Circular bioeconomy approaches for livestock manure and post-consumer wastes: opportunities for biofertilizers and bioenergy

Implications.

• In our current linear economy, organic residue streams such as livestock manures, processing wastes, and post-consumer wastes are largely managed with the main aim to prevent or limit human, animal and environmental health risks.

• Circular bioeconomy approaches aim to unlock the potential for these resources to produce multiple safe and viable products such as biofertilizers and/or bioenergy.

• This paper presents key outcomes from the chapter on livestock manures and post-consumer waste management of the FAO Livestock Environmental Assessment and Performance publication for “Integrating Circular Bioeconomy Approaches in the Environmental Assessment of the Livestock Supply Chains”.

• Adoption of circular bioeconomy technologies and products relies on coordinated action between technical, socio-economic, and governance, policy & regulatory entities.

Introduction

There is increasing interest in circular bioeconomy practices, technologies and products at the intersection of the circular economy and bioeconomy practices that promote more sustainable economic models, functioning within planetary boundaries (Muscat et al., 2021; Rockström et al., 2024). Circular bioeconomy approaches can recover a suite of products from some of the largest organic residue streams in livestock systems and supply chains (Ramirez et al., 2021) including: manures, processing and post-consumer streams (e.g., wastewaters and municipal sewage). While manures and post-farm gate consumer wastes are becoming increasingly regulated to prevent or limit environmental pollution (e.g., nutrient leaching and runoff, greenhouse gas (GHG) and ammonia emissions, emerging contaminants), circular bioeconomy approaches aim to shift away from waste management towards safely and efficiently valorizing these streams for the resources they contain (Sommer et al., 2013; Sigurnjak et al., 2020; Sutton et al., 2022) (Figure 1).

Figure 1.

Schematic illustration of manure and post-consumer waste pathways and opportunities for generating bioenergy and biofertilizer co-products (Source: FAO 2024).

This paper outlines circular bioeconomy opportunities for livestock manures and post-consumer wastes in the livestock supply chain for the purposes of biofertilizer and bioenergy production. It outlines current technologies and strategies for manure management and post-consumer wastes (e.g., wastewater and sewage), common bioenergy technologies for generating power and/or heat, and biofertilizers and soil amendments that are used for stabilization and returning nutrients and/or carbon back to agricultural soils. Both animal and human-derived excrement sources are considered, as both pose environmental and human health and safety risks that must be managed and are often tightly regulated if they are to be used produce bioenergy and/or biofertilizers. Technical, socio-economic and regulatory barriers and enablers for circular bioeconomy approaches are discussed, and key recommendations provided.

Pre- and Post-Farm Gate Residues

Pre-farm gate—manure management

Manures are the solid and liquid excrement produced by livestock. Manure management is critical to leverage the benefits from manures while preventing or reducing potential human, animal and environmental risks (such as pathogens and diseases, nutrient losses, contaminants, antimicrobial resistance (AMR) and GHG emissions) (Menzi et al., 2010). Manure management comprises the collection, storage, treatment, and utilization of this resource (Sommer et al., 2013). The quantity, quality and properties of manure depend on the animal species, feeding, rearing and manure management practices. Manure composition varies with the wide range of livestock production systems as influenced by climate, geography, culture, and economics.

Globally, the total number of live animals involved in food production has been reported to be 27.2 billion chickens, 1.3 billion sheep, 1.6 billion cattle, 1.3 billion ducks, 1.1 billion goats, 965 million pigs, 209 million buffaloes and 57 million horses in 2023 (FAO, 2020; FAOSTAT, 2023). Manure production is often expressed in terms of nitrogen (N) flows, with an estimated 125 million tons N produced in 2018. It is estimated that most manures are deposited on land; 88 million tons N were deposited on pastures (largely in grazing systems in Brazil, China, India, Ethiopia, and the United States of America) (FAO, 2020). Twenty-seven million tons N were land applied, 3 million tons N were used for other purposes such as heating or construction. It is estimated that 35 million tons N was lost via runoff and leaching, 23 million tons N was volatilized (largely as ammonia), and 7 million tons N was lost during manure management (FAO, 2020).

