V Experimental Design and Operation 5
VI Operating Results 11
VII Treatment Performance 17
VIII Discussion 33
IX References 35
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LIST OF FIGURES
Number Page
1 Schematic of Wastewater Handling System 7
2 Detail of Wastewater Distributor 8
3 Wastewater Applied vs Runoff 16
4 Suspended Solids vs Days of Operation 22
5 Chemical Oxygen Demand vs Days of Operation 23
6 Nitrogen vs Days of Operation 24
7 Phosphorus vs Days of Operation 25
VI
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LIST OF TABLES
Number Page
1 Winter Temperatures 13
2 Fraction of Applied Wastewater Measured as Direct Runoff 14
3 Quality of Raw Comminuted Wastewater for Two Study
Periods 18
4 Plot Runoff Quality 26
5 Specific Data for the Phosphorus Removal Study Covering
June 1973 Through February 1974 30
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SECTION I
INTRODUCTION
Overland-flow treatment is achieved by allowing a wastewater to trickle slowly over
gently sloping ground as sheet flow. Other names including " spray-runoff" and
"grass filtration" are also used to indicate this type of treatment. The term overland
flow has been used by the authors in a previous report and will also be used throughout
this second report in a series on treatment of raw domestic wastewater. The rationale
for testing the capability of overland flow to treat raw domestic wastewater was
covered in detail by Thomas, Jackson, and Penrod in the initial report of this
series, and a brief recapitulation is all that will be given in this report.
Briefly, the development of overland flow in the United States appears to have origi-
nated from experiences with a spray disposal system discussed by Luley in 1963.
Subsequent reports of other studies such as those by Bendixen, et al. , Law, Thomas,
4 5
and Myers , and Kirby provided background information supporting the hypo-
thesis that overland flow could be utilized as a practical system for rural communi-
ties in mild climates.
The results of the initial phase of this three-phase study showed that overland-flow
treatment can perform satisfactorily with an average load of 10 cm/week under cli-
matic conditions comparable to those in southcentral Oklahoma. A well-operated
system should produce an effluent with less than 10 mg/1 of suspended solids and
biochemical oxygen demand, while removing 70 to 90 percent of the total nitrogen.
Phosphorus removal, as expected, averaged about 50 percent for this initial phase
of the study project and is a factor deserving further assessment.
The principal objectives for the research period covered in this report were to (1)
evaluate the enhancement of phosphorus removal by addition of aluminum sulfate,
(2) continue the assessment of treatment capability for other parameters, and (3)
verify the reliability of the initial phase design data.
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SECTION II
SUMMARY
Data have been reported from a 36-month study of overland-flow treatment of raw
comminuted wastewater. This report, which is the second in a series, emphasizes
a study on phosphorus removal, while summarizing overall performance over two
study periods for other parameters. Data for the 36-month period continue to show
that overland flow is a simple and economical process, which achieves advanced
waste treatment without sludge production. Pretreatment needs only remove solids
which cannot be comminuted to pass nozzle orifices and provide for odor control at
the point of pickup .
The overland-flow process can produce an effluent of the following chemical quality
while treating a typical raw comminuted wastewater at a loading rate of about 10
cm/week in a mild climatic zone. Total suspended solids and biochemical oxygen
demand will be less than 10 mg/1 throughout the year. Total nitrogen will range from
2 to 10 mg/1 with concentrations greater than 5 mg/1 limited to a brief period of 2 to
3 months in the winter season, largely as nitrate. Total phosphorus will be about 5
mg/1 unless the system is designed especially for phosphorus removal. Use of alu-
minum to precipitate phosphorus reduces the phosphorus concentration to about 1.0
mg/1. The summer values for phsophorus will be slightly less than winter values,
but seasonal differences in phosphorus removal will be minor.
It is noteworthy that the effluent from this 36-month evaluation of the overland-flow
process is substantially better than established criteria for secondary treatment.
Satisfactory development and demonstration of several operating scale systems
employing the overland-flow approach will provide the waste treatment community
with a new tool which will have particular value for application in small rural com-
munities .
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SECTION III
CONCLUSIONS
It is feasible to utilize overland flow to achieve advanced waste treatment of raw
comminuted wastewater.
It should be practical to develop simple and economical systems for use at rural
communities in mild climates.
Such systems should perform satisfactorily when loaded at an average loading
of 10 cm/week when located at a site with climatic conditions comparable to the
test site.
A well-operated system should produce an effluent with an average of 10 to 15
mg/1 of suspended solids and about 10 mg/1 of biochemical oxygen demand.
The system is reliable and the quality of the system effluent is consistent.
A well-operated system should achieve 90 percent nitrogen removal in the sum-
mer, but nitrogen removal may drop to 75 percent in the winter.
Phosphorus removal should be about 50 percent with relatively minor seasonal
variation but can be improved to 90 percent by precipitation using aluminum
sulfate.
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SECTION IV
RECOMMENDATIONS
Overland flow should be tested and demonstrated at several locations in addi-
tion to the two sites already under study.
These communities should be located at places with varying climatic conditions
to determine climatic limits.
Capital and operating cost data should be included in all evaluation programs
for full-scale operational systems.
Pilot-scale studies should be conducted to evaluate the effect of pretreatment on
treatment efficiency and system loading .
Pilot-scale studies should be conducted to evaluate a combination of overland
flow followed by high-rate infiltration.
