svEPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-179 Oct. 1981
Project Summary
Production Engineering and
Marketing Analysis of the
Rotating Disk Evaporator
James A. Heidman and Robert P. G. Bowker
Recent EPA-funded research into
the on-site, mechanical evaporation of
wastewater from single family homes
revealed that a rotating disk evaporator
(RDE) could function in a nondischarg-
ing mode. Such a device has potential
use where site limitations preclude
conventional methods for on-site
disposal.
This study documents a marketing
analysis made of the RDE. The mar-
keting analysis defined the market
potential for RDE systems, developed
a practical design, estimated produc-
tion and installation costs, and refined
market estimates based on cost com-
parisons.
A small unit suitable for only the
most favorable climates would have
an FOB factory selling price of about
$10,000 if fabricated with aluminum
disks. Distribution costs and freight
will amount to about $3,300. An
additional $8,OOO is required for
installation (including a large storage
tank for periods when freezing prevents
evaporation), resulting in a total capital
cost of about $22,000. Including
amortized capital costs and O&M
costs, an RDE system would treat
household wastewater for about 3.4
cents/gallon.
Because of these high costs, the
potential RDE market is quite small. It
is limited to very expensive homes,
second homes with no winter occu-
pancy, and high-cash-flow—low-sew-
age-flow commercial establishments.
Furthermore, unfavorable climatic
conditions eliminate much of the nation
from consideration. In summary, it is
unlikely that manufacturers of RDE
systems would collectively generate
national sales of 100 units/year.
This Project Summary was devel-
oped by EPA's Municipal Environmen-
tal Research Laboratory, Cincinnati,
OH, to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same titte (see Project Report ordering
information at back).
Introduction
A number of U.S. Environmental
Protection Agency research projects
have addressed alternative on-site
wastewater treatment systems. In 1978,
the University of Colorado completed a
project concerned with disposal of
septic tank effluent by evapotranspira-
tion and by mechanically assisted evap-
oration.
The University of Colorado research
project indicated that a RDE could
function as an on-site disposal method
for many areas of the nation where site
restrictions preclude the use of other
disposal techniques. Furthermore, pre-
liminary cost data suggested the system
might be competitive with other on-site
disposal alternatives.
To assist in determining if a full-scale
demonstration of the RDE device was
appropriate, the EPA retained Environ-
mental Resources Management, Inc., to
review the University of Colorado re-
sults, define the market for such sys-
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terns, estimate capital and operating
costs for potential system designs, and
compare the market potential with other
on-site systems.
Rotating Disk Evaporator
(RDE) Unit
A schematic diagram of a typical RDE
installation is shown in Figure 1. The
RDE unit features a row of parallel disks
mounted perpendicularly to a rotating
horizontal shaft. The disks are partially
submerged in a basin containing septic
tank effluent. As the disks rotate in the
vertical plane, the effluent adheres to
the disks and evaporates to the atmo-
sphere.
The main advantage of evaporation is
that it provides for complete disposal of
sewage without discharge to ground or
surface waters. This allows the use of a
site otherwise limited by such condi-
tions as highly impermeable soils or
steeply sloping topography.
The RDE unit substantially increases
the effective evaporation surface for a
small rainfall catchment area. There-
fore, the RDE unit can function as a
nondischarging system in regions char-
acterized by other than arid and semi-
arid climates, e.g., areas with high
evaporation potential, but with signifi-
cant precipitation.
When ambient temperature drops
below 40°F, water on the disks may
begin to freeze. Therefore during low
temperature periods, wastewater inflow
must be held in storage.
RDE Unit Design
The University of Colorado research
determined the optimal operating char-
acteristics for disk submergence, rota-
tional speed, disk spacing, and disk
color. Possible materials for the con-
struction of disks are limited to two
basic classes—metals and plastics. On
the basis of disk material costs alone,
aluminum is six to eight times more
expensive than plastic. Nevertheless,
the use of plastic complicates the
anchoring of disks to the drive shaft;
turning moment about the shaft tends to
soften openings and creep and outright
failure could occur.
