Sequential shape-selective adsorption and photocatalytic transformation of acrylonitrile production wastewater

Advanced treatment of industrial wastewater by ozonation with iron-based monolithic catalyst packing: From mechanism to application

An Fe-based catalyst was prepared by oxidising waste Fe shavings directly in a solution. In engineering applications, Fe shavings were compressed and modified to form Fe-based monolithic catalyst packing. Both of which exhibited excellent catalytic activity in catalytic ozonation industrial wastewater after biochemical treatment. Fe-based monolithic catalyst packing has irregular channels, large porosity, small pore diameter, and the effective specific surface area (SSA) up to 3500 m²/m³, these characteristics are conducive to mass transfer, and promote the effective utilisation of •OH in the catalyst "action zone". A tower reactor (<3000 m³/d) and reinforced concrete construction reactor (>5000 m³/d) were designed according to the wastewater flow. Regression analysis showed that hydraulic residence time (HRT) and O₃/COD_in are important parameters in engineering design and operation. In addition, strategies for the application of Fe-based monolithic catalyst packing to wastewater with high salinity and high inorganic carbon concentration have been proposed. Fe-based monolithic catalyst packing catalytic ozonation is a relatively cost-effective and eco-friendly process with extremely broad application prospects in the advanced treatment of industrial wastewater.

A review of advanced oxidation process towards organic pollutants and its potential application in fracturing flowback fluid

Fracturing flowback fluid (FFF) including various kinds of organic pollutants that do harms to people and new treatments are urgently needed. Advanced oxidation processes (AOPs) are suitable methods in consideration with molecular weight, removal cost and efficiency. Here, we summarize the recent studies about AOP treatments towards organic pollutants and discuss the application prospects in treatment of FFF. Immobilization and loading methods of catalysts, evaluation method of degradation of FFF, and continuous treatment process flow are discussed in this review. In conclusion, further studies are urgently needed in aspects of catalyst loading methods, macromolecule organic evaluation methods, industrial process, and pathways of macromolecule organics' decomposition.

Accurate Removal of Toxic Organic Pollutants from Complex Water Matrices

Characteristic emerging pollutants at low concentration have raised much attention for causing a bottleneck in water remediation, especially in complex water matrices where high concentration of interferents coexist. In the future, tailored treatment methods are therefore of increasing significance for accurate removal of target pollutants in different water matrices. This critical review focuses on the overall strategies for accurately removing highly toxic emerging pollutants in the presence of typical interferents. The main difficulties hindering the improvement of selectivity in complex matrices are analyzed, implying that it is difficult to adopt a universal approach for multiple targets and water substrates. Selective methods based on assorted principles are proposed aiming to improve the anti-interference ability. Thus, typical approaches and fundamentals to achieve selectivity are subsequently summarized including their mechanism, superiority and inferior position, application scope, improvement method and the bottlenecks. The results show that different methods may be applicable to certain conditions and target pollutants. To better understand the mechanism of each selective method and further select the appropriate method, advanced methods for qualitative and quantitative characterization of selectivity are presented. The processes of adsorption, interaction, electron transfer, and bond breaking are discussed. Some comparable selective quantitative methods are helpful for promoting the development of related fields. The research framework of selectivity removal and its fundamentals are established. Presently, although continuous advances and remarkable achievements have been attained in the selective removal of characteristic organic pollutants, there are still various substantial challenges and opportunities. It is hopeful to inspire the researches on the new generation of water and wastewater treatment technology, which can selectively and preferentially treat characteristic pollutants, and establish a reliable research framework to lead the direction of environmental science.

