Bismuth impregnated biochar were synthesized to deal with wastewater pollution. Nitrogen adsorption-desorption isotherms, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy ...(FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to determine the characteristics of adsorbents and explore the main adsorption mechanism. Results showed that bismuth particle was carried successfully within the biochar matrix, making contributions to creating micropore and boost specific surface area. The loaded bismuth, served as the adsorption site, rather than the specific surface area played an important role in arsenic and phosphorus adsorption. Batch adsorption experiments demonstrated a fit Langmuir model for arsenic (As) and phosphorus (P) and a suitable Freundlich model for chromium (Cr). Thermodynamic parameters depicted the endothermic nature and the spontaneous process for phosphate and arsenic adsorption. Besides, this contaminant-loaded carbon adsorbent was further applied for the removal of methylene blue from aqueous solution.
•Bismuth activated carbons derived from wheat straw were fabricated.•Bismuth particles grown within biochar matrix.•BiBC500 showed high adsorption capacity to arsenic, phosphorus and chromium.•Adsorption mechanisms of arsenic, phosphorous and chromium were illustrated.•Phosphate depleted material could photodegrade dye pollutant.
Advanced oxidation processes (AOPs) are ideal alternative to remove contaminants of emerging concern (CECs). Nitrate and nitrite commonly co-exist with CECs in surface water, groundwater, and ...agricultural runoffs, which impact the performance of AOPs. Interests in investigation on the impacts of nitrate/nitrite on CEC degradation in AOPs have grown exponentially, due to the participation of reactive nitrogen species (RNS). RNS as a daughter radical in AOPs, are generally formed from photolysis of nitrate/nitrite or reactions of nitrate/nitrite with hydroxyl radical. It was documented that nitrate/nitrite in photochemical AOPs could accelerate CEC degradation, while that in non-photochemical AOPs usually play an inhibitory role. Except the performance of AOPs, nitrate/nitrite present in AOPs also have significant impact on the degradation pathway of CECs, of which the typical one is the nitration/nitrosation of CECs. Formation of nitrated/nitrosated CEC products in AOPs is almost inevitable when nitrite is present in water, because RNS are typical nitrating/nitrosating agents. The nitrated/nitrosated products not only show higher toxicity, but have higher formation potential of nitro/nitroso disinfection byproducts. Therefore, nitrate/nitrite can be used as a source of hydroxyl radical and RNS in photochemical AOPs (especially at λ > 280 nm), and should be avoided in non-photochemical AOPs. Besides, using pretreatment to turn nitrite to nitrate is a useful method to reduce the formation of nitrated/nitrosated CECs. Overall, this critical review aims to summarize the all-round impacts of nitrate/nitrite on AOPs, and provide practical implications to better utilize the naturally present nitrate/nitrite.
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•NO3−/NO2− enhances CEC degradation in photochemical AOPs (λ > 280 nm).•Photo induced decomposition of NO3−/NO2− leads to the nitr(os)ation of CECs.•NO2− play an important role in nitr(os)ation of CECs in non-photochemical AOPs.•Typical N-DBPs are generated from NO3−/NO2− when AOPs are set before disinfection.
Over the past decades, inspired by the outstanding properties of clay minerals such as abundance, low-cost, environmental benignity, high stability, and regularly arranged silica-alumina framework, ...researchers put much efforts on the interface assembly and surface modification of natural minerals with bare photocatalysts, i.e. TiO2, g-C3N4, ZnO, MoS2, etc. The clay-based hybrid photocatalysts have resulted in a rich database for their tailor-designed microstructures, characterizations, and environmental-related applications. Therefore, in this study, we took a brief introduction of three representative minerals, i.e. kaolinite, montmorillonite and rectorite, and discussed their basic merits in photocatalysis applications. After that, we summarized the recent advances in construction of stable visible-light driven photocatalysts based on these minerals. The structure-activity relationships between the properties of clay types, pore structure, distribution/dispersion and light absorption, carrier separation efficiency as well as redox performance were illustrated in detail. Such representative information would provide theoretical basis and scientific support for the application of clay based photocatalysts. Finally, we pointed out the major challenges and future directions at the end of this review. Undoubtedly, control and preparation of novel photocatalysts based on clays will continue to witness many breakthroughs in the arena of solar-driven technologies.
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•Kaolinite, montmorillonite and rectorite based photocatalysts were well reviewed.•The role of clay in composite photocatalysts was illustrated in detail.•We point out the major challenges and direction of clay based photocatalysts.•This review is meaningful for energy crisis and environmental remediation.
