Effects of Tourmaline on Dehydrogenase Activity of Activated Sludge

Ruigang WANG, Hailong LIU

Abstract The black tourmaline produced in Lingshou of Hebei Province was characterized by X-ray diffraction and scanning electron microscope， and the effect of tourmaline on dehydrogenase activity of activated sludge was studied. The results showed that tourmaline increased the dehydrogenase activity of activated sludge and enhanced the stability of dehydrogenase to pH change. It made the pH value of activated sludge with different initial pH value tend to about 7.4， and improved the dehydrogenase activity of activated sludge. In addition to affecting water molecular groups， it was also related to maintaining the constant weak alkaline pH of the system.

Key words Tourmaline; Activated sludge; Dehydrogenase

Received： April 9， 2022  Accepted： Jun 12， 2022

Ruigang WANG （1978- ）， male， P. R. China， associate professor， PhD， devoted to research about waste treatment and recycling.

*Corresponding author. E-mail： 122822404@qq.com.

Tourmaline is a cyclic silicate mineral of aluminum， sodium， iron， calcium and magnesium characterized by boron[1]. Tourmaline has a permanent spontaneous electrode[2]， and the electric field generated by tourmaline reflects the polarity of tourmaline[3]. It is of great significance to studying the electric field effect of tourmaline and expanding the application of tourmaline in the field of ecological environment.

In recent years， the research on the structure and function of water molecular clusters has become one of the hotspots of todays research. Water does not exist in the form of H2O single molecule， but the structure of water molecular group formed by the combination of several water molecules through hydrogen bond[4]. The change of water molecular group can produce a variety of biological effects[5]. Xia et al.[6] found that tourmaline can reduce water molecular group and water molecular association degree. Activated sludge plays an important role in wastewater biological treatment[7]. The essence of wastewater biological treatment is a series of biological redox reactions catalyzed by multi enzyme system produced by microorganisms， in which dehydrogenase can activate the hydrogen atom of oxidized organic matter and transfer it to specific hydrogen acceptors. Dehydrogenase activity can be used to reflect the active microbial biomass and its degradation activity to organic matter in the treatment system. Therefore， improving the dehydrogenase activity of activated sludge is of great significance for wastewater biological treatment[8]. Based on the above， the effect of tourmaline on dehydrogenase activity of activated sludge was discussed， which provides an experimental basis for the application of tourmaline in wastewater biological treatment.

Experiment

Materials

The tourmaline used in the experiment was black tourmaline produced in Lingshou of Hebei Province. The tourmaline powder was prepared by wet stirring mill ultrafine grinding process. The activated sludge used in the experiment was taken from the aerobic sludge in the aeration tank of sewage treatment plant.

Testing

XRD analysis of tourmaline powder and ceramsite was carried out by X-ray diffractometer. The instrument model was Smartlab-SE. The surface morphology of tourmaline was analyzed by scanning electron microscope. The instrument model was Zeiss Sigma 300. The activity of dehydrogenase was determined by TTC dehydrogenase activity determination method. The details， referred to the manual for microbiological inspection of environmental engineering [9]. The pH value of the system was measured by pH-3C precision pH meter.

Results

Tourmaline powder characterization

Content of elements in tourmaline

The mass fraction of each element in tourmaline is shown in table 1 through energy spectrum analysis.

According to the analysis in table 1， the tourmaline material used in the surface experiment is iron tourmaline.

XRD analysis of tourmaline powder

The phase structure of tourmaline powder was analyzed by X-ray diffractometer. The results are shown in Fig. 1.

The XRD pattern of tourmaline powder was shown in Fig. 1. It can be seen from Fig. 1 that the main component of tourmaline powder is black tourmaline. According to Scherrers formula for crystals， d=Kλ/（Bcosθ）， The larger the FWHM B value of XRD diffraction peak， the smaller the grain size D. The smaller the tourmaline powder is， the larger its surface area is， and the more likely the surface structure is to have defects， resulting in smaller diffraction intensity and wider diffraction peak. Therefore， when using tourmaline powder， it should be super refined as much as possible.

Fig. 2 is the SEM diagram of tourmaline ultrafine powder. It can be seen from Fig. 2 that the dispersion between large particles in tourmaline powder is good， and the small particles are bonded and adsorbed on the surface of large particles， resulting in agglomeration caused by tourmaline pyroelectricity， indicating that the attraction and repulsion between tourmaline powder particles coexist.

Effects of tourmaline dosage on dehydrogenase activity of activated sludge

Fig. 3 shows that different amounts of tourmaline were added to 100 ml of activated sludge， and the dehydrogenase activity of each group was measured under the condition of 37 ℃， pH=7.4. Under this condition， the enzyme activity of the tourmaline free group was 100%， and the relative enzyme activity was calculated.

It can be seen from Fig. 3 that adding different contents of tourmaline to the bacterial solution could improve the dehydrogenase activity of activated sludge. The amount of tourmaline in 100 ml of activated sludge was less than 2 g， and the dehydrogenase activity of activated sludge increased with the increase of tourmaline. The amount of tourmaline was in the range of 2.0-5.5 g. with the increase of tourmaline， the dehydrogenase activity of activated sludge tended to be flat. Compared with the control group without tourmaline， the addition of 2.0-5.5 g tourmaline to activated sludge increased the dehydrogenase activity by 33%-36%.

Effects of tourmaline treatment time on dehydrogenase activity of activated sludge

Fig. 4 shows that 2 g of tourmaline was added to 100 ml of activated sludge and cultured under the condition of 37 ℃， pH=7.4. The activated sludge was taken out at different times to determine the dehydrogenase activity. The enzyme activity of the tourmaline free group was 100% under the condition of 0 h， 37 ℃， pH=7.4， and the relative enzyme activity of each group was calculated.