Toward Selective Oxidation of Contaminants in Aqueous Systems

The presence of diverse pollutants in water has been threating human health and aquatic ecosystems on a global scale. For more than a century, chemical oxidation using strongly oxidizing species was one of the most effective technologies to destruct pollutants and to ensure a safe and clean water supply. However, the removal of increasing amount of pollutants with higher structural complexity, especially the emerging micropollutants with trace concentrations in the complicated water matrix, requires excessive dosage of oxidant and/or energy input, resulting in a low cost-effectiveness and possible secondary pollution. Consequently, it is of practical significance but scientifically challenging to achieve selective oxidation of pollutants of interest for water decontamination. Currently, there are a variety of examples concerning selective oxidation of pollutants in aqueous systems. However, a systematic understanding of the relationship between the origin of selectivity and its applicable water treatment scenarios, as well as the rational design of catalyst for selective catalytic oxidation, is still lacking. In this critical review, we summarize the state-of-the-art selective oxidation strategies in water decontamination and probe the origins of selectivity, that is, the selectivity resulting from the reactivity of either oxidants or target pollutants, the selectivity arising from the accessibility of pollutants to oxidants via adsorption and size exclusion, as well as the selectivity due to the interfacial electron transfer process and enzymatic oxidation. Finally, the challenges and perspectives are briefly outlined to stimulate future discussion and interest on selective oxidation for water decontamination, particularly toward application in real scenarios.

Different acetonitrile degraders and degrading genes between anaerobic ammonium oxidation and sequencing batch reactor as revealed by stable isotope probing and magnetic-nanoparticle mediated isolation

Microbial degraders play crucial roles in wastewater treatment processes, but their use is limited as most microbes are yet unculturable. Stable isotope probing (SIP) is a cultivation-independent technique identifying functional-yet-uncultivable microbes in ambient environment, but is unsatisfactory for substrates with low assimilation rate owing to the low isotope incorporation into DNA. In this study, we used acetonitrile as the target low-assimilation chemical in many wastewater treatment plants and attempted to identify the active acetonitrile degraders in the activated sludge, via DNA-SIP and magnetic-nanoparticle mediated isolation (MMI) which is another cultivation-independent approach without the requirement of substrate labeling. The two approaches identified different active acetonitrile degraders in a 3-day short-term anaerobic ammonium oxidation (ANAMMOX). MMI enriched significantly more acetonitrile-degraders than SIP, showing the advantages in identifying the active degraders for low-assimilation substrates. Sequencing batch reactor (SBR, 30-day degradation) helped in more incorporation of ¹⁵N-labeled acetonitrile into the active degraders, thus the same acetonitrile-degraders and acetonitrile-degrading genes were identified by SIP and MMI. Different acetonitrile degraders between ANAMMOX and SBR were attributed to the distinct hydrological conditions. Our study for the first time explored the succession of acetonitrile-degraders in wastewater and identified the active acetonitrile-degraders which could be further enriched for enhancing acetonitrile degradation performance. These findings provide new insights into the acetonitrile metabolic process in wastewater treatment plants and offer suggestive conclusions for selecting appropriate treatment strategy in wastewater management.

Photocatalytic degradation of industrial acrylonitrile wastewater by F-S-Bi-TiO2 catalyst of ultrafine nanoparticles dispersed with SiO2 under natural sunlight

Highly active photocatalyst, having certain anti-ionic interfering function, of F, S and Bi doped TiO2/SiO2 was used for the first time to degrade the organic pollutants in acrylonitrile industrial wastewater under natural sunlight. The photocatalyst were prepared and characterized by UV-Vis, XRD, TEM, EDS, Nitrogen physical adsorption and XPS technique. UV-Vis analysis revealed addition of F, S and Bi into the lattice of TiO2 led to the expansion of TiO2 response in the visible region and hence the efficient separation of charge carrier. The photocatalytic potential of as prepared catalyst to degrade acrylonitrile wastewater under simulated and natural sunlight irradiation was investigated. The extent of degradation of acrylonitrile wastewater was evaluated by chemical oxygen demand (CODCr). CODCr in wastewater decreased from 88.36 to 7.20 mgL-1 via 14 h irradiation of simulated sunlight and achieved regulation discharge by 6 h under natural sunlight, illuminating our photocatalyst effectiveness for refractory industrial wastewater treatment. From TEM results, we found that SiO2 could disperse the photocatalyst with different component distributions between the surface and the bulk phase that should also be responsible for the light absorption and excellent photocatalytic performance. The XPS analysis confirmed the presence of surface hydroxyl group, oxygen vacancies.

