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'<--Economics Report 86
May 1977
A Study
of Optimum
and
Number, Sizes,
Locations of Wastewater
Facilities in Alachua Cou
Treatment
nty,
Florida
Food and Resource Economics Department
Florida Agricultural Experiment Stations
Florida Cooperative Extension Service
Center for Rural Development
Institute of Food and Agricultural Sciences
University of Florida, Gainesville 32611
Jonq-Ying Lee
I II It --
ABSTRACT
Economies of scale provide the main incentive for regionalization of
wastewater treatment facilities. The cost of collecting wastewater in-
creases with the size of plant and serves to offset within plant scale
economies. Two types of secondary treatment and three tertiary treatment
processes were considered as feasible alternatives. They were high-rate
trickling filter system, activated sludge system, and two clarifier lime
clarification processes, lime recalcination, and ammonia stripping process,
respectively.
The.space and time dimensions of regionalization were considered. In
order to find the potential sites of regional treatment plants, a cost
minimization model was used. For the consolidation over time an exponential
objective function was minimized subject to discrete capacity requirements.
A least cost staging policy to satisfy the wastewater treatment re-
quirements of the nine cities in Alachua County, Florida for the years
1975, 1980, and 1990 was determined with the model. The results were sen-
sitive to the required quality of secondary effluents.
The possibility of substituting land spreading for tertiary treatment
is discussed, and the factors which should be considered in land treatment
are analyzed with the aid of an optimization model. The break-even dis-
tances of transmission pipelines for land treatment as a substitute for
tertiary treatment are calculated and presented.
Key words: Alachua County regionalization, wastewater treatment
facilities, land treatment, least cost staging policy.
ACKNOWLEDGEMENT
I greatly appreciate the academic and technical guidance as
well as criticism of Max R. Langham, which makes the preparation
of this publication both exciting and enjoyable. More than this,
he has provided a warm friendship in trying times. Bobby Eddleman,
Frederick Goodard, and Lloyd B. Baldwin critically reviewed the
manuscript. Special thanks also go to LeAnne Van Elburg and
Janet Eldred for their help in typing the preliminary drafts and
Molly Arnette for her typing the final draft.
Leo Polopolus, the faculty, and my fellow graduate students
of the Department of Food and Resource Economics have contributed
greatly to making this study period significant. My friends on
this campus have done likewise. To all I am grateful.
This study could not have been accomplished without the
financial support of the Center for Community and Rural Development
and the Florida Agricultural Experiment Stations. All computer work
was done at the facilities of Northeast Regional Data Center.
TABLE OF CONTENTS
ACKNOWLEDGEMENT . . .
LIST OF TABLES . . .
LIST OF FIGURES. . .
INTRODUCTION . . .
METHOD OF STUDY . . .
AREA OF STUDY AND SOURCE OF DATA
COST FUNCTIONS . . .
. . . . .
. e .... .. ...
e.o ee 0.
oeeeeoeeeeooeeee
Transmission Costs . . .
Secondary Treatment Costs . ... .
Tertiary Treatment Costs . . .
Assumptions About Cost Increases ..
POTENTIAL SITES FOR WASTEWATER TREATMENT PLANTS
CAPACITY EXPANSION SCHEME . . .
FUTURE SERVICE VALUE OF TREATMENT FACILITIES
RESULTS . . . . .
* .
LANDSPREADING SECONDARY EFFLUENT AS A SUBSTITUTE FOR TERTIARY
TREATMENT PROCESSES . . . . .
Landspreading . . . . . .
Irrigation and Crop Production . . .. .
Landspreading as a Substitute for Tertiary Treatment .
CONCLUSION . . . .. . . ..
REFERENCES . . . . . . .
i
i
* iii
. iii
. 1
. 2
. 6
. 7
. 7
. 9
. 9
. 10
. 11
. 13
. 14
. . . . .
* .
LIST OF TABLES
Table Page
1 Coordinates of municipalities in Alachua County in miles . 12
2 Reference numbers for time options in Alachua County,
Florida, 1975 to 1990 . . . . ... . 15
3 Present value of secondary treatment costs for the minimum
cost option for Alachua County, Florida, 1975 to 1990 . 20
4 Present value of secondary and tertiary treatment costs for
the minimum cost option for Alachua County, Florida, 1975
to 1990 . . . . . . 21
5 Present value of wastewater treatment costs for time option
5 for Alachua County, Florida, 1975 to 1990 . ... 23
6 Estimated returns and fertilizer costs per acre of selected
irrigated crops on the deep sands of North and West Florida 27
7 Nutrient composition of secondary effluent at southwest
treatment plant in Tallahassee, Florida . . 28
8 Estimated total expenses per acre of selected irrigated
crops on the deep sands of North and West Florida . 29
9 Estimated costs of land preparation and irrigation system 30
10 Present value of cost of transmission pipeline per mile,
pumping station, and irrigation systems for Alachua County,
Florida, 1975 to 1990 . . . . ... .. 33
11 Break-even length of transmission pipeline for land treat-
ment in Alachua County, Florida, 1975 to 1990 ....... 34
LIST OF FIGURES
Figure Page
1 Relative location of potential regional treatment sites for
activated sludge system and the distances from the cities
involved to these sites . . . ... ... 18
2 Relative location of potential regional treatment site for
trickling filter system and the distances from the cities
involved to this site . ... 19
A STUDY OF THE OPTIMUM NUMBER, SIZES, AND LOCATIONS
OF WASTEWATER TREATMENT FACILITIES IN
ALACHUA COUNTY, FLORIDA
Jonq-Ying Lee
INTRODUCTION
The environmental thrust of the 1970's has resulted in regu-
lations to clean up wastewater from a number of.sources including
industry, municipalities, and nuclear power generating stations.
Communities throughout the country faced with meeting the 1985
goal of zero discharge of pollutants into streams encounter both
economic and environmental constraints (Public Law 92-500, 1972).
The high cost of providing primary, secondary, and especially
teritary treatment by conventional methods places an economic
burden on communities, especially on the smaller ones typically
found in rural areas.
In the planning and design of a wastewater treatment facility
for a city, town, or an area where the requirements for treat-
ment are expected to increase with time, the initial size of the
treatment plant and the timing of capacity additions and/or
replacements over some time horizon heed to be answered in the
context of an optimal staging policy. Such a policy is affected
by the wastewater treatment requirements, the rates of interest
and inflation, construction cost, operating costs, maintenance
and repair, service life, and the staging efficiency of the system
to be designed.
JONQ-YING LEE is a research economist with'the Florida
Department of Citrus and assistant professor with the Department
of Food and Resource Economics, University of Florida.
Recently, the concept of regionalization of wastewater treat-
ment has been suggested as an effective means of meeting the water
quality goals at a minimum cost. Although economy of scale provides
the primary incentive for regionalization, a host of other advantages
such as more qualified operating personnel, and higher degrees of
automation may be gained through the utilization of this concept.
