Feb 2025, Volume 19 Issue 2
    

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  • REVIEW ARTICLE
    Wentao Pan, Hong Liu, Yongzhi Chen, Qi Wang, Yunxia Wang, Li Zhang, Yongzhen Peng

    Enhancing nitrogen removal is a very active branch in municipal wastewater treatment research, toward this end, anammox technology is a sustainable solution. This review systematically outlines the strategies employed to enhance mainstream anammox performance, including nitrite accumulation and microbial enrichment based on partial nitrification coupled anammox and partial denitrification coupled anammox, developed to address the challenges of low ammonium content in wastewater, nitrate accumulation in the effluent, and the influence of organic matter. The characteristics and advantages of novel anammox-coupled processes, including partial nitrification and partial denitrification coupled anammox, endogenous partial denitrification coupled anammox, and denitrifying anaerobic methane oxic coupled anammox are also comprehensively discussed; these aim to ensure the highly efficient and stable operation of anammox under diverse wastewater conditions by constructing a composite biological nitrogen removal system based on anammox, supplemented by nitrification-denitrification and other processes. Additionally, a novel anammox application route including mainstream partial denitrification/anammox and absorption-biodegradation as well as sidestream partial nitrification/anammox is proposed, and its application pathway in conceptual wastewater treatment plants is outlined, aiming to foster the development of cost-effective, efficient, and energy-saving advanced wastewater treatment processes. Finally, prospects are presented that indicate the gaps in contemporary research and potential future research directions. Overall, this review provides a reference for treating municipal wastewater with anammox and sheds new light on related strategies and nitrogen removal mechanisms.

  • RESEARCH ARTICLE
    Zuoyan Yang, Yuqi Zhou, Hongjie Cui, Zhenmin Cheng, Zhiming Zhou

    Direct air capture (DAC) using amine-functionalized solid adsorbents holds promise for achieving negative carbon emissions. In this study, a series of additive-incorporated tetraethylenepentamine-functionalized SiO2 adsorbents with varying tetraethylenepentamine and additive contents were prepared via a simple impregnation method, characterized by various techniques, and applied in the DAC process. The structure-performance relationship of these adsorbents in DAC was investigated, revealing that the quantity of active amine sites (or the tetraethylenepentamine content in the exposed layer), as determined by CO2-TPD measurement, was an important factor affecting the adsorbent performance. This factor, which varied with the tetraethylenepentamine content, additive type, and additive content, showed a positive correlation with the CO2 adsorption capacity of the adsorbents. The optimal adsorbent, 40TEPA-10PEG/SiO2 containing 40 wt % tetraethylenepentamine and 10 wt % polyethylene glycol (Mn = 200), exhibited a stable CO2 capacity of 2.1 mmol·g–1 and amine efficiency of 0.22 over 20 adsorption–desorption cycles (adsorption at 400 ppm CO2/N2 and 30 °C for 60 min, and desorption at pure N2 and 90 °C for 20 min). Moreover, even after deliberate accelerated oxidation treatment (pretreated in air at 100 °C for 10 h), the CO2 capacity of 40TEPA-10PEG/SiO2 remained at 2.0 mmol·g–1. The superior thermal and oxidative stability of 40TEPA-10PEG/SiO2 makes it a promising adsorbent for DAC applications.

  • RESEARCH ARTICLE
    Siqi Liu, Zhiqiang Zhou, Yuan Xiao, Huanhuan Duan, Guomin Cui

    This paper proposes an innovative simultaneous optimization approach for single and multi-component mass exchanger network synthesis (MENS). A retrofitted stage-wise superstructure and a parallelized random walk algorithm with compulsive evolution (RWCE) are adopted. An iterative calculation method is designed to satisfy the requirements of multi-component mass transfer, with a relaxation for the outlet composition of the lean streams. The parametric analysis shows that the relaxation coefficient plays a major role in driving the convergence of the method. To improve the robustness of the established model, an adaptive relaxation coefficient strategy is implemented for multi-component MENS problems. In a divergence situation, the outlet concentration of the lean stream can be adjusted automatically by a random relaxation coefficient. Finally, three industrial MENS examples are considered in this work, whose total annual cost (TAC) are reduced by 7179, 2212, and 551 $·year–1. The corresponding optimization times are obtained to be 336, 125, and 145 s. The results indicate improvements in the economy and time, demonstrating that the parallelized RWCE can yield an optimal TAC and optimization efficiency compared to previous results. Overall, the adaptive relaxation coefficient strategy enhances the convergence for multi-component MENS problems.

