EPA-660/2-74-087
DECEMBER 1974
Environmental Protection Technoic>v "-•-
Feasibility of Overland Flow for
Treatment of Raw Domestic Wastewater
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Corvallis. Oregon 97330
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development,
U.S. Environmental Protection Agency, have been grouped into
five series. These five broad categories were established to
facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in
related fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY STUDIES series. This series describes research
performed to develop and demonstrate instrumentation, equipment
and methodology to repair or prevent environmental degradation from
point and non-point sources of pollution. This work provides the
new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This report has been reviewed by the National Environmental
Research Center—Corvallis, and approved for publication. Mention
of trade names or commercial products does not constitute endorsement
or recommendation for use.
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EPA-660/2-74-087
July 1974
FEASIBILITY OF OVERLAND FLOW FOR TREATMENT
OF RAW DOMESTIC WASTEWATER
by
R. E. Thomas , K. Jackson, and L. Penrod
Robert S . Kerr Environmental Research Laboratory
National Environmental Research Center
Ada, Oklahoma 74820
Project No. 16080 WPH
ROAP 21-ASH, TASK 12
Prograw El«*ient IBB 045 .
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
For sale by the Superintendent of Documents, L'.S. Government Printing Office
Washington, D.C. 20402 - Stock No. 5501-00993
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ABSTRACT
A pilot-scale field study was conducted to evaluate the capability of
overland flow to provide complete treatment of raw comminuted waste-
water on a year-round basis in a mild climatic zone. Raw comminuted
wastewater was applied through a specially designed distribution sys-
tem which operated at low pressure and prevented the formation 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 deter-
mine seasonal.influences on treatment efficiency. Fifteen parameters
including suspended solids, biochemical oxygen demand, nitrogen,
and phosphorus were used to evaluate treatment efficiencies. The
results of this 18-month field study showed overland flow to be ah
effective process for achieving advanced waste treatment of raw
comminuted wastewater via a simple system with no sludge production.
This report was submitted in fulfillment of Project No. 16080 WPH
(Task 12, ROAP 21-ASH) as an in-house project by the Water Quality
Control Branch, Robert S. Kerr Environmental Research Laboratory,
under the sponsorship of the Environmental Protection Agency. Work
was completed as of June 1973.
11
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CONTENTS
Section Page
I CONCLUSIONS 1
II RECOMMENDATIONS 2
III INTRODUCTION 3
IV EXPERIMENTAL DESIGN AND OPERATION 6
V OPERATING RESULTS 11
VI TREATMENT PERFORMANCE 13
VII DISCUSSION 25
VIII SUMMARY 29
IX REFERENCES 31
in
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LIST OF FIGURES
No. Page
1 SCHEMATIC OF WASTEWATER HANDLING SYSTEM 8
2 DETAIL OF WASTEWATER DISTRIBUTOR 9
3 CHANGES IN TREATMENT EFFICIENCY DURING
SYSTEM AGING 16
4 REMOVAL OF SUSPENDED SOLIDS AND BIOCHEMICAL
OXYGEN DEMAND DURING WINTER OPERATION 19
5 NUTRIENT REMOVAL DURING WINTER OPERATION 21
IV
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LIST OF TABLES
No. Page
1 CHEMICAL CHARACTERISTICS OF RAW WASTEWATER
FOR 18-MONTH STUDY PERIOD 14
2 TREATMENT EFFICIENCY IMPROVEMENT DURING
SYSTEM AGING IN 1971 15
3 CHEMICAL QUALITY OF PLOT RUNOFF FOR WINTER
OPERATION FROM NOVEMBER 1971 THROUGH
APRIL 1972 18
4 CHEMICAL QUALITY OF PLOT RUNOFF FOR SUMMER
OPERATION FROM MAY 1972 THROUGH SEPTEMBER
1972 23
v
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SECTION I
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 containing less
than 10 mg/1 of suspended solids and biochemical oxygen demand.
• A well operated system should achieve 90 percent nitrogen removal
in the summer, but nitrogen removal may drop substantially in the
winter.
• Phosphorus removal should be about 50 percent with relatively
minor seasonal variation.
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SECTION II
RECOMMENDATIONS
Overland flow should be tested and demonstrated at selected
communities to validate the results of this pilot study.
Initially, these communities should be located at places with
climatic conditions comparable to or milder than the test site.
Capital and operating cost data should be included in all evalu-
ation programs for full-scale operational systems.
Pilot-scale testing should be continued to evaluate phosphorus
removal by chemical precipitation.
Pilot-scale studies should be conducted to evaluate the effect of
pretreatment on treatment efficiency and system loading.