Manure collection methods depend on the livestock production system and type of manure (Menzi et al., 2010). In grazing systems, livestock deposit urine and feces directly onto land. Manure management practices must ensure that nutrients are not applied in excessive amounts in high animal density areas (e.g., around water sources), and must prevent excretion from occurring directly into surface waters. In confined livestock systems, liquid manures (or slurries, dry matter content 1-10%) can be pumped through distribution systems or flow via gravity. Solid manures have a dry matter content greater than 10% and so cannot be pumped but can be scraped, stockpiled or composted. Livestock housing conditions can be improved for animal welfare, environmental performance and to reduce nutrient losses by lowering indoor temperatures, reducing emitting surfaces and soiled areas, and airflow over these areas. Smart barns can be designed to optimize environmental conditions such as ventilation for open housing systems, while pits and belts can collect solid manures or droppings for storage.

Manure storage is critical to prevent contamination (Sutton et al., 2022). Manure N shall not be lost via gaseous emissions and leaching of nitrate and other compounds. Methane emissions to the atmosphere must be reduced as much as possible to limit climate change impacts. Manure leakage must be prevented to avoid pollution of surface or ground water with N, P, and other potentially problematic compounds. Manures are largely stored outdoors in structures such as concrete pits, metal storage tanks, or lagoons. Specific guidelines should be consulted as manure storage may be restricted, to prevent issues associated with N production (See Box 1). For example, the European Union has minimum manure storage durations to ensure that application to crops occurs over time to meet crop nutrient demand.

Manure treatment and processing methods depend on the scale, intensity, specialization and regional concentration of livestock (Sommer et al., 2013). Options include direct land application, simple treatment, and advanced processing methods. Simple treatment and advanced processing methods may be necessary to meet regulatory environmental requirements (e.g., high livestock density, nutrient surplus for crops). Manure treatments may be single or multiple stage and designed to improve physical and/or chemical properties, such as fluidity (liquid–solid separation, dilution), stabilizing volatile nutrients (acidification), or reducing odor (aeration) (Sommer et al., 2013). Treatments may ease the handling, transport and application of manures by pelletizing or granulating manures for use with existing farm equipment. Single stage treatments are often applied on-farm near livestock production sites, while multistage processing may be on-farm or at decentralized or centralized plants. Processing methods vary by region and livestock system, e.g., in China 80% of manure arises from large-scale farms, of which 30% originates from pigs, while most processed manures (23%) in the USA are associated with dairy cattle (Wei et al., 2021; FAO, 2023). Manure processing must occur within economically viable distances for transport between farms and sites, where transport may be regulated (e.g., European Union Nitrate Directive (Sutton et al., 2022)). Relevant processing technologies include filtration, reverse osmosis, and ammonia scrubbing.

GHG and ammonia emissions from manures must also be managed; technologies have been developed to avoid or reduce emissions (Chadwick et al., 2011). Upstream technologies focus on modifying livestock diets through lowering dietary crude protein and increasing non-starch carbohydrate contents, adding calcium salts to slurries, and benzoic acids to acidify pig urine. Barn design, such as roof insulation or automated ventilation, can reduce emissions by reducing temperatures and air flow. Bedding can also reduce emissions by absorbing urine and increasing the bulk density of manure, as can slurry separation and increasing the frequency of manure removal. Modifications during manure storage can also significantly reduce ammonia emissions and as a result indirect nitrous oxide emissions, such as acid scrubbers absorb ammonia as an ammonium salt, or biofilters where microbial biofilms capture ammonia. Acidification, absorbents, urease inhibitors and bacterial cultures or enzymes can also alter manure biodegradability, while absorbents can reduce ammonia losses if added in sufficient quantities. Novel technologies include physical (e.g., pulse combination drying, air ammonia stripping, ceramic membrane distillation), chemical (plasma recovery) and biological methods (microalgae, phototrophic purple bacteria).

