A critical review on livestock manure biorefinery technologies: Sustainability, challenges, and future perspectives

Enhanced phosphorus recovery from digestate via solid-liquid separation using Mg2+ and Ca2+ modified biochar

Phosphorus (P) reserves are depleting globally, making P recovery from alternative sources imperative. The study investigates using Mg2+ and Ca2+ modified biochar and metal salts - kieserite (MgSO4·H2O) and CaCl2 - for enhanced P recovery from biogas digestate. Separation trials at varying concentrations and treatment times were performed in a laboratory setting. Modified biochar increased P recovery to 52%, while metal salts achieved 65%, compared to 35% in the control. P fractionation revealed that metal ions promoted the formation of non-labile P, reducing nutrient run off and improving long-term nutrient availability. The methods presented here highlight the potential of modified biochar and metal salts for sustainable P recovery from digestate, enabling existing biogas plants to improve nutrient management, reduce environmental impact, and contribute to circular economy practices in agriculture.

Organic matter and microplastics nexus: A comprehensive understanding of the synergistic impact on soil health

The interactional nexus of microplastics (MPs) and organic matter (OM) can subtly disrupt the delicate balance of soil ecosystems, influencing nutrient dynamics, biodiversity, and overall soil health. To explore this complex interplay between MPs and OM concerning several perspectives, a comprehensive keyword search was conducted across key scientific databases, and the retrieved data was curated according to the PRISMA guidelines to reflect the objectives. Several studies have highlighted that organic-based inputs, such as manures, composts, and sewage sludge, widely used for soil amendment, are potential sources of MPs to soil contamination. These coinciding sources of MPs and OM raise potential concerns about their impact on overall soil health. MPs and OM have parallel characteristics and play a critical role in the soil organic carbon (SOC) and dissolved organic matter (DOM), critical for biogeochemical transformations and nutrient cycling. In light of this, the present review explores the multifaceted nexus between MPs and OM, explaining their interaction mechanisms and their effects on the biological and physicochemical properties of the soil. Despite significant implications on soil ecosystem, challenges remain in accurately quantifying the effects of MPs due to the complexities introduced by DOM. The intricate interaction between MPs and DOM can obscure analytical results, complicating efforts to separate and identify these pollutants effectively. Given these challenges, this review underscores the urgent need for innovative methods to characterize and quantify MPs in complex environmental matrices. Finally, we discuss emerging research directions aimed at advancing the detection and management of MPs in soil ecosystems.

A dynamic optimization of soil phosphorus status approach could reduce phosphorus fertilizer use by half in China

Sustainable phosphorus (P) management is essential for ensuring crop production while avoiding environmental damage and the depletion of phosphate rock reserves. Despite local demonstration scale successes, the widespread mobilization of smallholder farmers to adopt sustainable management practices remains a challenge, primarily due to the associated high costs and complicated sampling. Here, we propose a dynamic optimization of soil P status (DOP) approach aimed at managing long-term soil P status within the range of agronomic and environmental soil P thresholds, which facilitates the precise determination of optimal P application rates without the need for frequent soil testing. We evaluate the DOP approach in 35,575 on-farm trials, and the results show that it is agronomically acceptable. Our evaluation extends to estimating future soil P status and P fertilizer inputs across all counties in China for three cereal crops (wheat, rice, and maize). The results indicate that, compared to current practices, the DOP approach can achieve a 47.4% reduction in P fertilizer use without any yield penalty. The DOP approach could become an effective tool for global P management to safeguard food security and enhance environmental sustainability.

Exploring the Molecular Composition of Dissolved Organic Matter and Its Connection to Microbial Communities in Industrial-Scale Anaerobic Digestion of Chicken Manure

Anaerobic digestion (AD) technology offers significant advantages in addressing environmental issues arising from the intensification of livestock production since it enables waste reduction and energy recovery. However, the molecular composition of dissolved organic matter (DOM) and its linkages to microbial biodiversity during the industrial-scale AD process of chicken manure (CM) remains unclear. In this study, the chemical structure of CM digestate-derived DOM was characterized by using multi-spectroscopic techniques and ultrahigh-resolution mass spectrometry, and the microbial composition was detected by using 16S rRNA gene sequencing. The results revealed that the DOM contained abundant free amino acids and protein-like compounds but fewer humic-like substances, identified as lignin/carboxylate-rich alicyclic molecules, lipids, and proteins/aliphatic compounds featuring enriched S5-6O1 and N1-5OX fragments. In addition, the 16S rRNA results revealed microorganisms that were centered on metabolic function in the production of volatile fatty acids, H2S/CH4, and the hydrolysis reaction in the AD process. Free amino acids and protein-like compounds were mainly associated with hydrolysis reactions and H2S production functional microorganisms. Lignin/carboxylate-rich alicyclic molecules were linked to microorganisms possessing hydrolysis reactions and, indirectly, CH4 production. This study elucidates the linkage with the microbial and molecular composition of DOM, establishing a theoretical foundation for employing AD in the disposal of CM.