The recent literature of city planning and regional science
contains few analytical studies concerned with facility planning
for public urban systems. The management of these systems needs
a coherent framework for planning which deals with facility size,
location, and timing.
This study develops a decision model to use as a guide.in
planning facilities for a specific wastewater treatment system.
An optimization technique will be utilized in selecting the optimum
program. The final plan will include the number of treatment
plants needed, treatment plant capacities, waste sources to be
served by each plant, disposal methods, and plant locations. A
feasibility analysis will be conducted with regard to substituting
tertiary treatment processed by landspreading of secondary ef-
fluent.
: METHOD OF STUDY
The primary factors which will be considered in selecting a
regional plan in this study include:
a) waste sources to be served;
b) number and capacitites of treatment plants needed;
c) treatment plant locations;
d) desired degrees of treatment;
e) collection system; and
f) cost functions.
Arrangement of outfall structure, cost allocation among par-
ticipants, methods of financing, and methods of implementation
will not be considered in this study. The influence of factors
(a) (f) on the selection of an optimal regional wastewater man-
agement system is described more fully below.
A general model was developed to supply answers regarding the
locations of treatment facility, capacities, and the number of
treatment plants. The model was developed to minimize the present
value of wastewater treatment costs for the cities of interest,
and subject to the following constraints:
1. Waste at each source must be satisfied for the time period
of interest;
2. The amount of waste flow into a location must be less than
or equal to treatment capacity at this location for the
time period of interest;
3. The amount of waste flow from a source to another location
must be less than or equal to its required transmission
capacity for the time period of interest;
4. The difference between required capacity and existing
capacity for transmission must be less than or equal to
the new capacity to be added for the waste flow from a
source to another location over the time period of interest;
and
5. The difference between required capacity and existing
capacity for treatment must be less than or equal to the
new capacity to be added for certain type of facility at
a location for the time period of interest.
This model involves three dimensions--space, time, and types
of facility. The first dimension to be considered in this study is
included because the existence of scale economies may permit rela-
tively large treatment plants to process their wastewater at lower
average cost per unit. Thus the cost for treating wastes from
several sources at a regional plant may be lower than the total
cost if wastes were treated at each source. There is a tradeoff
between the gains from scale economies and the losses incurred by
constructing transmission pipelines.
The second dimension to be considered in this study is the
consolidation of treatment.plants over time. Since the demand for
wastewater treatment increases with time and the inflation rate
may exceed the interest rate there may be a net gain by building
a treatment plant larger than necessary. This is the tradeoff
between the gains in economies of scale, savings in inflation,
and the losses in interest and in operating and maintaining
capacity.
The third dimension to be considered is the effect of dif-
ferent types of treatment facilities. In this study, we consider
only two types of secondary treatment plant, three tertiary
processes.
In order to find the optimal plan one needs information
about the amount of waste generated at each source, the cost
functions of treating and transporting the waste, and the locations
for regional wastewater treatment plants.
In this study, cost functions associated with the wastewater
treatment facilities will be divided into two categories--cost
functions of collection systems and cost functions of treatment
plant facilities (primary, secondary, and advances). Futhermore,
each cost function category will be subdivided into two sub-
categories i.e., construction cost functions and operation and
maintenance cost functions.
Since an optimal staging policy is also affected by the rate
of interest and inflation, one dollar spent today will not be
considered equivalent to one dollar spent at some future date.
The decision problem at hand is a multipoint-input, multipoint-
output allocative problem [Henderson and Quandt, 1958, p. 244]
with the demand given for output treatment capacity at each point
of time.
To project a year-by-year operating cost for each segment of
the proposed system, a percent value of future expenditures scheme
was used in the optimization decision. A basic operating cost for
the present year was set for each treatment plant and transmission
line. The value was then inflated at a parametric rate to re-
flect increased labor and maintenance expenditures in the future.
The present value of the resulting series of expenditures was
then added to the initial cost of each system component to
obtain a present value of costs over the planning horizon.
Let it be the market rate of interest and yt be the inflation
rate connecting marketing date t-1 and t. Then the present value
of one dollar payable at the end of tth marketing period is:
t. -1
[ n (1 + y ) (1 + i ) ] = V t = 1, .T (1)
T=O T t
T=0
For example, the total present value of costs (CCjkt) for a type
k treatment facility at location j at the end of time t is:
CCjkt (FCjk + FMkt) V (2)
where FCkt and FMkt are the construction cost and operation and
maintenance costs for type k facility at location j at time t,
respectively. This same rule will be used to calculate the present
value of a transmission system.
In order to solve this general model, we need information about
the potential sites for individual and/or regional treatment plants.
Theoretically, a regional treatment plant can serve more than two
cities, therefore, for a nine-city problem, such as this study, we
9 9 9
end up with E ( ) = 763 potential sites, where ( ) represents
i=l
the number of combinations of choosing i cities out of nine cities.
The potential location for a plant need not be situated in a
site of demand or supply. The question is how are location decisions
made?
Alfred Weber pioneered the Location Theory [Weber, 1909]. He
considered the location of an industry between two resources and
a single market where the criterion was minimization of transpor-
tation cost.
Cooper [1963] and Kuhn and Kuenne [1962] described an iterative
process for solving the generalized Weber problem. The problem
is to find the single point which minimizes the sum of the weighted
Euclidean distances to that point. The objective is
n
minimize z = E w. d.
i=l
where:
.th
wi = the weight attached to the i point (goods demanded,
resources sent, population, etc.);
th
x.,y = the location of the i point relative to some fixed
cartesian coordinate system;
x,y = the unknown coordinates of the central point;
d. = ((x x)2 + (Yi y)2) which is the Euclidean
distance from point i to central point;
n = the number of points are served.
Partial differentiation with respect to x and y yields a
pair of equations that are the first order conditions for minimum:
z= wi(xi -x) = 0 (3)
dx 1
z i i y) o (4)
ay 1 d
And these two equations were used to find potential sites for
regional treatment plants.
Equations (3) and (4) are used to solve the problem of consoli-
dation of treatment plants over space. The consolidation of treat-
ment plants over time is incorporated with the consolidation over
space, and solved simultaneously. Finally, a feasibility analysis
of substituting land treatment for tertiary treatment is conducted.
AREA OF STUDY AND SOURCE OF DATA
Alachua County, Florida was chosen as the study area. The county
has a total land area of 568,320 acres or 888 square miles. These
figures do not include the large bodies of water representing about 76.4
additional square miles [North Central Florida Regional Planning Council,
1973]. There are nine incorporated cities or population centers in Alachua
County. Only one of these nine incorporated communities has adequate waste-
water collection, treatment and disposal. The remaining eight incorporated
municipalities have either privies or septic tanks with the large flow users
such as hotels, restaurants, and service stations, primarily located along
major thoroughfares, being served by small package plants.
