Patent Application
20160202189
The invention relates to a method for detecting transparent exopolymer particles in a water sample according to preambles of the enclosed independent claims.
Transparent exopolymer particles, TEP, may be present in aqueous environments, both in natural waters and in industrial process waters or wastewaters. They are transparent biopolymer particles mainly made up of acidic polysaccharides from phytoplanktons and bacterioplanktons, and may have a form of deformable strings, disks or films up to several 100 μm long. TEP are very sticky, flexible and surface reactive, and they behave like gels and increase viscosity. They may coalesce in order to form larger gels and porous networks, and they easily cause biofouling, e.g. fouling of membranes in desalination processes, especially during algal blooms.
Hitherto the significance of TEP to various process problems in water-rich industries has been largely overlooked, because they have been extremely hard to detect and quantify. TEP are transparent, which means that they cannot be directly detected. One method for detecting TEP is described by U. Passow and A. L. Alldredge in Limnol. Oceanogr. 40(7), 1995, 1326-1335. In the described method TEP is stained with cationic dye Alcian Blue and the amount of dye complexed with TEP is colorimetrically determined. The detection method comprises a plurality of different steps: filtering, staining, washing, soaking and colorimetric determination. It is clear that the method is not suitable for industrial use, where rapid response is required. Furthermore, the interaction between the dye and TEP is based on ionic interaction and is non-selective. For example, possible anionic polymers or anionic impurities disturb the determination of TEP.
An object of the present invention is to minimise or even eliminate the disadvantages existing in the prior art.
An object of the invention is also to provide a method with which transparent exopolymer particles may be rapidly and reliably detected.
Another object of the invention is to provide a method with which the amount of transparent exopolymer particles may be easily monitored.
These objects are attained with the invention having the characteristics presented below in the characterising parts of the independent claims.
A typical method according to the present invention for detecting transparent exopolymer particles in a water sample, comprises
Now it has been surprisingly found out that a fast and reliable analysis of the amount of transparent exopolymer particles can be obtained if they are allowed to interact with a specific fluorochromatic reagent, and then the fluorescence signal is detected. This enables creation of rapid method, which can be used for industrial analysis of TEP in different natural or process waters. The invention makes it possible to improve the operational efficiency in water-intensive processes, where TEP concentration may vary significantly, for example, due to seasonal variations. The present method provides also possibility to obtain a greater insight in the water treatment process.
In the present invention a fluorochromatic reagent is introduced to the water sample. In this context the term “fluorochromatic” means a compound that fluoresces. The reagent is added in known, predetermined amount, which makes the obtained signals comparable with each other. A person skilled in the art may, without undue burden, determine suitable reagent amounts for each system.
According to one embodiment of the invention the fluorochromatic reagent is specific to vicinal hydroxide groups. In other words, the fluorochromatic reagent is specific to transparent exopolymer particles comprising at least two hydroxide groups attached to adjacent atoms. Thus, the reagent is selective to e.g. diols and triols. The fluorescence signal of the reagent changes when it comes into contact with vicinal hydroxide groups of transparent exopolymer particles.
According to one embodiment of the invention the fluorochromatic reagent is a boronic acid derivative, for example a phenylboronic acid derivative, such as 3-(dansylamino)phenylboronic acid (DAPB), 3,4,5-trifluorophenylboronic acid, 2-fluoro-5-nitrophenylboronic acid, 2-methoxyphenylboronic acid, N-benzyl-3-pyridiniumphenylboronic acid, o-dimethylaminomethylphenylboronic acid, 3-chloro-4-fluorophenylboronic acid or 4-bromophenylboronic acid. Further, the fluorochromatic reagent may be a boronic acid derivative, such as 8-quinolineboronic acid (8-QBA); 5-quinolineboronic acid (5-QBA); 6-(dimethylamino)-naphthalene-2-boronic acid (6-DMANBA); or phenoxathiin-4-boronic acid (4-POBA). The response which signals an interaction between TEP and boronic acid derivative is communicated by changes in fluorescence intensity either through chelation enhanced quenching or chelation enhanced fluorescence.