Post-farm gate: processing and post-consumer residues

Post-farm gate residues may also originate from point sources (confined animal operations, food processing plants, municipal sewage treatment plants) or diffuse sources (contaminated surface runoff) (Kundu et al., 2022). Globally, wastewaters are estimated to contain approximately 17 million tons of N, 3 million tons of P and 6 million tons of K, which could offset 13% of global agricultural demands for nutrients (Qadir et al., 2020). Wastewaters may have high chemical and/or biological oxygen demand with high microbial loads and suspended solids, nutrients, strong odors, and other contaminants (e.g., pathogens, heavy metals, pesticides, pharmaceuticals) (Hoang et al., 2022). Settling ponds and lagoons are often used to treat wastewaters and prevent contaminants directly entering surface or ground waters. Constructed wetlands may also be used to treat wastewaters prior to environmental release. Wastewaters also may be applied to crops via fertigation.

Solid residue and sludge management depends on the source (Kundu et al., 2022). Pond or lagoon systems are periodically dredged to remove accumulated solids, which can be land applied. While N can be lost during the wastewater treatment, other plant nutrients (P, K, micronutrients) are retained in the sludge, along with heavy metals that can pose risks to humans and the environment. From an agronomic perspective, sludge application needs to be amended with fertilizers to ensure that crops receive balanced nutrient inputs. Frequent sludge removal, while more expensive, can support sludge management over the lifetime of the storage basin. As sludges can contain 70-80% water even after dewatering, drying, blending and granulation technologies can support transporting sludges over long distances (Kundu et al., 2022). Additional technologies, such as thermal treatment or anaerobic digestion, can recover energy and some may reduce the weight of materials for transport.

Bioenergy Technologies

Anaerobic digestion

Energy can be produced using manures, processing residues and wastewaters as inputs (Ramirez et al., 2021). Developing process diagrams to outline feedstock properties, technologies for stabilization and/or energy production, and nutrient recovery can support the production of several co-products from the initial resource stream (Figure 2).

Figure 2.

Pathways for manure treatment and processing that facilitate co-production of bioenergy and biofertilizers (Adapted fromSommer et al. 2013).

Anaerobic digestion is the most widely used commercial technology, where microorganisms ferment biodegradable material in the absence of oxygen to produce a methane-rich biogas (Tsapekos et al., 2017). Biogas can then be used in place of natural gas after cleaning to remove impurities. Manure and other agrifood byproducts or residues (e.g., dairy wastewater, food waste, etc.) can be used to optimize methane production through anaerobic co-digestion (AcoD). Biogas can then be used to generate electricity for livestock production or processing, while the heat from electricity production is used to dry crops, feed ingredients, or reach meso- or thermophilic temperatures during AcoD. It is estimated that AD of wastewaters globally could generate approximately 1.9 billion megajoules (Qadir et al., 2020). Biogas units are also widely used at the household level in low and middle-income countries where manure can be used as substrates for replacing firewood for heating and cooking, and to reduce exposure to particulate pollution. To minimize emissions, digesters need to be gas tight, digestate storage should be included in the gas bearing system of the AD plant, and land application of digestate should be done with low emissions technologies. In smaller rural areas, managing biogas production can be difficult; storage allows for periods when biogas production exceeds demand (Makamure et al., 2021). Digestate contains high N and P concentrations and can be used as a biofertilizer or soil amendment. The complementary processes can contribute to circular bioeconomy processes by producing both energy and fertilizers.

Optimizing productivity of the AcoD process depends on biodegradability of the organic matter, substrate chemical composition, and operational parameters (temperature, pH, and organic loading rate) (Makamure et al., 2021). AcoD can occur at psychrophilic (25°C), mesophilic (35°C) and thermophilic (~55°C) temperatures, although mesophilic is most common (Makamure et al., 2021). To maximize biogas yields, it is preferable to maintain a digestate pH between 6.3-7.8. Optimizing the ratio of livestock manure to organic residues or energy crops is also essential for maximizing methane yields as it is strongly influenced by the carbon: nitrogen ratio. Combining two or more substrates may also provide a more desirable nutrient balance to support the microbial population (Tsapekos et al., 2017). The organic loading rate can also increase microbial diversity and improve biogas conversion. Longer retention times can improve effluent quality but reduce biogas production rates. These trade-offs must be considered on a case-by-case basis depending on the feedstock properties and the operational feasibility requirements for the AD unit.

