Acceleration of urbanization and industrialization has resulted in the drastic rise of waste generation with majority of them being biowaste. This constitutes a global challenge since conventional waste management methods (i.e., landfills) present environmental issues including greenhouse gases emissions, leachate formation and toxins release. A sustainable and effective approach to treat biowaste is through composting. Various aspects of composting such as compost quality, composting systems and compost pelletization are summarized in this paper. Common application of compost as fertilizer or soil amendment is presented with focus on the low adoption level of organic waste compost in reality. Rarely known, compost which is easily combustible can be utilized to generate electricity. With the analysis on critical approaches, this review aims to provide a comprehensive study on energy content of compost pellets, which has never been reviewed before. Environmental impacts and future prospects are also highlighted to provide further insights on application of this technology to close the loop of circular bioeconomy.

The increased bioeconomy targets for the biomass share of renewable energy production across Europe should be met using land unsuitable for food production. Miscanthus breeding programs targeted the production of plants with a diverse range of traits allowing a wider utilization of land resources for biofuel production without competing with arable crops. These traits include increasing tolerances to drought, chilling, and to metal(loid)s excess. Two novel Miscanthus hybrids, GNT41 and GNT34, were compared against Miscanthus x giganteus (Mxg) on metal-contaminated arable land in Poland. This study aimed at evaluating their yield, biomass quality and quantifying seasonal differences in photosynthetic and transpiration parameters. A secondary objective was to identify key physiological mechanisms underlying differences in metal accumulation between the investigated plants. The new hybrids produced a similar yield to Mxg (13–15 t ha−1 yr−1), had shorter shoots, higher Leaf Area Index and stem number. Based on gas exchange measurements, GNT34 exhibited isohydric (water-conserving) behavior. The stomatal response to light of the new hybrids was at least twice as fast as that of Mxg, a trait that is often associated with increased seasonal water use efficiency. This contributed to the almost 40% reduction in shoot Pb and Cd concentrations for the new hybrids as compared to Mxg. This suggested that promoting stomatal regulation in conjunction with improved water conservation may be a target for improving plants for wider use on metals contaminated land.

The objective of this study was to evaluate the potential of three C4 perennial grasses (Miscanthus x giganteus, Panicum virgatum and Spartina pectinata) for biomass production on arable land unsuitable for food crop cultivation due to Pb, Cd and Zn contamination. We assessed soil properties, biomass yield, metal concentrations, and the photosynthetic performance of each species. Physico-chemical and elemental analyses were performed on soil samples before plantation establishment (2014) and after three years of cultivation (2016), when leaf area index, plant height, yield and heavy metal content of biomass were also determined. Physiological measurements (gas exchange, pigment content, chlorophyll a fluorescence) were recorded monthly between June and September on mature plants in 2016. Cultivation of investigated plants resulted in increased pH, nitrogen, and organic matter (OM) content in soil, although OM increase (13%) was significant only for S. pectinata plots. During the most productive months, maximal quantum yield values of primary photochemistry (Fv/Fm) and gas exchange parameter values reflected literature data of those plants grown on uncontaminated sites. Biomass yields of M. x giganteus (15.0 ± 0.4 t d.m. ha−1) and S. pectinata (12.6 ± 1.2 t d.m. ha−1) were also equivalent to data published from uncontaminated land. P. virgatum performed poorly (4.1 ± 0.4 t d.m. ha−1), probably due to unfavourable climatic conditions, although metal uptake in this species was the highest (3.6 times that of M. x giganteus for Pb). Yield and physiological measurements indicated that M. x giganteus and S. pectinata were unaffected by the levels of contamination and therefore offer alternatives for areas where food production is prohibited. The broad cultivatable latitudinal range of these species suggests these results are widely relevant for development of the bioeconomy. We recommend multi-location trials under diverse contaminant and environmental regimes to determine the full potential of these species.

