Chemical Oxygen Demand Measurements Research Articles

A low cost UV-IR dual wavelength optical sensor with Chirp modulation for in-situ chemical oxygen demand measurements

Chemical oxygen demand (COD) is one of the most representative indicators in water quality monitoring. Among numerous methodologies of COD measurement, optical method has received increasing interests as it can avoid secondary contamination and the frequent replacement of electrodes. However, different with the evolving progress of Infrared (IR) based turbidity sensor, the optical measurements of COD with ultraviolet (UV) absorption still rely on the complex high-end hardware architecture to achieve high accuracy, which prevent its wide deployment in the large scale monitoring of fresh waters. Nonetheless, the essential reason is the weak and in-stable UV signals after absorption. This motivates numerous method in optic domain to enhance the Signal-to-Noise Ratios (SNR) of UV signal, which, as a trade off, have to involve the complex and precise hardware architecture. This paper chooses to ease this challenge from the digital domain, where the Chirp modulation has been applied to both UV and IR signals to form a UV-IR dual wavelength COD measurement system. With Chirp modulated signals, the effective SNRs have been effectively improved due to the convolution gain, while the cross interference of dual-wavelength has been avoided as well with the higher time resolution. Benefited by this simple architecture, a low cost, low power, and high-precision COD sensor has be designed to support the large scale in-Situ deployment.

Improving surface water quality of the Yellow River Basin due to anthropogenic changes.

Understanding of how changes in diverse human activities and climate contribute to water quality dynamics is crucial for sustainable water environment management especially in the arid and semi-arid regions. This study conducted a comprehensive estimation of the surface water quality change in the Yellow River basin during 2003-2017 and its responses to varied pollution sources and water volumes under socioeconomic and environmental influences. Basin-wide measurements of chemical oxygen demand (COD), ammonium nitrogen (NH+4-N) and dissolved oxygen (DO) concentrations were used in trend detection. Annual anthropogenic (covering six sectors) and natural (sediment-induced, flow-in from the upstream and stored last year) pollution sources and water components (inflow, natural runoff, water consumption, reservoir storage and evaporation) were compiled for each sub-basin. Bottom-up hierarchical analysis was then performed to differentiate individual contributions. Results showed significant decreasing trends in COD and NH+4-N concentrations and increasing trends in DO concentrations. The middle reaches that traverse the Loess Plateau however remained severely polluted with 11.3-39.0% inferior to level III in 2017. The pollutant load played major positive contributions that gradually increased from upper to lower reaches. Declines in urban, rural and industrial pollution discharges following environmental investments and rural depopulation contributed the most: 78-96% for COD and 55-100% for NH+4-N. The total surface water volume had dilution effects in the upper and middle reaches (3-28%) and condensing effects in the lower reaches (2-37%). Precipitation and vegetation dynamics contributed slightly. The primary unfavorable factors were the growing agricultural pollution discharges and water consumption in the upper and middle reaches that also threatened the lower reaches. This study is expected to provide in-depth insights for the systematic response of regional water quality to combined human interventions and references for water quality management in other arid and semi-arid river basins worldwide.

Efficient biodegradation of phenol at high concentrations by Acinetobacter biofilm at extremely short hydraulic retention times

Efficient biofilm-forming bacteria are crucial for biofilm wastewater treatment reactors. Nevertheless, finding a suitable bacterial culture with high biodegradation capabilities and ability to grow a stable and effective biofilm that can survive the reactor environment poses a challenge. Here, we present a newly isolated bacterium Acinetobacter EMY that exhibits excellent growth rate, biofilm formation capability, and ability to biodegrade phenol at high concentrations. The phenol degradation rate of Acinetobacter EMY immobilized on polyethylene biocarriers in batch and continuous moving bed bioreactors (MBBRs) treated with phenol as the sole carbon source was significantly higher than that of a bacterial suspension. The continuous MBBR demonstrated impressive phenol removal rates (8.11 and 10.95 kg/m3/d at extremely short hydraulic retention times of 0.5 and 0.25 h, respectively). The phenol removal efficacy was 100% for hydraulic retention times of ≥0.5 h and 67.25% at 0.25 h. The Acinetobacter EMY biofilm batch bioreactor loaded with 165, 330, 665, 1150, and 2100 mg/L phenol achieved the maximum biodegradation rates of 7.65, 7.03, 9.15, 4.48, and 4.16 kg/m3/d, respectively. The new Acinetobacter EMY isolate showed enhanced phenol biodegradation capabilities compared with other isolates in similar studies. Chemical oxygen demand measurements proved that Acinetobacter EMY also consumed the intermediates of phenol degradation. In summary, Acinetobacter EMY is a promising bacterium for use in MBBR systems that treat water containing phenols.