Thermochemical processes

Thermochemical processes are less common but are increasingly being applied for manure management and bioenergy production (Sigurnjak et al., 2020). Rout et al. (2023) reported that these technologies include combustion, pyrolysis, gasification, and hydrothermal liquefaction. Combustion completely oxidizes manure to produce heat and electricity. Pyrolysis is the thermal decomposition of biomass under an inert atmosphere to produce bio-oil and biochar. Adjusting the temperature and residence time determines the fraction of bio-oil vs biochar (e.g., fast pyrolysis operates at 450-650°C generating more bio-oil, while slow pyrolysis operates at 300-700°C generating more biochar). Biochars are rich in carbon and have been investigated for a range of purposes, such as feed supplements for livestock, litter and bedding materials, sorption materials for remediation, and as soil amendments. Gasification achieves partial oxidation and molecular dissociation at 600-1000°C to produce syngas and ash. As the primary components of syngas are hydrogen and carbon monoxide, these can be used to generate electricity or heat, or to manufacture hydrocarbon-based chemicals.

The high moisture content of most manures limits its direct use in pyrolysis and gasification, as considerable energy is needed for drying. However, net energy yields can be limited, and high volumes of ash and/or tar can be generated. Hydrothermal liquefaction can be used to avoid drying as this process can be applied to high moisture manures within a heated, pressurized and oxygen free reactor (250-400°C) (Guo et al., 2020). A bio-oil can be produced with a heating value like petroleum crude oil and can be upgraded for use in renewable diesel blend stocks. However, high energy inputs may be required, and the energy balance of these processes must be considered to determine whether these pathways are economically viable.

From a circular bioeconomy perspective, thermochemical processes can support both bioenergy and biofertilizer production and may destroy or immobilize common contaminants present in residue streams (Rout et al., 2023). However, these technologies are emerging and require additional research and translation to become fully commercially available and scalable, as do their end-products. For example, bio-oils can have suboptimal properties due to variation in feedstock composition (e.g., issues with viscosity, acidity, poor thermal stability) that may require additional treatment and energy for post-processing (Guo et al., 2020). The consumption of hydrogen and the requirements for high pressure and temperature affects the operational and capital costs of these treatments. Recent applications of thermal technologies have been occurring in municipal wastewater and sewage treatment to destroy organic pollutants such as PFAS (polyfluoroalkyl and perfluoroalkyl) substances, and to reduce storage and transport volumes of the sludge materials prior to land application (Rout et al. 2023). Biochars and ash materials also often require additional processing steps to offer a higher value product to farmers (e.g., balanced nutrient profile, granulation or pelletizing to assist on-farm spreading, etc.).

Biofertilizer Technologies

While there is no universal definition of “biofertilizer”, these inputs focus on supplying nutrients to crops, while soil amendments are any material that may improve soil properties (e.g., water holding capacity, pH, structure). N has both the largest and most rapid effect on crop yields and poses the largest environmental risks via leaching and atmospheric emissions (Sutton et al. 2022). P is a nonrenewable, mineral resource, where previous global conflicts and supply chain issues have rapidly increased P fertilizer prices and subsequently food prices (Cordell et al., 2021). P management requires a different approach to N, as soil P can accumulate to high concentrations over time. P losses from agricultural soils depends on manure type, soluble P concentrations, soil P sorption capacities or soil properties, and local climate (Wei et al., 2022). The over application of nutrients can pollute surface and ground waters, threatening the stability of earth’s ecological “planetary boundaries” (Rockström et al., 2024). Best practice considerations for biofertilizers must navigate regulatory, feedstock specifications, best available technologies (BAT), and farming systems (See Box 2).

Nutrients in organic materials are often not as readily available for plant uptake as synthetic fertilizers and may only be partly available for crop uptake in the first year of application (e.g., 20-70% N, 10-50% P) (Sutton et al., 2022). Some nutrients (zinc, copper) are immobile in soils and may accumulate to high concentrations that may be toxic or cause problematic soil physical properties (Jensen et al., 2016). Biofertilizers may provide broader benefits for soil properties (e.g., improving soil pH, water holding capacity, aeration, organic matter content, soil carbon, beneficial microorganisms) (Sigurnjak et al., 2020). Trade-offs should be considered between applying bulk organic residues versus extracting nutrients for targeted application on agricultural soils. Decision support tools are needed to integrate nutrient data and potential risks with specific soil, cropping, climate and local environmental conditions to optimize application. Initial and ongoing soil testing is essential to ensure that soils fertilized with organic materials meet crop nutrient demand, with synthetic fertilizers utilized to meet any deficiencies.