Harvesting of marine biomass for various applications may generate ecosystem services that currently lack a market price. One of these is nutrient uptake, which could counteract eutrophication. Market-based instruments (MBIs) such as cap & trade, compensatory mitigation, and payment for ecosystem services could help internalize such positive externalities. However, activities of the blue bioeconomy are diverse. We show that identifiable market characteristics can provide guidance concerning when to use these instruments and not. We find that the activities most suitable for MBIs are those that have positive environmental impacts but that are not (yet) financially viable. For activities that are already profitable on the biomass market, ensuring ‘additionality’ may be a significant problem for MBIs, especially for cap & trade systems or compensatory mitigation. We provide an overview of how some current biomass options fit into this framework and give suggestions on which biomass types to target.

PURPOSE OF REVIEW: Increasing environmental problems demand mitigation solutions to fulfill sustainability development goals. Microalgae offer possibility of valorizing the CO₂ and wastewater-derived nutrients to produce numerous industrial bioproducts. However, developing self-sustained systems for the complete valorization of algal biomass into valuable biobased products is challenging. Currently, sustainable algal processing faces several challenges including costly cultivation, difficult harvesting, and incomplete biomass valorization. This review assessed the prospects of emerging technologies focusing on the integrated approaches for sustainable algal biorefinery development ensuring the sustainability of environment-water-energy nexus. RECENT FINDINGS: Evaluation of various upstream, midstream, and downstream processing technologies provided insights into the processing issues. In upstream processing, high-rate algal ponds and integrated carbon capture and transformation technologies offer waste valorization into eco-friendly algal production. A brief comparison of harvesting technologies mainly focusing on chemical and biological flocculation has shown that integrating physical and biological harvesting methods are more reliable and efficient. Overview of downstream processing has indicated that biomass processing in a cascading manner offers the complete biomass valorization in a zero-waste paradigm. Assessment of cultivation-to-production technologies highlighted that “zero-waste” algal biorefinery has the potential to become reality by integrating the industry 4.0 and phenomics approaches with eco-friendly cultivation, harvesting, and processing technologies. Hybrid methods based on integrated cascading processing offer complete biomass valorization in a circular bioeconomy paradigm.

PURPOSE OF REVIEW: Effluent organic matter (EfOM) is a blend of organic matter, microbial constituents, biological metabolites, and synthetic chemicals which is originated mainly due to anthropogenic activities and is a matter of emerging environmental concern. The presence of EfOM poses a major challenge in the wastewater treatment processes. This review is aimed to assess the recent progress in developing innovative green approaches for the biotransformation of EfOM into ecofriendly products which is vital to attain the “zero-waste” paradigm to achieve wastewater reclamation and environmental sustainability under the umbrella of circular bioeconomy. RECENT FINDINGS: Characteristics of EfOM and its impact on wastewater treatment processes have been evaluated. The potential and shortcomings of the traditional, advanced, and biological approaches for the EfOM removal have been described. Recent strategies which are based on the combination of two or more of these technologies (hybrid systems) have been discussed to address the challenges/shortcomings of the standalone technologies and to improve the process efficiency. Microalgae and cyanobacteria-based removal of EfOM along with its subsequent utilization as a soil amender is proposed as a novel trend in the future. Assessment of the previously employed technologies provided an insight into their working mechanisms which have suggested several improvements in the processes. Besides, hybrid systems could be an ecofriendly removal of EfOM via biosorption.

Microalgal biomass–based biofuels are a promising alternative to fossil fuels. Microalgal biofuels’ major obstacles are the water and carbon sources for their cultivation and biomass harvest from the liquid medium. To date, an economically viable process is not available for algal based biofuels. The circular bioeconomy is an attractive concept for reuse, reduce, and recycle resources. The recovery of nutrients from waste and effluents by microalgae could significantly impact the escalating demands of energy and nutraceutical source to the growing population. Wastewaters from different sources are enriched with nutrients and carbon, and these resources can be recovered and utilized for the circular bioeconomy approach. However, the utilization of wastewaters and waste seems to be an essential strategy for mass cultivation of microalgae to minimizing freshwater consumption, carbon, nutrients cost, nitrogen, phosphorus removal, and other pollutants loads from wastewater and generating sustainable biomass for value addition for either biofuels or other chemicals. Hence, the amalgamation of wastewater treatment with the mass cultivation of microalgae improved the conventional treatment process and environmental impacts. This review provides complete information on the latest progress and developments of microalgae as potential biocatalyst for the remediation of wastewaters and waste carbon to recover resources through biomass with metabolites for various industrial applications and large-scale cultivation in wastewaters, and future perspectives are discussed.

