The separation of carbon dioxide and methane is vital for biogas upgradation and natural gas sweetening applications. Membrane separation is one of the techniques used for CO₂ and CH₄ separation for biogas upgradation and natural gas sweetening owing to its energy efficiency, low capital cost, portable, and ease of operation. Polymer membranes and inorganic membranes have a trade-off relationship between permeability and selectivity. A new class of membranes known as Mixed Matrix Membranes (MMMs) is being explored to overcome this trade-off by dispersing inorganic fillers in the polymer matrix. However, the addition of filler poses new interfacial morphological difficulties, such as poor dispersion, very strong interaction between filler and polymer, and formation of voids. These challenges can be tackled by suitable choice of filler and polymer, functionalization of filler and polymer, polymer blending. The hybrid membranes separation process or use of two or more strategies can lead to the formation of defect-free membranes with improved separation performance. In this review article, we provide a concise literature review and analysis of the strategies for improving the transport properties of MMMs based on MOF as filter materials for CO₂/CH₄ separation.

Constructed wetlands (CWs) are ecosystems artificially designed to mimic natural wetland systems for the treatment of effluents. Its adoption can be given both at a decentralized level and as an economic alternative for a variety of pollution controls: agricultural, industrial, mines and urban drainage effluents. Although a CW has larger area requirements than conventional energy-intensive treatment technologies, they have several advantages: lower costs; energy savings; fewer operating and maintenance requirements; enable wild habitat and natural leisure areas; and allow the use of solar energy. Thus, the treatment of effluents through CWs is highly promising. This review aims to encompass the current literature and state-of-the-art on CWs applied on domestic wastewater in decentralized systems, explaining with visual examples their constructions, processes and modalities.

Organic fraction of the municipal waste (OFMSW) is a valuable resource for biogas production through anaerobic digestion (AD). Bioplastics is widely used in daily activities, especially with food related items and collection bags, and can reach biogas plants through separate collection of OFMSW. PHAs, starch and cellulose based polymers with different compositions can degrade under anaerobic conditions. Cellulose and PHAs can degrade under both mesophilic and thermophilic conditions where, starch blends required thermophilic conditions in general. Other biopolymers, such as the most abundant PLA, are not able to degrade in the time frame of the facilities in most of the cases. Pre-treatment methods through abiotic and bio-augmentation, as well as post treatment methods, such as composting subsequent to AD are encountered as possible solutions for achieving better degradation or safer disposal of these polymers. The post-treatment/pre-disposal of the materials should be further studied as well as the pre-treatment methods. Studies on the effect of additives in biopolymers was not studied widely and requires further investigation. Degradation of biopolymers under AD, biogas production, pre-treatment and post-treatment methods as well as standard methods (or lack thereof) are discussed in detail in this paper, in order to point out to the possible scenarios that can be encountered when bioplastics end up in co-digestion conditions with organic material.

One of agriculture’s most important goals is finding the proper equilibrium between sustainability and intensification of production. The exponential growth of the world population, climate variability, and soil degradation are essential factors that require the development of novel agricultural practices to achieve food security. In this context, organo-mineral fertilization has been proposed as a promising approach. Such a concept is based on novel fertilizers formulations combining organic and mineral resources features, which could simultaneously address soil fertility and health issues. The manufacturing processes of organo-mineral fertilizers (OMF) are highly versatile and revolve around the co-processing of organic and mineral matrices. OMF’s peculiarity resides in using systemic methodologies for waste valorization to generate cost-effective and eco-friendly products in alignment with the bio-circular economy. Despite their advantages, OMF adoption by farmers is still not satisfactory, which could be attributed to the difficulty of accessibility and a stagnant market. This work critically reviews recent advances in the organo-mineral fertilization concept. Our review provides an in-depth understanding of the chemical, biological, and thermal methodologies used for OMF generation through mineral and organic matrices co-processing. We also discuss the positive effect of such products on the plant-soil system by focusing on the mechanism of action. Furthermore, this review scrutinizes the innovation profile of OMF based on trends of patent submission during the last 20 years. It also provides future research and development pathways based on current drawbacks and limitations of the industry.

BiOX (bismuth oxyhalides) are a ternary structure (V–VI–VII) of semiconductor materials with tunable band gaps, a low recombination rate, wide light absorption range, electro-magnetical and optical properties due to their unique crystallinity with tetragonal matlockite configuration. This article critically reviews the applicability of BiOX-based photocatalysts for water treatment and/or energy storage applications. To enhance their photocatalytic activities under visible light, a particular focus is given to the formation of heterojunctions, or plasmonic nanoparticles. Their technological strengths and limitations are evaluated and compared. Synthesis techniques such as precipitation, solvothermal, hydrolysis, and doping strategy of self-assembling BiOX including heterojunctions with other semiconductors in enhancing photocatalytic performance are presented. Research direction, challenges, and perspectives of BiOX-based photocatalysts for practical applications are elaborated. It is evident from a literature survey of 227 published articles (1972–2022) that the physico-chemical properties of BiOX-based photocatalysts such as energy band structures and anisotropic layered structure are responsible for UV light-driven photocatalytic performance. The hybridized valence band of O 2p and Bi 6s² orbitals in the Bi(III)-based compounds upshifts their valence band (vb) that narrows energy bandgap and expands the absorption of visible light range. Among the BiOX, BiOI and BiOCl are the most outstanding photocatalysts under UV Vis irradiation due to their narrow bandgaps (Eᵒ = 2.0 and 3.4 eV, respectively), large surface area, and strong light absorption. It is important to note that technical applicability, target pollutants, and cost-effectiveness represent the key factors in selecting the most appropriate BiOX-based photocatalysts for water treatment and/or energy storage applications.

