**3. Gaseous oxygen monitoring in wastewater**

**2.3. Visualization of scale inhibition mechanisms**

320 Desalination and Water Treatment

solution in the presence of 0.5–15 mg·dm <sup>−</sup><sup>3</sup>

1

A full-scale publication is under in preparation

Tkachenko and Maxim Oshchepkov.

rescence scanning microscope, as shown in **Figure 9b**.

Irrespective of the broad, successful, and long-term antiscalant applications, the mechanisms of scale inhibition still appear in the matter of discussions [14, 74–81]. In this sense, the fluorophore-tagged antiscalants can provide the unique and amazing opportunities to get a deep insight of the scale inhibition mechanisms. As far as we know, recently, such reports on the scale inhibition visualization are missing. However, our research group managed to synthesize a conjugate of 1,8-naphthalimide and HEDP: 1-hydroxy-7-(6-methoxy-1,3-dioxo-1*H*benzo[de]isoquinolin-2(*3H*)-yl)heptane-1,1-diyldi(phosphonic acid), (HEDP-F), as shown in **Figure 9a**. This reagent was tested as an antiscalant in gypsum scale formation experiments performed according to NACE protocol [82]. According to this protocol, a calcium-containing brine and a sulfate-containing brine are mixed to form a supersaturated gypsum aqueous

solution is kept for 24 h at 71°C, cooled, and analyzed for residual calcium content by EDTA titration. In a parallel run, the gypsum crystals have been isolated and analyzed with a fluo-

Unlike the scanning electron microscopy, the fluorescence provides a unique possibility to look inside the crystal. Therefore, all the steps of crystal formation become visible. One can see that the bright crystal rod ("lightsaber"), initially formed by nanoparticles, is completely covered with HEDP-F. Then, this rod becomes the center of gypsum layers' growth without any resistance or involvement of a HEDP-F antiscalant (massive dark layer). Finally, after the gypsum crystal formation is finished, the residual HEDP-F molecules get adsorbed on its surface, particularly at the edges

**Figure 9.** HEDP-F (a) and an image of a Gypsum crystal, isolated in presence of HEDP-F (b); laser scanning microscope LSM-710 Carl Zeiss, lambda mode with 458 nm excitation; 26.10.2017. Data presented by Semen Kamagurov, Sergey

of a crystal lattice, forming the outer layer. This is indicated by green spots and stripes<sup>1</sup>

of an inhibitor at ambient temperature. Then, this

. Evidently,

Biological treatment of wastewater includes activated sludge aeration. This in turn raises a problem of the gaseous oxygen content monitoring. One of the most promising solutions here is the fiber-optic oxygen sensor application. This method is based on the ability of oxygen molecules to suppress the luminescence of some luminofores [10, 83]. A fruitful application of some pyreneor decacylene-based fluorophores along with some ruthenium complexe is reported: (Ru(bpy)<sup>3</sup> , Ru(phen)<sup>3</sup> , [Ru(dpp)<sup>2</sup> Phen]2+ (dpp = 4, 7-diphenyl-1,10-phenanthroline, Phen = 1,10-phenanthroline) [84], as shown in **Figure 10**. Also some terbium(III) complexes have been immobilized

**Figure 10.** Structure of [Ru(dpp)<sup>2</sup> Phen]2+.

**Figure 11.** Structure of Tb(acac)<sup>3</sup> phen.

on aluminum oxide (Tb(acac)<sup>3</sup> phen), where acac-acetylacetone [85], as shown in **Figure 11**, as well as some porphyrin complexes of Pt and Pd [86], is worth mentioning.

Finally, one of the first known applications of fluorophores in water treatment should be mentioned. It is associated with water leaks detection in industrial pipelines. To solve this problem, some fluorescent indicators, for example fluorescein, have been merely added to the

Fluorescent Markers in Water Treatment http://dx.doi.org/10.5772/intechopen.76218 323

The fluorescent markers added to the circulating water or wastewaters find a broad spectrum of analytical applications for online quality monitoring. The most promising and a fastdeveloping field is a scale inhibitor concentration detection via antiscalant-tagged reagents. At the same time the visualization of scale inhibition mechanisms by the fluorescent-tagged antiscalants is a very promising tool of the scale inhibition theory development. Besides, these reagents can provide some unique opportunities for reverse osmosis membrane mapping, scale inhibition traceability, and a scale inhibitor localization in a circulation water

The authors would like to thank the Russian Foundation for Basic Research (Project No.

\*

[1] Duval R, Duplais C. Fluorescent natural products as probes and tracers in biology.

Natural Product Reports. 2017;**34**:161-193. DOI: 10.1039/C6NP00111D

1 Mendeleev University of Chemical Technology of Russia, Moscow, Russian Federation

For the present study, no economic interest or any conflict of interest exists.

circulating water [11].

**6. Conclusions**

facility.

17–08-00061).

**Acknowledgements**

**Conflict of interest**

**Author details**

**References**

Maxim Oshchepkov1,2 and Konstantin Popov2

\*Address all correspondence to: ki-popov@mtu-net.ru

2 PJSC "Fine Chemicals R&D Centre", Moscow, Russian Federation

The emitted blue light (~ 475 nm) of a photogenerator excites the fluorescence of a specially selected chemical complex, placed at the end of a fiber-optic oxygen sensor (sol–gel matrix). The exited complex generates fluorescence with a wavelength which is around 600 nm. This fluorescence gets suppressed by the oxygen present in a sample [87–89]. This provides an effective oxygen concentration measurement in water within the range from 0 to 40.7 ppm [90].

#### **4. Fluorescent total ATP count in wastewaters**

The total bacterial count in wastewater is based on bioluminescence. Normally it is used for the industrial and wastewater quality assessment, while for the drinking water it is not so common. The method is known since 1947, when McElroy has demonstrated that bioluminescence of a glowworm is closely associated with adenosine triphosphate (ATP) content [91]. Thus, the measurement of ATP provides an efficient indication of bacterial pollution of water according to **Scheme 3** [12]:

Analysis involves the firefly luciferase-luciferin system. Its contact with ATP molecules generates the "cold" light, counted by a luminometer within 15–20 s. The sensitivity of analysis is very high. It provides detection of 10–17 ATP moles per liter. Recently, there have been some standard solutions for luminometers present at the market: EnSURE™, SystemSURE Plus™ Clean Trace™, NovaLum™, Firefly 2™, Accupoint™, russian-made LYUM-1, Lumitester PD-20™ etc. [92].

**Scheme** 3. Bioluminescent reaction catalyzed by firefly luciferase.
