United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/014 Mar. 1988
4>EPA Project Summary
A Selection Guide for
Volatilization Technologies for
Water Treatment
Jeffrey L. Fleming
The full guide presents a methodol-
ogy for evaluating applicability of
volatilization technologies for remov-?
ing volatile organics from water. The
volatilization technologies assessed in
this, study include: surface sprayers,
surface aerators, bubble columns,
cooling towers, steam strippers,
unaided evaporation from an impound-
ment, spray columns, and packed air-
stripping columns. The guide enables
users to assess performance and cost
under a variety of operating conditions
(e.g., temperature, influent concentra-
tion, allowable liquid and gas effluent
concentration, and flow rates) for
representative equipment designs that
could be transported on a trailer 2.4
m wide, 13.7 m long, and with a
maximum height of 4.1 m. The designs
are used as a basis to calculate repre-
sentative contaminant removal effi-
ciency, treatment rates, air emissions,
and treatment costs of each technol-
ogy. A key parameter used in assessing
these technologies is the Henry's Law
constant (H). A tabulation of available
values of H is provided'for volatiles
designated as hazardous by the Com-
prehensive Environmental Response,
Compensation, and Liability Act
(CERCLA). Methods for estimating H
are also described. Qualitative guid-
ance is provided on other factors that
should be considered during site-
specific assessments of the technical
and economic feasibility of volatiliza-
tion technologies. Offgas treatment is
not described. An example problem is
solved to demonstrate the method-
ology.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
The purpose of this full guide is to aid
in determining whether volatilization is
an appropriate technology for the reme-
diation of a hazardous waste site or spill.
It describes how to evaluate the perform-
ance of common volatilization technol-
ogies arid provides a format for selecting
the appropriate technology for a given
situation. Data necessary for the evalua-
tion are described, and, whenever pos-
sible, background data given for selected
hazardous organics. In addition to being
useful for equipment selection, it can be
used as an educational tool for back-
ground data on volatilization technolo-
gies or as a decision-making tool for
purchasing a mobile technology. The
guide is, of necessity, written about
"representative" types of equipment and
about selected situations. Although the
final selection of equipment should take
into account the factors cited in the
guide, it will be necessary to consider
the individual characteristics of the
equipment and the situation in which it
will be applied.
The impetus for developing this guide
stems from the involvement of the
Hazardous Waste Engineering Research
Laboratory's Releases Control Branch in
technical assistance activities that
require assessment of the feasibility and
cost of various treatment options. It was
recognized that EPA On-Scene Coordi-
nators (OSC) and their technical support
-------
personnel are often faced with changing
or uncertain conditions that could affect
the: cost and feasibility of removing
volatile substances from water. As
conditions change or as some of the
uncertainties are resolved, the OSC's
technical support personnel are called
upon to revise their estimates accord-
ingly. It was recognized that the OSC and
their technical support staffs did not have
a concise guide on the subject of vola-
tilization technologies and their applica-
tion to spill cleanup operations.
People with some technical training in
chemistry and thermodynamics, but
limited experience in conducting or
coordinating cleanup activities at uncon-
trolled hazardous waste sites wilI f ind the
guide useful. The OSC can use this guide
to reduce duplication of effort, accelerate
the production of cost and performance
estimates for decision-makers, and
promote consistency in estimation proce-
dures. Technical personnel who support
the OSC by developing cost and perform-
ance estimates for water treatment
options are the principal audience for this
guide. An example problem is solved
using the methodology developed in this
guide to select the most suitable and
cost-effective volatilization technology
for a city drinking water field contam-
inated with trichloroethyiene.
How to Use This Guide
This guide assists the reader to apply
a five-phase process for evaluating the
applicability of a volatilization technol-
ogy:
Phase 1. Preliminary assessment of
the feasibility of volatil-
ization
Phase 2. Site characterization
Phase 3. Calculation of basic material
properties
Phase 4. Technology evaluation
Phase 5. Equipment selection
Figure 1 provides general instructions
for using this guide. Phase 1 should be
an analysis of the applicability of vola-
tilization technologies. Normally, volatil-
ization is considered for removing only
low concentrations of volatile materials.
Water with a high percentage of organics
should be treated in some other manner.
Further, compounds that will volatilize at
a rate close to or below the evaporation
rate of water are not likely candidates
for volatilization.