Composting aerobically decomposes organic matter to produce a solid compost and/or liquid compost tea, heat, and carbon dioxide (Pajura, 2024). Methods include windrow piles, reactors, pass-through and static processes. Composting is widely used under a range of conditions as it is relatively cheap but may require large land areas and can emit GHG or produce leachates if not managed properly. Compost can increase crop yields by approximately 40%, particularly in drier, warmer climates under acidic soils that have sandy or clay textures (Zhao et al., 2022). Effectiveness for crop yields, soil organic carbon and emission of nitrous oxide emissions can largely be predicted by eleven parameters, including compost properties, management practices, and local biophysical conditions (Zhao et al., 2022). Composting can mitigate pathogen risk and may degrade some antibiotics present in livestock manures, although this depends on the feedstock and composting parameters (Pajura, 2024). Compost N concentrations are a strong predictor of GHG emissions and N leaching, and can be mitigated by the addition of biochars, nitrification inhibitors, mineral sorbents or microbial inoculants (Zhao et al., 2022).

There are a range of chemical and biological methods for P recovery from manures and other post-farm gate residues (Sigurnjak et al., 2020). Examples of regional online repositories and information hubs for P recycling and recovery from waste streams include the European Sustainable Phosphorus Platform (ESPP), which aims to “bring together companies, scientists and stakeholders for sustainable phosphorus management and nutrient recycling.” Common technologies include ion exchange, precipitation and/or crystallisation methods which can be applied to liquid residues to create mineralized products such as struvite. Microbial processes can also be used, such as enhanced biological P removal (EBPR), where phosphate is accumulated into microbial biomass as polyphosphate (Karunanithi et al., 2015). Iron, aluminum and polymers are common flocculants used for precipitation, lowering dissolved P concentrations to below 0.1 mg/L, however the availability of P in these precipitates to the crop can be low (Karunanithi et al., 2015). Aluminum may also pose a toxicity risk in acidic soils. Trade-offs exist between efficiently removing P from the liquid phase and developing an agronomically viable product. Further processing may be required, and solid residues can be further subject to leaching, thermal treatment, and adsorption-based methods.

Novel biofertilizer technologies are being explored to develop cheaper processes for more isolated regions. These include insect-based technologies (black soldier fly (BSF), vermicomposting) and biochar. BSF uses Hermetia illucens larvae to consume solid organic residues and potentially inactivate pathogens. The larvae can be used as a feed ingredient, energy source, or for isolating secondary materials such as proteins, lipids, chitin and chitosan. BSF have been produced from a range of manures, human sewage, and food waste (Liu et al., 2022). It has a high nutritional value and can replace conventional ingredients like fishmeal and soybean meal in ruminant, poultry, and aquaculture diets.

Vermicomposting uses earthworms to accelerate the decomposition of organic matter and reduce pathogens and odors (Raza et al., 2022). Solid residue volumes can be reduced by up to 50%, with it applied to manures, sewage, and sludge from the paper processing industry. The solid (vermicast) and liquid (vermiwash) fractions are high in nutrients and can be used as a nutrient source (Raza et al., 2022).

Biochar is a co-product from pyrolysis or gasification of organic feedstocks (Joseph et al., 2021). Biochar properties depend heavily on the feedstock, the thermal process, particle size and composition. Some biochars have been reported to increase soil pH, porosity, water holding capacity, and soil organic carbon (Joseph et al., 2021). As biochars have highly reactive surface properties, they can be fortified with nutrients for use as slow release biofertilizers or used for remediation of contaminated soils.

Developing Viable Circular Bioeconomy Technologies and Products

This paper has largely focused on describing the technical opportunities for circular bioeconomy opportunities in livestock systems for manures, processing and post-consumer wastes. However, there are a range of technical, socio-economic, and regulatory factors that affect the viability of emerging pathways for circular bioeconomy technologies and products (Figure 3).

