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| United States Patent |
5,514,563
|
|
Tully
, et al.
|
*
May 7, 1996
|
Method of directly monitoring the concentrations of microbiocides in
aqueous systems
Abstract
A method for directly measuring the concentration of biocides in aqueous
systems comprising directly determining an absorbance or emission spectrum
of the aqueous system in a wavelength range of from 200 to 2500 nm and
applying chemometrics algorithms to the spectrum to determine the
concentration of the biocides.
| Inventors:
|
Tully; Jack C. (Wauconda, IL);
Kye; Larry M. (Hoffman Estates, IL)
|
| Assignee:
|
W. R. Grace & Co.-Conn. (New York, NY)
|
| [*] Notice: |
The portion of the term of this patent subsequent to March 3, 2013
has been disclaimed. |
| Appl. No.:
|
025693 |
| Filed:
|
March 3, 1993 |
| Intern'l Class: |
C12Q 001/06; G01N 021/25 |
| Field of Search: |
435/39,31,32,973
436/805
210/764
250/339,340,343
356/319,320
162/161
|
References Cited
U.S. Patent Documents
| 4661517 | Apr., 1987 | Martin et al. | 514/515.
|
| 5198453 | Mar., 1993 | LaZonby et al. | 514/367.
|
| 5210590 | May., 1993 | Landa et al. | 356/319.
|
| 5223715 | Jun., 1993 | Taylor | 250/343.
|
| 5242602 | Sep., 1993 | Richardson et al. | 210/745.
|
Other References
Stoeber et al, Biological Abstracts, vol. 71, No. 12, Ref. #84056, 1981.
Mitsui et al, Chemical Abstracts, vol. 113, p. 379, Ref. #103169t, 1990.
Xie et al, Chemical Abstracts, vol. 112, p. 878, Ref. #68749n, 1990.
Schulten et al, Chemical Abstracts, vol. 90, p. 118, Ref. #67509z, 1979.
Lu et al, Biological Abstracts, vol. 75, No. 8, Ref. #56583, 1983.
|
Primary Examiner: Wityshyn; Michael G.
Assistant Examiner: Mohamed; Abdel A.
Attorney, Agent or Firm: Troffkin; Howard J.
Claims
We claim:
1. A method for measuring biocide concentration in an industrial aqueous
system comprising the following steps:
1) determining absorbance or emission spectra in a wavelength range of from
200 to 2500 nm of at least ten samples of aqueous solutions containing
known concentrations of a biocide,
2) correlating the known concentrations of the biocide to the respective
absorbance or emission spectra to create a learning set and entering the
learning set into a chemometrics algorithm to generate a multiple sample
calibration,
3) directly determining an absorbance or emission spectrum of the
industrial aqueous system containing the biocide in a wavelength range of
from 200 to 2500 nm,
4) applying the multiple sample calibration to the absorbance or emission
spectrum of the biocide in the aqueous system to determine the
concentration of the biocide in the system.
2. A method according to claim 1 wherein the aqueous system is selected
from the group consisting of cooling water systems, metal working fluid
systems, and pulp and papermaking water systems.
3. A method according to claim 1 wherein the biocide is selected from the
group consisting of glutaraldehyde, isothiazolones, nitrilpropionamides,
thiocyanates, carbamates, quaternary ammonium chlorides,
trialkyltinoxides, hydantoin, and mixtures thereof.
4. A method according to claim 1 wherein the biocide comprises a mixture of
glutaraldehyde and an isothiazolone in a weight ratio of 5:95 to 95:5.
5. A method according to claim 1 wherein the biocide comprises a mixture of
glutaraldehyde and isothiazolone in a weight ratio of 10:90 to 90:10.
6. A method for determining effective biocide concentration in an
industrial aqueous system comprising a) determining the biocide
concentration in accordance with claim 1, b) monitoring total biomass
concentration with one or more bioassays and if the level of total biomass
increases, increasing the biocide concentration in the system until the
total biomass decreases or remains constant.
Description
FIELD OF THE INVENTION
The present invention is directed to a method for directly monitoring the
concentration of biocides in aqueous systems and more particularly to a
direct spectrometric method for quantifying biocides which have an
absorbance or emission spectrum in a wavelength range of from 200 to 2500
nm wherein the spectrum of the aqueous system containing the biocides is
determined and chemometric algorithms are applied to the spectrum.
