Effective oxidative degradation of coal gasification wastewater by ozonation: A process study

Electrocatalysis coupled heterogeneous electro-Fenton like treatment of coal gasification wastewater using tourmaline as catalyst: process parameters and response surface

Coal gasification technology is essential for realizing clean and efficient conversion of coal, as well as for reducing carbon emissions. However, coal gasification technology is accompanied by a large amount of coal gasification wastewater that is biodegradable. In this work, tourmaline was applied as a catalyst in electro-Fenton like process for treating coal gasification wastewater. The optimal applied parameters of coal gasification wastewater were investigated as follows: current density of 90 mA cm-2, tourmaline dosage of 8 g L-1, electrode gap of 1 cm, and temperature at 25 °C; the COD removal ratio reached 91.24% after 240-min treatment. In addition, the current density and tourmaline dosage were further optimized by response surface method. The result was about current density with 82.4 mA cm-2 and catalyst with 7.57 g L-1; the predicted COD removal efficiency was 86.91%. Under the optimal parameters the actual COD removal efficiency was 88.25% a little high than the predicted value. To explore the reusability of tourmaline as Fenton reaction catalyst, five cycles of experiments were carried out. The result demonstrated that tourmaline could be used as catalyst for treating coal gasification wastewater by electro-Fenton like process.

Effective degradation of quinoline by catalytic ozonation with MnCexOy catalysts: performance and mechanism

Quinoline inevitably remains in the effluent of coking wastewater treatment plants due to its bio-refractory nature, which might cause unfavorable effects on human and ecological environments. In this study, MnCexOy was consciously synthesized by α-MnO2 doped with Ce3+ (Ce:Mn = 1:10) and employed as the ozonation catalyst for quinoline degradation. After that, the removal efficiency and mechanism of quinoline were systematically analyzed by characterizing the physicochemical properties of MnCexOy, investigating free radicals and monitoring the solution pH. Results indicated that the removal rate of quinoline was greatly improved by the prepared MnCexOy catalyst. Specifically, the removal efficiencies of quinoline could be 93.73, 62.57 and 43.76%, corresponding to MnCexOy, α-MnO2 and single ozonation systems, respectively. The radical scavenging tests demonstrated that •OH and •O2- were the dominant reactive oxygen species in the MnCexOy ozonation system. Meanwhile, the contribution levels of •OH and •O2- to quinoline degradation were about 42 and 35%, respectively. The abundant surface hydroxyl groups and oxygen vacancies of the MnCexOy catalyst were two important factors for decomposing molecular O3 into more •OH and •O2-. This study could provide scientific support for the application of the MnCexOy/O3 system in degrading quinoline in bio-treated coking wastewater.

Treatment of Distillery Industrial Wastewater Using Ozone Assisted Fenton’s Process: Color and Chemical Oxygen Demand Removal with Electrical Energy per Order Evaluation

Ozonation is one of the most effective and efficient advanced oxidation processes (AOPs) and has shown great potential in the treatment of industrial effluent and wastewater. In the present work, the ozone-Fenton process for % COD and color removal together with electrical energy per order (EE/O) determination for distillery industrial wastewater (DIW) was established. The process was developed by combining the ozone (O3) with the Fenton (Fe2+/H2O2) process. The ozone-Fenton (O3/Fe2+/H2O2) was compared with other treatment processes such as O3, Fe2+, H2O2, O3/Fe2+, O3/H2O2, and Fe2+/H2O2 for EE/O together with % COD and color removal efficiency for DIW. The removal of color at 100% and chemical oxygen demand (COD) of 96.875% were achieved with a minimum of EE/O of 0.5315 kWh/m3 using the O3/Fe2+/H2O2 process by operating at optimum conditions. The % COD and color values obtained using O3/Fe2+/H2O2 were significantly higher than those obtained using O3, Fe2+, H2O2, O3/Fe2+, O3/H2O2, and Fe2+/H2O2 processes. The % color, % COD removal, and its associated EE/O were evaluated by varying Fe2+, H2O2, O3 inlet and COD concentration, and initial wastewater pH using the O3/Fe2+/H2O2 process. The synergy effect of the O3 and Fe2+/H2O2 processes was evaluated and reported. Our experimental findings suggest that combining O3 with the Fe2+/H2O2 process could effectively treat industrial effluent and wastewater.

Comparative study on air gasification of plastic waste and conventional biomass based on coupling of AHP/TOPSIS multi-criteria decision analysis

A broad range of conventional biomass and plastic waste types was considered and their air gasification process was modeled using a Gibbs free energy minimization coupled with Lagrange multiplier approach. The comparison between the performances of biomass and plastic waste gasification is the main issue of this study. Another important novelty and contribution of this study is analytical hierarchy process/technique for order performance by similarity to the ideal solution coupled method that is employed in gasification of conventional biomass and plastic waste, to prioritize the considered criteria and to select the best feedstock for gasification. Hydrogen production was linearly reduced in the case of conventional biomass with an in increase in the equivalence ratio; however, there was an optimum equivalence ratio to achieve the highest hydrogen production in plastic waste gasification. Plastic waste had a higher low heating value compared to conventional biomass. However, carbon monoxide and nitrogen production from conventional biomass was smaller than from plastic waste. Ten types of feedstock, comprising six types of conventional biomass and four types of plastic waste, were selected as alternatives. The multi-criteria decision analysis coupled method revealed that waste polypropylene and polyethylene were the best alternatives.