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SECTION III
INTRODUCTION
Treatment of wastewater by allowing it to trickle over gently sloping
ground is most commonly referred to as "spray-runoff" or "overland
flow." Overland flow is preferred by the authors and will be used in
this report on the treatment of raw comminuted sewage. Overland flow
has been selected frequently by the food processing industry for the
treatment of seasonal wastewater discharges and, in several cases, for
year-round wastewater discharges. Use of the overland-flow concept
by food processors in the United States appears to originate from exper-
iences with a spray disposal system discussed by Luley in 1963. Sub-
sequently, the concept has been further developed and purposely
installed as the treatment system at a number of locations. Treatment
of domestic wastewater by overland flow is also practiced at a few loca-
tions in foreign countries. The approach utilized at Werribee for treat-
ment of wastewater from the City of Melbourne, Australia is a good
example of a system which has been in service for many decades. The
treatment efficiency achieved by the overland-flow approach is contingent
on many factors, and the quality of the effluent produced can vary greatly.
It is this aspect of the overland-flow treatment process which will be
further elaborated in this report.
The variability of system design and effluent quality can be exemplified
by a comparison of the system at Werribee as described by Kirby in
1971 and the system at Paris, Texas as described by Law, Thomas, and
Myers in 1970. Kirby reports that the Werribee system consists of bays
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which are 365 meters long prepared as for border check irrigation and
seeded with Italian rye grass. Sedimented domestic wastewater is
treated continuously by introducting it into one end of the bay and
allowing it to trickle slowly over the length of the bay. The bay is
operated continuously throughout the winter season from May through
September at an average areal loading of 1.9 cm per day. This method
of operation results in some anaerobiosis at the inlet end of the bays,
but downslope aerobiosis contributes to good overall treatment efficiency.
Kirby estimates the removal of pollutants to be 96 percent for biochemical
oxygen demand, 95 percent for suspended solids, 60 percent for total
nitrogen, and 35 percent for total phosphorus. These percentage removals
would produce an effluent from the bays containing about 25 mg/1 of bio-
chemical oxygen demand and suspended solids. Concentration data for
nitrogen and phosphorus were not reported by Kirby. Law, Thomas,
3
and Myers report that the Paris, Texas system consists of graded slopes
with intercepting terrace ditches at 45- to 100-meter spacings. Screened
cannery wastewater is sprayed intermittently at the tops of the 2 to 6
percent slopes (just below an intercepting terrace) and the treated
wastewater is collected in the next intercepting terrace downslope. This
system is operated all year at an areal loading of 0.9 cm per day applied
during spraying periods of 6 or 8 hours. Law, Thomas, and Myers
reported that this system produced an effluent with an average biochemi-
cal oxygen demand of 9 mg/1; a suspended solids content of 16 mg/1; a
total nitrogen concentration of 2.8 mg/1; and a total phosphorus concen-
tration of 4.3 mg/1. These concentrations were obtained as a result of
98.5 percent reduction of biochemical oxygen demand, 93.5 percent
reduction of suspended solids, 84 percent reduction of total nitrogen,
and 40 percent reduction of total phosphorus. The treatment efficiencies
achieved by these two systems cited as examples and by other overland-
flow approaches reported in the literature indicate that overland flow has
potential for achieving a high level of advanced waste treatment and
should be developed as one method of achieving "best practicable waste
treatment technology" referred to in PL 92-500.
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4
A recent evaluation of research needs indicated that there were about
5,300 small communities in the United States which did not have waste
treatment facilities in 1965. In preparing this report on research needs,
the Federal Council for Science and Technology concluded that these
small communities, having an average population of 6,000 and repre-
senting a total population of 33 million, would find the cost of conven-
tional waste treatment a heavy burden and research toward low-cost
treatment methods was urgently needed. Overland flow is a low-cost
treatment method which should have its greatest utility in these rural
locations where ample land would be readily available for installation
of a system.
The principal objectives of the research project reported herein were
to (1) evaluate the practicality of year-round treatment of raw waste-
water by overland flow in a moderate semihumid environment, (2) deter-
mine allowable loading rates for achieving a high level of advanced waste
treatment, and (3) develop sufficient design data to implement a full-scale
system under comparable climatic conditions.
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SECTION IV
EXPERIMENTAL DESIGN AND OPERATION
The study was conducted at the field site of the Robert S. Kerr Environ-
mental Research Laboratory located in Ada, Oklahoma. The climate at
this location is suitable for year-round operation with minimal consid-
erations 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 temperatures are above
freezing for all months except January when the average minimum dips
to -1.0° C. Average daily maximum temperatures are greater than 10° C
throughout the year. The experimental system was designed without
special considerations for continuing operations during adverse weather
conditions and the downtime due to weather influences was included as
a variable for evaluation.