BACKGROUND OF THE INVENTION
Traditional water treatment analysis methods involve taking grab samples
and performing independent analytical procedures for each component of
interest. Typically these are time consuming and involve significant delay
between taking samples, obtaining results and finally making program
adjustments. Some recent on-line analysis techniques have been developed,
but these techniques are either not specific to a particular analyte, they
are limited to measuring single components or they require the use of
addition of reagents to develop a color intensity which is proportional to
the concentration of the analyte of interest. For example, on-line
analyzers have been developed which are capable of monitoring oxidizing
biocides, i.e., ORP--Oxidation Reduction Potential analyzers. However,
these analyzers are not specific and will respond to the presence of any
oxidizing compounds in the system. Colorimetric analysis are similarly
deficient due to:
1. Slow response time since most colorimetric reactions take several
minutes to develop.
2. Colorimetric reactions are subject to interference from background
contaminants and physical parameters. For example many colorimetric
endpoints are sensitive to temperature and pH.
3. Maintenance requirements. Periodic reagent replacement and
re-standardization.
Another technique that has been used to monitor aqueous systems relies on
the measurement of inert tracer components to indirectly monitor product
levels. However, active biocides which are used to treat water treatment
systems are not inert and are consumed or degraded under normal operating
conditions within the aqueous systems. For this reason periodic sampling
of the active biocidal agents must still be made to ensure system
protection.
Thus, there exists a need for a rapid, direct method of monitoring active
biocide concentrations in aqueous systems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for the
simultaneous direct measurement of active concentrations of one or more
biocides in an aqueous system and which does not require chemical reagents
and is generally unaffected by the presence of background interferences.
It is another object of the present invention to provide a method for a
simultaneous analysis and feedback to a control system to maintain and
adjust biocide feed rates in an aqueous system.
It is another object of the present invention to provide a method for the
direct and simultaneous determination of active biocide levels and tracer
levels in an aqueous system to determine overall treatment performance.
It is yet another object of the present invention to provide a method for
the identification and quantification of low levels of weak UV-vis-NIR
absorbing biocides in the presence of stronger absorbing UV-vis-NIR water
treatment agents which could not heretofore be quantified by conventional
UV-vis-NIR spectrometrics techniques.
In accordance with the present invention there has been provided a method
for measuring the concentration of one or more biocides in an aqueous
system with a unique combination of UV-vis-NIR spectrometry with the
application of chemometrics algorithms to determine active biocide levels
in the aqueous system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of an on-line analyzer.
FIG. 2 is a schematic of a multisample laboratory calibration.
FIG. 3 is a graph showing actual 5-chloro-2-methyl-4-isothiazoline-3-one
levels versus calibration predictions for a learning set used in a trial
on a synthetic cooling tower. The diagonal line in the figure represents
the perfect match and the absolute error of a prediction is represented by
the vertical distance between the line and the predicted point.
FIG. 4 is a graph of HPLC results versus the corresponding analyzer
readings for the synthetic cooling tower trial grab samples of
5-chloro-2-methyl-4-isothiazoline-3-one.
FIG. 5 is a line plot of analyzer readings and HPLC results (filled
circles) for the concentrations of 5-chloro-2-methyl-4-isothiazoline-3-one
in the synthetic cooling tower study.
FIG. 6 is a graph showing actual 2,2-dibromo-3-nitrilpropionamide levels
versus calibration predictions in a trial on a synthetic cooling tower.
The diagonal line in the figure represents the perfect match and the
absolute error of a prediction is represented by the vertical distance
between the line and the predicted point.
FIG. 7 is a graph of titration vs the corresponding analyzer readings for a
synthetic cooling tower trial containing 2,2-dibromo-3-nitrilpropionamide.
FIG. 8 is a line plot of analyzer readings and titration results (filled
circles) for the concentrations of 2,2-dibromo-3-nitrilpropionamide in the
synthetic cooling tower study.
FIGS. 9 and 10 are graphical summaries of field results where
concentrations of 5-chloro-2-methl-4-isothiazoline-3-one and
2,2-dibromo-3-nitrilpropionamide are plotted against mass balance
concentrations.