Over the last few decades, the globe is facing tremendous effects due to the unnecessary piling of municipal solid waste among which food waste holds a greater portion. This practice not only affects the environment in terms of generating greenhouse gas emissions but when left dumped in landfills will also trigger poverty and malnutrition. This review focuses on the global trend in food waste management strategies involved in the effective utilization of food waste to produce various value-added products in a microbiology aspect, thereby diminishing the negative impacts caused by the unnecessary side effects of non-renewable energy sources. The review also detailed the efficiency of microorganisms in the production of various bio-energies as well. Further, recent attempts to the exploitation of genetically modified microorganisms in producing value-added products were enlisted. This also attempted to address food waste valorization techniques, the combined applications of various processes for an enhanced yield of different compounds, and addressed various challenges. Further, the current challenges involved in various processes and the effective measures to tackle them in the future have been addressed. Thus, the present review has successfully addressed the circular bio-economy in food waste valorization.

Solid wastes generated from industrial sponge iron plants (ISP) are categorized as hazardous waste due to their extremely fine, loose texture, toxic metal concentrations, and being wind borne in summer; their unscientific disposal leads to severe land degradation and environmental pollution. In the present study, phytorestoration of such a hazardous waste dump in central India was carried out through blanketing with forest soil (substratum for vegetation growth) followed by plantation with Psidium guajava (L.) saplings (2500 saplings/ha). The present study aimed to assess the efficiency of fruit orchards in restoring the soil health of waste dumps (WD) without causing any health hazards, allowing the possibility for an economically viable after use of the degraded land. Heavy metal concentration (Mn, Zn, Cu, Cr, Ni) in blanketed topsoil, plant tissues (roots, leaves, fruits), and its associated risk due to consumption of guava fruits were analysed. Soil health with reference to organic carbon (1.7%), total nitrogen (1727.7 mg kg⁻¹), and exchangeable potassium (162.3 mg kg⁻¹) at the 7-year-old restored site was significantly higher than that of the initial stage of revegetation. No probables of health risk was found due to consumption of guava fruit (growing on WD) as the target hazard quotient (THQ) of all the metals in fruit was <1. Restoration cost analysis of the present study showed that only 5% of total costs were responsible for the development of fruit orchards. Therefore, the study concluded that fruit orchards could be a sustainable alternative for phytorestoration of WD, which will also provide socio-economic return to stakeholders.

In the context of the circular bioeconomy and cleaner production, the incorporation of the by-products of plant biomass production in the bioenergy chain is fundamental. However, lignocellulosic wastes have properties that hinder their use for the production of biofuels. This study aims to evaluate how blends of lignocellulosic wastes improve the physical, chemical, and mechanical quality of pellets destined to the industrial sector, and to identify the challenges associated with the use of agroforestry biomass as raw material for pelletizing. Pellets were produced from blends of soybean wastes, sorghum wastes, pine needles, rice powder, Eucalyptus sawdust, and charcoal fines. Additionally, pure pellets composed of soybean wastes, sugarcane bagasse, and pine wood were evaluated. The effect of biomass type on the energy density, ash content, net heating value, and ultimate analysis was significant. The pellets produced with soybean wastes presented high contents of N (3.5–4.9%) and ashes (16.4–26.7%), besides low mechanical durability (≤ 96%), hindering its commercialization for industrial purposes. Pellets with sugarcane bagasse presented N (1.5%), S (0.03%), ashes (5.6%), mechanical durability (96.6%), and net heating value (15.1 MJ kg⁻¹), suitable for industrial energy use in accordance with ISO 17225-6. The high N and ash contents and the low mechanical durability are the greatest challenges for the energy use of pellets produced from Brazilian agroforestry wastes.