Population estimates for this study were obtained from the estimates pro-
vided by North Central Florida Regional Planning Council [1973]. The amount
of wastewater produced was estimated by multiplying population estimates by
135 gallons per capital per day.1 The relationships between capacity and
costs (both construction and operation and maintenance) were obtained from
EPA studies [Michel and Johnson, 1970; Smith and McMichael, 1969; Smith and
Eilers, 1971]. The information about cost increases over time were provided
by EPA cost indexes. Other knowledge required to complete this study was
obtained from journals, textbooks, and miscellaneous publications on waste-
water treatment.
This study determined the optimum number, sizes, and locations of waste-
water treatment facilities in Alachua County. The time period involved was
from 1975 to 1990. Wastewater sources were limited to the nine incorporated
cities in the county. The hypothesis tested in this study is that some com-
bination of cities finds it economically attractive to transfer their waste
to a regional treatment facility in some selected location.
COST FUNCTIONS
Transmission Costs
The cost functions for transmission are as follows:
1. The relationship between flow and the diameter of sewers, which
minimizes the sum of the cost of frictional power and the debt service
for the pipe, estimated in Smith and Eilers [1971] as:
1Average daily flow found for 73 cities in 27 states in the United States
[Loehr, 1968].
Economic diameter (inches) = 8.55Q463 (5)
where Q = designed flow in mgd.
2. The cost associated with sewers which includes the amortization cost
and a small maintenance cost in terms of October, 1970 dollars was
estimated [Smith and Eilers, 1971] as follows:
Construction costs in dollars per mile = 1540.7(ID + 2.0436)1.37949 (6)
where ID = inside pipe diameter in inches. The cost of maintaining
the sewer was taken as $40/yr/mile.
3. The construction cost for pumping stations has been estimated [Smith
and Eilers, 1971] as:
Construction cost(dollars) = 76,300Q7682 (7)
where Q = average flow in mgd. and the operation and maintenance cost
for pumping stations has been estimated [Smith and Eilers, 1971] as:
cents/1000 gal. = 1.59Q-263 (8)
where electrical power was assumed to cost one cent per kw-hr, the hydraulic
efficiency of the pump was taken as 60%and the electrical efficiency of the
driving motor was taken as 80%. All costs are keyed to October, 1970.
The Ten State Standards [Great Lakes Upper Mississippi River Board of
State Sanitary Engineers, 1971] requires interceptor sewers to be sized to
carry 3.5 times the design flow for the plant. This factor is used in the
study for sizing both the pipelines and the pumping stations. Since the flow
of sanitary sewage reaching the treatment plant varies over time, and the
capacity of the sewage facility is fixed over the short run, excess capacity
(capacity above the average daily flow) is necessary to collect and treat the
sewage.
It is assumed that force main was used as the connecting pipelines be-
tween contributing cities and receiving regional plant, and raw sewage
pumping station has been sized to handle the sum of all the contributing flows.
2Smith and Eilers [1971] indicated that the cost of constructing force
is not significantly different from the cost of constructing gravity sewers;
hence, equation (6) may be used to find the construction cost for force mains.
However, by a conversation with Mr. Baldwin (Agricultural Engineer), this
approach may overestimate the cost of force main.
Secondary Treatment Costs
EPA [1973] has estimated cost equations with regression analysis using
data on accepted bids for construction of new municipal wastewater treatment
plants in several states between 1967 and 1969 as a function of design flow.
Costs were updated to September 1972 dollars by using the EPA Sewage Treatment
Plant Construction Cost Index. Their estimates were as follows:
1. For high-rate trickling filter system:
AC = 852049.58Q37461 (9)
2. For activated sludge system:
AC = 699835.09Q-3544 (10)
where:
AC = average construction cost, and
Q = amount of design flow in mgd.
And estimates of operation and maintenance cost collected from reports
on 600 plants between 1968 and 1970 in January 1968 dollars have the
following relationships [Michel and Johnson, 1970]:
1. For high-rate trickling filter system:
TC = 31959.50Q-6496 (11)
2. For activated sludge system:
TC = 46989.41Q'6023 (12)
where:
TC = total annual operation and maintenance cost, and
Q = amount of design flow in mgd.
Tertiary Treatment Costs
The estimated cost equations for three tertiary treatment processes
to be used in this study from the data provided by Smith and McMicheal,
primary treatment costs are included in the secondary treatment cost
figures.
[1969] are presented below:
1. Two clarifier lime clarification process without chemicals:
construction cost (million dollars) = 0.128371Q776102 (13)
0 & M cost (dollars/day) = 62.8518Q692928 (14)
2. Lime recalcination plus make up lime for use with lime
clarification:
construction cost (million dollars) = 0.196977Q*508007 (15)
0 & M cost (dollars/day) = 49.3768Q*728564 (16)
3. Ammonia stripping of lime clarified wastewater:
construction cost (million dollars) = 0.490535Q1]30744 (17)
0 & M cost (dollars/day) = 40.9442Q778987 (18)
where Q represents design capacity measured by millions of gallons per
day (mgd).
Assumptions About Cost Increases
In order to determine the rates of cost increases over time to be
used in the calculation of present values, regression analysis was used.
In this analysis, we assume the cost index to be a function of time, i.e.,
Cost indext = a + bt + ut, t = 1966, 1973
where a and b a parameters to be estimated, and ut is the disturbance
term at the time t.
Three different kinds of cost indices were used in this analysis,
they are: Sewer construction cost index (SW), sewage treatment plant
construction index (ST), and consumer price index for residential water
and sewage serivces (SR).5 All the September cost index figures from
There are some evidences that a coagulant aid such as iron might be
required in the second clarifier, since the need for this chemical is not
clearly established, it was not included in the cost.
5These three cost indices were provided by Advanced Waste Treatment
Research Laboratory, Cincinnati, Ohio.
1966 to 1973 were used for the estimation of parameters a and b, and the
results are as follows:
SW = -23567.0 + 12.0444t 2
t (1990.00)- (1.0104) R = 9595 (19)
ST = -20378.8 + 10.4313t 2
St (1585.40) (0.8050) R .9654 (20)
SR = -14604.9 + 7.4762t 2
S (973.204) (0.4941) = (
where the "hats" on top of SWt, STt, and SRt represent estimated values, the
figures in the parentheses are estimated standard errors or the parameters,
and R 's are multiple determination coefficients.
Parameter b represents the effect of a one unit change in t on the cor-
responding cost index, hence it can be explained as the annual rate of
increase in cost and can be used in equation (7) and (8). b in (20) was
used in the calculation of sewage treatment plant construction costs, and b
in (21) was used in the calculation of 0 &M. costs for both sewer and sewage
treatment plant. Service lives for pumping stations and wastewater treat-
ment plants was assumed to be 25 years, and for transmission pipelines 50
years. The interest rate was assumed to be 5 percent.