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SECTION V
EXPERIMENTAL DESIGN AND OPERATION
The study was conducted at the field site of the Robert S. Kerr Environmental
Research Laboratory located in Ada, Oklahoma. The climate at this location is
suitable for year-round operation with minimal considerations due to severe weather
conditions. Annual precipitation averages about 100 cm, and there is an average of
26 days per year with more than 1.25 cm of precipitation. Average minimum tem-
peratures are above freezing for all months except January, when the average mini-
mum dips to -1.0° C. Average daily maximum temperatures are greater than 10° C
throughout the year. The experimental system was designed without special con-
siderations for continuing operations during cold weather, and the downtime due to
freezing weather was included as a variable for evaluation. The period of operation
covered in this report includes two study periods. The first study period from
March 1971 through September 1972 was a study of varying loading rates. The second
period from November 1972 through March 1974 was a study of phosphorus removal
at a constant loading rate selected on the basis of the results of the initial study
period.
SITE PREPARATION AND WASTEWATER DISTRIBUTION
The preparation of the site and the wastewater distribution system were identical
for the latter part of the initial study period and throughout the second study period.
The subsoil at the selected site is a dense clay that provided the restriction to down-
ward movement of water which is necessary for successful installation and operation
of an overland-flow system. Plots measuring 11 meters by 36 meters were smoothed
to a uniform slope of 2 to 4 percent and provided with runoff sampling stations at
the toe of the slope. Raw domestic wastewater was obtained from the city sewer
main, settled for a few minutes to remove grit, skimmed to remove bothersome
floatables, and comminuted to a fine particle size before being applied to the plots
through a specially designed applicator. This wastewater handling system was
fully automated to minimize time required for operation and maintenance. A schematic
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of the wastewater handling system is shown in Figure 1. The mutrator, pumps,
and valves were controlled by a 7-day clock timer, permitting wastewater to be
applied for periods of 3 hours or more on any given day of the week.
The applicator was designed to apply the wastewater without creating an aerosol
and to operate at relatively low hydraulic pressures. The principal features of the
applicator are fixed fan nozzles, a lightweight horizontal boom, and an easily rota-
table vertical support. The applicators used to apply the wastewater to the experi-
mental plots are shown in detail in Figure 2. The nozzles used were FF series
flooding nozzles manufactured by Bete Fog Nozzle, Inc. They were the wide angle
145 degree nozzles made from PVC plastic. The boom was 2 cm schedule 40 PVC
pipe supported by a 2 cm steel channel on the bottom and guy wires as shown in
Figure 2. The rotatable vertical support was mounted in roller thrust bearings
fastened to a concrete anchored stand. The wastewater transmission line was con-
nected to the bottom of the rotatable vertical support with a standard hose swivel
connector. With proper alignment and counterbalancing, the hydraulic pressure
from the single fan nozzle with orifices as small as 0.5 cm and operating at a pressure
of 1.0 kg/sq cm (15 psi) provided ample thrust to rotate the distributor boom. The
variable loading rates for the first period of study were obtained by selection of
nozzle orifice size, while the constant loading rate for the second period of study was
obtained with a single size of orifice for all three plots. These distributor booms
were mounted at a height of 1.2 m and applied the comminuted wastewater over one-
third of the plot area on the upper part of the slope.
FIELD OPERATIONS AND SAMPLE PROCESSING
The principal variable to be evaluated in the first period of study was the effect of
loading rate on system performance under the influence of seasonal weather changes.
Nozzles with differing orifices were used to obtain average areal loadings of 7.4,
8.6, and 9.8 cm per week. The actual loading rate was seasonally adjusted so that
a 3-month-duration winter rate was 85 percent of the average rate, and a 3-month-
duration summer rate was 115 percent of the average rate, while the spring and
fall rates were equal to the average rate. Summer operation provided for 9 hours of
application per day for 6 days a week. Spring and fall operation provided for 8
hours of application per day for 6 days per week, and winter operation provided
for 8 hours of application per day for 5 days per week.
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The principal factors to be evaluated in the second period of study were continuing
performance at the high loading of 10 cm per week and enhancement of phosphorus
removal. The seasonal adjustments of the loading rate were somewhat different
from the first period of study with only a summer and winter level of loading being
used. The study of enhanced phosphorus removal included a control plot which
received no addition of aluminum sulfate, a plot receiving 20 mg/1 of Al, and a plot
receiving 15 mg/1 of Al. The Al was injected into the raw wastewater lines with a
metering pump. The point of injection was several feet beyond the field pump header
shown in Figure 1.
The runoff data for determining the water balance were obtained by installing a
V-notch weir in the collection ditch receiving the runoff from all three plots. This
point was chosen for measuring the runoff in order to increase the area included
and to reduce the influence of border effects. Previous attempts to measure runoff
from the individual plots indicated that the influence of border effects prevented
collection of reliable water-balance data.
Samples of the raw comminuted wastewater and the runoff from each of the three
experimental plots were collected at weekly or biweekly intervals throughout the
study, except for periods when operations were temporarily interrupted for removal
of vegetation, or because of severe freezing conditions. Initially, the raw wastewater
samples were collected as a composite of the comminuted wastewater being sprinkled
on the plots throughout the 8- or 9-hour application period. This sample was col-
lected into a container packed in ice to reduce compositional changes during sample
collection. Collection of composite samples was terminated about halfway through the
first study period after it had been determined that grab samples from the sedimenta-
tion tank provided comparable information on the quality of the raw wastewater.