Oxygen-enriched Nanobubbles for a Green Reactive Washing Process

In this study, we used the new nanobubbles technology to create a green reactive washing process for the textile industry, as one of the most polluting sectors where environmentally friendly process designs are indispensable to protect the environment. With this technology, the possibility of eliminating the soaping-off step from the reactive washing sequence was investigated. For the design of an environmentally friendly reactive washing process, the effects of increasing the process temperature of the soaping-off step as well as the use of oxygen-enriched NBs in all washing steps after reactive dyeing with three different dyes were investigated. The results were evaluated by comparing the color coordinates, strength, and fastness of dyed cotton towels washed according to the conventional and alternative processes as well as examining the absorbance and chemical oxygen demand values of the washing baths. Alternative washings did not cause significant differences in color coordinates, while the lowest color strength and highest fastness values were obtained after washing with nanobubbles. The absorbance graphs showed that the most colorful baths belonged to the first bath of the nanobubble washing regime. Chemical oxygen demand measurements revealed that the alternative washing systems were more environmentally friendly than the conventional ones. Based on the results of this study, we concluded that it was possible to implement more eco-friendly washing methods by eliminating the use of soap.

Sea-trial research on natural product-based antifouling paint applied to different underwater sensor housing materials

Biofouling is a common challenge for underwater sensors, especially for long-term in situ monitoring in marine environments. In this study, we assessed the antifouling efficacy of a paint containing a natural product camptothecin (CPT) on six materials (316 L stainless steel, TC4 titanium alloy, 7075 aluminum alloy, polyoxymethylene, polyvinyl chloride, and Teflon), which are frequently used in the construction of underwater sensor housings. Additionally, a buoy-based sea-trial was performed to test the antifouling performance of the CPT-based paint on housings of three in situ sensors used for practical seawater monitoring applications, namely a spectrophotometer for chemical oxygen demand (COD) measurements and two fluorimeters for biochemical oxygen demand (BOD) and chlorophyll a (Chl a) concentration measurements. The results showed significantly lower macrofouling coverage on the areas painted with the CPT-based paint compared to the unpainted areas for each tested material over 9 months of seawater immersion. The CPT-based paint exhibited different antifouling performance for the different materials; in particular, it exhibited better antifouling performance on the plastic materials compared to the metal materials. Furthermore, when applied on submersible sensor housings in the sea-trial test, the CPT-based paint kept the housings of the COD sensor and the Chl a sensor clean for over 4 months. In addition, the paint prevented fouling of the BOD sensor housing even after 6 months of seawater immersion. Thus, our results suggest that the CPT-based paint could be used as a potential solution to control the biofouling of sensor housings for long-term in situ applications in marine environments.

Achieving Electrochemical-Sustainable-Based Solutions for Monitoring and Treating Hydroxychloroquine in Real Water Matrix