SITE PREPARATION AND WASTEWATER DISTRIBUTION
The subsoil at the selected site is a dense clay that provided the
restriction to downward 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 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 rotatable vertical support. The appli-
cators used to apply the wastewater to the experimental 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 connected to the bottom of the rotatable
vertical support with a standard hose swivel connector. With proper
alignment and weight 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. These distributor booms were mounted at a height of
1.2m 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 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
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MUTRATOR
Row Sewage ^
Line
oo
WET
WELL
PUMP
1
l
I
^PTTI IMfi TAKIK
J,
V
i
i
i
i
L
FIELD PUMP
T_ AUTOMATIC
TIMING CONTROL
I'
PI
PI
Plot-l
Dt-2
ot-3 I
TO
WASTEWATER
DISTRIBUTOR
FIGURE I. SCHEMATIC OF WASTEWATER HANDLING SYSTEM
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Counter_
Weight '
0.6 m
3.0 m
Angle
Iron -?
Support ^
1.2m
Thrust Roller
Bearing
-Standard Hose
Swivel
/»•Ground Surface
j-—Fan Nozzle
\\
| | ^V0 ^ y* Supply Line
^"= = -=----"--3
ii
U
FIGURE 2. DETAIL OF WASTEWATER DISTRIBUTOR
-------
of application per day for 6 days a week. Spring and fall operation pro-
vided 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.
Samples of the raw comminuted wastewater and the runoff from each of
the three experimental plots were collected at weekly or biweekly inter-
vals 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 study period after it had been determined that
grab samples from the sedimentation tank provided comparable informa-
tion on the quality of the raw wastewater. Runoff samples from the treat-
ment plots were taken as a grab sample obtained while runoff was at its
peak flow. Previous experience during the study reported by Law,
3
Thomas, and Myers had shown that grab samples taken this way are
comparable in chemical quality to flow proportional composite samples.
All samples were subjected to analysis for 15 chemical parameters
frequently employed to characterize the solids content, oxygen demand,
and nutrient content of wastewater. The analytical procedures used
were selected from those published in "Methods for Chemical Analysis
of Water and Wastes, 1971. " 5
10
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SECTION V
OPERATING RESULTS
Results for operation of the wastewater distribution system will be pre-
sented in two sections because operating problems led to a major revision
of the distribution system design after a shakedown and system aging
period of operation lasting six 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 sedi-
mentation and skimming tank shown in Figure 1. Operating with this
design led to frequent nozzle plugging due to fragments of plastics, tin-
foil , 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 presedimentation and skimming tank; there-
fore, the distribution systein was modified to handle the wastewater as
shown in Figure 1.
AFTER ADDING SEDIMENTATION
Inclusion of the sedimentation and skimming tank substantially eliminated
the frequent plugging experienced during the shakedown period. The
tank used had a working depth of 0.4 m and provided a volume equal to
about 10 minutes of the pumping rate of the wet well pump. Since the
11
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wet well pump capacity was greater than the capacity of the plot distri-
bution pump, it was possible to utilize excess flow through the sedimen-
tation 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, 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.
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 protection. This experimental system was run without freeze
protection to get an estimate of storage requirements for a system
operated in this manner. Temperatures during the winter of 1971-72
were close to the norms with the December average temperature being
0.8° C above the norm of 6.5° C, the January average temperature being
0.9° C below the norm of 5.3° C, and the February average temperature
being 0.4° C above the norm of 7.5° C. Freezing interrupted operations
for a total of 10 days during January and February. 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 desirable
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 treatment performance.
12
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SECTION VI
TREATMENT PERFORMANCE
Results for the 18 months of operation covered will be presented in three
sections. The first section will cover the general characteristics of the
raw wastewater throughout the study period and the treatment efficiency
achieved during the 6-month shakedown period of operation. This initial
period of operation is a time when the system is undergoing rapid changes
in treatment efficiency due to adaptation of microbial organisms, establish-
ment of vegetation, and other environmental alterations commonly lumped
under the aggregate term of "aging." Treatment efficiency achieved
during this period of operation is not indicative of the efficiency expected
for a well matured system. The second section will cover the period from
November 1971 through April 1972 which encompasses a period of winter
operation for a reasonably well matured overland-flow system. The
third section will cover May through September 1972, which is repre-
sentative of summer operation for a well matured overland-flow system.
