Chemical Oxygen Demand Of Solution Research Articles

Long-lasting BDD/Si3N4–TiN electrodes for sustainable water remediation

Boron-doped diamond (BDD) thin films have the potential to revolutionize water remediation through electrochemical oxidation, converting persistent pollutants into CO2 and water. However, a significant challenge in implementing BDDs on a large scale is the choice of substrate material. Electrode failure typically occurs due to BDD delamination from the substrate. We propose using a ceramic composite of silicon nitride (Si3N4) and titanium nitride (TiN) as a substrate to address this issue. This electroconductive composite combines Si3N4's high wear resistance, chemical stability, and high affinity for diamond film growth with the TiN's metal-like conductivity. In this work, BDD films were grown by Hot Filament Chemical Vapor Deposition (HF-CVD) over Si3N4–TiN substrates containing 30%vol. TiN. The resulting BDD/Si3N4–TiN electrodes were analyzed concerning their microstructure, diamond quality, conductivity, adhesion strength, service life, and electrochemical properties. Phenol was used as a model to test the electrode's ability to oxidize pollutants. We found that the BDD/Si3N4–TiN electrode could eliminate phenol entirely and up to 98.8 % of the model solution's Chemical Oxygen Demand (COD) after 5 h of direct anodic oxidation, with an Average Current Efficiency (ACE) of 14 % and an energy consumption of 138 kW h kgCOD−1. Furthermore, the BDD/Si3N4–TiN electrode could withstand more than 2016 h of accelerated life test without film delamination. Overall, the results demonstrate that BDD/Si3N4–TiN electrodes are a potential long-lasting solution for large-scale water treatment by electrochemical advanced oxidation processes (EAOPs) in a sustainable manner, especially if combined with renewable energy sources.

Efficient Dye Contaminant Elimination and Simultaneously Electricity Production via a Bi-Doped TiO2 Photocatalytic Fuel Cell

TiO2 develops a higher efficiency when doping Bi into it by increasing the visible light absorption and inhibiting the recombination of photogenerated charges. Herein, a highly efficient Bi doped TiO2 photoanode was fabricated via a one-step modified sol-gel method and a screen-printing technique for the anode of photocatalytic fuel cell (PFC). A maximum degradation rate of 91.2% of Rhodamine B (RhB) and of 89% after being repeated 5 times with only 2% lost reflected an enhanced PFC performance and demonstrated an excellent stability under visible-light irradiation. The excellent degradation performance was attributed to the enhanced visible-light response and decreased electron-hole recombination rate. Meanwhile, an excellent linear correlation was observed between the efficient photocurrent of PFC and the chemical oxygen demand of solution when RhB is sufficient.

Preparation of Immobilized Sulfate-Reducing Bacteria-Microalgae Beads for Effective Bioremediation of Copper-Containing Wastewater

A strain of Desulfovibrio sp. sulfate-reducing bacteria (SRB) was isolated from a sludge sample. Novel immobilized SRB beads with microalgae (Chlorella vulgaris, Scenedesmus obliquus, Selenastrum capricornutum, and Anabaena spiroides) as the carbon source were prepared and then used to treat wastewater containing 60 mg/L Cu(II) and 600 mg/L sulfate in batch experiments. The microalgae were first degraded by co-existing fermentative bacteria into fatty acids, which then served as a carbon source for SRB. The solution chemical oxygen demand was significantly lower with microalgae substrates than with ethanol as a substrate. Different immobilization methods were evaluated with an orthogonal design, which indicated that the compositional parameters for preparing immobilized beads with an optimal sulfate reduction rate were polyvinyl alcohol (2%), sodium alginate (1%), calcium chloride (6%), silica sand (1%), and a 50-mL volume of SRB suspension. SRB activity in the immobilized beads was distinctly enhanced compared with that of suspended SRB. At an initial pH of 5.5, 72.4–74.4% of sulfate and over 91.7% of Cu(II) were removed, indicating that immobilized SRB beads with plentiful low-cost microalgae as a nutrient source may be an efficient method for acid mine drainage treatment.

