Depth treatment of coal-chemical engineering wastewater by a cost-effective sequential heterogeneous Fenton and biodegradation process

Hydrogen Peroxide Activation with Sulfidated Zero-Valent Iron for Synchronous Removal of Cr(VI) and BPA

In this work, the synchronous removal of Cr(VI) and bisphenol A (BPA) in a heterogeneous Fenton process with sulfidated nanoscale zero-valent iron (S-nZVI) as the reductant and catalyst was systematically evaluated. Compared to other systems including S-nZVI or H2O2 alone, a simultaneous BPA degradation and Cr(VI) removal could be achieved in the S-nZVI/H2O2 system at an optimum pH of 3. It was, interestingly, found that 7.8% of BPA and 98.2% of Cr(VI) were removed within 60 min in presence of S-nZVI alone, whereas, correspondingly, 98.2% of BPA and 96.9% of Cr(VI) were eliminated in the S-nZVI/H2O2 system. Specifically, humic acid (HA) and H2PO4− inhibited the deterioration of BPA but posed no significant effect on Cr(VI) removal. NO3− had a slight lifting effect on the removal of BPA and Cr(VI), while HCO3− showed a relatively weak prohibition. Experiments with EPR and radical probe tests also provide direct evidence that hydroxyl radicals was monitored in the S-nZVI/H2O2 system, which not only degraded BPA but also inhibited the reduction of Cr(VI). It could not be ignored that FeS accelerated Fe0 corrosion to release Fe2+. In, addition, Fe0, Fe2+ and S2+ could react with Cr(VI) while the most of produced Cr(III) was co-precipitated in the form of CrxFe1−xOOH film. The study confirmed that it was feasible for S-nZVI/H2O2 system to remove synchronously organic pollutants and heavy metal.

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.

Post-treatment of real municipal wastewater effluents by means of granular activated carbon (GAC) based catalytic processes: A focus on abatement of pharmaceutically active compounds

Pharmaceutically active compounds (PhACs) widely present in urban wastewater effluents pose a threat to ecosystems in the receiving aquatic environment. In this work, efficiency of granular activated carbon (GAC) - based catalytic processes, namely catalytic wet peroxide oxidation (CWPO), peroxymonosulfate oxidation (PMS/GAC) and peroxydisulfate oxidation (PDS/GAC) at ambient temperature and pressure were studied for removal of 22 PhACs (ng L^-1 level) that were present in secondary effluents of real urban wastewater. Concentrations of PhACs were measured using Ultra Performance Liquid Chromatography - Triple Quadrupole Mass Spectrometry (UPLC-QqQ-MS/MS). Catalytic experiments were conducted in discontinuous mode using up-flow fixed bed reactors with granular activated carbon (GAC) as a catalyst. The catalyst was characterized by means of N₂ adsorption-desorption isotherm, mercury intrusion porosimetry (MIP), elemental analysis, X-ray fluorescence spectroscopy (WDXRF), X-ray diffraction (XRD), thermal gravimetry and differential temperature analyses coupled mass spectrometry (TGA-DTA-MS). Results indicate that the highest efficiency in terms of TOC removal was achieved during CWPO performed at optimal operational conditions (stoichiometric dose of H₂O₂; TOC removal ~ 82%) followed by PMS/GAC (initial PMS concentration 100 mg L^-1; TOC removal ~73.7%) and PDS/GAC (initial PDS concentration 100 mg L^-1; TOC removal ~ 67.9%) after 5 min of contact time. Full consumption of oxidants was observed in all cases for CWPO and PDS/GAC at contact times of 2.5 min, while for PMS/GAC it was 1.5 min. In general, for 18 out of 22 target PhACs, very high removal efficiencies (> 92%) were achieved in all tested processes (including adsorption) performed at optimal operational conditions during 5 min of contact time. However, moderate (40 - 70%) and poor (< 40%) removal efficiencies were achieved for salicylic acid, ofloxacin, norfloxacin and ciprofloxacin, which can be possibly attributed to insufficient contact time. Despite high efficiency of all studied processes for PhACs elimination from urban wastewater effluent, CWPO seems to be more promising for continuous operation.

Electrochemical Properties and Chemical Oxygen Demand Depending on the Thickness of Boron-Doped Diamond

In this study, boron-doped diamond (BDD) film was deposited by hot-filament chemical vapor deposition (HFCVD) using acetone as the carbon source and trimethyl borate (TMB) as the boron source with the aim of lowering the manufacturing cost of BDD electrodes. The BDD film was deposited for 12 and 60 h to observe changes in the morphological behavior of the film as well as subsequent changes in the electrochemical properties. The morphology of the BDD film was not affected by the deposition time, but the thickness increased with increasing deposition time. As the deposition time increased, the deposition rate of the BDD film did not increase or decrease; rather, it remained constant at 100 nm/h. As the thickness of the BDD film increased, an increase in the potential window was observed. On the other hand, no distinct change was observed in the electrochemical activation and catalytic activity depending on the thickness, and there were not many differences. Chemical oxygen demand (COD) was measured to determine the practical applicability of the deposited BDD film. Unlike the potential window, the COD removal rate was almost the same and was not affected by the increase in the thickness of the BDD film. Both films under the two deposition conditions showed a high removal rate of 90% on average. This study confirms that BDD electrodes are much more useful for water treatment than the existing electrodes.