Shape-selective adsorption mechanism of CS-Z1 microporous molecular sieve for organic pollutants

A self-made microporous molecular sieve CS-Z1 has been found to have excellent adsorption performance for small molecular nitrile and pyridine pollutants in acrylonitrile production wastewater. In order to explore its adsorption mechanism, the adsorption kinetics, isotherms and thermodynamics of CS-Z1 for eight nitrile and pyridine organic pollutants with different structures and properties were investigated. Meanwhile, the analysis of molecular dynamics simulation based on density functional theory was conducted to revel the adsorption-diffusion process of different organic pollutants on the surface and in the pores of CS-Z1. Both the experimental and simulated results verified the shape-selective adsorption mechanism of CS-Z1 for these organic pollutants. The adsorption processes of CS-Z1 for these pollutants were spontaneous physical adsorption, and the adsorption efficiency of CS-Z1 mainly depended on the molecular size of pollutant. Benefitting from the flexible crystalline structure of CS-Z1 and the breathing vibration of CS-Z1 orifices, it could adsorb some pollutants with slightly larger size than its pore diameter. Molecular dynamics simulation results visually display the shape-selective adsorption process of CS-Z1 for these pollutants through the respiratory effect of CS-Z1 molecular sieve orifices.

Enhanced isophthalonitrile complexation-reduction removal using a novel anaerobic fluidized bed reactor in a bioelectrochemical system based on electric field activation (AFBR-EFA)

On account of the recalcitrant and highly toxicity of organonitrile substrates, traditional processes are limited by HCN poisoning thus inefficient. This article proposed a novel anaerobic fluidized bed reactor with electric field activation (AFBR-EFA) which had a 260-day continuous operation. The operation aims to explore the practicability of the enhanced reduction of isophthalonitrile (IPN), with emphasis on the optimum operation parameters and synergistic effect between electric field and anaerobic processes. The results showed that relatively higher voltage (1.0 V < V < 1.6 V) had a positive impact on reduction enhancement. High removal could be obtained at high initial concentration, low methanol dosage and short HRT which indicated that tolerance to shock loading was significantly enhanced in AFBR-EFA. Furthermore, EFA visibly motivated the enrichment of electrochemically active bacteria and various autotrophic IPN degradation-related species. The significantly efficient performance makes the potential for full-scale application of the AFBR-EFA markedly improved, particularly for treating hard-biodegraded contaminants.

Efficient photocatalytic degradation of acrylonitrile by Sulfur-Bismuth co-doped F-TiO2/SiO2 nanopowder

In this study, a simple sol-gel method was applied for preparing effectual photocatalyst of S-Bi co-doped F-TiO₂/SiO₂ (S-Bi-F-TiO₂/SiO₂) nanopowder. Optimal preparation conditions were obtained by optimizing the calcination temperature and the ratio of S and Bi. The synthesized powder was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), brunauer-emmett-teller (BET), UV-Visible diffuse-reflectance spectroscopy (UV-Vis DRS), photoluminescence spectroscopy (PL) and ammonia adsorption and temperature-programmed desorption (NH₃-TPD). The photocatalytic activity was evaluated by the degradation of acrylonitrile under simulated visible light irradiation. S-Bi-F-TiO₂/SiO₂ nanopowder possess excellent photocatalytic properties under visible light for the degradation of acrylonitrile, when the calcination temperature was 450 °C for 2 h and the ratio of S and Bi was 0.02: 0.007. The degradation efficiency of acrylonitrile reached to 81.9% within 6 min of visible light irradiation. Compared with F-TiO₂/SiO₂ sample, NH₃-TPD and PL results revealed the higher photocatalytic activity for S-Bi-F-TiO₂/SiO₂, which is mainly due to the increase strength and number of surface acid site with S doping. The co-doping with S & Bi improved the separation of electron-hole pairs and enhanced the photocatalytic oxidizing species. The UV-Vis DRS showed stronger absorption in S-Bi co-doped F-TiO₂/SiO₂ catalyst as compared to F-TiO₂/SiO₂ catalyst. XPS results demonstrated the presence of various surface species viz. oxygen vacancies, Ti³⁺, Ti⁴⁺, O^2- and OH group.