DETAILED DESCRIPTION
The present invention is directed to a novel method for directly monitoring
the concentrations of one or more biocides in an aqueous system. The
method, in general, involves directly determining an absorbance or
emission spectrum of the system water containing the biocide(s) in the
ultraviolet, visible and/or near infrared wavelength range, and then
applying chemometrics algorithms to the spectrum to determine the
concentration(s) of the biocide(s). The method of the present invention is
generally unaffected by the presence of background matrix interferences in
the system water such as pH changes or the presence of other active water
treating components, and thus does not require time consuming, off-line
separation or derivatization techniques. In addition, the method of the
present invention does not require or involve the use of additional
colorizing agents, dyes, titrations or other indirect monitoring
techniques.
The present invention is of general applicability with respect to biocides
which are presently used to treat aqueous systems, provided of course,
that the particular biocide(s) of interest has a detectable absorbance or
emission spectrum in the ultraviolet, visible and/or near infrared range
(i.e. in the wavelength range of from 200 to 2500 nm). For purposes of
this invention, a biocide is considered detectable if it has a chromophore
with at least about 0.1 absorbance units (or a corresponding measurable
response with an emissivity spectrometer) in the wavelength range of from
200 to 2500 nm under normal biocide treatment dosages. It is preferred
that the biocide has between 0.1 to 1.5 absorbance units in the above
wavelength range and dosage amounts.
Examples of biocides that have been found to be easily monitorable in
accordance with this invention include, but are not limited to
isothiazolones, glutaraldehydes, thiones, halogenated nitrilalkylamides,
carbamates, halogenated alkyl nitrodioxanic, halogenated alkylhydantoins,
halogenated nitroalkyldiols, thiocyanates, alkylphosphonium halides,
guanidines, benzyl ammonium halides, alkylsulfonium methosulfates and the
like. Table 1 provides a list of specific examples of these biocides and
their typical active dosage amounts that have been found to be monitorable
using the method of this invention.
TABLE 1
______________________________________
Biocides Used as Cooling Water Treatments
ppm Active Active Ingredient
______________________________________
1.5% 5-chloro-2-methyl-4-isothiazoline-3-one 2-
methyl-4-isothiazolin-3-one
10% methylene bis(thiocyanate)
20% tetrahydro-3,5-dimethyl-2H-1,3,5-
thiadiazine-2-thione
15% sodium dimethyldithio carbamate
15% disodium ethylene-bis-dithiocarbamate
12.5% N-alkyl-dimethyl benzyl ammonium chloride
2.14% bis(tri-n-butyl) tinoxide
20% 2,2-dibromo-3-nitrilpropionamide
45% glutaraldehyde
60% 1-bromo-3-chloro-5,5-dimethylhydantoin
27.4% 1,3-dichloro-5,5-dimethylhydantoin
10.6% 1,3-dichloro-5-ethyl-5-methylhydantoin
______________________________________
The individual concentrations of mixtures of two or more biocides may also
be simultaneously monitored in accordance with the present invention.
A particularly preferred biocide combination comprises a mixture of
glutaraldehyde and isothiazolones in a weight ratio of from 10:90 to 90:10
and is most preferably in a weight ratio of 1.5 to 10 of
isothiazolones:glutaraldehyde, respectively. Suitable isothiazolones for
use in this invention are commercially available from Rohm & Haas Company
under the Kathon.RTM. trademark. In accordance with the present invention,
the respective concentrations of both of these biocides can be directly
and simultaneously monitored by determining the spectrum of the aqueous
system containing the biocides, and then applying chemometrics algorithms
to the spectrum. As is apparent, the application of chemometrics
algorithms to a spectrum of an aqueous system is a powerful tool which
provides the ability to simultaneously determine the concentrations of
multiple components even in a complex matrix such as a cooling water
system containing a plurality of biocides as well as other water treatment
compositions or interferences.