Runoff samples from the treatment plots were taken as a grab sample obtained while
runoff was at its peak flow. Previous experience during the study reported by Law,
Thomas, and Myers had shown that grab samples taken this way are comparable in
chemical quality to flow proportional composite samples.
All samples collected throughout both study periods were subjected to analysis for
15 chemical parameters frequently employed to characterize the solids content,
oxygen demand, and nutrient content of wastewater. Total coliform, fecal coliform,
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and aluminum analyses were added to the analytical program during the second study
period from November 1972 through March 1974. The analytical procedures used
were selected from those published in "Methods for Chemical Analysis of Water and
Wastes, 1971."7
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SECTION VI
OPERATING RESULTS
Results from operation of the wastewater distribution system will be presented in
several sections covering an initial shakedown period of 6 months, the first study
period of 18 months, and the second study period of 15 months.
SHAKEDOWN PERIOD
The initial design of the distribution system provided for the wet well wastewater
pump to feed directly to the mutrator rather than the sedimentation and skimming
tank shown in Figure 1. Operating with this design led to frequent nozzle plugging
due to fragments of plastics, tinfoil, and other materials which were cut into pieces
by the mutrator but would not pass through the 0.40 to 0.55 cm orifices being used
to apply the comminuted wastewater to the experimental plots. The frequency of
nozzle plugging was enough to require a full-time operator to visually inspect the
system during the application periods. Attempts to screen the wastewater after
comminution appeared to be substantially less practical than providing a presedimen-
tation and skimming tank; therefore, the distribution system was modified to handle
the wastewater as shown in Figure 1.
AFTER ADDING SEDIMENTATION
Inclusion of the sedimentation and skimming tank substantially eliminated the fre-
quent plugging experienced during the shakedown period. The tank used had a
working depth of 0.4m and provided a volume equal to about 10 minutes of the pump-
ing rate of the wet well pump . Since the wet well pump capacity was greater than the
capacity of the plot distribution pump, it was possible to utilize excess flow through
the sedimentation tank to flush grit back to the sewer line through a return flow line
in the bottom of the tank and to return skimmed floatables through an overflow line
at the top of the tank.
Operating with this arrangement, maintenance of the system required about one
hour per day. Duties performed were a routine checking and servicing of pumps,
11
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the mutrator, and the timer control system, Nozzle plugging was reduced to a
frequency of one or two per week per nozzle. Most of these plugs were partial plugs,
and a daily check of the system was sufficient to maintain the weekly loading to the
experimental plots at the scheduled rates. This arrangement for the distribution
system was used for the remainder of the first study period and throughout all of
the second study period.
WEATHER EFFECTS ON OPERATION
It was projected that climatic conditions at this and other comparable sites would
permit continuous operation throughout the winter with a minimum of freeze protec-
tion. This experimental system was run without freeze protection to get an estimate
of the difficulties which would be encountered for a system operated in this manner.
Temperatures for the three winter seasons included in the study period are shown in
Table 1 along with the long-term norms. December temperatures have fluctuated
about the norm while averaging 1° C less than the norm. February temperatures
showed a similar fluctuation with an average matching the norm. January has been
consistently colder than the norm, and has averaged 1.8° C less than the norm.
Freezing has interrupted operations for 5 to 10 days during January and February
each year.
It would be easy to provide adequate frost protection for the distribution system to
avert this problem, but the effects on treatment efficiency may make it more desir-
able to opt for short-term storage of the untreated wastewater. This influence of
weather conditions on treatment efficiency will be covered in the section on treat-
ment performance.
PERCENT RUNOFF
Combined runoff from the three plot area (0.13 ha) was measured using a V-notch
weir equipped with a stage recorder. No attempt was made to obtain a total water
balance including evaporative losses and the amount of deep percolation. The
specific purpose of these measurements was to approximate the fraction of the applied
water that would be recovered as immediate and direct runoff for discharge to surface
waters. Data for 87 runoff events from December 1973 through March 1974 totaling
7,815 m3 of measured runoff from 16,691 m3 of applied wastewater are summarized in
Table 2. These data indicate that the overall recovery as runoff was about 50 percent
of the applied wastewater, while the monthly recoveries ranged from a summer low of
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Table 1. WINTER TEMPERATURES
Mean Temperature ° C
Winter Season Dec . Jan. Feb.
1971-72 7.3 4.4 7.9
1972-73 3.4 2.4 5.4
1973-74 6.0 3.8 9.3
Three-year Average 5.6 3.5 7.5
Long-term Norms 6.5 5.3 7.5
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Table 2. FRACTION OF APPLIED WASTEWATER
MEASURED AS DIRECT RUNOFF
Month
J
F
M
A
M
J
J
A
S
0
N
D
Overall
Values
Events
Tabulated
10
9
9
6
0
8
8
12
5
5
11
4
87
Volume Applied
Per Event M 3
18
18
18
18
21
21
21
21
18
18
18
19.1
Runoff
Measured
Per Event M3
Mean
14.4
10.6
8.7
6.8
5.1
4.8
7.1
9.3
4.8
12.0
13.8
9.0
Range
10.1-17.
6.8-13.
5.5-11.
3.2- 9.
2.7- 8.
3.5- 7.
3.7-13.
5.9-12.
2.8- 8.
8.4-17.
12.5-16.
2.7-17.