It can be seen from Fig.4 that the dehydrogenase activity of activated sludge increased with the increase of culture time whether tourmaline was added or not. Tourmaline increased the activity of cell dehydrogenase. With the increase of tourmaline action time， the activity of dehydrogenase increased and had a certain cumulative effect.

Effects of temperature on the effect of tourmaline on dehydrogenase activity

Fig. 5 shows that 2 g of tourmaline was added to 100 ml of activated sludge and treated at different temperature for 30 min under the condition of an initial pH value of 7.4. The dehydrogenase activity of activated sludge was measured. Under the condition of 37 ℃， pH=7.4， the dehydrogenase activity of tourmaline free group was 100%， and the relative enzyme activity of each group was calculated.

It can be seen from Fig. 5 that whether tourmaline was added or not， the dehydrogenase activity had good thermal stability in the range of 30-40 ℃. Compared with the control group without tourmaline， adding 2 g of tourmaline to 100 ml of bacterial solution increased the cell activity by 25%-35%.

Effects of pH on the effect of tourmaline on dehydrogenase activity

Fig. 6 shows that 2 g of tourmaline was added to 100 ml of activated sludge and treated in 37 ℃ incubator for 24 h under different initial pH values. The dehydrogenase activity was measured. The dehydrogenase activity of tourmaline free group was 100% under the conditions of 37 ℃ and pH=7.4， and the relative enzyme activity of each group was calculated.

It can be seen from Fig. 6 that when there was no tourmaline effect， the optimum pH value of cell dehydrogenase activity was 8.0. The increase or decrease of pH value reduced the dehydrogenase activity. Under the action of tourmaline， the activity of cell dehydrogenase was less affected by pH value. The activity of dehydrogenase was very good in the range of pH value 5-11， which showed that activated sludge cells can be stable in a wide range of pH value under the action of tourmaline. Compared with the control group without tourmaline， adding 2 g of tourmaline to 100 ml of activated sludge solution increased the dehydrogenase activity by 35%-72%.

Control of tourmaline on pH value of the system

Fig. 7 shows the pH values measured at different times under different initial pH values when 2 g of tourmaline was added to 100 ml of activated sludge.

It can be seen from Fig. 7 that tourmaline made the pH values of the suspensions with different initial pH values tend to about 7.4， and the pH value rise rate of acidic solution was greater than that of alkaline solution.

Discussion

Nakamura et al.[2] first found that tourmaline has a permanent spontaneous electrode. Ji et al.[3] observed the existence of tourmaline polarity by means of scanning electron microscope， and its particles are similar to spontaneously polarized electric dipole. The electric field generated by tourmaline is an important reflection of its polarity. There is a field strength of 107-104 V/m in the range of more than ten microns of tourmaline surface thickness[3]. Tourmaline electric field will affect the structure and activity of water. Water molecules are electrolyzed under the action of electric field to form H+ and OH-， and finally form active molecules H3O+ and H3O-2， so that water molecules have strong interfacial activity[10]. Tourmaline electric field can change the dynamic hydrogen bond network system of water molecular clusters and destroy the hydrogen bond between water molecules， so as to change the structure of water molecular clusters[11]. Tourmaline emission wavelength 4-14 μm. Far infrared with emissivity above 0.92. The far infrared emitted by tourmaline resonates with the hydrogen bond in water， which can cut off the hydrogen bond of macromolecular groups and make the water molecular groups smaller[1].

Changing the size of water molecular group can change the role of water in organisms， reduce the number of molecules in water molecular group， increase the biofilm permeability of water， enhance the metabolic function of organisms， and achieve the effect of improving the function of organisms. The water of small molecular groups enters the cell， which can promote cell metabolism and enhance cell vitality[5]. The experimental results that tourmaline can affect water molecular groups and cause the change of dehydrogenase activity of activated sludge provide an experimental basis for the application of tourmaline in wastewater biological treatment. Meanwhile， it is of significance to improving the high added value of tourmaline and expanding the application of tourmaline in the field of ecological environment.

The tourmaline obtained from the experiment made the pH values of solutions with different initial pH values tend to about 7.4， and the rising rate of pH value of acidic solution was greater than that of alkaline solution. The result is consistent with that of Ji et al.[12]. The polarity of tourmaline particles affects the redox potential of water， and adjusts the pH value of the solution to weak alkalinity. The main factor that tourmaline reduces the pH value of alkaline solution is the polarity of tourmaline. In addition to the polarity， surface adsorption and ion exchange adsorption of H+ are also important factors to increase the pH value of acidic solution[12]. Constant acid-base balance is an important condition to maintain the normal metabolism of activated sludge. Under the action of tourmaline， the dehydrogenase activity of activated sludge was less affected by pH value. The pH stability of dehydrogenase was very good in the range of pH value 5-11， which showed that the activity of activated sludge can be stable in a wide range of pH value under the action of tourmaline.

Conclusions

① Tourmaline could reduce water molecular group， reduce water molecular association degree and improve dehydrogenase activity of activated sludge.

② Tourmaline made the pH values of activated sludge with different initial pH values tend to about 7.4. Under the action of tourmaline， the dehydrogenase activity of activated sludge was less affected by pH value. The pH stability of dehydrogenase was very good in the range of pH value 5-11， which showed that the activity of activated sludge can be stable in a wide range of pH value under the action of tourmaline.

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