Hydroxychloroquine (HCQ) has been extensively consumed due to the Coronavirus (COVID-19) pandemic. Therefore, it is increasingly found in different water matrices. For this reason, the concentration of HCQ in water should be monitored and the treatment of contaminated water matrices with HCQ is a key issue to overcome immediately. Thus, in this study, the development of technologies and smart water solutions to reach the Sustainable Development Goal 6 (SDG6) is the main objective. To do that, the integration of electrochemical technologies for their environmental application on HCQ detection, quantification and degradation was performed. Firstly, an electrochemical cork-graphite sensor was prepared to identify/quantify HCQ in river water matrices by differential pulse voltammetric (DPV) method. Subsequently, an HCQ-polluted river water sample was electrochemically treated with BDD electrode by applying 15, 30 and 45 mA cm−2. The HCQ decay and organic matter removal was monitored by DPV with composite sensor and chemical oxygen demand (COD) measurements, respectively. Results clearly confirmed that, on the one hand, the cork-graphite sensor exhibited good current response to quantify of HCQ in the river water matrix, with limit of detection and quantification of 1.46 mg L−1 (≈3.36 µM) and 4.42 mg L−1 (≈10.19 µM), respectively. On the other hand, the electrochemical oxidation (EO) efficiently removed HCQ from real river water sample using BDD electrodes. Complete HCQ removal was achieved at all applied current densities; whereas in terms of COD, significant removals (68%, 71% and 84% at 15, 30 and 45 mA cm−2, respectively) were achieved. Based on the achieved results, the offline integration of electrochemical SDG6 technologies in order to monitor and remove HCQ is an efficient and effective strategy.

Synthesis and characterization of CdO-SnO2 NPs with excellent performance for Naphthol Blue Black (NBB) dye photodegradation and multi-application study

Precipitation and sonication techniques have been used to successfully synthesise CdO-SnO2 nanocomposite material. It was characterised using high-resolution scanning electron microscopy (HR-SEM) with elementary dispersive X-rays (EDX), high-speed transmission electron microscopy (HR-TEM), XRD analysis, photoluminescence spectroscopy (PL), UV–Vis DRS and BET. Using simulated UV irradiation at 365 nm, the prepared nanocomposites were also tested for their ability to degrade naphthol blue black (NBB) in water. Chemical oxygen demand measurements confirm dye mineralization. The higher activity of CdO-SnO2 nanocomposite material is attributed to a realisable mechanism. This nanocomposite material was found to be durable and reusable as a result of the reaction. Compared to SnO2 nanocomposite material, CdO-SnO2 nanocomposite material showed the highest antibacterial activity and electrochemical activity.

Improved water quality monitoring indicators may increase carbon storage in the oceans

Indicators related to organic matter are important when assessing aquatic environment quality. The chemical oxygen demand (COD) is widely used as a water quality reference. However, oxidizing agents used to determine the COD can oxidize refractory organic matter that is not pollutant and can persist in the ocean for thousands of years. This means the COD can misrepresent the water quality. The actual water quality can be indicated better by the biochemical oxygen demand (BOD) than the COD, but determining the BOD is time-consuming and gives variable results. In this study, the optical properties of dissolved organic matter in water samples from the Chinese coast that had been incubated for a long time or directly oxidized using COD oxidant were analyzed. The results indicated that the oxidizing agent rapidly oxidized 22.93% ± 4.96% of refractory dissolved organic matter (RDOM) that was resistant to microbial degradation, implying that RDOM made a marked contribution to the COD. Meanwhile, size-fractional fluorescence spectroscopy and COD measurements indicated that the COD of the >0.7 μm fraction and the fluorescence intensity of the protein-like component significantly positively correlated with the BOD of the bulk sample. This indicated that, for monitoring organic pollutants in coastal waters, the COD of the >0.7 μm fraction could be used as a proxy for the standard COD and that the fluorescence intensity of the protein-like component could be used as a convenient proxy for the BOD. The method can help retain recalcitrant organic matter in seawater to act as a carbon sink.

Photocatalytic degradation kinetics of cationic and anionic dyes using Au–ZnO nanorods: Role of pH for selective and simultaneous degradation of binary dye mixtures