2
7
5
8
2
6
0
8
1
0
0
2
Percent
Runoff
80
59
48
38
24
23
34
44
26
66
76
47
14
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about 25 percent to a winter high of 80 percent. The seasonal relationship between
wastewater applications and measured runoff is shown in Figure 3. These results
for monthly values show that the seasonal loading pattern selected for use did not
maintain a consistent runoff fraction for this short period of record. Providing that
other factors did not become limiting, a greater increase in the warm weather loading
and extension of loadings from March through October could be utilized to obtain a
more consistent fraction of runoff and to have more flexibility for seasonal resting of the
treatment areas for maintenance operations. Seasonal shutdown for maintenance activi-
ties , such as vegetation removal, is an integral part of the overall operating plan.
SYSTEM ODORS
The potential for obnoxious odors in the vicinity of wastewater management systems
utilizing land application techniques is a question frequently encountered at symposia
and conferences. Odors in the vicinity of the raw sewage wet well, the distribution
booms, and the general plot area were assessed qualitatively throughout the 3-year
period of operation. The sewage arriving at the wet well through the sewerage
system was septic and, consequently, had the characteristic septic odor. Some type
of odor control at this point is a key factor, if one wishes to maintain odors at a low
level throughout the remainder of the system components. The arrangement provided
for settling and comminution (Figure 1) for this pilot system aerated the sewage and
reduced the odor to the "musty" odor typical of fresh domestic sewage. Residence
time in the distribution system was not sufficient for a return to septic conditions
and the concommitant return of obnoxious odors to be emitted at the boom nozzles.
Transient odors were noticed occasionally near the boom nozzles when pumping
was resumed following an extended shutdown period. Otherwise, the vicinity of the
distribution boom was characterized by the "musty" odor of fresh sewage. This odor
dissipated rapidly with distance and was usually dispersed within a distance of
15 m. Occasional detection of this odor beyond the 15 m distance was associated
with brisk winds and comparatively high humidity. The general area of the overland-
flow plots other than in the vicinity of the distribution booms was characterized by
absence of any odors. Visitors to the site were repeatedly surprised by this lack
of odors in view of the fact that raw sewage was being applied directly to the land.
15
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SECTION VII
TREATMENT PERFORMANCE
Treatment performance for the first study period from March 1971 through September
1973 has been presented in detail and discussed by Thomas, Jackson, and Penrod .
Data from this initial period of operation will be utilized again to illustrate the con-
tinuing performance of the system over the 36-month operating period, but it will
not be covered in detail comparable to that in the previous report. The emphasis
in this report will be placed on overall performance for the entire study period from
March 1971 through March 1974, and the phosphorus removal phase of the study
from November 1972 through March 1974.
WASTEWATER QUALITY
The raw wastewater data summary in Table 3 compares the results of analyses for
25 samples taken during the first 18-month study period and 14 samples taken during
the second 15-month study period. The parameters listed are commonly used to
express the solids content, the oxygen demand, the major nutrient content, and the
bacterial population of wastewaters. Aluminum was measured in the second study
period, because aluminum sulfate was being added to precipitate phosphorus. The
data presented in Table 3 indicate two factors of special interest for assessment of
the project results. Overall, the suspended solids, oxygen demand, major nutrient
content, and bacterial population are within the range that is considered normal for
domestic wastewaters. Differences in the composition of the wastewater between the
two study periods were slight except for the suspended solids content. This marked
increase in the total suspended solids and other differences directly associated with
this definite increase was not identified as to cause, because wastewater characteri-
zation was not an objective of the study. It does appear that the change was asso-
ciated with a nonorganic since the oxygen demand and total organic carbon content
of the wastewater showed no comparable change. There was an apparent effect on
treatment efficiency, which will be covered in a later section.
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Table 3. QUALITY OF RAW COMMINUTED WASTEWATER
FOR TWO STUDY PERIODS
Mean concentration, mg/1
Parameter First 18 months Last 15 months
Number of Samples 25 14
Total Solids 1014 1110
Total Volatile Solids 300 310
Total Suspended Solids 160 240
Total Volatile Suspended Solids 123 180
Total Dissolved Solids 854 880
Biochemical Oxygen Demand 150 160
Chemical Oxygen Demand 314 334
Total Organic Carbon 89 94
Total Nitrogen 23.6 21.3
Kjeldahl Nitrogen 22.8 21.2
Ammonia Nitrogen 17.0 12.5
Nitrate plus Nitrite Nitrogen 0.8 0.1
Total Phosphorus 10.0 9.8
Aluminum 0.7
Total Coliform 7.2 x 106
Fecal Coliform 1.0 x 106
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Using the mean values from Table 3 and the average liquid loadings, one can calcu-
late the mass loadings for parameters of interest. For example, the biochemical
oxygen demand loadings for the first 18-month study were 125, 147, and 169 kg/ha/
week, respectively, for the liquid loadings of 7.4, 8.6, and 9.8 cm/week. The
biochemical oxygen demand loading was 180 kg/ha/week for all three plots in the
15-month study, because all plots were dosed at the 9.8 cm/week liquid loading,
and there was a slight increase in the average biochemical oxygen demand. It is of
particular interest to note that nitrogen loading ranged from 910 to 1,200 kg/ha/year
in the 18-month study and was at the 1,200 kg/ha/year value on all plots for the
15-month study.
STUDY OF APPLICATION RATES - 18 MONTHS
The results of the first 18-month study have been detailed in a previous report ,
so coverage in this report will be a condensation to provide background for detailed
coverage of treatment obtained over the entire 36-month period of operation, and for
detailed coverage of phosphorus removal during the second 15-month study period.