WASTEWATER QUALITY AND SHAKEDOWN OPERATION
The raw wastewater data summary in Table 1 shows the results of
analyses for 25 samples taken during the 18-month study period. The
parameters listed are commonly used to express the solids content, the
oxygen demand, and the major nutrient content of wastewaters. The
data presented in Table 1 indicate that the suspended solids, oxygen
demand, and major nutrient content of the wastewater used in the study
are within the range that is considered to be normal for domestic waste-
waters . Using the mean values from Table 1 and the average liquid
13
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Table 1. CHEMICAL CHARACTERISTICS OF RAW WASTEWATER
FOR 18-MONTH STUDY PERIOD
Concentration, mg/1
Parameter
Total Solids
Total Volatile Solids
Total Suspended Solids
Total Volatile Suspended Solids
Total Dissolved Solids
Biochemical Oxygen Demand
Chemical Oxygen Demand
Total Organic Carbon
Total Nitrogen
Kjeldahl Nitrogen
Ammonia Nitrogen
Nitrate plus Nitrite Nitrogen
Total Phosphorus
Mean
1014
300
160
123
854
150
314
89
23.6
22.8
17.0
0.8
10.0
Maximum
1660
525
420
306
1504
273
620
198
36.8
36.8
29.0
15.0
Minimum
650
149
52
40
525
84
130
21
10.7
8.3
6.9
4.8
loadings of 7.4, 8.6, or 9.8 cm per week, one can calculate the mass
loadings for parameters of interest. For example, the biochemical oxy-
gen demand loadings at the 9.8 cm/week rate average 147 kg/ha/week
with a summer high of 169 kg/ha/week and a winter low of 125 kg/ha/
week. It is of particular interest to note that continuous year-round
operation results in annual nitrogen loadings ranging from a low of
910 kg/ha to a high of 1,200 kg/ha. This nitrogen loading is substantially
more than can be removed by crop uptake and harvesting.
As has been stated, nozzle plugging interfered with the scheduled
operation of the system during the shakedown period. The nozzle plugging
problem and other start-up operational problems reduced the plot waste-
water loadings to about 80 percent of the scheduled 7.4, 8.6, and 9.8
cm/week rates. This was not considered to be a problem in evaluating
treatment performance because it was known that a several-month
14
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period was needed to age the system and to establish vegetative cover
on the newly prepared and seeded plot area. The major stabilization
period took from two to four months, as is shown by the time plots for
total nitrogen and total suspended solids in the runoff from the 9.8
cm/week loading in Figure 3. As is shown, the concentration of total
nitrogen in the plot runoff declined rapidly from an initial level of about
18 mg/1 to values of about 5 mg/1 within 60 days, while the total sus-
pended solids declined more slowly from an initial value of about 120
mg/1 to values of less than 25 mg/1 after 120 days of operation.
Chemical data showing the treatment efficiency changes for other param-
eters during the period of system aging are presented in Table 2. All of
the nitrogen forms and total phosphorus exhibited the rapid changes
illustrated by the plot for total nitrogen in Figure 3. Biochemical oxygen
demand exhibited a slower change more comparable to that illustrated by
the graph for total suspended solids in Figure 3. Changes for chemical
oxygen demand and total organic carbon were less dramatic and also
extended over most of the period of aging. A comparison of the mean
values of all parameters for June and July indicates that treatment
efficiency was adequately stabilized for initiation of the comparison of
seasonal influences on treatment efficiency for the three loading rates.
Table 2. TREATMENT EFFICIENCY IMPROVEMENT
DURING SYSTEM AGING IN 1971
Mean monthly concentration in runoff
for all rates, mg/1
Parameter
Total Suspended Solids
Biochemical Oxygen Demand
Chemical Oxygen Demand
Total Organic Carbon
Total Nitrogen
Kjeldahl Nitrogen
Ammonia Nitrogen
Total Phosphorus
March
172
102
158
56
17.8
16.7
12.9
5.9
April
71
44
148
55
11.6
11.5
4.2
3.9
May
42
41
104
36
5.1
5.1
1.8
2.4
June
21
29
71
31
5.0
4.3
1.6
2.4
July
25
23
95
42
6.7
5.2
1.4
2.3
15
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120 —
100
o> 80
u."
u.
o
z
cc
z 60
z
o
QC
I-
u
o
z
o
40
20
TOTAL SUSPENDED SOLIDS
TOTAL NITROGEN
25
50 75
ELAPSED TIME, days
100
125
FIGURE 3. CHANGES IN TREATMENT EFFICIENCY
DURING SYSTEM AGING
16
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Since treatment efficiency was stabilizing and nozzle clogging was inter-
fering with achievement of the desired loading, it was decided to shut
the system down in August 1971 to incorporate the sedimentation and
skimming tank into the distribution system. With these modifications
completed, the system was placed back into operation in November 1971
at the scheduled loading rates.
WINTER TREATMENT PERFORMANCE
This data reporting period covers operations from November 1971 through
April 1972 and covers the first winter season of operation for the test site.