Degradation kinetics of target compounds and correlations with spectral indices during UV/H2O2 post-treatment of biologically treated acrylonitrile wastewater

In this study, the post-treatment of biologically treated acrylonitrile wastewater was investigated during UV/H₂O₂ process. Five contaminants in the effluent were selected as target compounds, including Furmaronitrile (FMN), 3-Pyridinecarbonitrile (3PCN), 1,3-Dicyanobenzene (1,3-DCB), 5-Methyl-1H-benzotriazole (5MBT), and 7-Azaindole (7AID). Under optimal reaction conditions, the UV/H₂O₂ post-treatment exhibited good performances in destruction of organic compounds and toxicity. The photo-chemical parameters of the target compounds were measured and it was found that 5MBT and 3PCN had fast degradation rate constants under direct UV photolysis. The second-order rate constants of the target compounds with hydroxyl radicals were determined to be in the range of (1.0-5.0) × 10⁹ M^-1 s^-1 at pH 3.0 and 25 °C. A simplified pseudo-first-order steady state (Sim-PSS) model, which considered direct UV photolysis and radical oxidation simultaneously, agreed well with the experimental data from the post-treatment of a biologically treated effluent. High-performance size exclusion chromatography (HPSEC) coupled with diode-array detector (DAD) and fluorescence detector (FLD) analysis revealed that humic-like sub-peak signals from different molecular weights of fluorescent organic matter decreased consistently during the oxidation process, which made humic-like fluorescence exhibit higher correlation with the target compounds' degradation than the spectral indices of UV absorbance at 254 nm (UVA₂₅₄) and protein-like fluorescence.

Post-treatment of bio-treated acrylonitrile wastewater using UV/Fenton process: degradation kinetics of target compounds

In this study, post-treatment of bio-treated acrylonitrile wastewater was performed using the UV/Fenton process. Five target compounds (furmaronitrile, 3-pyridinecarbonitrile, 1,3-dicyanobenzene, 5-methyl-1H-benzotriazole, and 7-azaindole) were selected as target compounds and their degradation kinetics were examined. Under optimal reaction conditions (H₂O₂ dosage 3.0 mM, Fe²⁺ dosage 0.3 mM, and initial pH 3.0), more than 85% of total organic carbon (TOC) was eliminated in 30 min when a 10-W UV lamp was employed, and the electrical energy per order of magnitude for TOC removal was as low as 2.96 kWh m^-3. Furthermore, the target compounds and the toxicity were largely removed from the bio-treated effluent. Size exclusion chromatography with organic carbon detector analysis revealed that organic components with a wide range of molecular weights were greatly reduced after the UV/Fenton process. A simplified pseudo steady-state (SPSS) model was applied to predict the degradation of target compounds during the UV/Fenton process. The concentrations of generated hydroxyl radicals were estimated to be 3.06 × 10^-12 M, 6.37 × 10^-12 M, and 10.9 × 10^-12 M under 5-, 10-, and 15-W UV lamps, respectively. These results demonstrate that the proposed SPSS model fitted well with experimental data on the post-treatment of real wastewater, and consequently indicate that this model can be a useful tool in the prediction of degradation of target compounds during the UV/Fenton process.

A high-efficiency denitrification bioreactor for the treatment of acrylonitrile wastewater using waterborne polyurethane immobilized activated sludge

The performance of a laboratory-scale, high-efficiency denitrification bioreactor (15L) using activated sludge immobilized by waterborne polyurethane in treating acrylonitrile wastewater with high concentration of nitrate nitrogen (249mg/L) was investigated. The bioreactor was operated at 30°C for 220days. Batch denitrification experiments showed that the optimal operation parameters were C/NO₃^--N molar ratio of 2.0 using sodium acetate as electron donor and carrier filling rate of 20% (V/V) in the bioreactor. Stable performance of denitrification was observed with a hydraulic retention time of 30 to 38h. A volumetric removal rate up to 2.1kgN/m³·d was achieved with a total nitrogen removal efficiency of 95%. Pyrosequencing results showed that Rhodocyclaceae and Pseudomonadaceae were the dominant bacterial families in the immobilized carrier and bioreactor effluent. The overall microbial diversity declined as denitrifiers gradually dominated and the relative abundance of other bacteria decreased along with testing time.