Advanced treatment of biologically pretreated coal chemical industry wastewater using the catalytic ozonation process combined with a gas-liquid-solid internal circulating fluidized bed reactor

Recent Developments in Activated Carbon Catalysts Based on Pore Size Regulation in the Application of Catalytic Ozonation

Due to its highly developed pore structure and large specific surface area, activated carbon is often used as a catalyst or catalyst carrier in catalytic ozonation. Although the pore structure of activated carbon plays a significant role in the treatment of wastewater and the mass transfer of ozone molecules, the effect is complicated and unclear. Because different application scenarios require catalysts with different pore structures, catalysts with appropriate pore structure characteristics should be developed. In this review, we systematically summarized the current adjustment methods for the pore structure of activated carbon, including raw material, carbonization, activation, modification, and loading. Then, based on the brief introduction of the application of activated carbon in catalytic ozonation, the effects of pore structure on catalytic ozonation and mass transfer are reviewed. Furthermore, we proposed that the effect of pore structure is mainly to provide catalytic active sites, promote free radical generation, and reduce mass transfer resistance. Therefore, large external surface area and reasonable pore size distribution are conducive to catalytic ozonation and mass transfer.

Removal of recalcitrant organics in reverse osmosis concentrate from coal chemical industry by UV/H2O2 and UV/PDS: Efficiency and kinetic modeling

The lack of stability in catalytic ozonation treatment of reverse osmosis (RO) concentrate from coal chemical industry calls for new advanced oxidation processes. Herein, UV/H₂O₂ and UV/PDS were employed to remove the bulk recalcitrant organics in the RO concentrate with a focus on the process efficiency and kinetic modeling. Results show that UV/H₂O₂ overmatched UV/PDS in reducing the COD and DOC of the wastewater and the advantage became more evident in aspects of biodegradability improvement and energy cost. Specifically, the COD and DOC were removed by 62.0% and 55.5% with UV/H₂O₂ (6 mM) while the BOD₅/COD was elevated to 0.54 at a specific energy consumption of 0.83 kWh g^-1 (lab-scale). The UV/H₂O₂ process also exhibited a good adaptability to the fluctuation of wastewater quality. Afterwards, the reaction rate constants of the bulk organics upon UV photolysis and HO^• oxidation were calculated based on pseudo-first-order kinetics and radical steady-state approximation of DOC removal in the bench-scale UV/H₂O₂ reactor. A computational fluid dynamics model was then developed for the analysis of distributions of flow, radiation and chemicals in flow-through reactors which facilitated the practical process efficiency assessment. This work demonstrates the applicability of UV/H₂O₂ in removing recalcitrant organics in the RO concentrate and presents an approach from bench-scale experiments to flow-through system evaluation.

Removal of polyethylene glycols from wastewater: A comparison of different approaches

Physicochemical methods such as adsorption on activated carbon, oxidation with either ozone or Fenton reagent, and chemical precipitation (coagulation), were assessed for the removal of polyethylene glycol (PEG) from wastewater. This contaminant is rarely investigated due to its low toxicity, although its presence limits the use of large water resources. The experimental tests showed that adsorption on activated carbon is well approximated by a Langmuir isotherm, and influenced by contact time, PEG molecular weight, pH, temperature, and initial PEG concentration. Ozonation allowed fragmenting the polymeric chains but was unable to remove completely the PEG, while about 85% of the total organic carbon (TOC) was removed by Fenton oxidation reaction by using a ratio between H₂O₂ and Fe^II close to 4. Coagulation did not produce results worthy of note, most likely because the uncharged PEG molecule does not interact with the iron hydroxide flocs. However, when performed after the Fenton oxidation (i.e., by simply raising the pH to values > 8), it allowed a further reduction of the residual TOC, up to 96% of the total, in the best case. Based on the resources used by each process studied and in consideration of the effectiveness of each of them, a semi-quantitative comparison on the sustainability of the different approaches is proposed.

Analysis of chemical characteristics of lignite upgrading wastewater and its agricultural utilization

The lignite upgrading wastewater (LUW) produced in the drying and upgrading process of lignite cannot be discharged directly. Conventional wastewater treatment methods are usually costly and unable to achieve efficient utilization of water resources which are rich in activity components. In this study, the water quality analysis showed that LUW belonged to seriously polluted waters with low pH and very high total nitrogen content. Fifty-five compounds, mainly phenols and organic acids, were identified by gas chromatography-mass spectrometry (GC-MS) analysis. The study confirmed that the LUW, after being diluted to an appropriate concentration, could significantly promote the growth of wheat seedlings. The phenols and organic acids were the activity material basis of LUW, which promoted seed germination possibly through playing a role similar to plant hormones and simultaneously enhancing the utilization of nutrient elements. LUW had the natural advantages of directly developing high-end liquid fertilizers in terms of its physical form, chemical composition, biological activity, safety and economy. This study confirmed the feasibility of applying LUW to agricultural field as liquid fertilizer only through simple dilution without other treatments. Applying LUW as liquid fertilizer can not only supply a fertilizer product with low production cost and outstanding efficacy, but also provide an efficient and green way for the treatment of upgrading wastewater, which utilize the LUW as natural resources instead of purifying and discharging.

Mineralization of quinoline in aqueous solution by microwave-assisted catalytic wet peroxide oxidation system: process optimization, products analysis and degradation route research

The experimental design methodology was used to optimize the experimental parameters of quinoline mineralization by microwave-enhanced catalytic wet peroxide oxidation (CWPO). Initial pH value, temperature, H₂O₂ dosage, and microwave power were selected as independent variables. The mineralization efficiency approached 83.82% under the optimized conditions: initial pH 6.00, temperature 60 °C, H₂O₂ dosage 0.09 mol/L, and microwave power 565.10 W. Regression analysis with an R² value of 0.9867 showed a good agreement between the experimental results and the predicted values. Furthermore, based on the detection and identification of products by gas chromatography mass spectrometry, the oxidation degradation pathways of quinoline were proposed. The energy balance and costs analysis indicated that the total cost of the microwave-enhanced CWPO process for wastewater treatment was 40.60 yuan/m³.

Promotion of catalytic ozonation of aniline with Mn-Ce-Ox/γ-Al2O3

In this study, Mn-Ce-O_x/γ-Al₂O₃ supported catalysts were adopted to promote the removal efficiency of aniline in simulated wastewater with ozone. Mn-Ce-O_x/γ-Al₂O₃ catalysts were prepared by the impregnation-calcination method. Its phase structure, specific surface area, loading amount and distribution of active units were analyzed by XRD, BET, ICP-AES and TEM/SEM respectively. The characterization results demonstrated that the catalysts had a good dispersion of Mn-Ce-O_x active sites and an abundant porous structure from the γ-Al₂O₃ support. The catalytic ozonation results showed that with Mn₃-Ce₁-O_x/γ-Al₂O₃(1.0), the aniline removal efficiency was highly improved, 15.0% higher than that of ozonation without a catalyst. Furthermore, from the variation in loading amounts of Mn and Ce, it can be seen that the molar ratio of Mn and Ce within the Mn-Ce-O_x plays a key role in accelerating the ozonation of aniline in simulated wastewater with ozone, while Mn:Ce = 1.9:1 showed the best performance. More importantly, the catalysts showed high recycling performance and could be reused at least 12 times without obvious loss of activity.