Attenuated cadmium and arsenic enrichment in rice by co-application of organic composting and chemical fertilization

A pot experiment was conducted on arsenic (As) and cadmium (Cd) co-contaminated soil to discern the influence of varying proportions of pig manure compost (PM) vis-à-vis chemical fertilizers (NPK) on the mitigation of Cd and As absorption by rice. Our findings illustrated that by increasing the PM proportions from 25 to 100%, it manifested a statistically significant reduction in the mobilized fractions of Cd, accounting for up to 77% reduction in soil CaCl2-Cd concentrations. Conversely, the NaHCO3-As reactions were contingent on the distinct PM application rates. Furthermore, augmented PM application rates correlated with a substantial surge in Cd and As concentrations within the iron (Fe) and manganese (Mn) plaques, ranging from up to 116.6% and 85.9%, respectively. This led to a concomitant decline in Cd and As concentrations within the grains, up to 72.6% and 74.5%, respectively. Notably, grain concentrations of As and Cd diminished progressively with increased PM application, reaching a nadir with the 75% PM treatment. In summary, the observed mitigation in contamination is postulated to stem from the modulation of soil attributes via PM addition, which curtails Cd availability, combined with the bolstered immobilization of As and Cd by the Fe/Mn plaques.

Occurrence, fate and control strategies of heavy metals and antibiotics in livestock manure compost land application: A review

Composting is a sustainable method for managing livestock manure, but the residual heavy metals and antibiotics in the compost pose can pose environmental risks when applied to land. Although many studies focus on occurrence and risk mitigation of heavy metals and antibiotics in manure compost land application, there is a lack of systematic analysis covering the entire chain from source to process and final disposal. Given this, this article provides a comprehensive review of the sources, migration, fate, risk assessment, and risk reduction of heavy metals and antibiotics contamination in land application of livestock manure compost for the first time. The main pollutants of concern are heavy metals, particularly Cu and Zn, and antibiotics such as quinolones, tetracyclines, and sulfonamides. The coexistence of these contaminants can easily trigger co-contamination, threatening soil ecosystems and human health. Risk reduction strategies, emphasizing the use of additives during composting and phytoremediation after land application, are discussed. Challenges remain in understanding the interactions between heavy metals and antibiotics and developing effective strategies for mitigating co-contamination. Furthermore, the paper proposes the future prospects on the interactions study and the simultaneous control strategy of heavy metals and antibiotics contamination. It is expected to promote the whole process management of livestock manure and the control of heavy metal-antibiotic co-contamination in the future.

Methodological study on carbon sequestration accounting for emission reductions from the whole-chain utilization of livestock and poultry manure

Effective livestock manure management is crucial for carbon neutrality. Scientific accounting methods and integrated management strategies can help guide reductions in carbon emissions and promote green development. To reduce greenhouse gas emissions by livestock manure, this study analyzed current accounting systems and focused on the complete chain of "collection-treatment-storage-use-returning" of manure based on the theoretical framework of greenhouse gas emissions accounting in the IPCC 2019 Guidelines. Combined with a life cycle assessment, the accounting list and boundaries were clarified, and the whole chain of livestock and poultry manure greenhouse gas accounting methodology system was proposed. Using swine breeding as a case study, this study evaluated the carbon emission reduction and sequestration effect of the whole manure chain using a typical technology model and a typical technological framework. It predicted the carbon reduction potential and sequestration benefits of utilizing swine manure in 2025 and 2030 in four scenarios. The findings indicated that the greenhouse gas emission factor of the whole chain of the six typical swine manure utilization modes in China was -48.82-40.54 kgCO2et-1. In 2022, the net greenhouse gas emissions from swine manure in China totaled approximately 2.0 × 107 tCO2e, with manure resource utilization reducing emissions by 3.2 × 107 tCO2e. Our projections suggest that emissions from swine manure in China may range from -1.8 × 107 to 1.3 × 107 tCO2e by 2025 and from -3.1 × 107 to 4.5 × 106 tCO2e by 2030. This can help guide optimal greenhouse gas emission reduction pathways for livestock and poultry farming and aid in the formulation of policies.

IS6 family insertion sequences promote optrA dissemination between plasmids varying in transfer abilities

Plasmids are the primary vectors for intercellular transfer of the oxazolidinone and phenicol cross-resistance gene optrA, while insertion sequences (ISs) are mobile genetic elements that can mobilize plasmid-borne optrA intracellularly. However, little is known about how the IS-mediated intracellular mobility facilitates the dissemination of the optrA gene between plasmid categories that vary in transfer abilities, including non-mobilizable, mobilizable, and conjugative plasmids. Here, we performed a holistic genomic study of 52 optrA-carrying plasmids obtained from searches guided by the Comprehensive Antibiotic Resistance Database. Among the 132 ISs identified within 10 kbp from the optrA gene in the plasmids, IS6 family genes were the most prevalent (86/132). Homologous gene arrays containing IS6 family genes were shared between different plasmids, especially between mobilizable and conjugative plasmids. All these indicated the central role of IS6 family genes in disseminating plasmid-borne optrA. Thirty-three of the 52 plasmids were harbored by Enterococcus faecalis found mainly in humans and animals. By Nanopore sequencing and inverse PCR, the potential of the enterococcal optrA to be transmitted from a mobilizable plasmid to a conjugative plasmid mediated by IS6 family genes was further confirmed in Enterococcus faecalis strains recovered from the effluents of anaerobic digestion systems for treating chicken manure. Our findings highlight the increased intercellular transfer abilities and dissemination risk of plasmid-borne optrA gene caused by IS-mediated intracellular mobility, and underscore the importance of routinely monitoring the dynamic genetic contexts of clinically important antibiotic resistance genes to effectively control this critical public health threat. KEY POINTS: • IS6 was prevalent in optrA-plasmids varying in intercellular transfer abilities. • Enterococcal optrA-plasmids were widespread among human, animal, and the environment. • IS6 elevated the dissemination risk of enterococcal optrA-plasmids.

