Original research articleExperimental investigation of optical properties of oily sewage with different pH environment
Introduction
Optical measurement has attracted more attention due to its fast detection speed, and has been applied to detect oily sewage. The optical properties are the basis of optical measurement [[1], [2], [3], [4], [5], [6]], and the accuracy of optical detection is greatly influenced by pH [7]. Especially oily sewage contains a lot of alkaline substances, resulting in high pH value of oily sewage [8]. Therefore, it is of great significance to obtain the optical properties under different pH for optimization and testing the oily sewage optical parameters.
At present, many domestic and foreign scholars have done a lot of research on the effect of pH on optical measurement [[9], [10], [11], [12], [13], [14], [15], [16], [17]].Yi et al. [18] studied the fluorescence spectra of oily sewage in the pH range of 3˜12, the experimental results showed that the fluorescence intensity increases with the increase of acidity. Under alkaline conditions, with the increase of alkalinity, the fluorescence intensity decreased continuously, and the position of the fluorescence peak has no change, which remained at the wavelength of 398 nm. Zhou et al. [19] studied the spectral characteristics of phycoerythrin in the pH range of 4.2˜10.5, and pointed that the light transmittance of phycoerythrin achieve the maximum at pH of 7.6, under acidic or alkaline conditions, the spectrum of phycoerythrin became weakened gradually. Sugandhi et al. [20] studied the effects of three different pH values on the optical properties of the tris-glycine zinc chloride in aqueous solution, and found that tris-glycine zinc chloride crystals have better transmittance at pH of 3. Göde et al. [21] studied the effect of pH on the structure and optical properties of chemical deposition MnTe films, and obtained the film refractive index and extinction coefficient at pH of 9, 10, 11 and 12 respectively. Khalid [22] obtained the red algal protein spectra in the range of 350˜700 nm by experiment, and the red algal protein had better transmittance in the pH range of 2.5˜11.0. From above, we can see that pH is an important factor in optical measurement. Because of the high pH value of oily sewage [[23], [24], [25], [26], [27]], and less research on the optical properties, it is more meaningful to explore the influence of pH value on the optical properties of oily sewage.
In this work, the optical properties of oily sewage were experimentally studied. Besides, the optical properties of different pH were obtained by the transmittance method combined with the double thickness inversion model.
Section snippets
Material and transmittance spectra measurement
The oily sewage sample was obtained from the joint station of oilfield (oil content of oily sewage is 6.32 mg/L). The transmittance spectra were measured by spectrophotometer (TU-1900) and the pH of the samples was measured by PHS-3C acidity meter (range of 0.00˜14.00). The pH value of oily sewage adjusted by NaOH (analysis pure) and HCl (analysis pure) was 6.5, 7.4, 8.7, 9.6, 10.6 and 11.8, respectively.
The calculation model
Spectrophotometer TU-1900 was used to measure the total transmittance of the oily sewage
Influence of pH on the transmittance spectra of oily sewage
The transmittance spectra of different optical path and different pH of oily sewage in the range of 190˜900 nm were obtained, as shown in Fig. 2.
As shown in Fig. 2, the transmittance of different optical path all decrease with the increase of pH in range of 8.7˜11.8 and has the same variation tendency. There are absorption region (200˜230 nm) and high transmittance area (400˜800 nm) in the transmittance spectra of different optical path. In the absorption region, with the increase of pH in the
Conclusions
In this work, the transmittance spectra of oily sewage under different pH were measured by the spectrophotometer TU-1900, and the oily sewage transmittance spectra under different optical path were analyzed. Besides, the optical properties of the oily sewage were obtained according to the method of double thickness inversion model (the refractive index and the absorption index) and the normalized standard deviations of the refractive index and the absorption index were calculated by max-min
Funding
The financial support provided by the Project Funded by China Postdoctoral Science Foundation through Grant No. 2018T110267, the PetroChina Innovation Foundation through Grant No. 2018D-5007-0608, and Talent Training Projectof Northeast Petroleum University through No. SJQHB201801.
Acknowledgements
The authors report there no conflicts of interest.
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