From November 1, 1971 through December 15, 1971 and from March 16,
1972 through April 30, 1972, the system was operated at the 7.4, 8.6,
and 9.8 cm/week loading rates. In the interim period from December 16,
1971 through March 15, 1972, the system was operated at the 6.3, 7.3,
and 8.2 cm/week winter loading rate. Therefore, the average loading
for this reporting period was 6.8, 8.9, and 9.1 cm/week. Chemical
quality data for the runoff from the three plots for this period of opera-
tion are summarized in Table 3. Differences in the treatment performance
achieved at the three rates of loading were minor and inconclusive, as
far as identifying one rate as being superior. Each of the three loading
rates was identified as the best performer for three or more of the
parameters listed in Table 3. Using total suspended solids and bio-
chemical oxygen demand as key measures of treatment efficiency, the
higher loadings have a slight advantage over the lowest loading. Alter-
natively , using the major nutrients nitrogen and phosphorus as the key
parameters for consideration, the lowest loading rate shows a distinct
advantage over the higher loading rates. The small and inconsistent
differences exhibited during this period of operation suggest that the
optimum loading of raw comminuted wastewater to an overland-flow
system exhibits a rather flat peak and that all three of the evaluated
loading rates fall close to the optimum.
The hypothesis that all three rates fall near a broad optimum for loading
is substantiated by the fact that the quality of runoff from all three plots
17
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is indicative of a relatively high level of advanced waste treatment.
Treatment efficiency for suspended solids and biochemical oxygen demand
was 92 to 95 percent. As shown by the data plotted as a moving 3-point
average in Figure 4 for each of the three rates of loading, the concentra-
tion of suspended solids and biochemical oxygen demand increased slightly
during winter operation even though the loading rate was reduced for
winter operation. Even with the slight increase, the maximum concen-
trations for these parameters remained well below 20 mg/1, which is
considered an excellent level of secondary treatment. The other mea-
sures of solids and oxygen demand, as shown by the data in Table 3,
substantiated the high treatment efficiency illustrated by the graphic
presentation of data for total suspended solids and biochemical oxygen
demand.
Table 3. CHEMICAL QUALITY OF PLOT RUNOFF FOR WINTER
OPERATION FROM NOVEMBER 1971 THROUGH APRIL 1972
7
Parameter
Total Solids
Total Volatile Solids
Total Suspended Solids
Total Volatile Suspended Solids
Total Dissolved Solids
Biochemical Oxygen Demand
Chemical Oxygen Demand
Total Organic Carbon
Total Nitrogen
Kjeldahl Nitrogen
Ammonia Nitrogen
Nitrate Nitrogen
Total Phosphorus
Mean
.4 cm/wk
plot
702
174
12
7
690
12
53
22
5.4
2.4
0.5
2.8
4.4
concentration ,
8.6 cm/wk
plot
722
174
8
5
714
11
48
14
7.2
3.6
2.0
3.4
5.4
mg/1
9.8 cm/wk
plot
727
169
9
5
718
8
46
15
6.8
2.9
1.3
3.7
5.1
18
-------
20
16
12
8
f 4
LL.
U.
O
Z
3
IT
7.4 cm/week
9.8 cm/week
-^
.6 cm/week
TOTAL SUSPENDED SOLIDS
DEC.
JAN.
FEB.
MAR.
APR.
z
o
QL
15
u
a
§ '2
a
7.4 cm/week
9.8 cm/week
BIOCHEMICAL OXYGEN DEMAND
DEC.
JAN.
FEB.
MAR.
APR.
FIGURE 4.
REMOVAL OF SUSPENDED SOLIDS AND
BIOCHEMICAL OXYGEN DEMAND IN WINTER
19
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Total nitrogen removal ranged from 70 percent for the 8 .6 cm/week load-
ing to 77 percent for the 7.4 cm/week loading. This level of nitrogen
removal was being achieved while vegetation was dormant and at nitro-
gen loadings of 15 to 20 kg/ha/week (equivalent to 774 to 1,020 kg/ha/
year) . Crop uptake could not contribute significantly to the observed
loss of more than 10 kg/ha/week of nitrogen from the wastewater on the
overland flow plots. The 3-point moving average plot in Figure 5, shows
a substantial nitrogen peak in the plot runoff during January and February.
This increase was the result of a comparatively high nitrate concentration
during this period. For three sampling dates from January 13, 1972
through February 10, 1972, the mean nitrate concentration in the plot
runoff was 6.0, 7.4, and 6.4 mg/1, respectively, for the 7.4, 8.6, and
9.8 cm/week plots. These results for the winter season show that there
was a definite seasonal influence on total nitrogen removal. It may be that
this is a true seasonal influence or it may be largely due to the brief
shutdown periods necessitated by freezing weather conditions since Law,
Thomas, and Myers have observed that high nitrate in the effluent occurs
when system operation is resumed following system shutdown.
Total phosphorus removal during winter operation was about 50 percent
with a small range between the three loading rates as shown in Table 3.