Adaptation of Chlorella vulgaris immobilization on rice straw with liquid manure to create a sustainable feedstock for biogas production and potential feed applications

Rice straw (RS) is a widely available agricultural residue with significant potential for biogas production and feed applications; however, its poor digestibility and nutritional value limit its utilization. This study explores an innovative approach to enhance the digestibility and nutritional value of RS by cultivating Chlorella vulgaris through immobilization technology on RS, using liquid manure (LM) as an alternative to the traditional BG11 medium. The results showed an increase in chlorophyll a (Chl a) after 12 days for both the BG11 medium and LM-based treatments, from 0.13 to 0.34 and 0.24 mg Chl a/g product (DM), respectively. Additionally, the immobilized microalgal biomass increased to 284.18 and 170.14 mg algal biomass/g product (DM), respectively. Soaking under microaerobic conditions during cultivation led to the partial degradation of RS. This, combined with the formed microalgal biofilm, contributed to an improved digestibility of the dry matter, reaching 69.1% and 65.9% for the final products based on the BG11 medium and LM mediums, respectively, compared to 52.1% for the raw RS. Furthermore, the crude protein and lipids contents were significantly improved with the potential for applications in feed, reaching 21.4% and 4.1% for the BG11 medium-based product, while they were observed to be 12.8% and 3.0%, respectively, for the LM-based product. Additionally, carbon-to-nitrogen ratio was significantly reduced compared to the raw RS. The higher digestibility and improved nutritional value contributed to increased biogas production, reaching 129.3 and 118.7 mL/g (TS) for the products based on the traditional medium and LM medium, respectively, compared to 86.7 mL/g (TS) for the raw RS. The immobilization mechanism and biofilm development could be attributed to the roughness of the RS and extracellular polymer substances. This study demonstrates that integrating C. vulgaris cultivation on RS with LM as a nutrient source not only enhances the digestibility and nutritional value of RS but also offers a sustainable waste management solution with potential applications in biogas production and animal feed.

Phytoremediation of Hg and chlorpyrifos contaminated soils using Phaseolus vulgaris L. with biochar, mycorrhizae, and compost amendments

Anthropogenic activities, encompassing vast agricultural and industrial operations around the world, exert substantial pressure on the environment, culminating in profound ecological impacts. These activities exacerbate soil contamination problems with pollutants such as mercury (Hg) and chlorpyrifos (CPF) that are notable for their widespread presence and detrimental effects. The objective of this study is to evaluate the phytoremediation potential of Phaseolus vulgaris L., augmented with various combinations of biochar, mycorrhizal, and compost amendments, as a sustainable alternative for the remediation of soils contaminated with Hg and CPF. For this purpose, soil from a mining area with mercury contamination has been taken, to which CPF has been added in different concentrations. Then, previously germinated Phaseolus vulgaris L. seedlings with an average height of 10 cm were planted. Electrical conductivity, pH, organic matter, CPF, and Hg, as well as seedling growth parameters, have been evaluated to determine the processes of absorption of soil contaminants into the plant. A combination of biochar with mycorrhiza has been found to be an optimal choice for CPF and Hg remediation. However, all amendments have proven to be efficient in the remediation processes of the tested contaminants.

Comprehensive review of technologies for separate digestate treatment and agricultural valorisation within circular and green economy

Anaerobic digestion (AD) has the potential to catalyse the shift from a linear to a circular economy. However, effective treatment and management of both solid (DSF) and liquid (DLF) digestate fraction treatment and management require adopting sustainable technologies to recover valuable by-products like energy, biofuels, biochar, and nutrients. This study reviews state-of-the-art advanced technologies for DSF and DLF treatment and valorisation, using life cycle assessment (LCA) and techno-economic analysis (TEA) in integrated digestate management (IDM). Key findings highlight these technologies' potential in mitigating environmental impacts from digestate management, but there's a need to improve process efficiency, especially at larger scales. Future research should prioritize cost-effective and eco-friendly IDM technologies. This review emphasizes how LCA and TEA can guide decision-making and promote sustainable agricultural practices. Ultimately, sustainable IDM technologies can boost resource recovery and advance circular economy principles, enhancing the environmental and economic sustainability of AD processes.

Hormesis of black soldier fly larva: Influence and interactions in livestock manure recycling

Black soldier fly larvae (BSFL) are considered important organisms, utilized as tools to transform waste including manure into valuable products. The growth and cultivation of BSFL are influenced by various factors, such as the presence of toxic substances in the feed and parasites. These factors play a crucial role in hormesis, and contributing to regulate these contaminants hermetic doses to get sustainable byproducts. This review aims to understand the effects on BSFL growth and activities in the presence of compounds like organic and inorganic pollutants. It also assesses the impact of microbes on BSFL growth and explores the bioaccumulation of pharmaceutical compounds, specifically focusing on heavy metals, pesticides, pharmaceuticals, indigenous bacteria, insects, and nematodes. The review concludes by addressing knowledge gaps, proposing future biorefineries, and offering recommendations for further research.