Combinations of blocides with dispersants and/or biocide protectors may
also be monitored in accordance with this invention. As used herein,
biocide protector refers to a composition which inhibits the degradation
of biocides in the presence of deleterious materials. For example, it is
known that isothiazolone degrades under certain pH ranges or in the
presence of iron metal. However, this degradation may be inhibited by the
addition of one or more biocide protectors such as acetate, carbonates,
chlorides, bromides, sulfates, phosphates, metal oxides, molybdates,
chromates, zinc salts, copper salts, cadmium salts, dialkylthioureas,
alkoxylated rosin amines, azoles, phosphonates, zinc dust, metal nitrates,
or nitrites and the like, and mixtures thereof. This technology is more
fully described in Canadian Patent Application 529,467, U.S. Pat. No.
4,031,055 and U.S. Pat. No. 3,820,795 which are incorporated herein in
their entirety. In accordance with the present invention the concentration
levels of biocides in combination with these biocide protectors and/or
dispersants may also be directly and simultaneously monitored and
quantified using the chemometrics algorithms hereinafter described.
Another embodiment of this invention is directed to a combination of
monitoring methods to provide not only the concentration of one or more
biocides in an aqueous system, but also the total biomass of living
organisms in the system. The combined use of these technologies provides
fast accurate tracking of biocide levels. This information is critical for
determining system control parameters such as biocidal kill rates,
effective biocide concentrations (and thereby avoid overdosing the
biocides) as well as frequency of biocide addition. The method comprises
directly determining the biocide concentration in accordance with the
method of the present invention in combination with a bioassay technique
such as an Adenosine triphosphate (ATP) test (as disclosed more fully in
"Standard Methods for Examination of Water and Wastewater 17th Edition"
(Washington, D.C.: American Public Health Association, 1989) pp 9-37 which
is incorporated herein in its entirety), Deposit Accumulation Test System
(DATS), a biofilm coupon as disclosed in U.S. Pat. No. 5,051,359 (which is
incorporated herein by reference in its entirety), infrared monitoring
systems which monitor biofilm growth as a function of infrared absorbance
and the like. These bioassays may be run continuously or intermittantly
over a period of time. If the bioassays indicate an increase in microbial
growth over time it is apparent that the current level of biocide is too
low, and accordingly, the dosage amount should be increased.
Aqueous systems which are suitable for monitoring in accordance with the
method of this invention generally include any industrial aqueous systems
where the system water is clear enough to obtain an absorbance or emission
spectrum. These include, but are not limited to open or closed cooling
water systems, process water systems such as e.g. pulp and paper making
systems, air washers, metal working fluids, and the like. The system water
is generally sampled in an area that is well mixed to assure that it is
representative of this aqueous system. If the particular aqueous system is
known to have relatively large amounts of particulate matter, it is
advisable to filter the system water prior to obtaining its spectrum.
Generally, any commercial grade UV, visible and/or near infrared
spectrometer may be used in accordance with this invention. For example,
it is possible to use fixed wavelength detectors where discrete elements
are placed at specific wavelengths which generally correspond to the
absorbance or emission maxima for the particular water treatment
composition. Charged coupled device (CCD) analyzers may also be used. It
is preferred that the spectrometer have a resolution of at least 10 nm,
preferably 2 nm and most preferably 1 nm.
A diode array spectrometer having a wavelength range of from 200 to 2500 nm
is preferred for use in this invention and most preferably has a
wavelength range of from 200 to 800 nm. Instrument stability is an
important consideration when operating in areas with a high potential for
electrical and mechanical noise. The spectrometer is preferably designed
to operate at 40.degree. C. to eliminate any varying temperature effects.
The spectrometer may be used to monitor off-line samples, or in a preferred
embodiment, is equipped with an on-line fiber optic probe. For on-line
measurements a flow through optical chamber (optrode) is preferred. In
these systems, light from a xenon flash lamp (or other suitable source) is
transmitted to the optrode via a quartz fiber optic cable. The light is
transmitted through the steam generator aqueous solution and collected in
a second fiber optic cable which transmits the light to the diode array
spectrometer. In the spectrometer the light is converted into an analog
voltage for each pixel of the array. The array is then read by a computer
and by subtracting a previously stored deionized water scan from the
sample scan a true absorption spectrum is generated. The resultant
spectrum is then processed by a chemometrics calibration algorithm to
generate a quantitative multicomponent analysis for any and all of the
water treatment compositions of interest.