POTENTIAL SITES FOR WASTEWATER TREATMENT PLANTS
In order to reduce the possible number of potential sites, a computer
program written in FORTRAN IV was developed [Lee, pp. 122-134]. This com-
puter program calculates:
1. The coordinates in miles from the orgin (29030' parallel of latitude
north and 82037'30" meridian of longitude west) for each of the
cities of this study (Table 1).
2. Construction costs and operation and maintenance costs for waste-
water treatment plants, transmission pipelines, and pumping stations
for each city using equations (5) through (18), and,
Table 1.--Coordinates of municipalities in Alachua County in miles
City
Number
High Springs
Newberry
Archer
Alachua
Gainesville
urban area
La Crosse
Micanopy
Waldo
Hawthorne
Coordinate
East (x)
1.6190
0.8572
6.1428
7.9524
18,0476
13.1904
20,9524
27.6190
32.5714
aThese coordinates are calculated from
West and 29030' latitude North in miles,
the origin 8037'30" longitude
These numbers will be used later to present the corresponding cities.
North (y)
22.4526
10.0476
2.0952
20.2380
10.4762
23.6666
0.3810
20.0476
6.6190
r
3. The transmission cost from each source to the potential sites were
obtained using equations (3) and (4).6 Finally, the program compares
the sum of pumping stations costs, transmission costs, and regional
wastewater treatment costs for each site with the wastewater treat-
ment costs for a completely disaggregated system (i.e., one in
which each of the nine cities build their own facilities). If the
regional cost is less than or equal to the sum of individual costs,
the program prints out the related cost figures. An iterative
procedures suggested by Kuhn and Kuenne [1962] and by Cooper [1963]
was used to solve these two equations for x and y.
There.are 763 potential sites for each time option, five time options,
two kinds of secondary treatment, and one package of three tertiary treat-
ment processes. The program is instructed to choose one secondary treat-
ment with and without tertiary treatment processes, one time option, and
one potential site at a time to calculate cost figures, and give answers
to .the feasibility of regional treatment until all the possible combina-
tions of treatment types, time options, and potential sites are exhausted.
This is a brute-force search for the solution of the optimization model'
mentioned in the last section. A regional treatment plant in this study
is defined as one serving more than one city.
CAPACITY EXPANSION SCHEME
Incremental savings in construction and operation and maintenance
cost due to economies of scale make it desirable to bear the cost of
overcapacity until demand catches up. A major decision variable in public
and private wastewater treatment plant staging policy is the amount of
excess capacity to be built initially into a new system and the staging of
capacity additions and/or replacements (as the old plants become uneco-
nomical to run, being past their useful service life) to meet demands
increasing with time.
In this study, each treatment or transmission or pumping facility has
been assumed to operate at its design capacity. The reasons are: 1) there
6
w. represents transmission pipeline cost per mile from city i as
calculated from equation (6).
is not enough information about short-run cost functions, especially for
advanced treatment process, 2) this study was for planning purpose and
emphasis was placed on the long-run effect, and 3) in most cities the
differences in demands for wastewater treatment over time are not large,
therefore, the differences between long-run cost estimates under design
capacity and short-run cost estimates under capacity in use may not be
substantial.
In this study, interest is in satisfying the demands for wastewater
treatment in 1975, 1980, and 1990. The demand functions for wastewater
treatment over time were considered as step functions rather than as
continuous functions. One of the disadvantages of using step functions
for wastewater treatment demands is that one may underestimate the quantity
of demand toward the end of each time period, but if each time period is
not large, this underestimation will not be serious. The advantage of
using step functions is that it simplifies the staging process.
With the cost functions presented in the last section, one can prove
that it is more expensive to build two smaller treatment plants than a
large one to satisfy the same amount of demand over a specific time period
[Lee, 1975 pp. 67-69]. Hence, the problem is simplified to choosing the
minimum cost plan from the options in Table 2. For instance, option 1
in Table 2 represents the scheme which satisfies 1975 wastewater treatment
demand in 1975, and the difference in demand between 1975 and 1980 is
satisfied in 1980, and the difference in demand between 1980 and 1990
is satisfied in 1990.
FUTURE SERVICE VALUE OF TREATMENT FACILITIES
The service lives for treatment plants and pumping stations are assumed
to be 25 years, and for transmission.pipelines 50 years in this study. The
five options mentioned in the previous paragraph invlove building treatment
plants with different capacities in different years, in order to make a
comparison among the costs of these five options, the cost of unused
services of each option after 1990 should be subtracted from the total cost.
Table 2.-Reference numbers for time options in Alachua County, Florida,
1975 to 1990
Demand for wastewater
treatment
D1975
D1980 D1975
D1990 D1980
D19B0
D1990 1980
D1980
D1990- D1980
D1975
1990 D1975
D1990
Options
To be satisfied
in years)
1975
1980
1990
1975
1990
1975
1980
1975
1980
1975
aDt represents the demand for wastewater treatment in time t.
Costs make up the depreciation base for purchased assets. In setting
up a depreciation schedule a firm must establish a useful life and salvage
value of the asset in question. The most common methods of depreciation
are straight-line, declining-balance, sum of the digits, unit-of-production
of service [Dougall, 1973 p. 474]. Since the probable loss of capital
value is decidedly concentrated in the early part of life, the straight-
line writeoff is not a completely satisfactory method of depreciation for
productive equipment. Any realistic allocation procedure should get rid
of at least one half of the initial value over the first third of the
service life and at least two-thirds over the first half. The straight-
line method is perhaps less objectionable for buildings and structures
than for equipment [Terborgh, 1954 pp. 37-47].
In this study, wastewater treatment facilities are long-term invest-
ments, and a straight line method was used to calculate the depreciation
of facilities. The undepreciated balance of the assets was discounted
back to present value for each of the options mentioned above and sub-
tracted from the present value of costs.
RESULTS
Though simpler and cheaper to operate, the typical trickling filter
plant is being used less and less on domestic sewage in North America since
it does not achieve the percent removal of organic material that an activated
sludge plant does. The least cost method thus depends on the required
quality of the effluent. Typical effluents from trickling filter.plants
treating domestic wastes have BOD's and SS usually greater than 20 mg per
liter. Typical removal efficiencies for both BOD and SS are in the area
of 80%. Activated sludge plant effluents have BOD's and SS between 10
and 20 mg per liter and removal efficiencies in the area of 90%. Hence,
if the required quality of secondary effluent is set at 90% removal, a
trickling plant will not achieve this level of removal, and an activated
sludge plant would be required to provide the least cost method of treating
wastewater.