Essential role of composting industry in achieving China's dual-carbon goals: Case studies from Chinese composting companies

Composting is one of the primary methods for organic waste recycling in China. This study aims to analyze the product quality of organic fertilizer enterprises from the perspective of actual production and the relationship between production process variations and organic matter content in organic fertilizers based on 348 samples from 229 organic fertilizer companies across 22 provinces. Results showed that fertilizers produced through composting processes contain higher organic matter, averaging 45.42 %, compared to commercial organic fertilizers and bio-organic fertilizers. Raw materials, equipment, methods, operational scale, and personnel structure are key factors affecting the content of organic matter in products. Optimizing equipment and processes in Chinese organic fertilizer companies could increase organic matter content to 49.3 %, potentially reducing annual carbon emissions by an estimated 3.07 to 6.97 billion kg of CO2 equivalent, thereby supporting the realization of dual carbon goals.

A comprehensive review on agricultural waste utilization through sustainable conversion techniques, with a focus on the additives effect on the fate of phosphorus and toxic elements during composting process

The increasing trend of using agricultural wastes follows the concept of "waste to wealth" and is closely related to the themes of sustainable development goals (SDGs). Carbon-neutral technologies for waste management have not been critically reviewed yet. This paper reviews the technological trend of agricultural waste utilization, including composting, thermal conversion, and anaerobic digestion. Specifically, the effects of exogenous additives on the contents, fractionation, and fate of phosphorus (P) and potentially toxic elements (PTEs) during the composting process have been comprehensively reviewed in this article. The composting process can transform biomass-P and additive-born P into plant available forms. PTEs can be passivated during the composting process. Biochar can accelerate the passivation of PTEs in the composting process through different physiochemical interactions such as surface adsorption, precipitation, and cation exchange reactions. The addition of exogenous calcium, magnesium and phosphate in the compost can reduce the mobility of PTEs such as copper, cadmium, and zinc. Based on critical analysis, this paper recommends an eco-innovative perspective for the improvement and practical application of composting technology for the utilization of agricultural biowastes to meet the circular economy approach and achieve the SDGs.

Review of energy self-circulation systems integrating biogas utilization with Powerfuels production in global livestock industry

Energy self-circulation systems, defined as energy systems incorporating the recycling utilization of waste biomass, have been proposed to reduce greenhouse gases emissions from livestock sector. In this study, a comprehensive review of the situation and challenges of biogas utilization in the livestock industry was provided. Moreover, two technological routes were proposed for a circular livestock system combined with Powerfuels production (CP-CLS), starting from biogas combustion for power generation and steam reforming to the sustainable development path of synthesizing, storing, and utilizing Powerfuels. The self-circulation capability and comprehensive benefits of the CP-CLS life cycle was discussed, along with future application scenarios and proposed standards for Powerfuels. To realize this potential, continuous research, development, and policy support are crucial. This study envisions the next generation of energy self-circulation systems, which expects to reduce the negative effect of livestock industry on climate change and promote sustainable development.

Identification of factors affecting fattening efficiency of commercial pig herds and analysis of their impact at different performance levels

Improving fattening efficiency is an important goal of breeding commercial pigs, especially for the large-scale pig farms. Fattening efficiency index (FEI) can be used to evaluate the fattening efficiency. The aim of this study was to identify the factors affecting the fattening efficiency of commercial pigs in large-scale pig farms and further study the impact of these factors on the production performance of commercial pig batches at different production levels. The data of 9,570 batches was mainly consisted of four parts (farm facilities, general information of piglets, production performance of nursery pigs and finishing pigs). A total of 28 variables were evaluated by the multi-variable linear regression models. The differences in production factors significantly correlated with FEI at piglets-finishing stage were compared among high-performing (HP), moderate-performing (MP), and low-performing (LP) batches of commercial pigs during the nursery and finishing stage. Among the 28 variables, 18 were significantly correlated with fattening efficiency (P < 0.05), including 11 continuous variables and seven discrete variables. The significant differences among the 11 consecutive variables in the HP, MP, and LP batches of commercial pigs mostly persisted from the piglets-nursery stage to the growing-finishing stage, ultimately affecting the FEI at piglets-finishing stage. For the seven significant discrete variables, the HP batches had a lower proportions in owned source of piglets, number of the purchasing piglets in spring and winter, number of batches in the East and North regions and five-way crossbred pigs, while a higher proportions in the use of closed circuit television video (CCTV) and wastes treatment system. The fattening efficiency of commercial pigs in large-scale pig farms was comprehensively affected by farm facilities, piglets, and production performance at nursery and finishing stage. The low fattening efficiency may have started at the end of nursery stage.