Figure 3.

Technical, socio-economic, and governance & regulation barriers and opportunities for viable circular bioeconomy pathways for manure, processing, and post-consumer wastes.

Figure 3 provides a snapshot of various real-world examples that are being developed globally to address some of the critical barriers facing circular bioeconomy pathways in livestock production systems. Several recommendations can be made to summarize the key themes emerging from new opportunities in this space. From a technical perspective, there are two gaps: firstly, to develop rapid, low-cost fit-for-purpose manure and feedstock testing protocols to create multiple safe and viable circular bioproducts. Secondly, quantitative tools (e.g., material flow analysis, life cycle analysis) should be used to develop on-farm or supply chain baseline data that can support decision making (e.g., nutrient inputs and flows, manure quantity and composition, energy demand, etc.). From a socio-economic perspective, farmers should be included in RD&E activities to support the design of new technologies and management approaches, and to tailor circular bioeconomy approaches to suit farmer needs while increasing awareness of new innovations. Finally, from a governance and regulation perspective, there is a need to develop evidence-based policies to support circular bioeconomy pathways for manure and post-consumer waste valorization. This includes developing clear definitions (e.g., biofertilizers), ensuring coherent governance arrangements for framework development, and considering private and/or public policy tools where appropriate.

Conclusion

It is essential to continue developing circular bioeconomy approaches to safely recover valuable resources from manures, processing streams and post-consumer wastes, while reducing environmental pressures from these byproducts in livestock value chains and broader food systems. This paper outlined key processes involved in manure management, post-consumer wastewater and sewage processing, and opportunities for bioenergy and biofertilizer production. The successful adoption of circular bioeconomy technologies and products will depend on cooperation across research, industry, community and government sectors to successfully coordinate evidence-based actions that can address the technical, socio-economic, and policy & regulatory challenges facing innovation design, adoption and a system-scale shift towards biocircularity in this space.

About the Authors

Maja Arsic is a Research Scientist at CSIRO Agriculture & Food. She holds a PhD in Plant Nutrition (University of Copenhagen/University of South Australia) with a background in environmental chemistry. She works across the science-policy interface to enable circular bioeconomy transition pathways for sustainable agrifood systems, and is a national Science & Technology Australia STEM Ambassador. Maja currently works with a range of stakeholders and sectors, including aquaculture, water management, bioenergy, and livestock industries, to design and deliver pathways towards achieving circularity at local, regional and international scales.

Adibe L. Abdalla is an Associate Professor at the University of São Paulo, based at CENA/USP. He holds a degree in Agronomy and specializes in Animal Nutrition and the application of isotopes in ruminant metabolism. He completed postdoctoral research at Reading University (UK) and UC-Davis (USA). He focuses on sustainable ruminant production, including the mitigation of greenhouse gas emissions, alternative diets, and isotopic models for metabolic and sustainability assessments. He has contributed to the advancement of phytogenic additives, silvopastoral systems, and alternative feed supplements to enhance production efficiency. At CENA/USP, he integrates isotopes techniques, rumen microbiology, and sustainable management into teaching and research. His work aligns with global efforts to promote climate resilience in livestock systems.

Hongmin Dong is a Professor in the Institute of Environmental and Sustainable Development in Agriculture (IEDA), Chinese Academy of Agriculture Sciences (CAAS). Her research focusses on livestock, environment, manure management, and greenhouse gas emissions & mitigation. She has been the principal investigator of national projects on livestock manure management and low carbon livestock production. She was lead author of 2006 IPCC guideline, 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. She is one of the leading experts on the compilation of China’s GHG inventory from livestock sector, and action plan for carbon reduction and sequestration in agricultural and rural areas.

Laurence Loyon is a Research Scientist in the French UR OPAALE of INRAE. She holds a PhD in environmental chemistry with a specialization in water pollution. She directs his work to research and support for the evaluation and implementation of public policies to reduce the impact of agricultural activities on emissions to the environment (air, water, soil). After quantifying and evaluating techniques for reducing gaseous emissions linked to livestock farming, her latest work aims to identify key gaps in nutrient data and indicator availability from manure management for the design and implementation of public policies. At the same time, she analyses the balance between the multiple objectives of public policies focusing in environmental impact of livestock.