Findings of importance to the coverage of the overall 36-month period and the 15-
month phosphorus removal period include treatment changes during system start
up, seasonal variations in treatment capability, and the effects of loading rates on
treatment capability.
It was observed that a several-month period was needed to age a newly prepared
and seeded treatment area. The major stabilization period took three to four months,
but gradual changes extended for a much greater time for some parameters. The
steady state removal of suspended solids and oxygen demanding substances at about
95 percent was not achieved until a dense vegetative cover was developed some nine
months after the start of operations. Conversely, phosphorus removal started out
at about 40 percent removal, improved rapidly to about 75 percent removal for a few
months, and then declined to a steady state seasonal range of 40 to 60 percent removal.
These observations indicated a need for a conditioning period when collecting data
to evaluate new operating procedures. The collection of data to evaluate the removal
of phosphorus by adding aluminum sulfate was preceded by a 3-month conditioning
period with all three plots on the same operating mode. Collection of data during this
period showed that the plots were fully acclimated, and performed as replicates at
the initiation of the phosphorus removal study. Data for the acclimation period is
presented and discussed in the coverage of the treatment for the 36-month period.
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Seasonal variations in treatment capability observed during the initial 18-month study
period were comparatively minor except for removal of the nutrients, nitrogen and
phosphorus. Nitrogen removal dropped off during this first winter period of opera-
tion. The drop-off in nitrogen removal resulted in a substantial increase in the
4
nitrate nitrogen content of plot runoff. Law, Thomas, and Myers have observed
that high nitrate in overland-flow effluent occurs when system operation is resumed
following system shutdown. It may be that the observed drop-off in winter nitrogen
removal was largely due to the brief shutdown periods necessitated by freezing
weather, rather than a loss of the capability of a regularly operating system to remove
nitrogen. Seasonal variation in the removal of phosphorus was less pronounced
than the variation in the removal of nitrogen. The change in the concentration of
phosphorus in the runoff from summer to winter amounted to a total mass of phos-
phorus comparable to that removed by plant harvesting. These results indicate that
the observed difference between summer and winter phosphorus removal is compar-
able to plant uptake and removal by harvesting.
The effects of loading rates on treatment capability were comparatively slight. Each
one of the rates, 7.4, 8.6, and 9.8 cm/week showed slight advantages for removal
of one or more constituents. The two higher rates showed somewhat better consis-
tency than the lower rate, and the 9.8 cm/week rate showed a slight overall advan-
tage. These results indicated that the optimum hydraulic load exhibits a broad
peak, and that further study could be focussed on the higher loading rate of about
10/week. The hydraulic application rate of 10 cm/week was selected for use in the
phosphorus precipitation phase of the overland-flow study.
OVERALL STUDY - 36 MONTHS
The overall study provides data for several comparisons on long-term trends and
seasonal patterns, as well as the specific hydraulic load and phosphorus removal
evaluations. The overall study period covers two summer and three winter seasons
and a 15-month period when the three plots were operated essentially as replicates
for all parameters except for phosphorus. Sixteen parameters were measured to
evaluate treatment capability with some 40 determinations being made for each para-
meter during the 36-month study period. Data summaries for all parameters are
included in the appendices. Data presented in the text are focussed on treatment
efficiencies for suspended solids, biochemical oxygen demand, chemical oxygen
20
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demand, nitrogen, phosphorus, and coliform bacteria. The presentation of data
addresses concentration data and does not imply a mass balance of constituents.
Plots in Figures 4 through 7 are 3 point moving averages. This technique was used
to obtain smoother curves, which better illustrate small differences. A tabular sum-
mary of plot runoff quality for both phases of the 36-month study is presented in
Table 4.
Suspended Solids Removal
Treatment efficiency for suspended solids (TSS) is summarized in Figure 4. Data for
all three plots exhibit a period of about 100 days during which the TSS in the plot
runoff declined steadily. Following this period of acclimatization removal of TSS
remained very stable at about 95 percent. The concentration of TSS was relatively
low with all recorded values in the range of 4 mg/1 to 41 mg/1 after 100 days of opera-
tion . As was shown in Table 3, the average TSS content of the raw wastewater was
160 mg/1 during the first 18 months of study and 240 mg/1 during the final 15 months of
study. This difference in raw wastewater concentration was reflected in plot runoff
concentration. The average TSS concentration in the runoff for all plots was 8 mg/1,
when that of raw wastewater was 160 mg/1, and 16 mg/1 when that of the raw waste-
water was 240 mg/1. Seasonal variation for TSS in the plot runoff may be influenced
by this change in raw wastewater characteristics. Regardless of this possible influence,
there is no difference between summer and winter treatment efficiency. The concen-
tration of TSS was 11 mg/1 for both seasons.
Comparison of TSS data for the three plots operating at the same hydraulic load
indicates close agreement for data from the three plots. As shown in Table 4, the mean
values were 16, 15, and 18 mg/1, and a statistical comparison shows that the observed
difference is not statistically significant at the 5 percent level of probability.
Overall, the TSS data collected during this 36-month period of operation shows that
overland-flow treatment produces an effluent containing less than 20 mg/1 consis-
tently with influent TSS up to 240 mg/1 and hydraulic load up to 10 cm/week.
BOD Removal
Treatment efficiency for biochemical oxygen demand (BOD) was determined analyt-
ically throughout the 18-month hydraulic load study as shown by the data in Table 4.