The results show that if only secondary treatment is required, the
least cost method would involve the cities of High Springs, Alachua,
Archer, and Newberry cooperating to build a regional treatment plant in
1975 to satisfy their 1980 demands. Added demands in 1990 were satisfied
in the solution by the construction of individual plants. For the other
five cities, time option 2 was used to satisfy their demands by.building
individual activated sludge plants for each. If tertiary treatment pro-
cesses are required, two regional activated sludge plants would be built,
one for the cities of:High Springs, Alachua, Archer, and Newberry, and
one for Waldo and Hawthorne in 1975 to satisfy the 1980 demands of the six
cities. Added demands in 1990 were satisfied in the solution by the con-
struction of individual plants. For the other cities--Gainesville Urban
Area, LaCrosse, and Micanopy--time option 2 and individual activated sludge
plants were used to satisfy demands.
If the required quality of secondary effluent is set at 80% removal,
a trickling filter plant will provide the least cost method of treating
wastewater. The solution suggests that each city should build its own
high-rate trickling filter plant according to time option 2. However, if
tertiary treatment processes are required, one would build a regional high-
rate trickling filter plant for the cities of Alachua, Archer, and Newberry
in 1975 to satisfy the 1980 demands of the three cities. Added demands for
these three cities in 1990 were satisfied in the solution by the construc-
tion of individual plants. For the other six cities-High Springs, the
Gainesville Urban Area, LaCrosse, Micanopy, Waldo, and Hawthorne--time
option 2 and high-rate trickling filter plants should be used to satisfy
the demands.
Figures 1 shows the locations of the regional activated sludge treat-
ment plants and the lengths of pipelines from the cities to these two sites.
Figure 2 does the same for the regional trickling filter treatment plant.
Tables 3 and 4 show the details of the minimum cost schemes for secondary
treatment and advanced treatment, respectively. The figures in parentheses
are the corresponding treatment capacities in mgd to be built. The differ-
ence in treatment capacities between secondary treatment and tertiary
treatment in the Gainesville Urban Area is due to the fact that the Gaines-
High Springs
LaCrosse
5.5 miles
Alachua
:ential /3.3 miles
site 7i
16.72 miles
Gainesville
Hawthorne
Archer
Micanopy
Figure l.--Relative location of potential regional treatment sites
distances from the cities involved to these sites
for activated sludge system and the
9.7 mill
Newberry
Waldo
miles
LaCrosse
High Springs
Alachua
tential site
.02, 12.03)
10.2 miles
0
Waldo
Gainesville
0
Hawthorne
Archer
Micanopy
Figure 2.--Relative location of potential regional treatment site for trickling filter system and
the distances from the cities involved to this site
Newberry
Table 3.--Present value of secondary treatment costs for the minimum
cost option for Alachua County, Florida, 1975 to 1990 a
Activated sludge High-rate trickling
City system Filter system.
1975 1990 1975 1990
i
High Springs
Newberry
Archer
Alachua
Gainesville
Urban Area
LaCrosse
Micanopy
Waldo
Hawthorne
R(1, 2, 3, 4)b
Subtotal
39,059a
(.0871)
23,559
(.0385)
21,182
(.0324)
48,008
(.1215)
6,204,332d
(6.5446)
366,428
(.0655)
520,765
(.1161)
533,672
(.1208)
675,850
(.1775)
3,588,569c
(1.2756)
11,889,616
Total
969,928
(.4455)
583,362
(.2011)
438,274
(.1498)
1,016,294
(.4792)
697,737 5,410,354
(9.0876) (6.5446)
13,438
(.0155)
6,441
(.0047)
12,325
(.0135)
16,799
(.0223)
284,666
(.0655)
410,530
(.1161)
421,134
(.1208)
538,577
(.1775)
878,548 10,118,119
12,768,164 ---
33,919
(.0871)
20,183
(.0385)
18,094
(.0324)
41,920
(.1215)
652,094
(9.0876)
11,337
(.0155)
5,324
(.0074)
10,373
(.0135)
14,260
(.0223)
807,504
10,925,623
aAll costs are in September 1974 dollars.
Which represents the regional plant for cities High Springs,
Newberry, Archer and Alachua.
CThis figure includes pumping and transmission costs.
dTop figure represents present value dollar cost; figure in
parentheses represents plant capacity (mgd).
Table 4.--Present value of secondary and tertiary treatment costs for
the minimum cost option for Alachua County, Florida, 1975 to
1990.a
Activated sludge High-rate trickling
City system filter system
1975 1990 1975 1990
High Springs -- 73,790 2,248,431 68,651
(.0871) (.4455) (.0871)
Newberry --- 43,890 --- 39,514
(.0385) (.0385)
Archer -- 38,313 --- 35,225
(.0324) (.0324)
Alachua --- 92,373 --- 86,285
(.1215) (.1215)
Gainesville 31,090,496; 1,535,004 30,296,512 1,489,361
Urban Area (16.0046) (4.5876) (16.0446) (4.5876)
LaCrosse 673,327 23,738 591,564 21,637
(.0655) (.0155) (.0655) (.0155)
Micanopy 986,469 11,089 876,234 9,972
(.1161) (.0047) (.1161) (.0047)
Waldo --- 21,690 900,693 19,739
(.0135) (.1208) (.0135)
Hawthorne --- 29,997 1,176,076 27,458
(.0223) (.1775) (.0223)
R(8, 9)b 2,297,853c
(.2983)
R(2, 3, 4)d -- -- 4,474,878c
(.8301)
R(1, 2, 3, 4)e 6,506,944c --
(1.2756)
Subtotal 41,555,089 1,869,884 40,564,388 1,797,842
Total -- 43,424,973 --- 42,362,230
aAll costs are in September 1974 dollars.
Represents the regional plant for cities Waldo and Hawthorne.
cIncludes pumping and transmission costs.
dRepresents the regional plant for cities Newberry, Archer, and
Alachua.
eRepresents the regional plant for cities High Springs, Newberry,
Archer, and Alachua.
Top figure represents present value dollar cost; figure in
parentheses represents plant capacity (mgd).
ville Urban Area has secondary treatment plants with capacity 9.5 mgd, but
has no tertiary treatment facilities... Therefore, if tertiary treatment is
required, the facilities should be large enough to handle all the waste-
water generated in this area.
The results shown in Table 3 and 4 were calculated under the assump-
tion that one can build a treatment plant as small as one likes. However,
this assumption may not be realistic. If one suspects that the capacity,
for instance, required for Micanopy in 1990 under time option 2 is too
small to be practical, then option 5 would provide second best solutions.
The present value of cost for each city of regional plant for both secon-
dary treatment and secondary treatment with tertiary processed for time
option 5 are presented in Table 5. The conclusions are still the same
as those from time option 2, except the cost figures are different. Again
the figures in parentheses under each set of cost figures are the capacities
to be built.
