While ‘renewable’ is the keyword in a bioeconomy and resource conservation is the motivation behind a circular economy, a circular bioeconomy is one in which waste streams from renewable bio-resources are looped back into the technosphere—open-loop or closed-loop recycling or conversion from matter to energy. This systematic review brings together 385 publications from 2015 to 2021, originating from 50 countries and appearing in 150 journals, into a coherent account of the status quo of published research on circular bioeconomy. The numbers bear testimony to the growing interest in this field of research. Germany is the leading contributor to the scientific literature base (10%), while the Journal of Cleaner Production (9%) tops the list of journals in the fray. The methodology adopted has been clearly explained, and the discussion has been segmented into sub-sections and sub-sub-sections to do justice to the diversity of the nature of the publications. A little flexibility in organisation of the flow of the text has been availed of, to improve readability. The circular bioeconomy can be visualised as a set of ‘many through many to many’ relationships, enabling both economies of scale and scope in the longer run. This calls for extensive collaboration and cooperation among the numerous stakeholders involved. Several barriers will have to be overcome. Technology impact assessments and sustainability risk appraisals need to be carried out in order to ensure and convince stakeholders that they are on the right path. But as one knows and will appreciate, challenges lurk where there exist opportunities to be availed of, to replace the take-make-use-dispose paradigm of a linear economy to the grow-make-use-restore alternative. Graphical abstract

Paddy fields emit considerable amounts of methane (CH₄), which is a potent greenhouse gas (GHG) and, thereby, causes significant environmental impacts, even as they generate wealth and jobs directly in the agricultural sector, and indirectly in the food-processing sector. Application of biochar in rice production systems will not just help to truncate their carbon footprints, but also add to the bottom-line. In this work, the authors have reviewed the literature on climate change, human health, and economic impacts of using organic residues to make biochar for the addition to croplands especially to rice paddy fields. Biochar-bioenergy systems range in scale from small household cook-stoves to large industrial pyrolysis plants. Biochar can be purveyed in different forms—raw, mineral-enriched, or blended with compost. The review of published environmental life cycle assessment (E-LCA) studies showed biochar has the potential to mitigate the carbon footprint of farming systems through a range of mechanisms. The most important factors are the stabilization of the carbon in the biochar and the generation of recoverable energy from pyrolysis gases produced as co-products with biochar as well as decreased fertiliser requirement and enhanced crop productivity. The quantitative review of E-LCA studies concluded that the carbon footprint of rice produced in biochar-treated soil was estimated to range from −1.43 to 2.79 kg CO₂-eq per kg rice grain, implying a significant reduction relative to rice produced without a biochar soil amendment. The suppression of soil-methane emission due to the biochar addition is the dominant process with a negative contribution of 40–70% in the climate change mitigation of rice production. The review of the life cycle cost studies on biochar use as an additive in farmlands demonstrated that biochar application can be an economically-feasible approach in some conditions. Strategies like the subsidization of the initial biochar capital cost and assignment of a non-trivial price for carbon abatement in future pricing mechanisms will enhance the economic benefits for the rice farmers.

Sweden aspires to become totally carbon dioxide-neutral by 2045. Indisputably, what is needed is not just a reduction in the emissions of CO₂ (greenhouse gases in general) from the technosphere, but also a manipulated diversion of CO₂ from the atmosphere to ‘traps’ in the lithosphere, technosphere, hydrosphere, and biosphere. The case study in this paper focused on Stockholm Exergi’s proposed waste-to-energy incineration plant in Lövsta, which is keen on incorporating carbon capture and storage (CCS), but is also interested in understanding the potential of carbon capture, utilization, and storage (CCU/S) in helping it to achieve ‘carbon-dioxide-negativity’. Waste-to-energy incineration plants (in cases where the petro-plastics in the waste mix can be substantially reduced) are a key component of a circular bio-economy, though the circularity here pertains to recovering energy from materials which may or may not be recyclable. CCS (storage in the North Sea) was compared with CCU/S (CO₂ sintered into high-quality building blocks made of recycled slag from the steel sector) from techno-economic and environmental perspectives. The comparative analysis shows, inter alia, that a hybridized approach—a combination of CCS and CCU/S—is worth investing in. CCU/S, at the time of writing, is simply a pilot project in Belgium, a possible creatively-destructive technology which may or may not usurp prominence from CCS. The authors believe that political will and support with incentives, subsidies, and tax rebates are indispensable to motivate investments in such ground-breaking technologies and moving away from the easier route of paying carbon taxes or purchasing emission rights.