Chemometrics is the application of statistical and pattern recognition
techniques to chemical analysis. Quantitative estimates of chemical
concentration in reagentless UV-vis-NIR spectroscopy are based on
algorithms, the parameters of which are determined in calibration
sequences called learning sets. Learning sets consist of a large number of
known samples that are used to determine the parameters of the algorithms.
The number of samples required depends on the complexity of the matrix,
the number of spectroscopic interferences that are present, and the number
of variables used in the algorithm. In general, the number of samples
should be at least 10 times the number of independent variables employed.
In the presence of known and unknown interferences, a multiple sample
calibration averages out the effects of these interferences. The learning
set solutions are prepared in a manner to typify the interferences and
their variability that will be experienced in the steam generating system.
The invention preferably uses a multi-sample calibration based on either
principle component regression analysis or rotated principle component
analysis of absorbance or emissivity, and subsequent derivative data. The
rotated principle component analysis method is most preferred and involves
a rotation of the principle components which allows the concentration of
all the relevant information for a particular analyte into a single
rotated principle component. The use of rotated principle components
enables one to detect weak UV-vis-NIR species that would not normally be
quantifiable using more conventional chemometric techniques. Thus, the use
of rotated principle components gives the invention the ability to detect
weak UV-vis-NIR species that would normally not be quantifiable using more
conventional chemometric techniques.
The most accurate calibration method for each analyte may be determined by
selecting the particular method having the highest coefficient of
determination (r.sup.2) value.
Without further elaboration, it is believed that one of ordinary skill in
the art using the foregoing detailed description can use the present
invention to its fullest extent. The following examples are provided to
illustrate the present invention in accordance with the principles of this
invention, but are not to be construed as limiting the invention in any
way except as indicated in the appended claims. All parts and percentages
are by weight unless otherwise indicated.
EXAMPLES
In all of the examples given the following operating parameters,
calibration methods and chemical techniques were employed.
Operating parameters:
On-line analyzer.
Resolution 2 nm.
Solution path length 1.3 cm.
Operating temperature 40.degree. C.
Static solution measurements.
Chemometric Techniques
Learning set size (10-70) samples.
Wavelength range for calibration (30 wavelengths in the range 230-346 nm).
Calibration based on principle component regression of adsorbance, first
derivative or second derivative.
Calibration based on rotated principle component on adsorbance spectrum,
first derivative or second derivative.
Chemical Referee Techniques
All analytical solutions were prepared to volumetric standards.
Referee techniques used were HPLC for
5-chloro-2-methyl-4-isothiazoline-3-one and a spectrophotoiodometric
method for 2,2-dibromo-3-nitrilpropionamide.
EXAMPLE 1
This example demonstrates the ability to monitor biocides on-line. This
experiment was run on a common cooling water microbiocide,
5-chloro-2-methyl-4-isothiazolin-3-one, in a simulated cooling tower (SCT)
which comprised an automated 36 liter capacity pilot cooling tower
equipped with an evaporative column, heat exchangers and controller. This
controller monitors and controls various functions such as pH,
conductivity, makeup and blowdown. The typical half-life of the system is
18 hours. The tower was treated with a standard corrosion/scale control
product during the evaluations.
The analyzer was set-up so that water samples were removed from areas of
good circulation and returned to the basin of the cooling tower. The
analyzer's digital outputs were recorded by a commercial telecommunication
program via a RS-232 connection.
A common cooling water biocide containing
5-chloro-2-methyl-3-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one
was tested in the SCT unit with the analyzer monitoring the active
constituents concentration. This biocide was chosen as a test biocide
since it possesses absorbance characteristics suitable for the required
chemometric algorithms and there is a High Pressure Liquid Chromatography
(HPLC) reference method available to validate analyzer predictions. The
HPLC method has an average relative error of 4.1% based on more than 20
control samples tested on various occasions.
The following SCT operating conditions were maintained during this trial:
______________________________________
pH 8.3
Conductivity 1.33 mmhos
Calcium Hardness 500 ppm as CaCO.sub.3
Total Hardness 830 ppm as CaCO.sub.3
M-Alkalinity 60 ppm as CaCO.sub.3
Ortho-Phosphate 0.6 ppm
Total Phosphate 2.0 ppm
Temperature 43.degree. C. (110.degree. F.)