During this study period, 40 sets of data were collected to determine the ratio of
BOD to chemical oxygen demand (COD) and to total organic carbon (TOC) . The mean
21
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ratio of BOD to COD was 0.18 with a range of .16 to .21, while the mean ratio of BOD
to TOC was 0.54 with a range from . 47 to .62. These data showed that mean BOD could
be estimated accurately from the COD and TOC data, and BOD was not measured
directly during the 15-month phosphorus study.
BOD values measured during the 18-month hydraulic study and the calculated
values for the 15-month phosphorus study show that overland-flow treatment produces
an effluent with a BOD of less than 15 mg/1 when receiving a raw wastewater con-
taining 150 to 160 mg/1 BOD at hydraulic loads up to 10 cm/week. Seasonal and long-
term trends for BOD removal were comparable to those for COD and TOC, which are
covered in detail in the next section.
COD And TOC Removal
Treatment efficiencies for COD and TOC were very similar and will be covered
together. The COD data are illustrated in Figure 5 and are representative of TOC
data and the overall treatment efficiency pattern for BOD. Data for all three plots
exhibit similar changes over the duration of the study. The time period for reaching
75 percent removal of COD was quite comparable to the 100-day period observed for
reaching the stable 95 percent removal of TSS; however, the removal of COD continued
to improve slowly for an additional 100-day period and stabilized at about 85 percent
some 200 days into the study.
The COD and TOC data in Table 4 indicate that there may be a slight but definite
improvement associated with the addition of aluminum sulfate. Pooled averages for
the two study periods show that COD removal was 84 percent for the 10 cm/week load
without aluminum sulfate, and 88 percent for the two plots receiving aluminum sul-
fate. TOC removals for the same comparison were 80 and 84 percent, respectively.
Treatment efficiency for COD also exhibits small but definite seasonal changes with
removal being best during the winter to early spring and poorest during the summer.
Comparison of mean data for the three cold seasons (December through February)
versus the data for the two warm seasons shows 87 percent and 83 percent treatment
efficiencies, respectively. The weighted mean COD in the plot runoff was 44 mg/1
during the warm season. Overall, the data show that overland-flow treatment
stabilizes rather slowly for removal of COD and TOC and may not reach a steady
state until the second year of operation. The stable treatment efficiency for both
27
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parameters is in the 80 to 85 percent range. For conditions at this site and with a
hydraulic load of 10 cm/week, the plot runoff COD varied seasonally from 45 to 55
mg/1, and the plot runoff TOC was in the 15 to 20 mg/1 range.
Nitrogen Removal
Treatment efficiency for the plant nutrient nitrogen is illustrated in Figure 6. Data
for all three plots exhibit similar patterns of behavior with pronounced periods of
sharply differing treatment efficiency. The acclimatization period was about 80
days, which is somewhat less than the 100-day period to reach a stable level of 95
percent TSS removal. Nitrogen is intimately involved in microbial metabolism and
plant nutrition, and the subsequent periods of sharply changing treatment efficiency
can be attributed to this fact. It is reasonably well accepted that microbial denitrifi-
cation is a principal mechanism influencing nitrogen removal, and it is well documen-
ted that crop uptake and harvest also are important factors. Tracing operational
procedures and seasonal management in relation to these two factors provides sup-
porting evidence to explain the observed patterns of nitrogen removal following the
acclimatization period.
The sharp increase in runoff nitrogen at day 110 results from an extended shutdown
to modify the distribution system. Extended shutdown of a system changes the
oxygen status to inhibit the denitrification process, and substantial nitrate nitrogen
will be present in the runoff. The slow decline in runoff nitrogen following day 110
suggests that full recovery of microbial denitrification may be much slower in fall
and winter than initial acclimatization in summer. The sharp rise in runoff nitrogen
in late winter at day 330 was associated with a severe cold snap. Temporary shut-
downs, temperatures in the teens, or the combined influence of both, severely inhi-
bited denitrification and nitrate concentrations up to 10 mg/1 were measured in the
plot runoff. A similar but less noticeable period occurred in the winter of 72-73,
and there was virtually no such period in the mild winter of 73-74. The excellent
treatment efficiency observed in the summer is the result of favorable climatic con-
ditions for both microbial denitrification and removal by plant harvest.
Overall treatment for nitrogen removal at this site with the 10 cm/week hydraulic
load was about 85 percent. There was a seasonal pattern directly related to the
severity of winter conditions. Summer removal was consistent at about 90 percent,
28
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while winter removal ranged from less than 75 percent in the severest winter to
about 85 percent in the mildest winter. The 3-year mean nitrogen concentration in
the plot runoff was 5.8 mg/1 for winter and 2.0 mg/1 for summer.
Phosphorus Removal
Treatment efficiency for the nutrient phosphorus is illustrated in Figure 7. During
the hydraulic rate study, data from all three plots exhibited similar patterns of
behavior. A period of rapidly improving treatment efficiency during the period of ac-
climatization lasted about 80 days. This initial sharp improvement in treatment
efficiency to a maximum value of about 80 percent was followed by a gradual loss in
treatment efficiency through the summer and fall of 1971 to values of about 50 percent.