Mild alkaline conditions affect digester performance and community dynamics during long-term exposure

This paper examines the adaptive responses of microbial communities to gradual shifts in pH toward the mild alkaline range in anaerobic digestion (AD) systems. The results indicate that a pH of 8.0 serves as a critical upper limit for stable AD operation, beyond which microbial efficiency declines, underscoring the importance of microbial resilience against elevated pH stress. Specifically, hydrolysis genera, e.g. Eubacterium and Anaerobacterium, and syntrophic bacteria were crucial for reactor stability. Fibrobacter had also been shown to play a key role in the accumulation of propionate, thus leading to its dominance in the volatile fatty acid profile throughout the experimental phases. Overall, this investigation revealed the potential adaptability of microbial communities in AD systems to mild alkaline pH shifts, emphasizing the hydrolysis bacteria and syntrophic bacteria as key factors for maintaining metabolic function in elevated pH conditions.

Coupling hydrothermal liquefaction and anaerobic digestion for waste biomass valorization: A review in context of circular economy

In light of the substantial global production of biomass waste, effective waste management and energy recovery solutions are of paramount importance. Hydrothermal liquefaction (HTL) and anaerobic digestion (AD) have emerged as innovative techniques for converting biomass waste into valuable resources. Their integration creates a synergistic framework that mitigates inherent limitations, leading to improved efficiency, enhanced product quality, and the comprehensive utilization of biomass. This review paper investigates the integration of HTL and AD, highlighting its significance and potential benefits as well as the optimal sequencing (HTL followed by AD and AD followed by HTL). The review encompasses experimental procedures, factors influencing both sequencing options, energy recovery characterizations, final product outcomes, as well as toxicological assessments and discussions on reduction. Additionally, it delves into the transition towards a circular bioeconomy and discusses the challenges and opportunities intrinsic to these processes. The findings presented in this review offer valuable insights to shape future research in this evolving field.

Barriers to commercial deployment of biorefineries: A multi-faceted review of obstacles across the innovation chain

Realizing integrated biorefineries producing multiple fuels, chemicals and materials from sustainable biomass feedstocks holds promise for transitioning industries onto low-carbon trajectories. However, widespread commercial implementation remains elusive despite two decades of technological advancements. This review synthesizes current literature to provide a comprehensive analysis of key multi-dimensional barriers inhibiting the scale-up of biorefineries. The review discusses the technical challenges around biomass conversion processes. Economic viability concerns such as high capital costs and lack of market competitiveness are also assessed. The review also evaluates the regulatory and policy complexities that poses risks and uncertainties in the scaling up of biorefineries. Socio-political acceptance hurdles including community engagement and public perception are also reviewed. The interconnected nature of these challenges is emphasized and strategies are recommended to enable full potential realization, covering areas such as enhanced stakeholder collaboration, advanced process intensification, supportive policy frameworks, innovative financing models and strategic marketing initiatives. International pilots and cross-sectoral knowledge exchange are highlighted as priority enablers. In conclusion, this review synthesizes insights from extensive demonstration efforts to identify priorities and pathways for accelerating the global commercial transition towards sustainable biorefinery implementation. It aims to inform strategic decision-making and collaborative actions amongst stakeholders in research, industry and policy domains.

Recycling potassium from cow manure compost can replace potassium fertilizers in paddy rice production systems

The prevalence of K deficiency and negative K balance in rice production increases the demand for K fertilizer. However, the primary source of K fertilizer, potash rock, is limited. Recycling K from cow manure compost (CMC) is a sustainable solution. Nevertheless, the effects of substituting K fertilizer with CMC on rice yield, soil K fertility, and partial K balance (PKB) are not well understood. Therefore, a field experiment with four treatments (control - unfertilized, MNP K - CMC plus NPK fertilizer, MNP ½ K - CMC plus NP and 50 % K fertilizer, and MNP - CMC plus NP fertilizer) was conducted from 2020 to 2022 to study the effects of replacing K fertilizer with K from CMC on rice growth, yield, plant K uptake, soil K fertility, and PKB. The results indicated that K input from CMC exceeded the recommended K fertilizer level, sufficient for optimal rice growth and yield over three growing seasons and plant K uptake in the last two seasons. Plant K uptake increased with total K input and reached a plateau when total K input approached the maximum plant K uptake. In the MNP treatment, PKB was negative in the first two seasons but became positive in the last season, owing to the equivalence between K input from CMC and plant K uptake. Key factors influencing PKB in this treatment were K input from CMC and plant K uptake. Increasing the CMC application rate during the first two seasons could lead to a positive PKB. In this treatment, soil exchangeable K changed correspondingly with PKB, decreasing in the first two seasons but increasing in the last season. Overall, determining the appropriate amount of CMC application for a positive PKB is vital for the sustainability of substituting K fertilizer with K from CMC in paddy rice systems.