Recognizing that design flow has a
substantial impact on RDE costs and
that RDE systems would likely incorpo-
rate flow conservation measures in the
household, it was decided to use a
design flow of 225 gallons/day (850
L/day). This design flow represents a
compromise between average flow
based on field measurements and flow
rates used by regulatory agencies for
design purposes.
Pan evaporation rates and tempera-
ture data were used to size RDE units for
a number of locations in the United
States. The 1 8-inch-diameter size
selected by the University of Colorado
was used. Results are shown inTable 1.
Estimate of Potential Market
Both temperature and evaportion rate
affect the applicability of the RDE
device. Disk area varies inversely with
evaporation rate. Design storage re-
quirements are based on the number of
days the temperature drops below40°F.
An initial estimate of areas where
climatic conditions could support the
use of RDE was based on the following
criteria: (1) pan evaporation >40
inches/year, and (2) no more than 50
days with mean daily temperature on an
annual smooth course less than 32°F.
Application of these criteria indicated
that the states listed in Table 2 would be
suitable for RDE units.
Data on new and second home con-
struction were evaluated in conjunction
with estimates of sewer and land avail-
ability to determine the market potential
for mechanical systems. The potential
market for these systems is shown in
Tables 3 and 4. These tables do not
include the potential market for com-
mercial applications; however, the
magnitude of the commercial market
appears small in comparison.
The maximum potential market over
the next 20 years (developed from
Tables 3 and 4) is as follows:
South 25,500
units/year \
West 6,500
units/year Total 32,000/year
The low estimate of 1 percent of new
housing translates to about 8,000
units/year. This range of 8,000 to
32,000 units/year represents the
House
Septic Tank
Reservoir
RDE Unit
K-1 vu in El—
iv...—.•:.••- •v-.-w.i. •.-.T
1
Figure 1. Typical installation of RDE system.
2
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Table 1. RDE - Storage System Design Sizes
Location
Billingame, California
Ho/land, Virginia
Medford, Oregon**
Laven, Texas
Dixon Dam, Kentucky
Wanship Dam, Utah**
Martin Dam, Alabama
Athens, Georgia
Hialeah, Florida
Boulder, Colorado
Canton, New York**
Fairhope, Alabama (1975)
Fairhope, Alabama (1977)
Maximum
Average
RDE Evap-
oration
Rate
(L/hrm2)
0.07
0.07
0.05
0.11
0.045
0.06
0.055
0.075
0.090
0.100
0.045
0.055
0.065
Number
of
Disks*
118
118
165
75
183
137
150
110
92
82
183
150
127
Unit
Storage
Required
(L/rrfj
160
140
200
200
120
200
81
120
85
310
130
84
112
Storage
Required
(L)
81,000
71,000
140,000
64,000
94,000
120,000
52,000
57,000
34,000
1 10,000
110,000
54,000
61,000
*Based on 850 L/day (225 gal/day) design flow, 4.3 m2 exposed surf ace area/disk
(78-inch diameter, 28-inch submergence), and exclusive of any safety factor.
**Outside RDE geographic market in Table 2.
Table 2. States Suitable for RDE
Arizona
Alabama
Arkansas
California
Florida
Georgia
Kentucky (75%)
Louisiana
Mississippi
New Mexico (50%)
North Carolina
Oklahoma
South Carolina
Tennessee
Texas
Virginia (50%)
potential market for mechanical-based
systems.
Within the wastewater treatment
business, rarely doesa particular manu-
facturer capture a major portion of the
market for any product. Although this is
not true for the mechanical-based
alternative on-lot systems market,
relatively new products in this market
have captured only a small share. It is
unlikely that a RDE product would make
Table 3. Potential Market for Mechanical-Based Systems for New Single Family
Housing Within RDE Geographic Market Areas
Primary Residence
South
West
Time Inside
Horizon SMSA*
1981-1990 100,000
1991-2000 100,000
2001-2010 90,000
2011-2020 90,000
1981-1990 20,000
1991-2000 20,000
2001-2010 10.000
2011-2020 10,000
Outside
SMSA
30,000
30,000
30,000
30,000
10,000
10,000
10.000
10,000
*Standard Metropolitan Statistical Area
Table 4. Potential Market for Remedial Retrofits
Region Existing Housing
South
West
5,000/year
1.000/year
Second
Home Total
60,000
70,000
70,000
50,000
20,000
20,000
30,000
20,000
Future
190,000
200,000
190,000
170,000
50,000
60,000
50,000
40,000
Housing
1,000/year
a major penetration. A very strong
marketing program would very likely be
required to gain as much as 10 percent
of the market over the next 20 years.