  • RESEARCH ARTICLE
    Vasiliki P. Aravani, Shiya Wang, Wen Wang, Vagelis G. Papadakis

    Rapid population growth, economic development, resource constraints and various geopolitical problems, as well as intensifying environmental issues are leading to a worsening energy crisis. Oil, natural gas and coal are still the main sources of primary energy. Biofuels, such as biochar, bio-oil, biogas, and hydrogen, are one of the most significant renewable and sustainable energy sources. Their use can reduce net greenhouse gas emissions as well as dependence on imported fossil fuels, in response to the above, while the production and exploitation of biomass mainly from agricultural residues can also create jobs in rural and depopulated areas. In this study, a market analysis for biochar, bio-oil, biogas, and hydrogen was conducted worldwide intending to provide detailed information for the economic viability of sustainable agricultural systems and to specify the prospects for an economically viable introduction of each of the bio-products into the energy market. The results revealed that indeed these biofuels are one of the most significant and energy sources offering sustainability by reducing gas emissions into the atmosphere but also by managing residual biomass, thus contributing to waste management. A rapid acceleration is expected in the next years followed by price reduction.

  • VIEWS & COMMENTS
    Antony Rajendran, Arumugam Sakthivel, Zhiwei Dong, Wenying Li

    Biochar belongs to the category of low-cost, stable, and environmentally benign carbon-based materials. In this article, the reasons that highlight the advantages of biochar materials to be used in carbon dioxide (CO2) adsorption are briefly viewed with recent examples. Also, the issues to be solved for recommending biochar materials in the practical applications are listed.

  • RESEARCH ARTICLE
    Larissa Pinheiro de Souza, Flávio Olimpio Sanches-Neto, Júlio César de Oliveira Ribeiro, Bruno Ramos, Valter H. Carvalho-Silva, Antonio Carlos Silva Costa Teixeira

    This study introduces an innovative screening approach to evaluate advanced oxidation processes (AOPs) as a preliminary diagnostic tool for degrading emerging contaminants (EC). It includes the design, prototyping, and cost-benefit analysis of circular photochemical reactors with flat and spiral internal geometries. Three-dimensional (3D) printing was used for reactor prototyping, providing flexibility and economy, and this stage was assisted by the hydrodynamic analysis of the prototypes based on residence time distribution (RTD) and macromixing models. The research evaluates the degradation of a model contaminant of emerging concern, fluoxetine (FLX) hydrochloride, using the solar/persulfate (PS) process in two water matrices (i.e., ultrapure water and sewage treatment plant effluent) to optimize reactor performance. The study also proposes primary theoretical pathways for fluoxetine degradation involving hydroxyl and sulfate radicals, as well as predicting the toxicity of the parent compound and its primary metabolites using quantitative structure-activity relationship (QSAR) models. The spiral reactor exhibits improved hydrodynamic behavior, closely resembling continuous stirred and plug flow reactors in series. Despite a slightly lower specific degradation rate in real wastewater, the solar/PS process remains effective for both matrices. By-products generated via the sulfate radical pathway are expected to be less toxic than those formed by hydroxyl radicals (HO·) attack.

  • RESEARCH ARTICLE
    Pin Cui, Ying Tang, Aixia Guo, Chenxu Wang, Minmin Liu, Wencai Peng, Feng Yu

    The use of metal-organic frameworks (MOFs) as CO2-gas-capture materials has attracted extensive research attention. In this study, two types of MOFs—Zn-MOF and ZnCe-MOF—were synthesized utilizing the microchannel reaction method, with water being employed as the solvent. The specific surface area, pore size, and pore volume of Zn-MOF and ZnCe-MOF were 1566.4 and 15.6 m2·g–1, 0.65 and 7.32 nm, as well as 1.65 and 0.03 cm3·g–1, respectively. Furthermore, Ce doping not only increased the pore size of ZnCe-MOF but also its adsorption energy from −0.19 eV (Zn-MOF) to −0.53 eV (ZnCe-MOF). At 298 K, the adsorption capacities of Zn-MOF and ZnCe-MOF were 0.66 and 0.74 mmol·g–1, respectively. In addition, the CO2 adsorption behaviors of Zn-MOF and ZnCe-MOF were linear and logarithmic, respectively. Theoretical calculations show that the results of adsorption thermodynamic simulations were consistent with the experiments. Thus, the preparation of ZnCe-MOF materials using a microchannel reactor provides a new approach for the continuous preparation of MOFs.