LANDSPREADING SECONDARY EFFLUENT AS A
SUBSTITUTE FOR TERTIARY TREATMENT PROCESSES
Landspreading
The technology employed in wastewater treatment has not advanced much
in the past several decades. There are several difficulties one encounters
when attempting to remove more than 95% of the BOD and SS with the standard
processes. Greater removal requires very large increases in detention times
and a corresponding increase in tank sizes. A second treatment problem in-
volves the removal of nutrients. Nitrogen and phosphorous compounds are
more likely to be responsible for excess weed growth than BOD. Standard
processes do not do a good job of removing these nutrients. These two
problems can be handled by tertiary treatment processes; however, the cost
for these treatment processes alone is higher than the cost of conventional
treatment porcesses. Land treatment is therefore considered as an alter-
native to tertiary waste treatment.
. 23
Table 5. --- Present value of wastewater treatment costs for time option 5-
for Alachua County, Florida, 1975 to 1990a.
Activated sludge High-rate trickling
City system filter system
tertiary processes tertiary processes
with without with without
High Springs
Newberry
Archer
Alachua
Gainesville
Urban Area
LaCrosse
Micanopy
2,554,474 1,087,224
(.5326) (.5326)
41,808,368f
(20.6322)
775,558
(.0810)
1,013,231
(.1208)
Waldo
10,602,925
(15.6322)
417,534
(.0810)
533,672
(.1208)
569,520
(.1343)'
40,650,256
(20.6322)
684,164
(.0810)
900,693
(.1208)
969,109
(.1343)
726,721 1,277,120
(.1998) (.1998)
Hawthorne
R(8,9) b
R(2,3,4)d
R(1,2,3,4)e
652,435
(.2396)
547,699
(.1822)
1,174,284
(.6007)
9,444,815
(15.6322)
326,139
(.0810)
421,134
(.1208)
450,637
(.1343)
580,857
(.1998)
2,478,977c
(.3341)
5,185,699C
(1.0225)
7,474,954c 4,052,585c
(1.5551) (1.5551)
53,551,088 16,902,957 52,221,515
All costs are in September 1974 dollars.
bRepresents the regional plant for cities
cIncludes pumping and transmission costs.
dRepresents the regional plant'for cities
Waldo and Hawthorne.
Newberry, Archer, and Alachua.
eRepresents the regional plant for cities High Springs, Newberry,
Archer, and Alachua.
fTop figure represents present value dollar cost; figure in
parentheses represents plant capacity (mgd).
Total
14,685,224
Briefly stated, land treatment involves the use of agricultural land
and crops or forest products to absorb and filter nitrates, phosphates, and
other elements from wastewater that has undergone primary and, usually,
secondary treatment. Excess "purified" water is then returned to the water
course. The methods of applying wastewater to the land can be identified
as infiltration systems, crop irrigation systems, and spray-runoff systems
[Thomas, 1973; Thomas and Law, 1968]. Infiltration systems are usually
designed to prevent surface runoff. High loading rates make evaporative
losses relatively insignificant, and up to 99% of the applied wastewater
may be contributed to ground water as recharged [Laverty et al., 1961].
Crop irrigation systems may or may not control surface runoff. Low loading
rates allow much of the applied wastewater to be lost through evapotrans-
piration, and the contribution to ground water is largely dependent on
evapotranspiration losses [Dalton and Murphy, 1973; Graveland and Vickerman,
1972; Parizek et al., 1967; Sprout and Hopkins, 1972; Young et al., 1972].
Spray runoff systems are designed to return 50% or more of the applied
wastewater as direct surface runoff, evapotranspiration losses are variable
but relevant, and the selection of sites with impermeable soils restricts
the contribution to ground water [Law et al., 1970].
The application of wastewater to land serves the following purposes:
promotes growth of crops, conserves water and nutrients that are normally
wasted, provides economical treatment of the wastewater, and reduces the
pollution load on surface water supplies. From research on the effect of
sewage farming on crop yields, it is evident that most crops produce much
higher yields when irrigated with effluent than when not irrigated or when
irrigated with ordinary water but not commercially fertilized [Parizek et
al., 1967; Day and Tucker, 1959].
In this study, we assume that secondary treatment and chlorination are
required for the effluent to be used in land treatment. According to the
results in the previous section, if only the trickling filter system is
required, there is no need to build any regional treatment plant, and each
city can satisfy its demands from 1975 to 1990 by the second option mentioned
in that section. If land treatment is used as a substitute for tertiary
treatment and added to the secondary treatment plants, the feasibility
of regional land treatment operations comes into question.
The answer to this question depends on the economies of scale inland
treatment and whether the gains in economies of scale are large enough to
offset the increased costs of transmitting effluent to regional land treat-
ment sites.
Unfortunately, data do not exist to investigate the economies of scale
in land treatment operations. However, there are studies [Wills, 1956;
Madden, 1967] on farm size which suggest that economies of size in agricul-
tural production are exhausted by family size farm units, and that cost
6
functions are homogeneous of degree one for modest size units. One would
expect a similar situation for land treatment operations.
Irrigation and Crop Production
Although in Florida a number of experiments have been conducted to
show the effect of irrigatingwastewater on pasture and selected crops, very
few have made estimates of the yield response to wastewater and fewer ex-
periments have been conducted to develop new management techniques for a
land treatment system [Alexander, 1972; Hortenstine, 1973; Institute of
Food and Agricultural Sciences, 1973; Overman, 1971; Overman and Smith,
1973]. Such management techniques may include the following: What crop
should be grown, what type of irrigation system is best for the desired
agricultural enterprise, what is the best irrigation frequency for disposing
of wastewater, what is the harvesting requirement for forage crops (grasses)
and how often is removal of the forage required. The use of crops and land
to renovate wastewater and thus eliminate unwanted materials through so called
"living filters" is different from the conventional problems in agricultural
production. In a conventional agricultural production problem one tries to
maximize net returns subject to limited resources or, on the other hand, to
use minimum amounts of resources to produce a certain level of returns. The
emphasis has been placed on agricultural production research. While in
6Which means if one doubles his input costs he would double his output.
land treatment systems, the emphasis is placed on the disposal of wastewater
and agricultural production plays a secondary role. As a result there is a
serious lack of knowledge of management techniques in the areas of negative
marginal productivities of resources.
Based upon the input-output relationships developed by the IFAS Irri-
gation Task Force, Holt [1972] has provided estimates of the production
practice necessary to produce crops under irrigation on formerly unfarmed
deep sand soils in North and West Florida. A center pivot irrigation system
is used to cover a 138-acre area in his study, the initial investment esti-
mate is $200 per acre, and the variable cost estimate is $1.25 per acre per
inch of water applied. Table 6 shows the estimates for six selected
irrigation crops. Column one shows that for six crops, the returns over
specified expenses are all negative except sorghum for silage using the 1971
unit prices given in column two. With higher prices the crops would be
more profitable. Column three shows the cash expenses on fertilizer for
the crops.
Overman and Smith [1973] have studied the nutrient composition of
secondary effluent at the southwest treatment plant in Tallhassee, Florida.