Photocatalysis with ecofriendly and low cost materials is attractive for degradation of organic pollutants without aid of strong reagents. In this regard, Au nanoparticle decorated ZnO nanorods (Au–ZnO) with good crystalline quality was synthesized by cost-effective and scalable hydrothermal method followed by photo-reduction of Au salt. This study addresses variation of photocatalytic degradation kinetics of different nature of dyes with various scavengers and pH conditions. Further, the process versatility is demonstrated by selective or simultaneous degradation of binary dye mixtures with optimized parameters. From Langmuir-Hinshelwood kinetic model, dye concentration range for first order limiting case was determined, and further validated from measured surface area of photocatalyst and change in dye absorbance before irradiation. Better adsorption with faster degradation exhibited by Methylene Blue (MB) dye showed efficient mineralization, revealed from chemical oxygen demand measurements. In Au–ZnO photocatalysis, generation of hydroxyl radical and its significant role in dye degradation was demonstrated using different scavengers. Variation of dye adsorption with pH dependent surface charge characteristics of photocatalyst resulted about one order higher degradation rate constant of MB at high pH. Strong pH dependent MB degradation is shown to be useful for its selective or simultaneous degradation with other dyes. Results of this study are useful for designing photo-reactors and these nanoparticles are efficient for degradation of different dyes, their combinations and industrial effluents under low power UV lamp for treatment different organic pollutants.

Smart COD sensor using UV–Vis spectroscopy against optical window surface contamination

A typical method for real-time and unpolluted measurement of chemical oxygen demand (COD) is UV–Vis absorption spectroscopy, however, contamination of the measuring system’s optical window surface affects the measurement accuracy during long-term monitoring. This study proposes an optical window surface contamination (OWSC) compensation method, and a multi-wavelength smart sensor for long-term accurate COD measurement was developed.This study uses equivalent absorption spectrum (EAS) to describe OWSC, and explores its spectral characteristics. Therefore, we can predict the EAS of OWSC between 250 and 380 nm based on the measured absorption spectrum between 380 and 440 nm, and subtract the EAS of OWSC to get the absorbance of COD to complete the spectrum compensation.Furthermore, we designed a smart COD sensor which has the advantages of real-time warning and maintenance-free. We proved that the OWSC compensation has excellent applicability through experiments using the COD sensor, and long-term accurate COD measurement can be achieved.

Implications of COD analysis use in the peracetic acid-based wastewater treatment.

Peracetic acid (PAA) stands out as a safe and environmental-friendly oxidant and disinfectant which has been effectively used in wastewater treatment. Chemical oxygen demand (COD) is a very popular analysis in wastewater treatment; however, the interference of residual PAA on the COD measurement is still unknown. In this context, this study investigated the implications of applying the COD analysis in PAA-based treatment. Each 1 mg·L-1 of PAA increased the COD concentration around 13.5 mg O2·L-1. Residual PAA and hydrogen peroxide (H2O2) were efficiently neutralized by sodium metabisulfite (SMBS) at the optimal SMBS/PAA ratio of 10.2:1 in a wide pH range (5 to 9). The effect of PAA addition on the COD concentration was evaluated in different water matrices (potassium hydrogen phthalate and wastewater solutions). The COD results with the SMBS addition at optimal SMBS/PAA ratio were lower than the ones without it. It may happen due to the neutralization of residual H2O2/PAA and the complexity of the water matrices which can interfere in the COD results. This study discussed the impact of the residual H2O2/PAA neutralization before the COD analysis, and this investigation can be used as a practical guideline for the correct COD measurement in PAA-based treatment.

Precious Data from Tiny Samples: Revealing the Correlation Between Energy Content and the Chemical Oxygen Demand of Municipal Wastewater by Micro-Bomb Combustion Calorimetry

Wastewater treatment plants (WWTP) are aimed to be transformed from sinks into sources of energy and material. For fostering corresponding engineering efforts and economic assessments, comprehensive knowledge of the energy content of wastewater is required. We show in this proof-of-concept study that these data can be gathered by combining micro-bomb combustion calorimetry with freeze-drying. Thereby, the methodology for measuring the combustion enthalpy (ΔcH) of wastewater is significantly improved by decreasing the time demand for the drying process as only tiny amounts of samples are required. Here, the effluent of the primary clarifier of a wastewater treatment plant treating low-strength municipal wastewater was sampled on a weekly basis for 1 year, yielding 53 composite samples that were analyzed for ΔcH and standard wastewater parameters. A robust correlation between the chemical oxygen demand (COD) and ΔcH of −14.9 ± 3.5 kJ gCOD−1 (r = 0.51) was determined, verifying previous results obtained with more laborious and time-demanding methodologies. The global chemical energy potential of the sampled WWTP is presumably higher as the first treatment steps and losses during sample preparation reduced the amount of energy-rich compounds. A stronger correlation was observed between ΔcH and the biochemical oxygen demand (BOD5, r = 0.64), suggesting its usage for predicting the potential of wastewater as feedstock for biotechnological applications. This demonstrates that micro-bomb combustion calorimetry can be applied for deriving precious information on the energy content of wastewater from simple COD measurements.