Refractory organic compounds in coal chemical wastewater treatment by catalytic ozonation using Mn-Cu-Ce/Al2O3

A composite Mn-Cu-Ce tri-metal oxide supported on γ-Al₂O₃ (Mn-Cu-Ce/Al₂O₃) catalyst was prepared by an impregnation-calcination method and investigated in the catalytic ozonation treatment of real coal chemical wastewater (CCW). The catalyst was characterized by XRD, SEM, TEM, XRF, BET, and XPS techniques. The results showed that Mn, Cu, and Ce metal oxides were evenly distributed on the Al₂O₃ surface and the catalyst maintained a large surface area and a high pore volume compared with the pristine Al₂O₃. The synergy between Mn, Cu, and Ce oxides greatly enriched the catalytic active sites and enhanced the ozonation performance. The catalytic ozonation process with Mn-Cu-Ce/Al₂O₃ increased the removal rate of total organic carbon (TOC) by 31.6% compared with ozonation alone. The ketones, aromatic compounds, phenols, and nitrogen-containing heterocyclic compounds in CCW have been effectively degraded and mineralized by Mn-Cu-Ce/Al₂O₃ catalytic ozonation process, and its biodegradability has also been significantly improved. The experimental results of ∙OH scavengers revealed that the mechanism of Mn-Cu-Ce/Al₂O₃ catalytic ozonation was to promote the generation of ∙OH radicals. The catalytic activity of Mn-Cu-Ce/Al₂O₃ was only a slight decrease in six consecutive catalytic ozonation treatments, showing good stability. Therefore, Mn-Cu-Ce/Al₂O₃ can be used as a candidate catalyst for the advanced treatment of refractory organic wastewaters upon catalytic ozonation.

Regeneration of [Bmim]BF4 ionic liquid by ozonation: hydrogen bond roles, synergistic effect, and DFT calculation

Ionic liquids (ILs) are a kind of promising extractants for removing undesirable organics from industrial wastewater and crude oil, etc. Herein, IL regeneration by ozonation was proposed for its recycling. 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄) and phenol were used as the representative IL and organic matter, respectively. The regeneration performance, stability of [Bmim]BF₄, and roles of hydrogen bonds between O₃ and [Bmim]BF₄ in the phenol removal were studied. The experimental results showed that 90.2% of phenol was degraded in [Bmim]BF₄ after ozonation treatment for 30 min with the O₃ concentration of 1.2 mg/L. The nonvolatility of [Bmim]BF₄-made phenol was adequately degraded, while the concentration of phenol increased during ozone treatment in the conventional extractants (ethanol, ethyl acetate, and dichloromethane) due to their high volatility. The reuse experiments, spectra of Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance spectroscopy indicated that [Bmim]BF₄ was steady under the ozonation process. Density functional theory simulation confirmed that hydrogen bonds between [Bmim]⁺ and O₃ could be formed, and calculational results of Hirshfeld charges indicated that the nucleophilicity of O₃ was enhanced by the hydrogen bonds. The enhanced nucleophilicity resulted in the increase of phenol degradation efficiency by ozonation, and the synergistic effect between O₃ and ILs was proportional to the hydrogen bond donor ability of ILs.

Investigation on carbide slag catalytic effect of Mongolian bituminous coal steam gasification process

Carbide slag may pollute the environment because it is difficult to handle. In this paper, carbide slag without pretreatment served as the new source of calcium and was added to bituminous coal for gasification experiments to realize waste utilization. The gasification experiment after adding carbide slag to bituminous coal enhances H₂ production, which reduced the activation energy of the gasification reaction. The results show that the catalytic effect on steam gasification was evident when the carbide slag was added to Mongolian bituminous coal. The coal char at reaction temperature was prepared and characterized by X-ray diffraction (XRD), Raman, Scanning electron microscope (SEM), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and FT-IR spectroscopy. The carbon structure evolution and calcium structure changes of coal char under reaction temperature were studied, and the influence of coal char structure changes on gasification performance was analyzed. The results show that in the coal char added with carbide slag, the oxygen-containing functional groups generated by the polycondensation reaction interacted with calcium to form a calcium-oxygen-carbon complex. The existence of this structure not only leads to the highly uniform dispersion of CaO in the char but also hinders the graphitization process of the char. Highly dispersed CaO and disordered carbon structure significantly improved the reactivity of bituminous coal steam gasification. Si and Al in the bituminous coal affected the dispersion of Ca during steam gasification.

Removal of trace organic pollutants (pharmaceuticals and pesticides) and reduction of biological effects from secondary effluent by typical granular activated carbon

Residual trace organic pollutants (TOPs) and associated biological effects from secondary effluent (SE) are attracting much attention because of their safety concerns. Granular activated carbon (GAC) adsorption, due to its low cost and high efficiency, is widely applied for further wastewater treatment, but its selective removals of TOPs and biological effects are poorly understood. In the present study, the surface physicochemical characteristics of four types of typical GACs were investigated, and their correlation with luminescent bacteria toxicity was discussed. Based on the biological effect control, shell GAC, with a great adsorption capacity and high functional group contents was selected for further study, including for the removal of fluorescent dissolved organic matter (DOM), 21 TOPs, and 3 biological effects. The shell GAC showed a promising property of removing fluorescent DOM and TOPs. The total concentration of 21 detected TOPs, including 12 pesticides and 9 pharmaceuticals, achieved 82% removal when 30 g/L shell GACs was added. Individual chemicals removal by GAC adsorption was not well described by an individual parameter (e.g., logD, molecular size, charge, functional groups), but rather by a variety of physical and chemical interactions among TOPs, DOM, and GAC. The biological effects from SE were mainly caused by TOPs and DOM. Hence, shell GACs also showed high removal efficiencies of luminescent bacteria toxicity, genotoxicity, and photosynthetic inhibition effect. The removal mechanisms of the three biological effects from SE were deeply discussed. Therefore, the GAC treatment is considered to be one of the most suitable options to ensure the ecological safety of discharged wastewater, because it can effectively control DOM, TOPs, and associated biological effects.