Table 7 shows the nutrient composition of secondary effluent in their study
and the amounts of nutrient content in the effluent if the irrigation rate
is two inches per week for twenty-five weeks. If these nutrients can be
used to eliminate the costs of fertilizer, and if there are no adverse
effects, then it would be profitable for all the six crops mentioned in
Table 6 except soybeans for beans (see column 4). Further, if calcium is
obtained from secondary effluent, all the six crops would be profitable.
However, the possibility of having adverse effects by the application of
excess water and nutrients were not considered by Overman.
Table 8 shows the estimated total expenses per acre of the irrigated
crops mentioned above by Holt [1972]. Table 9 shows the land preparation
and irrigation system costs from three studies. Based on a 640-acre irri-
gation site, Muraro [1972] has estimated the costs for a land-spreading
system. Anderson and Hipp [1973] have estimated the costs of land prepar-
7Based in an irrigation frequency of 5 days, 6 inches annually, and
total initial investment includes deep well, pump, power unit and system,
but no depreciation.
Table 6.--Estimated returns and fertilizer costs per
of North and West Florida
acre of selected irrigated crops on the deep sands
Return over specified Unit price Cash expenses for Net return
Operation Expenses (dollars)a of output fertilizer (dollars)c (dollars)
(1) (2) (3) (4)
Corn for grain -29.89 $ 1.10/bu. 39,20 9.31
Corn for silage -5.12 $ 8.00/ton 41.70 36.58
Sorghums for grain -33.76 $ .90/bu. 34.70 0.94
Sorghums for silage 9.93 $ 7.50/ton 41.70 43.63
Soybeans for beans -11.02 $ 2.20/bu. 8.70 -2.32
Coastal Bermudagrass for hay -7.15 $30.00/ton 52.70 45.55
a Expenses do not include unallocated overhead
farm buildings, tractors and equipment, farm taxes,
costs such as insurance
or pickup expenses.
or depreciation charges on
b
Prices are those experienced in 1971.
C These figures do not include the cash expenses in lime, which is $3.33 per acre at an application
rate of .33 ton per acre. And these figures include the expenses on N, P205, K2P, and FTE 504 except for
soybeans for beans, in which there is no expense on nitrogen.
Source: Holt [1972].
Table 7.--Nutrient composition of secondary effluent at southwest treatment
plant in Tallahasse, Florida
Element lb./acre-ina Irrigation rate (2 in/wk)b
(Ib/acre)
N 8.2 410
P 2.7 135
K 1.4 70
Ca 7.1 355
Mg 2.2 110
Na 8.9 445
Cu less than 0.02
Fe 0.11 5.5
Zn 0.033 1.6
a From composite samples for period April 5, 1972 to September 27,
1972.
b
Based on twenty-five weeks
Source: Overman and Smith [1973].
of irrigation.
Table 8.--Estimated total expenses per acre of selected irrigated
West Florida
crops on the deep sands of North and
Cash expenses Total
Operation Land rent Total
Total(1) Fertilizer(2) Lime(3) (1)-(2)-(3) Expenses
Corn for grain 103.73 39.20 3.33 61.20 17.00 78.20
Corn for silage 128.00 41.70 3.33 82.97 17.00 99.97
Sorghum:for grain 88.23 34.70 3.33 50.20 17.00 67.20
Sorghum for silage 121.23 41.70 3.33 76.20 17.00 93.20
Soybeans for beans 64.44 8.70 3.33 52.41 17.00 69.41
Coastal Bermudagrass for Hay 178.02 52.70 3.33 122.00 17.00 139.00
Source: Holt [1972].
Table 9.--Estimated costs of land preparation and irrigation system
Cost estimates
Item
Muraro Anderson and Hipp Holt
I. Land preparation (per acre)
Pongola pasture $100.70 --
Bermudagrass and clover or
SPongola and clover pasture --- $109.67
straight Bermudagrass or
Pongola pasture --- $101.91
Bahia and clover pasture --- $ 93.26
straight Bahia pasture --- $ 89.52
Argentina-Bahia pasture -- $ 98.26
II. Irrigation system
permanent overheada
construction $596.64/acre ---
0&M $133.48/acre/year
self-propelled volume guna
construction $490.40/acre --
O&M $211.95/acre/year
central pivot
construction -- --- $200.00/acre
O&M -- --- $ 1.25/acre-inch
a
These are estimates calculated from an effluent flow at 5 mgd,
mately 2.05 inches per acre per week.
and application rate at approxi-
ation for selected pastures. And Holt [1972], as mentioned before has
estimates for central pivot irrigation system.
For a 140-acre field, Westberry [1974], has estimated the costs of
owning and operating a central pivot irrigation system, and the cost of
corn production with and without irrigation. According to his estimation,
the cost per bushel of corn is $1.70 with irrigation, and $1.75 without
irrigation with estimated productions of 155 bushels per acre and 60 bushels
per acre, respectively. His results show that a corn grower receives a
higher expected revenue with an irrigation system.
The results from HoltI[1972] and Westberry [1974] show that irrigation
has the potential not only to increase yield but to provide insurance
against the possibility of serious yield reduction due to prolonged dry
periods.
Landspreading as a Substitute for Tertiary Treatment
The most important unknown is whether an agricultural land treatment
system will adequately purify water to meet acceptable standards. If so,
the cost of such treatment is considerably below that for tertiary treat-
ment. If one assumes that on site a land treatment operation can break-even,
one can estimate how far secondary effluent can be pumped to a land treatment
site and still compete with tertiary treatment.
Westberry [1974] has estimated the fixed cost of a center pivot irri-
gation system as $51.07 per acre annually, and a variable cost of $2.06 per
acre inch of water applied. A center pivot system operates in a 160-acre
block and irrigates a circular area of 138 acres. Baldwin [1975] has esti-
mated a fixed cost of $96 per acre annually and a variable cost of $1.65
8
per acre inch of water applied for such a system.
Table 10 shows pipeline and pumping station costs for time options 2
and 5 (Table 2) and the estimated irrigation system cost from Westberry
[1974] and Baldwin [1975].
If these estimates are correct, and if soil and crops could eliminate
nutrients and unwanted materials from secondary effluent effectively, then
the cost for land treatment would be the difference between the site per-
paration, transmission and pumping costs, and the net return from crop
i)ductions, which is considerable less expensive than tertiary treatment.
From these cost figures, one finds that time option 2 (see Table 2)
provides a minimum cost of pipeline per mile for the cities of High Springs,
Newberry, Archer, Alachua, and the Gainesville Urban Area, and time option
5 provides a minimum cost for LaCrosse, Micanopy, Waldo, and Hawthorne. The
different time option for the latter four cities is probably due to their
small population changes between 1975 and 1990.
Wastewater estimates for all cities in Alachua County except those for
the Gainesville Urban Area were small. Therefore, time option 5 was used
to calculate irrigation system costs for all communities except for the
Gainesville Urban Area. If other time options had been used, some flows
would have been to small to be realistic for the construction of an irri-
gation system. Time option 2 was used for the Gainesville Urban Area.