Ana Paula Contador Packer is a Research Scientist at Embrapa Environment and has served as its General Head since 2022. She is an Agronomist Engineer, graduated from ESALQ-USP, and holds a Master’s and PhD in Analytical Chemistry from the Institute of Chemistry of São Carlos (IQSC-USP). Paula works at the interface between agriculture and the environment, focusing on research in Climate Change and the Sustainability Assessment of Agricultural Systems. Her work encompasses research, the promotion of open innovation partnerships, and the assessment and implementation of public policies to reduce the impact of agricultural activities on GHG emissions. She also contributes to developing and applying adaptation strategies for tropical agriculture, ensuring resilience and sustainability in the sector.

Chayan Kumer Saha is a professor at the Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh and frontier researcher in innovating and adapting climate smart agricultural technologies and renewable energy-based technologies in Bangladesh. He also advocates adapting circular bioeconomy approach in the agriculture of Bangladesh. He has 25 years of research experience as PI, Co-PI, associate director, research coordinator and researcher of different national and international projects in collaboration with different international research institutions. He has established Green Energy Knowledge Hub (GEKH) in Bangladesh Agricultural University, Bangladesh. He is a member of Technical Advisory Group (TAG) of Circular Bioeconomy of FAO-Rome, and preparing circular bioeconomy guideline for livestock production system. He is a national advisor of Smart Agro-Technology Innovation Youth Network (SAIYN).

Buchun Si is an Associate Professor in Department of Agricultural and Biological Engineering at the China Agricultural University. He received his Ph.D. in Agricultural Engineering from China Agricultural University. His research interests span a broad range of topics in the field of agricultural waste treatment, sustainable energy and environmental technologies. He currently studies the integration of systems for the next generation of waste-to-energy conversion technology (including anaerobic fermentation for hydrogen and methane production, design and development of technologies and equipment for wastewater treatment and hydrothermal liquefaction and gasification for biofuels production).

David Meo Zilio is a Research Scientist in the role of the Italian Council For Agricultural Research and Economics (CREA), Research Centre for Animal Production and Aquaculture. He holds a PhD in Animal Production and Products’ Quality (University of Florence, Italy) with a background in meat science, animal welfare and animal feeding and nutrition. Currently his major interests are sustainable livestock production, methane emission measurements and reduction, and precision livestock farming. He is Italian focal point for the Livestock Research Group of the Global Research Alliance and of the Global Methane Pledge sector Agriculture.

Barbara Renate Amon is an Associate Professor for Environmental Engineering and Agricultural Engineering at the University of Zielona Góra, Poland, and board representative for research at the Leibniz Institute for Agricultural Engineering and Bioeconomy in Potsdam, Germany. Having had many years of practical, hands-on experience in agriculture alongside extensive research experience, she completed her habilitation in Agricultural Engineering at the University of Natural Resources and Life Sciences in Vienna in 2007. In addition to her research, she sits on many panels looking at sustainable agriculture, including the Intergovernmental Panel on Climate Change, UN Environment Programme, and the FAO LEAP partnership. She is also the Co-Chair of the Agriculture and Nature Panel as part of the UNECE Task Force on Emission Inventories and Projections and of the Expert Panel on Mitigation of Agricultural Nitrogen under the UNECE Task Force on Reactive Nitrogen. Corresponding author: bamon@atb-potsdam.de.

Conflict of interest statement. The authors declare no real or perceived conflicts of interest.

Author contributions

Maja Arsic (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Validation, Writing—original draft, Writing—review & editing), Adibe L. Abdalla (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing—original draft, Writing—review & editing), Hongmin Dong (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing—original draft, Writing—review & editing), Laurence Loyon (Conceptualization, Data curation, Formal analysis, Methodology, Validation, Writing—original draft, Writing—review & editing), Ana Paula Contador Packer (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing—original draft, Writing—review & editing), Chayan Kumer Saha (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing—original draft, Writing—review & editing), Buchun Si (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing—original draft, Writing—review & editing), David Meo Zilio (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing—original draft, Writing—review & editing), and Barbara Renate Amon (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Validation, Writing—original draft, Writing—review & editing)