Synthesis and characterization of CeO2 NPs using Cardiospermum halicacabum L photocatlyst with excellent performance for Rh B dye and electrochemical activity

Effective use of unique structural and electronic properties of UV light has made more researchers extremely involved for photocatalytical systems. The synthesis of CeO2 nanoparticle (NPs) has been successfully achieved by using Cardiospermum halicacabum L leaf Extract. The nanoparticle was characterized by High-resolution scanning electron microscopy (HR-SEM) with elementary dispersive X-ray (EDX), High-resolution transmission electron microscopy (HR-TEM), XRD analysis, FT-IR, FT-Raman, photoluminescence spectroscopy (PL) and UV–Vis DRS. This plant extract CeO2 nanopartricles has high photocatalytic activity of Rh B dye that of chemical method CeO2 nanopartricles and at various parameters was reported. Mineralization of dyes is confirmed by measurements of chemical oxygen demand. The reaction of this nanoparticle was described as a feasible mechanism. This catalyst was found to be stable and reusable. This nanoparticle has electrochemical activity showed highest activity by bio synthesis of CeO2 nanoparticle compared that of chemical synthesis CeO2 nanoparticle was reported in this article.

Fast and Reliable Determination of Organic Compounds in Washing Water Samples Using Electrochemical-based Measurements of Chemical Oxygen Demand

Chemical Oxygen Demand (COD) is referring to the total amount of oxygen used for a chemical oxidation of organic compounds in a water sample. COD stands as an important tool for water safety and water quality standard. Fast-scan cyclic voltammetry (FSCV) has been reported as a simple and a rapid method for electrochemical measurements, particularly for neurotransmitter compounds in brain and biological systems. The main explicit characteristics of FSCV comes from the usage of small volumes of analytes and by adapting carbon-fiber microelectrode as a working electrode with a scan rate of milliseconds. In this research project, FSCV has shown promising results as an alternative method that correlates the COD of traditional measurements. Traditionally, COD is more often estimated using oxidizing agents and toxic chemical reagents that have a serious environmental impact on lifecycle. Unlike traditional oxidation methods, FSCV was used as a powerful an electrochemical tool that allows for measuring COD of Iceberg lettuce washing water samples without using any oxidizing or toxic reagents in few minutes. In addition, FSCV measurements showed a high recovery percentage for both batches, low organic materials, and high organic materials. FSCV provides a fast and reliable platform to measure all chemically oxidizable organic compounds in lettuce washing water samples, which is directly related to COD with an environmentally friendly model based on the oxidation potential.

Removal of Tetracycline Oxidation Products in the Nanofiltration Process

The possibility of removing tetracycline (TRC) from water in an integrated advanced oxidation and membrane filtration process was investigated. Ozonation and UV/H2O2 photooxidation were applied for the destruction of TRC. Six oxidation products (OPs) retaining the structural core of TRC have been identified. One new TRC oxidation product, not reported so far in the literature, was identified—ethyl 4-ethoxybenzoate. All identified OPs were effectively retained on the membrane in the nanofiltration process. However, chemical oxygen demand (COD) measurements of the filtrates showed that in the case of UV/H2O2 oxidation, the OPs passed through the membrane into the filtrate. Various water matrices were used in the research, including the river water untreated and after ozone treatment. It has been shown that organic matter present in surface water can improve pharmaceutical retention, although it contributes to significant membrane fouling. Pre-ozonation of the river water reduced the membrane fouling. The XPS analysis was used to show ozone and H2O2 influence on the top polymer layer of the membrane. It was shown that the oxidants can damage the amide bond of the polyamide.