The 3-point moving average graphs in Figure 5, show a seasonal
variation similar to that exhibited by the concentration of total nitrogen
but the magnitude of the relative midwinter peak was substantially less
than for nitrogen. This change in the concentration of phosphorus in
the plot runoff amounts to a relatively small mass of phosphorus. The
average phosphorus load to the overland-flow system ranges from 385
kg/ha/year for the 7.4 cm/week plot to 510 kg/ha/year for the 9.8
cm/week plot. This means that the equivalent of about 200 to 250
kg/ha/year is being retained on the overland-flow area and the remain-
ing phosphorus is being discharged in the plot runoff. Phosphorus
removal by plant uptake and harvest is sufficient to have a major
influence on phosphorus behavior under these conditions and it is
20
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18
15
12
U.
U.
O
Z
Z
O
z
UJ
NITROGEN
8.6 cm/week
DEC.
JAN.
FEB.
MAR. APR.
10
o 8
O
PHOSPHORUS
8.6 cm/week
.4 cm/week
•9.8 cm/week
DEC.
JAN.
FEB.
MAR.
APR.
FIGURE 5.
NUTRIENT REMOVAL DURING WINTER
OPERATION
21
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probable that dormancy of vegetative growth accounts for the observed
changes in the concentration of phosphorus in the plot runoff.
There are many factors which could contribute to the observed behavior
of nitrogen and phosphorus during the winter period of vegetative dor-
mancy and freezing weather conditions which necessitated brief shutdown
periods. Probable causes for the observed increases of total nitrogen and
total phosphorus in the plot runoff during winter operation will be covered
in the Discussion section.
SUMMER TREATMENT PERFORMANCE
This data reporting period covers operation from May 1972 through
September 1972 and represents the second summer of system operation.
The data for this period are indicative of data from a reasonably well
matured system and can be expected to be representative of stabilized
operating conditions. The system was operated at the average scheduled
loadings of 7.4, 8.6, and 9.8 cm/week from May 1, 1972 through June 15,
1972 and at 8.5, 9.9, and 11.3 cm/week from June 15, 1972 through
September 30, 1972; therefore, the average loading for this summer
period of reporting was 8.2, 9.5, and 10.8 cm/week. Chemical quality
data for the plot runoff for this summer period are summarized in Table 4.
As was the case for winter operation, differences in the chemical quality
of plot runoff between loading rates were relatively minor. Although the
differences between loading rates were minor, there was a consistent
trend toward a better effluent from the intermediate and highest loading
rate than from the lowest rate except for the removal of total phosphorus.
As was the case for winter operation, the data collected for this summer
period of operation do not identify a single rate as being superior, but
it does support the hypothesis that the optimum loading of raw commi-
nuted wastewater to an overland-flow system has a relatively broad peak.
For this period of operation, there is also a trend for treatment efficiency
at the highest loading rate to be somewhat better than the treatment
efficiency at the lowest loading rates.
22
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Table 4. CHEMICAL QUALITY OF PLOT RUNOFF FOR SUMMER
OPERATION FROM MAY 1972 THROUGH SEPTEMBER 1972
V
Parameter
Total Solids
Total Volatile Solids
Total Suspended Solids
Total Volatile Suspended Solids
Total Dissolved Solids
Biochemical Oxygen Demand
Chemical Oxygen Demand
Total Organic Carbon
Total Nitrogen
Kjeldahl Nitrogen
Ammonia Nitrogen
Nitrate Nitrogen
Total Phosphorus
Mean
.4 cm/wk
plot
814
142
8
5
806
11
73
23
2.6
1.8
1.0
0.4
4.0
concentration ,
8 . 6 cm/wk
plot
848
143
6
4
842
7
59
18
2.2
1.7
0.7
0.5
4.3
mg/1
9.8 cm/wk
plot
817
140
8
4
809
8
58
19
2.2
1.7
0.6
0.4
4.3
The quality of runoff for all three loading rates continued to be indicative
of the high degree of advanced waste treatment observed during winter
operation, although there were substantial shifts in the percentage
removal for several of the measured parameters. Removal of total sus-
pended solids showed a slight but consistent improvement over the
results for winter operation. Volatile solids and volatile suspended
solids exhibited similar percent removals, while total solids and dis-
solved solids showed expected increases in response to greater evapora-
tive losses during the summer season. Biochemical oxygen demand
showed a slight improvement while chemical oxygen demand and total
organic carbon showed small but consistent increases in comparison to
winter values reported in Table 3. Percentage removal for total sus-
pended solids and biochemical oxygen demand equalled or exceeded 95
percent and the concentration of these constituents in the plot was con-
sistently less than 10 mg/1.