UV-Based Oxidation Processes for Removal of Clopyralid: Optimal Conditions, Efficiency, and By-Products

Abstract UV/Fenton process was employed to remove clopyralid; meanwhile, various UV-based oxidation processes were compared, such as UV irradiation, UV/H2O2, and UV/Fe(II). Results illustrated that UV/Fenton exhibited the highest degradation rate, and UV irradiation alone hardly affected degradation of clopyralid. Rate constants, T1/2 (half-time) and EEO (electrical energy per order) were calculated to evaluate degradation rate and energy consumption among all these approaches. Some influencing factors, such as pH, irradiation time, and molar concentration ratio of hydrogen peroxide to ferrous ions, were studied to obtain an optimal degradation condition for UV/Fenton process. To evaluate the efficiency of UV/Fenton process applied for clopyralid degradation in aqueous solution, change of chemical oxygen demand in solution after UV/Fenton treatment was measured. Ion chromatograph was used to analyze formation of inorganic ions and short-chain carboxylic acids during photodegradation process. It was found ...

Electrochemical degradation of the herbicide picloram using a filter-press flow reactor with a boron-doped diamond or β-PbO2 anode

Galvanostatic electrolyses are performed in a filter-press reactor to investigate the electrochemical degradation of picloram (100mgL−1, from a commercial herbicide formulation) using a boron-doped diamond (BDD) or β-PbO2 anode. The effect of pH (3, 6, or 10), applied current density (japl=10, 30, or 50mAcm−2), and absence or presence of Cl– ions (25mM) in the supporting electrolyte (aqueous 0.10M Na2SO4) is investigated, while the picloram concentration, solution chemical oxygen demand (COD) and total organic carbon content (TOC), and energy consumption are monitored as a function of electrolysis time. From the obtained results, it is clear that the electrochemical degradation of picloram is possible using either of the anodes, but with different overall performances. In general, the presence of Cl– ions in the supporting electrolyte (leading to electrogenerated active chlorine) has a positive effect on the performance of both anodes, except for TOC abatement using the BDD anode; the best electrodegradation performances are attained at pH values around 6, when HClO is the predominant active-chlorine species. Faster rates of initial electrodegradation of picloram and of solution TOC abatement are obtained as japl is increased, but, as expected, lower energy consumptions are always attained at the lowest value of japl. The performances of the two anodes are virtually the same in the initial degradation of picloram; however, the BDD anode greatly surpasses the β-PbO2 anode in the abatement of solution COD or TOC. This confirms the importance of the oxidation power of the anode, even when indirect oxidation by active chlorine plays a concomitant role.

Effect of ozone pre-treatment on sludge production of aerobic digestion processes

The effect of ozone in a chemical sludge disintegration process was evaluated. Sludge solution chemical oxygen demand (COD), total suspended solids (TSS) and settling were investigated in single and sequential processes. A significant influence of ozone dose on sludge disintegration was observed: ozone was utilised to degrade the soluble organic matter and to destroy cell surfaces and release the cell liquids. For a single ozonation step, we found an optimum ozone dose in the range of 0.008–0.013 g O3/g TSS to give the best COD and TSS removal efficiency. Disintegrated sludge was treated in a sequential process consisting of consecutive ozonation and bio-aeration (i.e. O3 + biological treatment). The tendency was dependent on accumulated ozone, treatment time and operational conditions. An accumulated ozone dose of 0.055 g O3/g TSS in two separate ozonation processes followed by biological treatments led to COD and TSS removal efficiency of 53 and 46.6%, respectively. The removal efficiency was improved by increasing aerobic treatment time and/or by mixing ozonated sludge with non-ozonated sludge. The settling ability of sludge was found to be fast at very low specific ozone doses. An observed tendency was the effect of ozone on cell disintegration and protein liberation. The use of sequential processes improved the settling tendency of sludge.