The 12-month period following showed a minor seasonal pattern with somewhat better
treatment efficiency in summer when plant uptake was at its highest level. Overall,
the treatment efficiency for this 12-month period averaged about 55 percent ranging
from a summer high of 60 percent to a winter low of 50 percent. This relatively stable
phosphorus removal at about 55 percent contributed to the decision to initiate the
phosphrous removal study in November 1972. All three plots were adjusted to the
same hydraulic load of 10 cm/week and were operated as true replicates for about 2
months. Aluminum sulfate addition was started early in January 1973 and continued
to the end of the study in March 1974. Data for the plot not receiving aluminum sulfate
exhibited a more distinct seasonal pattern than it had in the previous year with late
fall treatment efficiency reaching about 70 percent instead of 60 percent. Data for
both plots receiving aluminum sulfate exhibited a quick response with the phosphorus
concentration in the runoff dropping below 2.0 mg/1 within 2 months. The phosphorus
concentration in the plot runoff remained below this value for the remainder of the
study. Specific data on the phosphorus removal study presented in Table 5 will be
used to further detail the improved phosphorus removal achieved by addition of
aluminum sulfate.
We encountered considerable difficulty with our system for adding aluminum as a
concentrated aluminum sulfate solution using a metering pump. The concentration
of aluminum at the distribution-boom nozzle varied greatly as shown in Table 5,
and after 15 months of operation, it was determined that a precipitate was deposited
in the delivery line between the point of injection and the distribution-boom nozzle.
These operational problems undoubtedly affected the treatment efficiency and may
29
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Table 5. SPECIFIC DATA FOR THE PHOSPHORUS REMOVAL STUDY
COVERING JUNE 1973 THROUGH FEBRUARY 1974
Aluminum Plot Runoff Concentrations day 770 thru 1100 mg/1
Added rog/1 Aluminum Phosphorus
Mean Range Mean Range Mean Range
Control plot
Low Al plot
High Al plot
0
14
20
2-27
<5-40
.15
.22
.34
.07-. 16
.06-. 30
.10-. 82
3.4
1.5
0.9
1.9-6.0
0.3-3.9
0.5-1.4
30
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account for observed anomalies between the low and high aluminum additions. The
raw wastewater contained 0.7 mg/1 of aluminum with a range of 0.13 to 1.3 mg/1, and
the phosphorus in the raw wastewater was 10.4 mg/1 with a range of 9.0-12.4 mg/1
during the last 10 months of the phosphorus study. Referring to Figure 7, we
observe that the 14 mg/1 aluminum addition reduced phosphorus in the plot runoff
sharply to less than 1. 0 mg/1 where it remained for about 6 months followed by an
abrupt increase during the last 3 months of study. This sharp increase was
associated with a decrease in aluminum concentration at the distribution-boom
nozzle. During the period having less than 1 mg/1 of phosphorus in the plot runoff,
the aluminum concentration at the nozzle averaged 15 mg/1 and ranged from 11 to
27 mg/1. During the last 3 months, the aluminum concentration at the nozzle
averaged 9 mg/1 with a range of 7 to 11 mg/1.
The 20 mg/1 aluminum addition produced a sharp decrease to about 1.5 mg/1 followed
by a gradual but steady decrease to less than 1.0 mg/1 at the end of the study.
During this period of gradual but steady decrease, the aluminum concentration at
the nozzle averaged 23 mg/1 with a range of 17 to 40 mg/1.
The addition of aluminum to the raw sewage did cause a slight increase in the runoff
concentration of aluminum. As shown in Table 5, the increase was directly propor-
tional to the amount of aluminum added to the raw wastewater but was a small
fraction of the total added.
Although the observed results are confounded by operating problems, it is clear
that addition of aluminum to the raw wastewater enhances phosphorus removal. There
are definite indications that a 1: 1 stoichiometric balance of aluminum to phosphorus
reduces a raw wastewater concentration of 10.4 mg/1 to about 1.5 mg/1, while a
2: 1 balance achieves an additional reduction in the runoff concentration to about 1.0
mg/1.
Coliform Reduction
During the 15-month phosphorus study, total coliform and fecal coliform were deter-
mined in the raw wastewater and the plot runoff. There was no difference in the
degree of reduction between plots for total coliform, while the two plots receiving
aluminum sulfate had somewhat lower counts for fecal coliform. Overall, the reduc-
tion was about 95 percent for total coliform. Fecal coliform reduction was about 90
percent without aluminum sulfate and 97.5 percent with aluminum sulfate. The total
31
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coliform counts in the plot runoff were about 200,000 per 100 ml, while the fecal coli-
form counts in the plot runoff were about 90,000 per 100 ml without aluminum sulfate
addition and about 25,000 per 100 ml with aluminum sulfate addition.
32
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SECTION VIII
DISCUSSION
Data collected over a 3-year period show that overland flow is capable of providing
year-round treatment of raw domestic wastewater in mild climates. Removal of sus-
pended solids, biochemical oxygen demand, nitrogen, and phosphorus exceeds
removals achieved by conventional secondary processes. Overall, overland flow
would be classified as an advanced waste treatment process. Removal of suspended
solids and oxygen demanding substances are readily explained as a result of micro-
bial biooxidation. There is a wealth of published information to support this expla-
nation. Removal of nitrogen and phosphorus are not explained as readily on the
basis of well-documented theory. Hoeppel, Hunt, and Delaney (1974) and Thomas,
Jackson, and Penrod have discussed the removal of these constituents and offered
hypotheses to explain their removal by overland-flow treatment. Complementary
research is now in progress to test the hypothesis that denitrification is a dominant
factor in nitrogen removal.