23
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The behavior of the nutrients nitrogen and phosphorus exhibited more
noticeable changes in relation to winter performance of the overland-flow
system. The concentration of total nitrogen in the plot runoff which had
started to decline rapidly with the onset of vegetative growth in the
spring continued its decline until it reached values of less than 2.5 mg/1
and remained at these levels throughout the summer, as shown by the
data in Table 4. Plant uptake and harvesting can easily account for the
mass of nitrogen involved in the difference between the winter removals
of 70 to 77 percent and the summer removals of 89 to 93 percent. It is
probable that plant uptake is a major contributor to this difference
between summer and winter.performance, although many other factors
could contribute to the observed difference in nitrogen removal. Removal
of nitrogen will be covered more extensively in the Discussion section.
Removal of total phosphorus also improved somewhat with the onset of
spring and rapid vegetative growth, as is illustrated by comparing the
data in Table 4 to that in Table 3. Summer concentrations of phosphorus
in the plot runoff ranged from 4.0 to 4.3 mg/1, in comparison to 4.4 to 5.4
mg/1 for winter concentrations. The improved phosphorus removal during
the summer is not sufficient to have a major influence on the overall
removal of phosphorus . The differences between summer removals and
winter removals are well within the influence expected from crop uptake
and removal by harvesting, and removal by crop harvesting is the most
logical cause for the observed difference between winter and summer
performance. Phosphorus removal and probable explanations of the
seasonal differences will be covered in more detail in the Discussion
section.
24
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SECTION VII
DISCUSSION
The overland-flow process has been utilized as a practical tool for treat-
ment of organic wastewaters at a number of locations but little has been
reported to identify or elaborate the mechanisms involved in the actual
treatment process. The removal of suspended solids and biochemical
oxygen demanding substances are readily explained as the result of
biooxidation by the microbial population of the soil. There is a wealth
of published information to support this explanation and there is little
doubt that the explanation is valid. Explanations for the observed
removals of the nutrients nitrogen and phosphorus cannot be explained
so readily on the basis of existing information. Since the removal of
nitrogen and phosphorus from wastewaters is becoming increasingly
important for preventing the accelerated eutrophication of receiving
waters, the removal of these two wastewater constituents by the overland-
flow process will be discussed in detail.
As indicated in the Introduction, Kirby and Law, Thomas, and Myers
have reported that overland flow achieves substantial removal of total
nitrogen. The results of this pilot study corroborate the results of
the previous research efforts. As was the case in the study by Law,
3
Thomas, and Myers , the nitrogen loading to the overland-flow system
evaluated in this report greatly exceeds the nitrogen which can be
accounted for by crop removal, retention in the soil, or loss in the runoff
and it is apparent that nitrogen removal involves one or more additional
mechanisms. The apparent loss of substantial masses of nitrogen to the
25
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atmosphere observed under these closely-controlled experimental condi-
tions and work being conducted by Hoeppel, Hunt, and Delaney support
the theory that the micro environmental conditions established in a well
operated overland-flow system promote the conversion of reduced
nitrogen forms to gaseous nitrogen through the mechanism of microbial
nitrifi.cation-denitrificati.on. It is our theory that nitrification takes place
near the air water interface where the rate of oxygen transfer from the
air into the liquid phase and oxygen diffusion through the liquid phase
can meet the biochemical oxygen demand exerted by the constituents in
the wastewater. Denitrification takes place deeper in the water phase
where diffusion of oxygen fails to meet the biochemical oxygen demand
of the wastewater constituents and the oxygen status of the liquid phase
becomes favorable for denitrification. In essence, the theory stipulates
that the loading of oxygen demanding constituents regulates the oxygen
status to prevent anaerobic metabolism from becoming dominant, yet
supports active denitrification. This theory offers a ready explanation
of the substantial amount of nitrogen removal achieved by the overland-
flow process which cannot be explained by crop removal or retention in
the soil. The theory is also in keeping with the vast amount of published
information on the environmental factors influencing the nitrification-
denitrification process. Acceptance of this theory leads one to project
the following general pattern for determining optimum nitrogen removal
in relation to biochemical oxygen demand loading for the overland-flow
process. (1) Nitrogen removal is a continuing process and should
neither increase nor decrease substantially with age; (2) an underloaded
system, from the standpoint of biochemical oxygen demand, will have a
lower nitrogen removal capability and will produce an effluent contain-
ing high nitrate; and (3) an overloaded system, from the standpoint of
biochemical oxygen demand, will also have a lower nitrogen removal
capability but the effluent will contain reduced nitrogen forms rather
than nitrate. This projected behavior of nitrogen can be used as a guide
to balance the biochemical oxygen demand loading during preliminary
tests for design purposes.