The intrusion detection method of power industrial control systems is a crucial aspect of assuring power security. However, traditional intrusion detection methods have two drawbacks: first, they are ...mainly used for defending information systems and lack the ability to detect attacks against power industrial control systems; and second, although machine learning-based intrusion detection methods perform well with the default hyperparameters, optimizing the hyperparameters can significantly improve its performance. In response to these limitations, a random forest (RF)-based intrusion detection model for power industrial control systems is proposed. Simultaneously, this paper proposes an improved grid search algorithm (IGSA) for optimizing the hyperparameters of the RF intrusion detection model to improve its efficiency and effectiveness. The proposed IGSA boosts the speed of calculation from O(nm) to O(n × m). The suggested model is evaluated based on the public power industrial control system dataset after hyperparameter optimization. The experiment results show that our method achieves a superior detection performance with the accuracy of 98% and has more outstanding performance than the same type of work.
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•TiO2 nanoparticles were rationally monodispersed on the kaolinite surface.•The composite’s reaction rate constant is about 6.90 times higher than that of pure TiO2.•The synergistic ...effect between kaolinite and TiO2 charged for performance enhancement.•This study provides a promising candidate for wastewater treatment.
Lamellar kaolinite supported monodispersed TiO2 was prepared through rational design and 0D/2D structural assembly, which showed significantly improved photocatalytic performance towards ciprofloxacin. After systematic evaluation, the pseudo-first-order kinetic constant rate of TiO2/kaolinite composite can reach to 0.04549 min−1, which was 6.90 and 1.81 times higher than that of pure TiO2 and P25, respectively. The nano-TiO2/kaolinite composite photocatalyst also displayed good reusability performance, only a slight decline occurred after four repeated experiments, which is beneficial for the large-scale application of photocatalysts. Various characterizations indicated that enhanced photocatalytic performance can be ascribed to the synergistic effect between natural kaolinite and the well distributed TiO2, which enhanced the light absorption ability, assisted the dispersion of pure TiO2, resulted in co-catalysis effect, improved the separation facilitation of photo-induced carriers and promoted the stronger adsorption capacity, etc. These merits effectively regulated the carriers’ lifetime and migration velocity of the photogenerated charge carriers. Considering the excellent properties of natural kaolinite (low cost, abundance, stability, etc.), our study provides a promising candidate for effective degradation of trace amounts of pharmaceutical and personal care product (PPCP) or contaminants with potential high-toxic risk.
For aquaculture wastewater with low ammonium nitrogen concentration, combining the carrier adsorption and biological nitrogen removal processes can maximize their respective advantages. Functional ...ceramsite that has excellent ammonium nitrogen adsorption performance and excellent biocompatibility was the key to the moving bed biofilm reactor (MBBR) adsorption—shortcut simultaneous nitrification and denitrification (shortcut SND) process. Our group prepared a high-strength lightweight ceramsite that met those requirements. In this study, we applied functional ceramsite in MBBR to cope with low-concentration ammonium aquaculture wastewater. The findings show that utilizing functional ceramsite as a filler was conducive to the adhesion of microorganisms. The biofilm has a minimal effect on the adsorption capacity of ceramsite due to the existence of pores on its surface. Our study further examined the NH4+-N adsorption mechanism of bio-ceramsite. The Freundlich adsorption isotherm model and the quasi-second-order kinetic model had better fitting effects on the NH4+-N adsorption process. The adsorption of bio-ceramsite to NH4+-N was an endothermic process that included physical and chemical adsorption. Furthermore, the results of adsorption thermodynamics suggested that bio-ceramsite has an affinity for the adsorption of NH4+-N. Consequently, this functional ceramsite can be a promising option for MBBR to improve nitrogen removal from aquaculture wastewater.
Excessive discharge of ammonia nitrogen wastewater from intensive aquaculture has worsened in recent years. Therefore, there is an urgent need to develop an effective and energy-saving ...denitrification technology. This study intends to adopt a moving bed biofilm reactor (MBBR) to remove ammonia nitrogen through the combination of adsorption and shortcut simultaneous nitrification and denitrification (SND). The research focuses on the operational parameters and regeneration mechanism of the MBBR adsorption-shortcut SND process. The optimal operating parameters in the adsorption stage were a hydraulic retention time of 8 h and an agitation rate of 120 r/min. For the shortcut SND stage, the ideal optimal parameters were two times alkalinity and dissolved oxygen (DO) 1.0 mg/L. Under optimal operating parameters conditions, the SND rate, TN removal rate, NH4+-N removal rate and nitrite accumulation rate were 89.1%, 84.0%, 94.3%, and 86.4%, respectively. The synergetic actions of ion exchange and microorganisms were the main driving force for regenerating ceramsite zeolite components. The synergistic inhibitory effect of high-concentration free ammonia and low-level DO on nitrite-oxidizing bacteria was the key to achieving stable and efficient NO2−-N accumulation. NO2−-N produced in shortcut nitrification entered the ceramsite through complex mass transfer, and denitrifying bacteria can reduce these NO2−-N to N2.