______________________________________
There are two types of learning set samples which can be used in
calibration. Learning set samples can be taken directly from the cooling
tower without further modification or background waters can be removed and
spiked with the analyte of interest at various levels. The latter
technique is often referred to as the standard addition method. The SCT
Biocide #1 learning set included both types of calibration samples.
Background waters collected over a one week period were spiked with
different levels of biocide. Some background waters were collected while
being chlorinated and some with no chlorine present. Approximately 50
individual samples were made and scanned for calibration. Several
different calibrations were made from the information obtained and
evaluated using an off-line analysis program. The best calibrations were
selected and uploaded to the analyzer computer to be used for on-line
monitoring of the SCT run.
Four spikes of the isothiazolin-3-one mixture were made to the basin of the
cooling tower to achieve 4, 12, 7 and 5 ppm as active biocide. After each
spike of the isothiazolin-3-one, biocide levels were allowed to deplete to
near 0 ppm before another spike was added. The analyzer was programmed to
read every 20 minutes and the results were recorded by an external
computer, while two to three grab samples were collected daily for HPLC
analyses. These grab samples were stored in a cold room at
2.degree.-3.degree. C. prior to HPLC analysis to prevent any sample
degradation.
The analyzer readings (line plot) and HPLC results (filled circles) for
total isothiazolin-3-one levels obtained over the nineteen day evaluation
were in excellent agreement (see FIG. 5). The analyzer output curve
clearly indicates that each biocide spike was followed with the predicted
exponential decay. No analyzer data is available for days 5 and 10 due to
power failures caused by local storms.
FIG. 3 shows actual isothiazolin-3-one levels versus calibration
predictions for the learning set used in the trial. The diagonal line in
the figure represents the perfect match and the absolute error of a
prediction is represented by the vertical distance between the line and
the predicted point.
FIG. 4 is a plot of HPLC results versus the corresponding analyzer readings
for the trial grab samples. Although prediction error for FIG. 4 is
slightly larger than that obtained for the learning set, it is easily seen
that the analyzer can produce extremely reliable numbers in an on-line
analysis situation. The calculated correlation coefficient (R.sup.2) for
the data in FIG. 4 is 0.99 where 1.0 represents the ideal.
EXAMPLE 2
This experiment demonstrated the ability to directly monitor another common
cooling water microbiocide 2,2-dibromo-3-nitrilpropionamide (DBNPA) in the
SCT unit with the analyzer monitoring active concentration. The absorbance
pattern for DBNPA is quite different from that of the isothiazolin-3-one.
An iodometric titration reference method for DBNPA was used to validate
analyzer predictions.
The SCT rig operating conditions were modified slightly to extend the
half-life of DBNPA in the cooling tower. The conditions were as follows:
______________________________________
pH 7.0
Conductivity 1.33 mmhos
Calcium Hardness 570 ppm as CaCO.sub.3
Total Hardness 950 ppm as CaCO.sub.3
M-Alkalinity 10 ppm as CaCO.sub.3
Ortho-Phosphate 0.4 ppm
Total Phosphate 1.7 ppm
Temperature 38.degree. C. (100.degree. F.)
______________________________________
The DBNPA learning set consisted of 70 samples and was established in the
same manner as described in the previous example.
Five DBNPA spikes were made to the basin of the cooling tower to achieve
15, 3, 20, 7 and 30 ppm as active DBNPA. After each spike, biocide levels
were allowed to deplete to near 0 ppm before an additional spike was made.
Again, the analyzer took a reading every 20 minutes and several grab
samples were collected daily for immediate titration.
FIG. 8 shows the corresponding analyzer readings (line plot) and titration
results (filled circles) over the ten day evaluation period. Shorter but
consistent exponential decay patterns were observed following each spike
of DBNPA when compared to those obtained in the isothiazolin-3-one trial.
This difference may be related to the relative degradation rates of the
two biocides. The analyzer showed very good predictions for the
mid-concentration range and slightly lower predictions for the upper and
lower concentration ranges.
Learning set and SCT run plots are contained in FIGS. 6 and 7 and again it
is evident that the analyzer can produce extremely reliable predictions of
biocide concentrations. The R.sup.2 value for the sensor readings and grab
sample analyses is 0.94 (FIG. 7).
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