26
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Phosphorus removal by the overland-flow process is relatively low in
comparison to removal of suspended solids, biochemical oxygen demand,
and nitrogen. This would be expected since the behavior of phosphorus
in the plant-soil environment is substantially different from the behavior
of any of these other constituents. Behavior of phosphorus in the plant-
soil environment has been studied extensively and it is well established
that the fraction of phosphorus involved in microbial processes and the
fraction of phosphorus removed by crop uptake is relatively small in
comparison to the fraction of phosphorus involved in chemical interactions
within the soil matrix. The fact that it is well established and documented
that most fine textured soils have the capacity to retain large quantities of
phosphorus as insoluble compounds has little utility for designers of
overland-flow systems. Other constraints on the design and operation
of an overland-flow system dictate that close contact between the liquid
phase and the soil be restricted severely. It is highly improbable that
one could design and operate overland-flow systems which would achieve
consistently high phosphorus removals while maintaining comparable
removals of biochemical oxygen demand and total nitrogen without
special consideration for phosphorus removal. For those who need to
achieve a high level of both nitrogen and phosphorus removal, a proba-
ble solution is available through the chemical precipitation of phosphorus
by addition of suitable cation species. The theory for this approach is
readily available in the waste treatment process literature and an
overland-flow system operated to achieve nitrogen removal should be
amenable to phosphorus removal by chemical precipitation. Further study
is in progress to explore the practicality of improving phosphorus removal
by chemical precipitation.
Another alternative for achieving efficient phosphorus removal would be
the utilization of soil infiltration following overland flow. This alternative
provides the needed soil contact for phosphorus retention and would also
provide additional polishing for removal of suspended solids, oxygen
27
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demanding substances, and fecal organisms. Studies to be initiated at
the Robert S. Kerr Environmental Research Laboratory in 1974 will
evaluate the overall treatment efficiency of overland flow and soil
infiltration in series.
28
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SECTION VIII
SUMMARY
Data have been reported for an 18-month operational period of an overland-
flow system designed to treat raw comminuted wastewater. Fifteen chemical
parameters were measured to evaluate the treatment efficiency of this waste-
water treatment system. The results of this 18-month pilot study show that
the overland-flow process is capable of achieving advanced waste treat-
ment of raw comminuted wastewater when designed as a single pass
treatment process with no production of sludge. Pretreatment needs are
brief sedimentation for grit removal and skimming to remove floatables
which may lodge in nozzle orifices after comminution.
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. The summer
values for phosphorus will be slightly less than winter values, but
seasonal differences in phosphorus removal will be minor.
It is noteworthy that the effluent from this pilot evaluation of the overland-
flow process is substantially better than established criteria for secondary
treatment. Satisfactory development and demonstration of several operating
29
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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 communities.
30
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SECTION IX
REFERENCES
Luley, H. G. Spray Irrigation of Vegetable and Fruit Processing
Wastes. J. Water Pollut. Contr. Fed. 35: 1252-1261, October
1963.
Kirby, C. F. Sewage Treatment Farms—Post Graduate Course
in Public Health Engineering, Session No. 12. Department of
Civil Engineering, University of Melbourne, Melbourne,
Australia. 1971. 14 p.
Law, J. P., R. E. Thomas, and L. H. Myers. Cannery Waste-
water Treatment by High-Rate Spray on Grassland. J. Water
Pollut. Contr. Fed. 42:1621-1631, September 1970.
U.S. Committee on Water Resources Research. A 10-year program
of Federal Water Resources Research. Government Printing Office,
Washington, D. C . February 1966. 88 pp.
Methods for Chemical Analysis of Water and Wastes. Environ-
mental Protection Agency, Cincinnati, Ohio. Publication
No. 16020 07/71. July 1971. 312 p.
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.
31
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-660/2-74-087
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
FEASIBILITY OF OVERLAND FLOW FOR TREATMENT
OF RAW DOMESTIC WASTEWATER
5. REPORT DATE
July 1974
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
R. E. Thomas, K. Jackson, andL. Penrod
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Robert S. Kerr Environmental Research Laboratory
Post Office Box 1198
Ada, Oklahoma 74820
10. PROGRAM ELEMENT NO.
1BB045
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
National Environmental Research Center
Office of Research and Development
Corvallis, Oregon 97330
13. TYPE OF REPORT AND PERIOD COVERED
Final 3/71 through 6/73
14. SPONSORING AGENCY CODE
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 parameters including
suspended solids, biochemical oxygen demand, nitrogen, and phosphorus 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
02/03 Pri.
14/02 Sec.
13. DISTRIBUTION STATEMENT
Release unlimited.
19. SECURITY CLASS (ThisReport)
21. NO. OF PAGES
31
20. SECURITY CLASS (Thispage)
22. PRICE
EPA Form 2220-1 (9-73)
U.S. GOVERNMENT PRINTING OFFICE: 1975-697-805/72 REGION 10
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