Site Characterization (Phase 2) re-
quires a complete evaluation; a checklist
of important s(te data for the evaluation
is provided in Table 1.
Phase 3 involves determining the
properties of the spilled material. The
Henry's Law constant, solubility, lower
flammability lihnits, and azeotrope con-
centrations of selected compounds are
provided; hovyever, for a variety of
different organ'ics, other sources must be
used to determine the characteristics of
the spilled material.
Phase 4, (Technology Evaluation) is
designed to eliminate technologies from
consideration at each evaluation step,
thus avoiding additional work on tech-
nologies that are not suitable for the
application. In the Technology Evaluation
phase the fojlowing parameters are
determined in the sequence shown:
1. Removal ranges
2. Flowratejand time requirements for
treatment
3. Emissions generated by treatment
Technologies still under consideration
after evaluation of these performance
parameters should then be examined on
the basis of their costs. Costs for pre-
treatment, disposal of treated water,
emission controls, and water polishing
units should I be added to costs for
treatment by volatilization (Section 4).
This process is intended to eliminate
technologies based on performance,
allowing the tjest technology to remain
based on cost. |
Based on the differences inherent in
accurately estimating operating costs, it
is recommended that cost differences of
a factor of two or more should be used
as a basis for eliminating technology
from further consideration.
Phase 5 enables the user of the guide
to select a specific volatilization treat-
ment unit to be used at the site. This
is a complexj decision for which no
summary method is possible. The guide
provides background information on
volatilization technologies as well as
equipment designs and evaluations to
help the reader participate in making a
well-informed selection.
Scope of the Guide
The guide specifically addresses vol-
atile organics that are classified as
hazardous substances under the Com-
prehensive Environmental Response,
Compensation, and Liability Act
(CERCLA). A Materials Property Table for
74 compounds is provided in the guide
and includes data—water solubility,
vapor pressure,, and theoretical and
empirical Henry's Law constant—that
are commonly used in estimating the per-
formance of volatilization technologies.
Because the guide is targeted to
support removal actions that require
relatively rapid mobilization and short
set-up times, only those technologies
that can be legally transported by truck
(i.e., vehicles and trailers no more than
2.4 m wide, 13.7 m long, and 4.1 m high)
are considered. For each class of tech-
nology selected, the largest transportable
design is considered for performance
comparisons between technology types.
The volatilization approaches that are
addressed are: solar evaporation from a
pond, surface spraying, high speed
surface aeration, bubble column air
stripping, spray column air stripping,
countercurrent packed tower air strip-
ping, cooling tower air stripping, and
steam stripping. These technologies
provide a wide range of options in terms
of capital and operating costs, removal
efficiencies, treatment rates, complexity,
availability, and air emissions.
A variety of other technologies, such
as cross-flow air stripping and a prop-
rietary activated carbon/stripping hybrid
technology, are not included because of
their similarity to other technologies or
because systems are not available for
widespread use. Mobile or transportable
technologies for treating the offgases
from the described volatilization pro-
cesses are not described.
Development of Performance
Estimates
System performance is estimated in
the manual for material removal efficien-
cies, treatment time requirements, and
emission rates. Cost data are also
provided.
For each type of technology, a repre-
sentative design is chosen that has the
largest available treatment capacity and
meets the transportability requirements
described above. For each design, several
operating conditions are selected, per-
formance estimates are made, and the
results are tabulated or plotted. Organic
removal efficiency and the time required
to treat a model impoundment are
calculated for each design case system
and operating condition.
-------
Preliminary Assessment
Phase I
Determine Applicability of Volatilization
Sections 1 and 2
Site Characterization
Phase 2
Collect Data on the Site
Section 2
Consider Pilot
Testing
Develop Requirements for the Treatment System
Section 2
Calculation of Material Properties
Phase 3
Calculate Material Properties
Section 3
Consider Pilot
Testing
Technology Evaluation
Phase 4
Equipment Selection
Phase 5
Calculate Material Removals
Section 4
Select Technologies that Give the
Desired Removals
Eliminate Inappropriate
Technologies
Calculate Time Requirements
Section 4
Select Technologies Giving Desired
Treatment Times and/or Flowrates
1 1
Eliminate Inappropriate
Technologies
Calculate Emissions
Section 4
Determine Available
Emission Controls
JL
Select Technologies that are
Within Desired Emission Criteria
I
Eliminate Inappropriate
Technologies
Calculate Costs
Section 4
Compare Costs for
Treatment Options
Eliminate Options with
Much Greater Costs
Identify Available Equipment
for Cost-Effective Options
_L
Compare Available Equipment to
Design Case Systems
Section 5
_L
Estimate Performance and Costs of
Available Equipment Under Field Conditions
Sections 5 and 6 Along with Vendor Data
T
Select Equipment
Figure 1. Decision tree for volatilization process selection.