All systems costs include construction and operation and maintenance costs.
The difference between the cost of tertiary treatment and site costs
for land spreading were used to estimate break-even distances over which
effluent could be moved for land spreading purposes (Table 11). Baldwin's
[1975] cost estimates (column 6 in Table 10) and a high-rate trickling
filter system were used for the calculation. Break-even distances show how
far one could transport the secondary effluent from each source for land
spreading and be indifferent between land spreading and tertiary treatment.
Table 11 shows the break-even distances for time options 2 and 5. These
results show that secondary effluent can be transported considerable dis-
tances for land treatment and still compete with tertiary processes.
In estimating break-even distances, it was assumed that Newberry, Archer
and Alachua shared regional tertiary treatment costs in proportion to their
wastewater flows. The shares of their wastewater flow are 0.2423, 0.1805,
and 0.5773, and their corresponding assessment in 1975 was assumed to be
$579,569, $432,747, and $1,380,872, respectively.
The state of the arts in advanced wastewater treatment is still in
its developmental stage. There remains considerable uncertainty as to
the effectiveness of both chemical and land spreading methods for advanced
Table 10.--Present value of cost of transmission pipeline per
systems for Alachua County, Florida, 1975 to 1990a
mile, pumping station, and irrigation
Pipeline-per mile Pumping station Irrigation systems
City b b b b
City Option 2 Option 5 Option 2 Option 5 Westberry Baldwin
High Springs 27,877 28,482 315,585 350,995 48,417 86,525
Newberry 18,917 19,066 174,045 193,161 21,796 38,939
Archer 16,605 16,735 140,007 157,414 16,535 29,582
Alachua 29,180 30,343 335,233 384,084 59,487 106,883
Gainesville
Urban Area 219,401 237,686 2,572,519 4,400,404 630,597 1,125,887
LaCrosse 11,795 11,751 75,543 85,852 ;7,337 13,139
Micanopy 14,414 13,919 113,312 115,766 11,135 19,750
Waldo 14,833 14,584 117,850 125,306 12,805 21,898
Hawthorne 17,681 17,488 157,389 168,615 18,286 32,558
a All costs are in September,1974 dollars.
bSee Table 2 for a definition of time option.
See Table 2 for a definition of time option.
Table ll.--Break-even length of transmission pipeline for land treatment
in Alachua County, Florida, 1975 to 1990
Tertiary process' cost a Break-even b
City distance (miles)
Option 2 Option 5 Option 2 Option 5
High Springs 1,313,235 1,467,250 32.68 36.94
Newberry 598,880 658,683 20.40 22.55
Archer 448,878 500,970 16.82 18.91
Alachua 1,425,237 1,651,628 33.69 39.78
Gainesville
Urban Area 25,723,425 31,205,441 100.39 117.04
LaCrosse 317,198 358,025 19.45 22.04
Micanopy 470,352 479,559 24.23 24.72
Waldo 488,925 518,472 23.94 25.46
Hawthorne 650,697 696,263 26.35 28.31
Calculated from Tables 3, 4, and 5.
b
Calculated from Table 10. These figures were obtained by sub-
tracting costs of pumping station and Baldwin's irrigation system cost
from tertiary process cost then divided by the cost of pipeline per
mile.
treatment. The effectiveness of land spreading seems to be site specific
and a function of such factors as type of soil and slope of land. The
effectiveness of tertiary processes in a real world treatment situation
also remains in question.
CONCLUSION
The main purpose of this study was to consider the time and space
dimensions of regional wastewater treatment planning. Because of distances
between cities, the gains in economies of scale in the construction of
regional treatment plants to serve more than one city are more than offset
by transmission costs of raw sewage from each source to potential treatment
sites. Therefore, only ten combinations of cities were selected by the
cost minimization model. In studies where the cities are closer together,
the scanning process used by this study may create a larger number of
potential sites. If so, the search to find the optimum sites for treatment
plants would be more involved and may require the imposition of other
constraints.
Requirements for the transmission of wastewater depends on the to-
pographic condition of the area studied. In the design of pipelines and
pumping stations, topographic conditions should be taken into consideration.
In this study, it was assumed that a pumping station was required for each
regional plant, of course, more than one pumping station may be needed in
some cases. The process of scanning all the possible sites makes it very
difficlut to take the topographic factor into consideration for each site.
However, if a site is excluded from the solution by the assumption of only
one pumping station, it would not appear in the solution if more than one
pumping station were required. Therefore, the assumption is not critical
to the results.
The ability of the environment to restore itself is limited and more
or less constant over a given period of time. If a regional treatment plant
treats wastewater for the whole county and releases its tertiary effluent
at one location, the rate of pollutants released at this location is still
tremendous even though the pollutant contents of the effluent are low, and
hence creates an environmental hot spot. This damage to the environment
may discourage the regionalization of wastewater treatment facilities.
In the study of consolidating wastewater treatment facilities, both
over time and over space may face a large number of alternatives, the method
developed in this study may provide an effective means to narrowing these
large number of alternative down to several most possible ones, and make
empirical engineer cost estimation possible.
The break-even distances over which one can transport secondary ef-
fluent from sources to land treatment sites as an alternative to tertiary
treatment were estimated. An important study topic is the income generated
by crop production through the disposal of secondary effluent, and how
this income is distributed. This topic has important implications for
rural and urban development.
Land costs, including easement costs, were not estimated in this study.
This is a very important variable in the actual implementation of a treatment
program--particularly for land treatment.
Another aspect of regionalization, centralization of administration,
was not considered for the situation in Alachua County. Since all the cities
are not far from each other and their wastewater treatment demands are low,
the centralization of management and administration may be feasible to
utilize personnel more thoroughly.
REFERENCES
Alexander, E.L., "Suggested Modification of Present Design Systems," in
Seminar--Spreding of Sewage Effluent on Soil, U. S. Department of
Agriculture, Soil Conservation Service, 1972, pp. 83 92.
Anderson, C.L. and T.S. Hipp, Requirements and Returns for 1000-cow Beef
Herds on Flatwood Soils in Florida, Cooperative Extension Service,
University of Florida, Circular 385, April 1973.
Baldwin, L.B., The Soil-Plant System and Advanced Waste Treatment--Some
Economic Considerations, unpublished paper, 1975.
Cooper, L., "Location-Allocation Problems," Operations Research, Vol. 11,
1963, p. 331.
Dalton, F.E. and R.R. Murphy, "Land Disposal IV: Reclamation and Recycle,"
Journal of Water Pollution Control Federation, Vol. 45:7, July 1973,
pp. 1487 1507.
Day, A.D. and T.C. Tucker, "Production of Small Grains Pasture Forage Usine
Sewage Plant Effluent as a Source of Irrigation Water and Plant
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