Control of odorants in swine manure and food waste co-composting via zero-valent iron /H2O2 system

Odors have posed challenges to the advancement of aerobic composting. This work aims to identify the primary components responsible for odors and assess the effectiveness and mechanisms of the zero-valent iron/H2O2 system controlling various odorants in aerobic composting. Swine manure and food waste were used as composting materials, with the addition of zero-valent iron and hydrogen peroxide to mitigate odor emissions. Results revealed that odorants included ammonia, hydrogen sulfide, and 22 types of volatile organic compounds (VOCs), with ethyl acetate, heptane, and dimethyl disulfide being predominant. Among the odorants emitted, ammonia accounted for 75.43%, hydrogen sulfide for 0.09%, and identified VOCs for 24.48%. The ZVI/H2O2 system showed a significant reduction in ammonia and VOCs emission, with the reduction of 51% (ammonia) and 41.3% (VOCs) respectively, primarily observed during the thermophilic period. The occurrence of Fenton-like reactions and changes in key microbial populations were the main mechanisms accounting for odor control. The occurrence of Fenton-like reaction was confirmed by X-ray photoelectron spectroscopy and reactive oxygen detection, showing the oxidation of zero-valent iron by H2O2 to higher valence elemental iron, and the simultaneous production of ·OH. Microbial analysis indicated that an enrichment of specific microorganisms with Bacillus contributed to feammonx and Bacillaceae contributed to organic biodegradation. Redundancy analysis highlighted the role of key microbial species (Bacillaceae, Bacillus, and Ureibacillus) in effectively reducing the level of ammonia and volatile organic compounds. These novelty findings illustrated that the potential of this system is promising for controlling the emission of odorants and aerobic composting reinforcement.

Enhanced heavy metal stabilization and phosphorus retention during the hydrothermal carbonization of swine manure by in-situ formation of MgFe2O4

Hydrothermal carbonization is an efficient technique for the disposal of livestock manure, enabling its harmless treatment, quantity reduction, and resourceful utilization. Co-hydrothermal of modified materials facilitates the production of more valuable carbonaceous materials. However, further exploration is needed to understand their potential impact on the environmental risks associated with livestock manure disposal and the application of products derived from it. Therefore, the carbonization degree, heavy metals stabilization, and phosphorus retention during the hydrothermal treatment of swine manure were systematically investigated in this study under the influence of in-situ formed MgFe2O4. The results revealed that the in-situ formation of MgFe2O4 improved the dehydration and decarboxylation of organic components in swine manure, thereby improving its carbonization degree. Furthermore, both hydrothermal carbonization and MgFe2O4 modified hydrothermal carbonization resulted in an enhanced stabilization of heavy metals, leading to a significant reduction in their soluble/exchangeable fraction and reducible fraction. Phosphorus was predominantly retained in the hydrochars, with the highest retention rate reaching 88%, attributed to the significant decrease in soluble and exchangeable phosphorus fractions facilitated by the in-situ formation of MgFe2O4. Moreover, MgFe2O4 modified hydrochars exhibited remarkable adsorption capacity for Pb(II) and Cu(II) without any leaching of heavy metals. Overall, the findings indicated that the in-situ formation of MgFe2O4 positively influenced the hydrothermal of swine manure, improving certain economic benefits in its practical application.

Trends and social aspects in the management and conversion of agricultural residues into valuable resources: A comprehensive approach to counter environmental degradation, food security, and climate change

The circular economy is essential as it encourages the reuse and recycling of resources while reducing waste, which ultimately helps to reduce environmental pollution and boosts economic efficiency. The current review highlights the management of agricultural and livestock residues and their conversion into valuable resources to combat environmental degradation and improve social well-being. The current trends in converting agricultural residues into useful resources emphasize the social benefits of waste management and conversion. It also emphasizes how waste conversion can reduce environmental degradation and enhance food security. Using agricultural residues can increase soil health and agricultural output while reducing pollution, greenhouse gas emissions, and resource depletion. Promoting sustainable waste-to-resource conversion processes requires a combination of strategies that address technical, economic, social, and environmental aspects. These multiple strategies are highlighted along with prospects and considerations.

A review of the definition, influencing factors, and mechanisms of rapid composting of organic waste

Composting is a traditional method of treating organic waste. A growing number of studies have been focusing on accelerating the process to achieve "rapid composting." However, the specific definition and influencing factors of rapid composting remain unclear. Therefore, we aimed to gather more insight into the features of rapid composting by reviewing the literature concerning organic waste composting published in the Web of Science database in the past 5 years. We selected 1615 sample studies with "composting" as the subject word and analyzed the effective composting time stated in each study. We defined rapid composting within 15 days using the median test and quartile method. Based on this definition, we summarized the influencing factors of "rapid composting," namely materials, reactors, temperature, and microorganisms. Finally, we summarized two mechanisms related to humus formation during organic waste rapid composting: high temperature-promoting maturation and microbial driving mechanisms. This literature review compiled useful references to help promote the development of rapid composting technology and related equipment.

Directional transformation and migration pathways of nitrogen during pig manure supercritical water gasification

Nitrogen is a valuable nutrient element in pig manure. This work focuses on investigating the distribution, directional transformation, and migration pathways to facilitate the recovery of nitrogen from supercritical water gasification products. Results indicated that no nitrogen-containing gas was detected and 12.65 % of nitrogen remained in solid products. 82.49 % of nitrogen migrated into liquid products, which are predominated by ammonia. Catalysts were employed to promote the conversion of solid nitrogen to liquid nitrogen and organic nitrogen to ammonia. Finally, 85 % of nitrogen is enriched into liquid products and ammonia predominated the liquid nitrogen. The percentage of ammonia increased to 97.51 % at 620 °C in the presence of potassium carbonate. The migration pathways indicated that nitrogen was transformed into ammonia by various intermediates such as indole. The rest of the nitrogen remained in solid products with stable quaternary-nitrogen. These findings provide valuable insights into nitrogen management and recovery.