-------
Tab/a 1. Checklist for Site Evaluation
• Influent characterization
—Contaminant identity
—Contaminant concentration (mole
fraction) in water
—Total quantity of water to be treated
—Number, type, and thickness of
nonaqueous layers
—Influent f lowrate
• Effluent requirements
—Available discharge options
—Available discharge capacity
—Discharge concentration limits
—Discharge flow requirements
• Properties of spilled material (see
Section 3)
—Henry's Law constant (mole
fraction)
—Solubility
—Toxicity
—Sorptive properties
—Reactivity (hydrolysis, photolysis,
biodegradation)
—Flammability of vapor
—Handling requirements (safety)
—Disposal requirements for
concentrated material
—Other contaminants in water
• Climate
—Season during which water
treatment is anticipated
—Average ambient air temperature
—Average precipitation
—Solar radiation
—Wind
—Relative humidity
• Site-specific considerations
—Water temperature
—Site accessiblity
—Water location (surface/ground
water)
—Response time requirements
—Volatile emissions limits
—Altitude
• Integration with other treatment
options
—Relationship with other water
treatment technologies at the site
—Emission control devices
• Environmental considerations
—Residential characteristics
—Ambient air quality
—OSHA requirements
—Municipal requirements
Organic Removal Efficiency
Estimation
The air stripping and steam stripping
systems are compared based on the
calculated organic removals achievable
using a representative design on a
single-pass basis. A total of 32 perform-
ance curves (He vs. percent removed) are
presented forthese column systems. The
performance curves are generated for a
range of configurations (single unit,
parallel, and series; one-pass vs. recycle
treatment of'an impoundment), and
operating conditions (i.e., gas and liquid
flow rates, number of theoretical stages,
and packing). The performance compu-
tations are based upon the premise that
the effect of the air flow rate, He, and
the number pf theoretical stages is
described mathematically for a continu-
ous isotherrpal air stripper in the
Kremser equation:
f =
1 - (G/L)(H)
-[(G/L)H]H
where:
f = fraction 'of material left in liquid
phase;
G = molar flow rate of gas [in moles/
sec, for air, G = 73.68 x flow rate
(cmVsec)];
L = molar flow rate of liquid [in moles/
sec, for water, L = 1.74 x flow rate
(I/sec)]; I
H = Henry's Law constant of strippable
compon'ent (mole fraction/mole
number);
N = number of stages in column.
Although steam stripping is a compar-
atively expensive and complex technol-
ogy, the use of appropriate vent controls
can reduce air emissions below those
produced by treatment technologies that
discharge the contaminants directly into
the air, such jas air stripping. However,
caution must be exercised, since a
concentrated (product from steam strip-
ping can also pose health and flamma-
bility hazards;
The columh diameter of the model
system is limited by the physical size and
weight of the auxiliary system equipment
required to bperate the column. The
largest standard column diameter (and
consequently heat duty) that "can be
placed on a flatbed trailer is 0.46 m.
Random packing is preferred over trays
because of ease of cleaning and over rigid
packing because of availability. The
height of the packing in the model steam
stripper is 7.6 m, which is a realistic size
for a flatbed trailer. Performance is
estimated for four different boil-up ratios
(3%, 5%, 10%, and 30%). The treatment
rate varies from 6 to 1.5 I/sec. The
organic removal efficiency for evapora-
tion, surface aeration, and surface
spraying is considered only as a function
of operating time.
Treatment Time Requirements
A model impoundment with a volume
of 2834 m3 (30.5 m x 30.5 m x 3 m) is
used as the basis for comparing the
treatment time required to remove
organic contaminants from water for the
described systems. It is assumed that
there is no net flow into or out of the,
impoundment during the treatment
period (i.e., batch system). The mo.del is
representative of a typical body of
contaminated water and is large enough
to accommodate available commercial-
sized mechanical agitation equipment.