Advanced electrochemical degradation of basic yellow 28 textile dye using IrO2/Ti meshed electrode in different supporting electrolytes

One of the most concerning recent environmental threats is textile wastewater effluents. Although versatile methods exist for the treatment of textile effluents, electrochemical degradation is considered an efficient and promising approach. In the present study, the effect of an IrO 2 /Ti meshed electrode in the presence of Na 2 SO 4 or NaCl as a supporting electrolyte on the decolorization and mineralization of Basic Yellow 28 (BY28) textile dye is demonstrated. The results showed that the optimum conditions were a current density of 0.03A cm −2 , initial dye concentration of 2 × 10 −5 M, pH of 2.5 or 6.5 for Na 2 SO 4 or NaCl, and a supporting electrolyte concentration of 0.08 or 0.03 M for Na 2 SO 4 or NaCl, respectively. The degradation efficiency was followed using Ultraviolet-visible (UV–Vis) spectrophotometry, cyclic voltammetry, and chemical oxygen demand (COD). Cyclic voltammetry was carried out in the potential window from +1.0 V to −1.0 V. After 15 min, the color removal of the BY28 dye was 92.9% and 93.3% and the COD removal was 26.8% and 46.2% in the presence of Na 2 SO 4 and NaCl, respectively. Besides, the corresponding current efficiency and energy consumption were estimated to validate the proposed electrochemical method. The results revealed that NaCl was more powerful than Na 2 SO 4 as a supporting electrolyte. • Electrochemical decolourization of textile dye, Basic Yellow 28, was investigated. • Based on its performance, IrO 2 /Ti meshed electrode was selected and used in the presence of Na 2 SO 4 or NaCl as a supporting electrolyte. • Most effective parameters such as current density, pH, initial dye, and supporting electrolyte concentrations were tested and optimized. • The degradation efficiency was followed up using UV–Vis, CV and COD measurements. The results demonstrated that the oxidation process in NaCl electrolyte is more powerful than Na 2 SO 4 .

A batch microfabrication of a microfluidic electrochemical sensor for rapid chemical oxygen demand measurement.

Chemical oxygen demand (COD) is one of the key water quality parameters in environmental monitoring. However, fabricating a COD sensor with the characteristic of batch-processing and rapid measurement is always a challenging issue. This paper reports a microfluidic electrochemical sensor for the organic matter measurement based on advanced oxidization within a fixed microvolume detection chamber by a microfabrication technique/MEMS. By fabricating a silicon-based Ag/AgCl reference electrode and employing PbO2 as the working electrode with Pt as the counter electrode, we verified the superiority of the as-fabricated sensor by continuous potassium acid phthalate detection; an acceptable limit of detection (4.17 mg L-1-200 mg L-1), a low limit of detection (2.05 mg L-1), a desirable linearity (R2 = 0.982) and relative stability at different pH values and Cl- concentrations was witnessed. Particularly, a shorter detection time (2 s) was witnessed for the as-proposed sensor compared with traditional organic matter measurement methods. Each sensing process takes only 2 seconds for sensing because a micro-cavity with a volume of 2.5 μL was fabricated and used as a detection pool. Moreover, as the sensor was fabricated by a mass-production technique, potential response consistency of multiple sensors was expected and was verified via a series of parallel experiments. In this paper, a miniaturized (8 mm × 10 mm), low-cost and reliable COD sensor was designed and fabricated by MEMS, and it provided a core sensor component for construction of an online water environment monitoring network to meet the substantial demand for COD sensors in the Internet of Things (IOT) era.

Synthesis, Characterization and Comparative Study of TiO2 and ZnO Nanoparticles and their Application as a Photocatalysts for a Trichromatic Dye