Degradation of ibuprofen and phenol with a Fenton-like process triggered by zero-valent iron (ZVI-Fenton)

It is shown here that ZVI-Fenton is a suitable technique to achieve effective degradation of ibuprofen and phenol under several operational conditions. Degradation of ibuprofen was possible in the pH interval 3-6 in both synthetic laboratory systems and actual wastewater (secondary treatment effluent), but operation at the higher pH values required higher H₂O₂ concentration and/or higher ZVI loading. In the case of real wastewater we offset the lower degradation efficiency, caused by the occurrence of organic and inorganic interfering agents, by carrying out multiple H₂O₂ additions. The studied wastewater sample had a buffer-capacity minimum at pH 4-5, and optimal treatment for ibuprofen degradation might take place at either pH 4 or 6. With a reagents cost in the order of 0.06-0.10 $ m^-3, the technique appears as very competitive and promising for tertiary wastewater treatment. There is a clear trade-off between savings in pH-fixing reagents and higher consumption of ZVI-Fenton reagents at the different pH values. The final choice in real application scenarios could be based on cost considerations (which favour pH 4) and/or the eventual fate of wastewater. For instance, wastewater reuse might place requirements on the salinity that is increased by the acidification/neutralization steps: in this case, operation at pH 6 is preferred. Interestingly, the ZVI-Fenton degradation of ibuprofen led to very low generation of toxic 4-isobutylacetophenone (IBAP, which is the ibuprofen by-product raising the highest concern), because of the combination of low formation yields and limited IBAP stability in the optimal reaction conditions. In addition to ibuprofen, phenol could be degraded as well by ZVI-Fenton. Interestingly, the ability of ZVI-Fenton to degrade both ibuprofen and phenol under similar conditions might open up the way to apply this technique to additional pollutants as well as to pollutant mixtures.

Synthesis of Petal-Like MnO2 Nanosheets on Hollow Fe3O4 Nanospheres for Heterogeneous Photocatalysis of Biotreated Papermaking Effluent

Owing to the implementation of increasingly stringent water conservation policies and regulations, the pulp and paper mill industry must make increased efforts to meet the limits for pollutant emissions. The primary pretreatment and secondary biochemical treatment methods used currently generally fail to meet the country-specific environmental regulations, and the wastewater must be processed further even after being subjected to secondary biochemical treatments. In this work, we synthesized Fe₃O₄/MnO₂ nanocomposites (FMNs) with a flower-like structure for use in the heterogeneous photocatalytic treatment of biotreated papermaking wastewater. FMNs1.25, which were formed using a KMnO₄/Fe₃O₄ molar ratio of 1.25, could be separated readily using an external magnetic field and exhibited higher photocatalytic activity than those of the other samples as well as MnO₂ and Fe₃O₄. The effects of various experimental parameters on the photocatalytic activity of FMNs1.25, including the initial pH of the wastewater and the catalyst dosage, were determined. The common chemical oxygen demand (COD_Cr) reduction rate in the case of this sample reached 56.58% within 120 min at a pH of 3, the COD_Cr of effluent after treatment was 52.10 mg/L. Further, even under neutral conditions, the COD_Cr of the treated effluent was below the current limit for discharge in China. Moreover, the nanocomposites exhibited good recyclability, and their catalytic activity did not decrease significantly even after five usage cycles. This study should serve as a platform for the fabrication of effective photocatalysts for the advanced treatment of biotreated papermaking effluent and refractory organic wastewater.

Application of Catalytic Wet Peroxide Oxidation for Industrial and Urban Wastewater Treatment: A Review

Catalytic wet peroxide oxidation (CWPO) is emerging as an advanced oxidation process (AOP) of significant promise, which is mainly due to its efficiency for the decomposition of recalcitrant organic compounds in industrial and urban wastewaters and relatively low operating costs. In current study, we have systemised and critically discussed the feasibility of CWPO for industrial and urban wastewater treatment. More specifically, types of catalysts the effect of pH, temperature, and hydrogen peroxide concentrations on the efficiency of CWPO were taken into consideration. The operating and maintenance costs of CWPO applied to wastewater treatment and toxicity assessment were also discussed. Knowledge gaps were identified and summarised. The main conclusions of this work are: (i) catalyst leaching and deactivation is one of the main problematic issues; (ii) majority of studies were performed in semi-batch and batch reactors, while continuous fixed bed reactors were not extensively studied for treatment of real wastewaters; (iii) toxicity of wastewaters treated by CWPO is of key importance for possible application, however it was not studied thoroughly; and, (iv) CWPO can be regarded as economically viable for wastewater treatment, especially when conducted at ambient temperature and natural pH of wastewater.