The criterion for comparison is the
half-life of the organic contaminant in the
model impoundment. The half-life (th) is
the operating time required to reduce the
organic concentration to 50% of its
original level. Valuesfortnforthesurface
sprayer, surface agitator, and solar
evaporation are calculated from the
following equation, which is derived in
the text:
th = 0.693/(KLs)
where KL isthe overall mass transfer rate
coefficient (m/hr), and s is the specific
surface area of the liquid phase (mVm3).
Values of th vs. He are plotted for both
surface spraying and surface aeration for
two sizes of commercial units. No
attempt is made to quantify effects of
other incidental variables such as cli-
matic conditions of wind and tempera-
ture, differences in a particular equip-
ment design, and quality of the
contaminated water. Instead, reasonable
average values for the key variables are
estimated based on probable field
conditions.
The operating time required to obtain
a desired removal efficiency can be
determined by multiplying th by the
number of half-lives (n) required to
determine the desired percent reduction
(R) in the contaminant concentration.
The continuous systems of air and
steam stripping could be used to aug-
ment volatilization from an impound-
ment. In this case, the discharge from
the treatment system could either be
placed back into the impoundment or
-------
sent to off-site disposal. When the
discharge is returned to the impound-
ment, the half-life in the pond is governed
by the equation:
th = 0.693
V
L(l-f)
where:
th -. half-life or organic in the
impoundment;
V == volume of the impoundment;
L ==• liquid flowrate of the treatment
unit;
f ;= fraction of organic remaining after
treatment, based on the Kremser
equation.
The results of this equation have been
plotted in Figures 12-1 9 of the guide for
the design case systems and operating
modes in treating the model
impoundment.
These performance estimates neglect
volatilization that would naturally occur
from the impoundment. The actual half-
life, including this or any other competing
removal mechanism, may be obtained
using the following equation:
J_
th
where:
thi
th2
on the
th = half-life of the organic
impoundment; and
thx = half-life of the organic consider-
ing mechanism x.
Examination of the Half-life figures allows
the conclusion that surface aerators are
normally the best option to agument
volatilization from an impoundment.
However, operational constraints of
surface aeration, the desire to control
organic emissions, or the unavailability of
a surface aerator may require the use of
another unit for this service.
For handy reference, a list of advan-
tages and disadvantages appears in each
technology subsection. The guide also
compares the design case continuous
treatment based on the assumption that
off-site discharge is available. In this case,
the treatment time is purely a function
of liquid flow rate.
Emission Rates and Costs
The guide also considers additional
factors affecting the performance and cost
evaluation process of specific technolo-
gies. These include material-specific
factors such as multicomponent mixtures,
safety considerations of toxic and com-
bustible emissions, absorption and
adsorption, decomposition in water, and
site-specific factors like season and water
quality.
Conclusion
By following the evaluation process in
the guide, the user will be able to identify
promising types of volatilization technol-
ogies and will find the information useful
for more in-depth evaluations of cost and
performance of specific technologies.
However, the manual is not designed to
be the sole reference for making the final
selection of a treatment system. There are
situation-specific considerations that are
beyond its scope. Examples of such
considerations include addressing the
problems caused by poor water quality
due to salts, solids, biological material,
etc.; evaluating the significance of differ-
ences between equipment of the same
type or performing pilot tests. Appropriate
sources are cited.
This document is submitted in fulfil-
lment of EPA Contract No. 68-03-3069
(MOD-29) by IT Corporation under the
sponsorship of the U.S. Environmental
Protection Agency. This report covers the
period of February 1, 1984 to June 29,
1984. Work was completed as of June 29,
1984. The document was edited in partial
fulfillment of EPA Contract No. 68-03-
3255 by Enviresponse, Inc. under the
sponsorship of the U.S. Environmental
Protection Agency.
Jeffrey Fleming is with IT Corporation, Knoxville, TN 37923.
Michael D. Royer is the EPA Project Officer (see below).
The complete report, entitled "A Selection Guide for Volatilization Technologies
for Water Treatment,"(Order No. PB 88-165 683/AS; Cost: $19.95, 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:
Releases Control Branch
Hazardous Waste Engineering Research Laboratory—Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
-------
-------
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information i
Cincinnati OH 45268 ;
BULK RATE,
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-88/014
•&U.S. GOVERNMENT PRINTING OFFICE: 1988—548-013/87025
------- |