• Energy Research
• 2016-2025close

Agri-food residues or by-products have increased their contribution to the global tally of unsustainably generated waste. These residues, characterized by their inherent physicochemical properties and rich in lignocellulosic composition, are progressively being recognized as valuable products that align with the principles of zero waste and circular economy advocated for by different government entities. Consequently, they are utilized as raw materials in other industrial sectors, such as the notable case of environmental remediation. This review highlights the substantial potential of thermochemical valorized agri-food residues, transformed into biochar and hydrochar, as versatile adsorbents in wastewater treatment and as promising alternatives in various environmental and energy-related applications. These materials, with their enhanced properties achieved through tailored engineering techniques, offer competent solutions with cost-effective and satisfactory results in applications in various environmental contexts such as removing pollutants from wastewater or green energy generation. This sustainable approach not only addresses environmental concerns but also paves the way for a more eco-friendly and resource-efficient future, making it an exciting prospect for diverse applications.

An expanding number of human activities are contributing to the rising levels of aromatic compounds, which pose a major threat to the ecosystem. However, readily available microbial enzymes might be used to remediate contaminated wastewater in an economical and environmentally benign manner. In this study, an efficient method of laccase-oriented immobilization on modified Immobead 150P was proposed. The oriented immobilization technique using aminated laccase exceeds in both protein loading onto the carrier (4.26 mg/g) and immobilization yield (93.57%) due to the availability of more active sites. The oriented aminated laccase preserves 100% and 95% of its original activity after six and ten cycles of operation, respectively. The thermal stability performance of the oriented enzyme was the best among both free and random immobilized forms, since it was able to conserve 79% and 44% of its initial activity after 6 h at 50 °C and 60 °C, respectively. The ideal pH of oriented immobilized laccase was altered from 3.0 to 4.0, and it was more stable than both free and random immobilized laccases at pH 7.0. Finally, the integration of the adsorption capacity of Immobead 150P and the biodegradation ability of laccase promises the efficient removal of aqueous phenolics. Oriented immobilized laccase may provide a significant new approach for wastewater treatment, according to these findings.

Hydrothermal carbonization (HTC) is a facile, low-cost and eco-friendly thermal conversion process that has recently gained attention with a growing number of publications (lower 50 in 2000 to over 1500 in 2020). Despite being a promising technology, problems such as operational barriers, complex reaction mechanisms and scaling have to be solved to make it a commercial technology. To bridge this current gap, this review elaborates on the chemistry of the conversion of lignocellulosic biomass. Besides, a comprehensive overview of the influence of the HTC operational conditions (pH, temperature, water:biomass ratio, residence time and water recirculation) are discussed to better understand how hydrochar with desired properties can be efficiently produced. Large-scale examples of the application of HTC are also presented. Current applications of hydrochar in the fields of energy, biocatalysis and environment are reviewed. Finally, economic cost and future prospects are analyzed.

Several pesticides and pharmaceuticals (PP) have been detected in the effluent of a full-scale Portuguese Wastewater Treatment Plant (WWTP). Their presence contributed to the environmental burdens associated with the existing treatment of the Municipal Wastewater (MWW) in the impact categories of Human Carcinogenicity, Non-Carcinogenicity, and Freshwater toxicities on average by 85%, 60%, and 90%, respectively (ReciPe2016 and USEtox methods). The environmental and economic assessment of the installation of an Anodic Oxidation (AO) unit for PPs’ removal was performed through Life Cycle and Economic Analysis, considering two types of anodes, the Boron-Doped Diamond (BDD) and the Mixed Metal Oxides (MMO). The operation of the AO unit increased the environmental burdens of the system by 95% on average (USEtox), but these impacts can be partially compensated by the avoided the production of non-renewable energy in the Portuguese electricity mix by biogas cogeneration at the WWTP. If the construction of the AO unit and the manufacturing of the electrodes are considered, the Human and Freshwater Toxicities are often higher than the environmental benefits derived from the PPs’ removal. On the economic side, the MMO configuration is clearly more advantageous, whereas BDD is environmentally more favorable. The issue of the presence of PP in MWW effluents has to be addressed as an integrated solution both improving upstream PP’s management and adopting PP’s removal technologies strongly supported by renewable energies. Further insights are needed for the assessment of fate and of the environmental effects of PP in the sludge.

Globally, tougher legislation in greenhouse gases emissions is prompting the hunt for more sustainable and competitive strategies to synthesize biodiesel. Although enzyme-catalyzed processes are considered as a more environmentally-friendly option, there are still challenges to be approached like the replacement of traditional solvents due to their well-known disadvantages such as their volatility, toxicity or carcinogenic character. Thus, the emergence of neoteric solvents such as perfluorocarbons, liquid polymers, ionic liquids, deep eutectic solvents or supercritical fluids has opened up new opportunities to reach truly green processes. Nonetheless, literature analysis reveals the scarcity of research works, which are exclusively restricted to the last three types of solvents. One of the critical points to take into account refers to the performance of enzymes in this kind of milieu, as this environment may be deleterious in terms of protein structure, leading to enzyme deactivation. Therefore, the final purpose of this review paper is to identify the current trends of research in the field of neoteric solvents applied to enzyme-catalyzed synthesis of biodiesel and to shed light on the possible existing gaps. Xunta de Galicia | Ref. GRC2013/003

In this work, the fermentative and oxidative processes taking place in a microbial fuel cell (MFC) fed with glucose were studied and modeled. The model accounting for the bioelectrochemical processes was based on ordinary, Monod-type differential equations. The model parameters were estimated using experimental results obtained from three H-type MFCs operated at open or closed circuits and fed with glucose or ethanol. The experimental results demonstrate that similar fermentation processes were carried out under open and closed circuit operation, with the most important fermentation products being ethanol (with a yield of 1.81molmol(-1) glucose) and lactic acid (with a yield of 1.36molmol(-1) glucose). A peak in the electricity generation was obtained when glucose and fermentation products coexisted in the liquid bulk. However, almost 90% of the electricity produced came from the oxidation of ethanol.

Nowadays, the contamination of wastewater by organic persistent pollutants is a reality. These pollutants are difficult to remove from wastewater with conventional techniques; hence, it is necessary to go on the hunt for new, innovative and environmentally sustainable ones. In this context, advanced oxidation processes have attracted great attention and have developed rapidly in recent years as promising technologies. The cornerstone of advanced oxidation processes is the selection of heterogeneous catalysts. In this sense, the possibility of using metal–organic frameworks as catalysts has been opened up given their countless physical–chemical characteristics, which can overcome several disadvantages of traditional catalysts. Thus, this review provides a brief review of recent progress in the research and practical application of metal–organic frameworks to advanced oxidation processes, with a special emphasis on the potential of Fe-based metal–organic frameworks to reduce the pollutants present in wastewater or to render them harmless. To do that, the work starts with a brief overview of the different types and pathways of synthesis. Moreover, the mechanisms of the generation of radicals, as well as their action on the organic pollutants and stability, are analysed. Finally, the challenges of this technology to open up new avenues of wastewater treatment in the future are sketched out.