Water is a non substitutable resource and a social good, which governments must perforce provide to its citizens in the right quantity and quality. An integrated urban metabolism model is useful in understanding the status quo of an urban water and sanitation system. By defining and measuring the values of relevant hydrological performance indicators—deliverables of the model referred to—a thorough knowledge of the present performance and the gaps, which need to be plugged en route to a sustainable urban water infrastructure, can be obtained, as demonstrated in this paper. This then forms the bedrock for decision-making and policy formulation for change to be introduced top-down as well as advice, which would enable the much needed bottom-up support to policies. The authors have chosen Delhi as the case study city, but would like to point out that this application can be reproduced for any other town/city/region of the world. The water balance within the chosen system boundaries shows that the annual unutilized flows, amounting to 1443 million cubic meters, dominate the metabolic flows of water in Delhi, and the annual groundwater withdrawal, which exceeds 420 million cubic meters, is much greater than the recharge rate, resulting in a rapid depletion of the groundwater level. There is an urgent need thereby to improve the rate of infiltration of stormwater and reduce the rate of runoff by focusing on increasing the share of permeable surfaces in the city, as well as to consider the wastewater streams as potential sources of water, while not forgetting demand side of management measures, as the pressure on the urban water system in the city is likely to intensify with a combination of population growth, economic development, and climate change in the near future. The recommendations provided by the authors towards the end of the article, can, if suitable measures are undertaken and robust policies are implemented, result in Delhi’s enjoying a water surplus in the short term, and progressively attain complete sustainability with regard to the utilization of its water resources.

Hydrothermal carbonization (HTC) has been seen as a potentially beneficial process for converting wet biomass into value-added products. It is, however, necessary to overcome the challenges associated with handling the powdered form of hydrochar—a solid product of the HTC process—by controlling the formation of dust and facilitating smoother transportation and distribution in a potentially wide marketplace. In this paper, the authors investigate the environmental consequences of different alternatives for using hydrochar pellets produced from mixed sludges from pulp and paper mills in Sweden, using the environmental life cycle assessment (E-LCA). Two scenarios for possible end-uses of hydrochar in combined heat and power (CHP) plants as a source of energy (heat and electricity) were assessed. In these scenarios, hydrochar pellets were assumed to be combusted in CHP plants, thereby avoiding the use of combustible solid wastes (Scenario A) and coal (Scenario B), respectively, to recover energy in the form of electricity and heat. The environmental damages to Human Health, Ecosystem Quality, Climate Change, and Resources are evaluated based on 1 tonne of dry sludge as the functional unit. The results from this analysis illustrate that Scenario B, in which hydrochar replaces coal, offers the greatest reduction in all the environmental damage characterizations, except the Resources category. The displacement of energy-based coal due to hydrochar combustion contributed most significantly to the environmental damages wrought by the system—ranging from 52% in Resources to 93% in Ecosystem Quality. Overall, the results highlight that the application of hydrochar pellets for energy recovery to offset waste- and coal-based energy sources has great environmental benefits. The favorability of sludge hydrochar over solid wastes as fuel for CHP plants may be counter-intuitive at first, since HTC is an energy-intensive process, but when accounting for the necessity of dependence on imports of wastes for instance, the hydrochar pellet may well emerge as a good option for CHPs in Sweden.

The social aspect of sustainable and ‘clean’ production/manufacturing technologies is researched and understood by means of social life cycle assessment (S-LCA), a life cycle sustainability assessment (LCSA) tool, which is still in its infancy. In this paper, a search for all peer-reviewed publications on applied Social LCA, which have appeared in scientific journals, between O’Brien et al. (Int J Life Cycle Assess 1(4):231–237, 1996 ) and the latest one at the time of writing (April 2018), was carried out, using Scopus as the repository and using ‘S-LCA’ or ‘SLCA’ or ‘Social LCA’ or ‘social life cycle assessment’ as search phrases in title, abstract and keywords of publications, separately. Overall, 213 publications were unearthed, and the trend shows that there has been a near-exponential increase over time. A little over 55% of these publications—121 to be precise—were applications of S-LCA—often in combination with environmental LCA and life cycle costing analysis, in an LCSA. This paper discusses the contributions of a selected subset of these 121 publications to the body of S-LCA knowledge, with the focus being restricted to applications in developing and transition economies of the world, on the premise that there is a more urgent need to understand social aspects of production and manufacturing in these parts of the world. A SWOT analysis of S-LCA has been carried out towards the end. There is a consensus among many researchers that while LCC and E-LCA have matured a lot over time, S-LCA, the newest of the trio, is evolving slowly to become a harmonised tool which can serve as an effective complement to the aforesaid two, in LCSAs of products and processes in industry.