In the past few decades, pollution from microplastics has emerged as an important issue on a global scale. These plastic particles are mainly the result of anthropogenic activities. Urban sprawl, industrialization, indiscriminate use and poor waste management of plastic products are the main factors responsible for the accumulation of microplastics in different ecosystems of the environment. The presence of microplastics in the soil matrix is considered an emerging threat to agroecosystems. Since most of the studies on microplastics have been done in the aquatic environment. The understanding of the ecotoxicological effects of these contaminants in terrestrial ecosystems is still limited, especially in agroecosystems. The negative effects of microplastics on the physical, chemical and biological properties of soil are now revealing. But the effects of microplastics on plant growth and yield are largely unexplored. Microplastic contamination in the soil can alter the functioning of plants by affecting the microbial community of the rhizosphere and disturbing the homeostasis of the agroecosystem. Furthermore, it may transfer into the plant system through nutrient and water absorption channels and affect plant physiology. The pervasive nature of microplastics in the soil is considered a barrier to sustainable agriculture and ecosystem functioning. The present review gives an overview of the sources, dissipation and effects of microplastics with reference to the soil–plant system, highlights the research gaps, and deciphers the possible future threats to agroecosystems.

Digestate landspreading is a key aspect of the circular economy. However, organic matter (OM) stability in digestates is usually either poorly assessed or done through laborious methods. Spectroscopic methods are useful and easy to deploy alternatives to assess several aspects in anaerobic digestion (AD) studies such as process performance, waste classification and both OM composition and transformation. In these studies, a lack of agreement on analytical techniques, indicators and reference values is evident. This unclear scenario brings to the forefront the need for a meta-analytical study providing benchmarking values and trends. This review aimed to fill up this gap through the identification and evaluation of: (i) the most frequently applied techniques, their principles, deployment methods and limitations, (ii) the quantitative spectroscopic indices to define OM stability, (iii) the common trends of these parameters due to AD effect on the OM and (iv) the relevance of each technique based on the frequency of statistically significant results reported. Ultraviolet–visible and fluorescence spectroscopy have been identified as the most relevant techniques for aqueous phase study whereas mid-infrared and ¹³C cross-polarisation magic angle spinning nuclear magnetic resonance were the most appropriate for the solid phase. Their most applied indicators and their trends after AD have been summarised. Finally, the research studies that displayed statistically significant findings were described, the representativeness of the indices and the influence of sample preparation on their calculation were discussed and future research lines were suggested. Overall, this review demonstrates that spectroscopic methods provide relevant information for better digestate management.

Biogas from anaerobic digestion (AD), as an important alternative to fossil fuels, has contributed to energy recovery and environmental sustainability. Incomplete or inefficient mixing within anaerobic reactors can result in poor biogas production or energy wastage. Thus, identifying mixing performance is meaningful for the digester design, operation and maximum biogas production. Over the years, various experimental and computational fluid dynamics (CFD) techniques have been developed to characterize the mixing performance of digesters. This review described the critical impact of mixing on biogas production in AD. Then, experimental techniques available on local and global scales were reviewed and compared in terms of their advantages, disadvantages, characterization capabilities and scope of application. Moreover, the implementation, reliability, indicators and application of CFD techniques in AD were thoroughly discussed. Based on the above discussion, mixing significantly affects AD methane production, and intermittent mixing is preferred for maximum biogas production. Local experimental techniques have been considered to be the simplest and cheapest for arbitrarily sized digesters; global experimental techniques relying on computer systems have received increasing attention for their applications in AD flow fields. More research efforts are needed to discover new experimental techniques that overcome the limitations of digestate opacity and industrial reactor geometries, in addition, compartmental models based on CFD to couple hydrodynamics with biokinetics are interesting and allow for greater implementation of CFD applications.

The physical/chemical abatement of gas pollutants creates many technical problems, is costly and entails significant environmental impacts. Biological purification of off-gases is a cheap and ecologically safe way of neutralization of gas pollutants. Despite the recent advances, the main technological challenge nowadays is the purification of volatile organic compounds (VOCs) of hydrophobic character due to their low solubility in water. Among all known biological methods of air purification, the most cost-effective biodegradation of hydrophobic VOCs is conducted by biotrickling filters. In this context, fungi have gained an increasing interest in this field based on their ability to biodegrade hydrophobic VOCs. In addition, biotrickling filtration using fungi can support a superior hydrophobic VOC abatement when compared to the bacterial biofilters. This paper aims at reviewing the latest research results concerning biocatalytic activity of fungi and evaluating the possibilities of their practical application in biofiltration systems to remove hydrophobic VOCs.