According to one preferred embodiment of the invention the fluorochromatic reagent is 3-(dansylamino)phenylboronic acid (DAPB). 3-(dansylamino)-phenylboronic acid is cheap and easily available, whereby it is suitable for industrial purposes. DAPB interacts with vicinal diols and certain amino alcohols to form cyclic complexes that a have a fluorescence intensity and peak emission dependent on the environment of the fluorophore.
According to one embodiment of the invention the fluorescence signal of the free non-interacted fluorochromatic reagent is detected, for example when 3-(dansylamino)phenylboronic acid (DAPB) is used as fluorochromatic reagent. This means that the detected signal decreases with increasing TEP concentration. The amount of the fluorochromatic reagent, which is used, is sufficient when a fluorescence signal that is typical for the unreacted reagent is still obtainable. When the detected signal is smaller than a predetermined threshold signal value, it is a clear indication that the TEP concentration in the water sample has exceeded the permitted level.
According to another embodiment of the invention the fluorescence signal of the interacted fluorochromatic reagent is detected, for example when 8-quinolineboronic acid (8-QBA), 5-quinolineboronic acid (5-QBA) or 6-(dimethylamino)-naphthalene-2-boronic acid (6-DMANBA) is used as fluorochromatic reagent. This means that the detected signal increases with increasing TEP concentration. When the detected signal is stronger than a predetermined threshold signal value, it is a clear indication that the TEP concentration in the water sample has exceeded the permitted level.
According to one embodiment of the invention the water sample to be analysed for TEP is obtained from a water treatment process, and the feed of one or several process chemicals is adjusted and/or selected on basis of the detected fluorescence signal. For example, if the detected signal indicates that the TEP concentration exceeds the permitted level, it is possible to start feeding new chemicals to the process for reducing the concentration of TEP. Alternatively or simultaneously, the dose of constantly fed process chemicals may be changed for reducing the TEP concentration. Examples of such chemicals, feed of which may be adjusted and/or selected on basis of the detected signal, are coagulants and flocculants. When the feed and/or dosing of treatment chemicals is done based on the detected signal, the chemical costs may be reduced, as overfeeding may be avoided.
According to one embodiment of the invention the pH of the water sample is adjusted to a constant value before introduction of the fluorochromatic reagent. It has been observed that at least for some reagents the detected fluorescence signal may also be dependent on pH of the sample, in which case it is preferred to adjust the pH to a constant value in order to eliminate the pH dependency of the detected signal. pH adjustment may be performed by introduction of a suitable buffering agent, e.g. boric acid/potassium chloride/sodium hydroxide, or by introduction of a suitable strong base, such as NaOH, or acid, to the water sample. In such processes where the pH is constant, and very close to the value at which the fluorescence intensity maximum of the reagent is obtained, no pH adjustment step is necessary. A person skilled in the art is able determine the optimal pH range for used fluorochromatic reagent and for each sample system by using known methods.
When a phenylboronic acid derivative, such as 3-(dansylamino)phenylboronic acid (DAPB) is used as fluorochromatic reagent pH of the sample may be adjusted to a level>7, more preferably>8, in order to optimise the intensity of the fluorescence signal. pH of the water sample may be adjusted to the range of 7-10, more typically 8.5-9.5.
When 8-quinolineboronic acid (8-QBA) is used as fluorochromatic reagent pH of the sample may be adjusted to pH 4-10, more preferably pH 4.5-7.5, in order to optimise the intensity of the fluorescence signal.
When 5-quinolineboronic acid (5-QBA) is used as fluorochromatic reagent pH of the sample may be adjusted to pH>4, more preferably pH>7.5, in order to optimise the intensity of the fluorescence signal. pH of the water sample may be adjusted to the range of 7-10, more typically 8.5-9.5.