Based on the above and considering
that the market estimates are purposely
high, the potential market for RDE units
is about 1,000 units/year excluding
cost considerations.
Costs of RDE Systems
Three standard size systems were
selected and a production engineering
analysis was made for fabricating three
design sizes of 80, 110, and 140 disks
(78-inch diameter) at annual production
levels of 100, 1,000 and 10,000 units.
Estimated fabrication costs for 1,000
units/year are presented in Table 5.
If plastic were substituted for alumi-
num as disk material, costs would be
reduced substantially. Polystyrene disks
would cost about $6.00 each, repre-
senting a $3,400 reduction in material
costs for the 80-disk RDE. Elaborate
metal spiders are required with plastic
disks, however, and these are not
included in the cost estimates shown in
Table 5. A minimal design featuring
plastic disks and five metal spiders
conceivably would reduce the price of
the 80-disk unit by 50 percent.
Total capital costs for the 80-disk and
140-disk units were estimated as fol-
lows:
80 Disk
Unit
140 Disk
Unit
RDE (FOB Factory) $10,200 $16,800
Freight and
Distribution 3,300 5,400
Installation 8,100 13,500,
Total $21,600 $35,600
Installation costs include $3,800 for a
10,000-gallon fiberglass reservior.
Operation and maintenance costs were
estimated at $430/year.
The RDE system is many times more
costly than other on-lot disposal alter-
natives. It is obvious that for any soil
system suitable for a discharging sys-
tem, the RDE device cannot compete on
a cost basis.
Based on the cost data developed, the
potential market of RDE systems as a
nondischarging alternative for un-
clustered, single family homes was
judged to be insignificant. Manufac-
turers would very likely find it difficult to
generate sales of 100 units/year.
The full report, submitted in fulfill-
ment of Contract No. 68-03-2738 by-
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Table 5. FIDE Estimated Fabrication Costs
Cost Component
Aluminum disks, 78-in. diameter, 1/1 6 in. -
0.716 Ib/sf @ $1.60/lb = $48.50/disk
Spacers
Shaft, 84 in., 1 13 in., and 144 in. long @ $0.30/lb
Stub Ends @ $0.26/lb
Intermediate Support @ $.0.26 /Ib
Channel Supports @ $0.30/lb
Steel Plating for Tank @ $0.21 /Ib
Bearings
Large Gear
Small Gear
Chain
Drive Unit, complete
Paint, Tar, Grit
Subtotal, materials
Labor @ $7/hr
Factory Overhead
General and Administrative
Profit (25%)
Selling Price, FOB Factory
80 Disk ROE
$ 3,880
50
34
36
—
36
273
523
39
18
25
274
35
$ 5,223
427
854
1,148
2.551
$10,203
Costs ($)
1 10 Disk RDE
$ 5,335
65
46
36
17
46
328
785
39
18
25
274
44
$ 7,062
553
1.106
1,538
3,418
$13,677
140 Disk RDE
$ 6,790
87
58
36
17
56
382
785
39
18
25
274
52
$ 8.619
693
1,386
1.888
4.195
$16,781
Environmental Resources Management,
Inc., under sponsorship of the U.S.
Environmental Protection Agency, was
authored by Philip L. Buckingham.
The EPA authors James A. Heidman and Robert P. G. Bowker falso the EPA
Project Officer, see below) are with the Municipal Environmental Research
Laboratory, Cincinnati, OH 45268.
The complete report, entitled "Production Engineering and Marketing Analysis
of the Rotating Disk Evaporator," (Order No. PB 82-101 676; Cost: $8.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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