Iron minerals are important for arsenic immobilization in paddy fields; however, intensive ferrolysis causes arsenic (As) release. Bismuth-impregnated biochar derived from wheat straw (BiBC) was ...synthesized to immobilize arsenic by regulating the ferrolysis process in a paddy field. Further X-ray based analysis (XRD and XPS) results demonstrated that crystal particles of bismuth oxide and bismuth oxychloride were loaded on the biochar surface, helped create additional micropores and improved its specific surface area. The bioavailability of As, as determined via (non)specifically adsorbed As, decreased as the amended dosage of BiBC increased, while wheat straw biochar (WBC) resulted in arsenic release. The presence of biochar caused a faster reduction rate of iron oxides; however, BiBC promoted the sequential co-precipitation of iron and arsenic ions. Adsorption kinetic experiments indicated that ferrous ions facilitated precipitation of As on the surface of BiBC. The XRD analysis of soil samples showed BiBC facilitated the formation/stability of FeOOH. Thus, amendment with BiBC regulated ferrolysis to buffer iron leaching, which contributed to arsenic immobilization under flooding conditions. This study demonstrated the feasibility of As immobilization by metal-impregnated biochar in paddy soils.
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•Bismuth-impregnated biochar (BiBC) decreased the bioavailability of arsenic in paddy soils through regulation of ferrolysis.•Addition of BiBC to arsenic-contaminated soil promoted the reduction of iron oxides.•The reduced iron ions facilitated arsenic adsorption onto the BiBC surface.
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•Periphytic biofilm could remove As(III) from wastewater.•Calcite and the OH and CO groups in biofilm facilitate As(III) removal.•The BPS achieved stable and effective removal of ...As(III).•The As(III) adsorption process by biofilm obeys pseudo-second-kinetic model.
A biochar and periphyton-based system (BPS) comprising of a biochar column and a periphyton bioreactor was designed to avoid the toxicity issue associated with removing As(III) from wastewater. Results showed that the periphyton can grow when As(III) is less than 5.0mgL−1. The BPS obtained a high As(III) removal rate (∼90.2–95.4%) at flow rate=1.0mLmin−1 and initial concentration of As(III)=2.0mgL−1. About 60% of the As(III) was pre-treated (adsorbed) in the biochar column and the removal of the remaining As(III) was attributed to the periphyton bioreactor. The As(III) removal process by periphytic biofilm in the initial stage fits a pseudo-second-kinetic model. The calcite in the periphytic biofilm surfaces and the OH and CO groups were responsible for the As(III) removal. This study indicates the feasibility of the BPS for As(III) removal in practice.
High mobility and toxicity of arsenic As (III) limit its removal from an aquatic environment and pose a threat to human health. In this work, batch adsorption experiments were conducted to ...investigate the adsorption capacity of bismuth-impregnated aluminum oxide (BiAl). Continuous application of As (III) removal was achieved via a lab-scale column reactor. Bismuth impregnation decreased the specific surface area of aluminum oxide and affected its pore size distribution. However, because of its abundant and well-proportioned mesoporous character, it also enhanced its adsorption capacity through the surface complexation of As (III). Batch adsorption experiments demonstrated a suitable Freundlich model and a fitted pseudo-second-kinetic model for As (III) adsorption. The main mechanism was chemisorption with both bismuth and aluminum atoms; however, physisorption also contributed to arsenic adsorption at the initial stage of the reaction. The Adams-Bohart model better described the breakthrough curves than the Thomas model. BiAl exhibited efficient As (III) adsorption over a wide pH range and could be applied to As (III) removal from wastewater. A high As (III) removal efficiency (91.6%) was obtained at an initial As (III) concentration of 5 mg L−1 at a flow rate of 1 mL min-1. This study indicates the potential for the practical application of BiAl in As (III) removal.
•Bismuth impregnated aluminum oxide showed a strong ability for arsenic (III) removal.•Bismuth inclusion optimized the pore size distribution of aluminum oxide.•The chemisorption made the main contribution to arsenic (III) adsorption.•BiO bond played an important role in arsenic (III) adsorption.