Photodegradation study of congo red, methyl orange, methyl red and methylene blue under simulated solar irradiation catalyzed by ZnS/CdS nanocomposite

The nanocomposites of Zn X Cd1–X S were synthesized via controlled co-precipitation. The X-ray diffraction pattern, transmission electron microscopy image and BET method were used to characterize the synthesized nanocomposites. The cubic structure of nanocomposites were confi rmed using X-ray diffraction pattern. The photodegradation of congo red, methyl orange, methyl red and methylene blue catalyzed by prepared nanocomposites was studied under simulated solar irradiation. The Zn0.4Cd0.6S show the highest photoactivity among nanocomposites. The effect of samples pH and Zn0.4Cd0.6S dosage were adjusted to optimize the photodegradation process of dyes. The degradation efficiency of 95% were obtained within 20 min for congo red and 60 min for other dyes with initial concentration of 10 mg/l. The Zn0.4Cd0.6S indicate the stability in samples with pH of 3–11. The mineralization of dyes was confirmed using determination of chemical oxygen demand of solutions after photodegradation process.

Regeneration of granular activated carbon saturated with acetone and isopropyl alcohol via a recirculation process under H 2O 2/UV oxidation

This study examines a water-based system, coupling an adsorber and a photoreactor, for regeneration of granular activated carbon (GAC) saturated with acetone and isopropyl alcohol (IPA). Through water recirculation the regeneration reaction was operated in both intermittent and continuous ultraviolet illumination modes. With a periodic dosage of hydrogen peroxide not only was regeneration efficient but it was also catalyzed by GAC in the adsorber. The concentrations of acetone, solution chemical oxygen demand (COD), pH and organic residues on GAC surfaces were measured during regenerations. Both pH and solution COD were found to correlate with regeneration completion as measured by organic residue on GAC surfaces in four regeneration cycles with acetone. Solution pH decreased to the acidic values and then returned to near its original value when organic residues were 0.085–0.255 mg/g GAC, that is, destruction efficiency of adsorbed acetone on the GAC surface was more than 99%. Likewise, solution COD became low (<100 mg/l) at regeneration completion. The pH variation pattern was then applied to another four cycles of regeneration with IPA, and successfully reflected the timing of complete regeneration. The final levels of organic residue on GAC surfaces were between 0.135 and 0.310 mg/g GAC in each of four regeneration cycles, each of which had been stopped based on the measurements of pH and solution COD. Furthermore, nearly the same batch of GAC could be repeatedly used with little changes in physicochemical properties in each of eight cycles: adsorptive capacities were 95 ± 7 mg acetone/g GAC and 87 ± 3 mg IPA/g GAC, and breakthrough time was 0.86 ± 0.05 for acetone and 0.78 ± 0.03 h for IPA. An economic assessment of the system showed that the operating cost was about 0.04 USD for treating every gram of acetone in the air.

Development of an Integrated Enzymatic Treatment System for Phenolic Waste Streams

An integrated enzymatic treatment system, which includes Coprinus cinereus peroxidase (CIP) production, processing, and usage in batch or plug flow reactors, is being developed to remove phenolic compounds from the aqueous waste streams. CIP production at bench scale yielded a maximum growth medium activity of approximately 60 U CIP ml−1. A CIP enzyme solution was prepared for use in treatment by successive filtration steps. This yielded a 4.5-fold increase in enzyme activity, with 87% enzyme activity recovery, and 83% reduction in the solution's Chemical Oxygen Demand. The purity of CIP was observed to have no effect on the ability of the enzyme to remove phenol from the aqueous solutions within the range of enzyme solution purities tested. Contrary to observations reported for phenol removal from buffered solutions, the addition of polyethylene glycol to non-buffered reaction solutions had no positive effect on the phenol removal accomplished at pH 7 in these experiments. The efficiency of enzyme use in a plug flow reactor was improved by step additions of CIP and H2O2.

The Removal of Low Levels of Organics from Aqueous Solutions Using Fe(II) and Hydrogen Peroxide Formed In Situ at Gas Diffusion Electrodes

The removal of several organics (phenol, aniline, acetic acid, formaldehyde, and three azo dyes) from aqueous solutions (pH 2) containing Fe(II) and using hydrogen peroxide produced by the reduction of oxygen at a gas‐diffusion electrode is demonstrated. It is shown that chemical oxygen demand of solutions containing such organics may be reduced by >90% with a current efficiency >50%, leading to acceptable energy consumptions. The approach also clearly has considerable generality. The voltammetry of the gas diffusion electrodes, fabricated by screen printing an XC72‐R carbon powder/polytetrafluorene active layer on a carbon fiber paper support is also reported and discussed. © 1999 The Electrochemical Society. All rights reserved.