When phenoxathiin-4-boronic acid (4-POBA) is used as fluorochromatic reagent pH of the sample may be adjusted to pH 2-7, more preferably pH 2-4, in order to optimise the intensity of the fluorescence signal.
Preferably, the water sample is obtained or taken as a side stream from an aqueous process stream, for example in a water treatment process comprising a pre-treatment unit and a reverse osmosis unit. The water sample may be taken before or after the pre-treatment unit. A pH adjustment agent, such as buffering agent, may be introduced to the water sample side stream, and preferably, after reaching the desired pH level, the fluorochromatic reagent may be introduced continuously or at pre-determined intervals to the water sample side stream, and the fluorescence signal may be detected, respectively, continuously or at pre-determined intervals. The detected signal may optionally be filtered, if necessary, and/or it may be mathematically analysed. The TEP level in the process stream is determined by comparing the detected signal to predetermined reference signal(s).
The TEP level in the process stream may be determined by comparing the detected signal to predetermined reference signal(s). For example, when quenching of the signal of the fluorochromatic reagent in presence of TEP is detected, a fluorescence signal of reagent in ultrapure water may be used as a reference signal, whereby a maximum signal without any TEP is obtained. Alternatively a relative value for the TEP amount can be calculated by comparing the detected signal to the signal of ultrapure water. The signal of ultrapure water is given the value 100 and if there is TEP present in the sample the signal quenching is scaled accordingly.
Since natural waters may be a turbid media, the predominance of light scattering may become significant and distort the fluorescence emission spectrum. In that case it is possible, for example, to correct the detected fluorescence signal by considering the Raman scattering.
According to one embodiment of the invention the fluorescence signal is detected by using spectrophotometry or spectrofluorometry, for example by using cuvette, flow-through cuvette or probe. All these detection methods are known as such for a person skilled in the art.
The method according to the present invention is suitable for all water-intensive processes, where TEP may be present. Examples of such processes are different water purification processes, such as desalination, pre-treatment and water intensive manufacturing processes, such as pulping and paper making. Typically such processes in which the invention is useful include at least one microfiltration, ultrafiltration, nanofiltration and/or reverse osmosis step(s).
The method described herein may be used to detect or determine extracellular polysaccharides (EPS).
Brackish water was treated with different doses of ferric chloride (trade name: PIX-111, Kemira Oyj) at pH 5.5. 750 μl samples of treated water and untreated reference water were taken and 250 μl of buffer solution boric acid/potassium chloride/sodium hydroxide, pH 9, was added.
2.0·10−4 M 3-(dansylamino)phenylboronic acid (DAPB) reagent was made by dissolving it to 1 ml dimethylsulfoxide and diluting to 50 ml with water. 20 μl of this DAPB solution was added to each buffered water sample and the fluorescence of the samples was measured using spectrofluorometer, excitation wavelength was 325 nm and the emission intensities between 470-600 nm were integrated. The emission sum was then divided by the intensity of the Raman scattering peak at 650 nm. The result was then compared to the reference sample of ultrapure water. The unit is the decrease (%) of the relative intensity of the sample vs. the ultrapure water (reference).
For a comparison, transparent exopolymer particles were also determined from the same water samples using Villacorte's method (Villacorte L O, Kennedy M D, Amy G L, Schippers J C (2009): The fate of transparent exopolymer particles (TEP) in integrated membrane systems: Removal through pre-treatment processes and deposition on reverse osmosis membranes. Water Research 43: 5039-5052) and the results were compared, see Table 1. From the results can be seen that the relative results of the method according to the invention correlate with the results achieved with Villacorte's method. The measurement unit in Villacorte's method is mg Xanthan equivalent per liter using an arbitrary calibration factor of 0.114 mgXeq.
Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20135857 | Aug 2013 | FI | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FI2014/050648 | 8/26/2014 | WO | 00 |