City-level decoupling between livestock and crop production and its effect on fertilizer usage: Evidence from China

China is one of the largest producers of livestock production and also with tremendous fertilizer consumption in crop production, regional decoupling between livestock and crop production often results in fertilizer overuse and environmental pollution. However, city-level coupling analysis between livestock and crop production is rare, and its impact on fertilizer usage also remains unclear. Here, we evaluated the nitrogen (N) nutrient supply from the livestock breeding sector and the N nutrient demand of cropland during the 2007-2020 period in a typical agricultural region in China. The city-level coupling degree of livestock and crop production and the effect on fertilizer usage were explored with spatial analysis and regression methods. Our results show that the province level has a relatively high coupling degree. However, significant spatial heterogeneity was found at the city level, especially in western Sichuan Province due to the highly unbalanced distribution of livestock and crop production, and this decoupling phenomenon may hinder fertilizer reduction. Furthermore, we reveal that technological development is not an effective way to achieve sustainable agriculture without other policy instruments, such as livestock spatial relocation, which must be considered when formulating crop-livestock integration policies. The findings expand city-level knowledge of the livestock-crop system and provide important implications for adjusting agricultural practices to realize sustainable agricultural development.

A review on the effects of discharging conventionally treated livestock waste to the environmental resistome

Globally, animal production has developed rapidly as a consequence of the ongoing population growth, to support food security. This has consequently led to an extensive use of antibiotics to promote growth and prevent diseases in animals. However, most antibiotics are not fully metabolized by these animals, leading to their excretion within urine and faeces, thus making these wastes a major reservoir of antibiotics residues, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) in the environment. Farmers normally depend on conventional treatment methods to mitigate the environmental impact of animal waste; however, these methods are not fully efficient to remove the environmental resistome. The present study reviewed the variability of residual antibiotics, ARB, as well as ARGs in the conventionally treated waste and assessed how discharging it could increase resistome in the receiving environments. Wherein, considering the efficiency and environmental safety, an addition of pre-treatments steps with these conventional treatment methods could enhance the removal of antibiotic resistance agents from livestock waste.

Resourcelized conversion of poultry feces to ordered carbon with electron poor/rich microregions for water purification induced by peroxymonosulfate

For the sustainable reutilization of poultry feces (PF) to reduce environmental pollution, we present a novel approach for converting PF into a highly effective catalyst, consisting of trace copper (Cu) and sulfur (S) linked with ordered graphitized carbon (CS/CPF) for wastewater purification. Raman and EPR results verified that the disorderly organic matters in PF are transformed into orderly graphene structures that complexed with Cu to form large numbers of electron-poor/rich microregions on CS/CPF surface. The electrons from electron-rich organic pollutants can be directly captured by dissolved oxygen (DO) to produce abundant reactive oxygen species due to the enhanced electron polarization via the construction of Cu-S-C bond bridge on CS/CPF surface, which greatly enhance the removal efficiency of pollutants. CS/CPF achieves 100% removal for 2,4-dichlorophenoxyacetic acid (2,4-D) in just 10 min after adding trace peroxymonosulfate (PMS), keeping efficient catalytic activity after continuous reactions for 240 h. This strategy offers a practical and sustainable solution for the efficient resource recovery of poultry feces.

Recent progress on emerging technologies for trace elements-contaminated soil remediation

Abiotic stresses from potentially toxic elements (PTEs) have devastating impacts on health and survival of all living organisms, including humans, animals, plants, and microorganisms. Moreover, because of the rapid growing industrial activities together with the natural processes, soil contamination with PTEs has pronounced, which required an emergent intervention. In fact, several chemical and physical techniques have been employed to overcome the negative impacts of PTEs. However, these techniques have numerous drawback and their acceptance are usually poor as they are high cost, usually ineffectiveness and take longer time. In this context, bioremediation has emerged as a promising approach for reclaiming PTEs-contaminated soils through biological process using bacteria, fungus and plants solely or in combination. Here, we comprehensively reviews and critically discusses the processes by which microorganisms and hyperaccumulator plants extract, volatilize, stabilize or detoxify PTEs in soils. We also established a multi-technology repair strategy through the combination of different strategies, such as the application of biochar, compost, animal minure and stabilized digestate for stimulation of PTE remediation by hyperaccumulators plants species. The possible use of remote sensing of soil in conjunction with geographic information system (GIS) integration for improving soil bio-remediation of PTEs was discussed. By synergistically combining these innovative strategies, the present review will open very novel way for cleaning up PTEs-contaminated soils.

Nitrogen evolution during membrane-covered aerobic composting: Interconversion between nitrogen forms and migration pathways

Aerobic composting is a promising technology for converting manure into organic fertilizer with low capital investment and easy operation. However, the large nitrogen losses in conventional aerobic composting impede its development. Interconversion of nitrogen species was studied during membrane-covered aerobic composting (MCAC) and conventional aerobic composting, and solid-, liquid-, and gas-phase nitrogen migration pathways were identified by performing nitrogen balance measurements. During the thermophilic phase, nitrogenous organic matter degradation and therefore NH3 production were faster during MCAC than uncovered composting. However, the water films inside and outside the membrane decreased NH3 release by 13.92%-22.91%. The micro-positive pressure environment during MCAC decreased N2O production and emission by 20.35%-27.01%. Less leachate was produced and therefore less nitrogen and other pollutants were released during MCAC than uncovered composting. The nitrogen succession patterns during MCAC and uncovered composting were different and NH4+ storage in organic nitrogen fractions was better facilitated during MCAC than uncovered composting. Overall, MCAC decreased total nitrogen losses by 33.24%-50.07% and effectively decreased environmental pollution and increased the nitrogen content of the produced compost.