Thomas, Jackson, and Penrod detailed factors influencing phosphorus removal by
overland flow. They suggested that phosphorus removal could be improved by chem-
ical precipitation without adverse effects on removal of other constitutents. The
results of the 15-month phosphorus removal study demonstrate that phosphorus
removal can be increased to about 90 percent by adding 1.5 to 2.0 mg of aluminum
for each mg of phosphorus. This addition of aluminum does increase the aluminum
content of the plot runoff by 50 to 100 percent with the actual concentration being
raised from 0.15 mg/1 to a high value of 0.34 mg/1. The addition of 20 mg/1 of
(7)
aluminum matches the National Academy of Science's recommended maximum con-
centration in irrigation waters for up to 20 years' use on neutral to alkaline soils.
Although it is possible to remove phosphorus by precipitation with aluminum, addi-
tional work is needed to determine management practices for avoiding aluminum
toxicity in the soil. Another alternative for achieving phosphorus removal is the
33
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use of soil infiltration following overland flow. This approach has the added bene-
fits of virtually complete removal of suspended solids, oxygen demanding substances,
and fecal bacteria. This combination of overland flow followed by high-rate infil-
tration is now under study at the Robert S. Kerr Environmental Research Laboratory.
The next research report in this series on overland flow will cover this treatment
train.
Reliability is an important consideration for determining the practical implementation
of a waste treatment process. Over the 36-month duration of this pilot study, the
system has shown excellent reliability, and the quality of the plot runoff has varied
very little once the system was stabilized. The three-point moving averages plotted
in Figures 3 through 7 are indicative of this consistency, but they do mask some of
the variability in the data. Relative frequency data give a clearer picture of this
consistency. From day 110 to day 1080, the maximum suspended solids value
recorded was less than 50 mg/1 for all three plots and 90 percent of all values were
less than 25 mg/1. Similar reliability was observed for other parameters including
oxygen demand measurements and the nutrients nitrogen and phosphorus.
The encouraging results from this 3-year pilot study are being tested at operational-
scale facilities in Oklahoma and South Carolina at flows in the 8 to 16 m per hour
(50,000 to 100,000 gpd) range. These field studies will evaluate the performance
of overland flow in two modes of operation, with raw wastewater as one source, and
oxidation pond effluent as the other source. Evaluation of design components will
include hydraulic load, distribution devices, operational requirements, and system
costs. Assessment of system performance will focus on treatment capability for
traditional parameters, but it will also include studies on aerosols, odors, crop
quality, soil properties, and groundwater quality.
34
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SECTION IX
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. 31 p.
2. Luley, H. G. Spray Irrigation of Vegetable and Fruit Processing Wastes. J.
Water Pollut. Contr. Fed. 35: 1252-1261, October 1963.
3. Bendixen, T. W., R. D. Hill, F. T. Dubyne, and G. G. Robeck. Cannery
Waste Treatment by Spray Irrigation-Runoff. J. Water Pollut. Contr. Fed.
41:385-391, March 1969.
4. Law, J. P., R. E. Thomas, andL. H. Myers. Cannery Wastewater Treatment
by High-Rate Spray on Grassland. J. Water Pollut. Contr. Fed. 42: 1621-1631,
September 1970.
5. Kirby, C. F. Sewage Treatment FarmsPost Graduate Course in Public Health
Engineering, Session No. 12. Department of Civil Engineering, University of
Melbourne, Melbourne, Australia. 1971. 14 p.
6. Hoeppel, R. E., P. G. Hunt, and T. B. Delaney, Jr. Wastewater Treatment on
Soils of Low Permeability. Water Ways Experiment Station, Corps of Engineers,
Vicksburg , Miss . Miscellaneous Paper Y-73-2. 1974.
7 . Methods for Chemical Analysis of Water and Wastes . Environmental Protection
Agency, Cincinnati, Ohio. Publication No. 1602007/71. July 1971. 312 p.
8. Water Quality Criteria, 1972. National Academy of Sciences, National Academy
of Engineering, Washington, .DC. EPA Series No. R3-73-033, March 1973.
pp 338-340.
35
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/2-76-131
2.
1. RECIPIENT'S ACCESSIOC+NO.
4. TITLE AND SUBTITLE
OVERLAND FLOW TREATMENT OF RAW WASTEWATER WITH
ENHANCED PHOSPHORUS REMOVAL
5. REPORT DATE
June 1976 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
R. E. Thomas, B. Bledsoe, and K. Jackson
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Robert S. Kerr Environmentr I Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
10. PROGRAM ELEMENT NO.
P.E. 1BC631 AP No. L611C
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
Final 3/71 through 6/73
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A pilot-scale field study was conducted to evaluate the capability of overland flow
to provide complete treatment of raw comminuted wastewater on a year-round basis
in a mild climatic zone. Raw comminuted wastewater was applied through a specially
designed distribution system which operated at low pressure and prevented the for-
mation of aerosols. This specially designed applicator operated at a pressure of
1.0 kg/sq cm (15 psi) and was used to apply wastewater to three experimental plots
at 7.4, 8.6, and 9.8 cm/week rates of loading. Wastewater and plot runoff samples
were collected periodically to compare treatment efficiencies for the three loading
rates and to determine seasonal influences on treatment efficiency. Fifteen para-
meters including suspended solids, biochemical oxygen demand, nitrogen, and phos-
phorus were used to evaluate treatment efficiencies. The results of this 18-month
field study showed overland flow to be an effective process for achieving advanced
waste treatment of raw comminuted wastewater via a simple system with no sludge
production.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Sewage treatment
Land use
Nitrogen cycle
Phosphorus cycle
Overland flow
2C
14B
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
44
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
36
- U S. GOVERNMENT PRINTING OFFICE: 1976-657-695/5't'tO Region No. 5-11
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