Background:The textile industrial effluents cause profound imbalances in ecosystems, when released into nature; dyes are oxidized by micro-organisms, resulting in a decrease in the dissolved oxygen, which is necessary for the aquatic life. For this reason, it is important to implement economic, efficient, and green methods ensuring both the discoloration and detoxification of water.Objective:TiO2and ZnO nanoparticles were synthesized by sol-gel and precipitation methods, respectively. These two nanoparticles were used to compare photocatalytic degradation under UV and solar irradiation for three reactive azoic dyes (trichromatic): Reactive Bezactive Yellow (RBY), Reactive Bezactive Red (RBR), and Reactive Bezactive Blue (RBB).Methods:The structural, i.e., morphological surface properties of the synthesized photocatalysts were characterized by Fourier Transform Infrared, X-ray diffraction, UV-Visible diffuse reflectance spectroscopy, and Scanning Electron Microscopy.X-ray diffraction shows that TiO2has a tetragonal structure with an anatase form. The effects of some operational parameters, such as the amount of TiO2 and ZnO, initial dye concentration, dye mixtures, and pH, were examined. The progress of photodegradation reaction was monitored by UV-Visible spectroscopy for decolorization and by High-Performance Liquid Chromatography for degradation, and the efficiency of degradation was confirmed by Chemical Oxygen Demand measurement.Results:The dye degradation was found to be better in the presence of solar irradiation than under UV irradiation. The photocatalytic activity of ZnO was higher than TiO2 when used in its optimal conditions.Conclusion:The percentage of degradation of each dye is different, and the order of degradation of the three reactive dyes is as follows: RBY> RBR> RBB.

Turbidity compensation method based on Mie scattering theory for water chemical oxygen demand determination by UV-Vis spectrometry.

In view of the problem that chemical oxygen demand (COD) measurement in water using UV-Vis spectrometry was easily affected by turbidity, this paper proposed an analytical method for determining the complex refractive index of particles in water based on Lambert-Beer's law and K-K (Kramers-Kronig) relationship. The obtained complex refractive index was used to establish the turbidity compensation model in the COD characteristic spectral region, and the COD concentration inversion were achieved by using the PLS algorithm. The results show that the turbidity compensation method based on Mie scattering theory can improve the accuracy of COD measurement by UV-Vis spectroscopy. Compared with before turbidity compensation, R2 (determination coefficient) between true values and predicted values of COD increased from 0.2274 to 0.9629, and RMSE (root mean square error) of predicted values decreased from 21.73 to 3.12mgL-1. Compared with 350nm PC, derivative method, and improved MSC method, the turbidity compensation method for COD measurement based on Mie scattering theory is simple, fast, and highly accurate. And the calculated spectrum can represent the scattering characteristics of the measured spectrum. The average relative error between the fitted spectrum and the original normalized spectrum in the 55 mixed solutions was 0.52%, and the maximum relative error was 6.65%. This method can be useful for online COD measurement. Graphical abstract.

Photoelectrocatalytic reactor improvement towards oil-in-water emulsion degradation

Oil-in-water (O/W) emulsion is critical wastewater that is challenging to eliminate and requires a long treatment process, and it is necessary to develop highly effective removal methods before releasing it into natural water sources. This research has selected the photoelectrocatalytic (PEC) technique to solve this problem by developing a PEC reactor for high efficiency in O/W degradation and understanding the essential factors related to the PEC reactor's efficiency improvement. The PEC reactor has been designed on a large scale with suitable positioning of an electrode that is, designing a light source near the anode electrode to enhance light irradiation efficiency and including a circulating pump to provide continuous flow to the solution through the electrode surface. We studied the main factors of supporting the electrolyte, electrode characteristics, and catalytic process. We investigated the O/W-degradation efficiency using a UV/Vis spectrophotometer, chemical oxygen demand (COD) measurement, and GC-MS analysis. We optimized the PEC reactor using the developed BiVO4 photoanodes and placed them parallel with the zinc plates. Then, we controlled the applied potential at 1.0 V in 0.1 M Na2SO4 supporting an electrolyte under visible light irradiation. The developed PEC reactor can be degraded in the O/W emulsion up to 76% and decreased the COD value up to 78% for 7h. This PEC cell can be completely decomposed of many functional groups, such as carbonyl, ester, nitrile, amine, phosphate, chloro group, and nitro group, that were contained in the O/W substance. The highlight of this research is the designed light source and circulating pump inside of the PEC reactor to enhance the light irradiation, refresh the anode electrode, and understand the critical factor for the improvement of O/W-degradation efficiency. This PEC reactor presents a high-efficiency O/W degradation with practical use and a fast process suitable for further application in high turbidity of wastewater treatment from the oil industry.