Towards sustainable management of agricultural resources: A framework to assess the relationship between water, soil, economic factors, and grain production

As the requirements for environmental protection and high-efficiency economies increase, grain production (GP) across the globe faces more stringent ecological constraints and economic pressure. Understanding the relationships between natural resources and economic and agricultural factors in grain-producing regions is paramount for ensuring global food security. This paper proposes a methodological framework to explore the relationships between water and soil resources (WSRs), economic input factors (EIFs), and GP. We employed the northeast region of China as a case study to advance our understanding of the factors driving the development of grain-producing capacity. We first constructed and calculated the region's water and soil comprehensive index (WSCI) to describe water-soil properties. We then used hotspot analysis to explore the spatial agglomeration characteristics of WSRs, EIFs, and GP. Finally, we used threshold regression analysis to understand the effects of EIFs and GP with the WSCI as the threshold variable. With the improvement of the WSCI, the positive impact of fertilizer and irrigation on GP shows a U-shaped curve in elasticity coefficients. The positive effect of agricultural machinery on GP decreases significantly, and the impact of labor input on GP is insignificant. These results provide new insights into the relationship between WSRs, EIFs, and GP and a reference for improving GP efficiency globally. This work thus contributes to advancing our capabilities to enable food security while considering aspects of sustainable agriculture in important grain-producing regions across the globe.

Investigation of heavy metal and micro-macro element speciation in biomass ash enriched sewage sludge compost

The objective of this study was to enrich the nutrient content of compost and to investigate the passivation and solubilization of plant micronutrients (Fe, Al, Cu, Ni, Zn, Na, Mn), macroelements (P, K, Mg, Ca), and heavy metals (Cr, Cd, Pb) during sewage sludge composting with nutrient-rich biomass ash additives. T0: 0%, T1: 3.5%, T2: 7.0%, and T3: 14.0% dry weight (DW), weight/weight (w/w) biomass ash was added to the sewage sludge + sawdust mixture (volume, 1:1) to obtain the final NPK content and monitored over a 45-day period. Sawdust was used as auxiliary material. The sequential extraction method was used to determine the elemental species. Cr, Cd and Pb showed higher affinity to the residual fraction and occluded in the oxide fraction, which decreased the bioavailability factor (BF) (<1% BF-Cr, 21% BF-Cd and 9% BF-Pb) compared to the control treatment (46% BF-Cr, 47% BF-Cd and 80% BF-Pb). As the amount of biomass ash increased (T1-T3), the percentages of residual Cr (Res-Cr) (10-65%), exchangeable Cd (Exc-Cd) and organically bound Cd (Org-Cd) (14% and 21%), and oxides-Pb (Oxi-Pb) (20-61%) increased. In all composts, Fe, Al, and Cu were associated with organically bound and oxides-entrapped fractions. More than 50% of total Mn and Mg were concentrated mainly in exchangeable fractions, suggesting high mobility and bioavailability (42% BF-Mn and 98% BF-Mg). Ni, Zn, and Na tended to be present in oxide-bound, organically bound, and residual fractions, while K and P were associated with exchangeable and organically bound fractions. The overall results suggest that composting sewage sludge with biomass ash may be the best strategy and technique to overcome soil application bottlenecks because it passivates heavy metals and improves the bioavailability of plant nutrients.

Impact of bentonite on greenhouse gas emissions during pig manure composting and its subsequent application

Additives were widely investigated to retain the nutrients and mitigate the greenhouse gas emissions (GHGs) during manure composting. However, the sustained effects of additives on the GHGs emissions following incorporation of composts to soil were scarcely explored. This study evaluated the effects of bentonite added at the beginning of pig manure composting on the GHGs emissions during two successive processes, i.e., composting and soil incubation amended with composting products. Addition of bentonite did not hinder the composting process and alter the total CO2 emission. On the other hand, reduction by about 17% and 29% for CH4 and N2O emission, respectively, was achieved in the presence of bentonite during composting. Incorporation of the final composting products to soil enhanced significantly the soil C and N of various forms, and gas emissions of CO2 and N2O. However, no significant differences were observed between bentonite-manure co-compost and manure-only compost application except for the N2O emission. Compared to the manure-only compost, compost amended with bentonite reduced N2O loss by around 6.8%, but not statistically significant. This study confirmed that addition of bentonite at the composting stage can mitigate the GHGs emission considering both composting and compost application stages, with all reductions occurring at the composting stage.

Role of suspended solids on the co-precipitation of pathogenic indicators and antibiotic resistance genes with struvite from digested swine wastewater

Struvite recovered from wastewater contains high concentration of fecal indicator bacteria (FIB), porcine adenoviruses (PAdV) and antibiotic resistance genes (ARGs), becoming potential resources of these microbial hazards. Understanding the precipitation behavior of pathogenic indicators and ARGs with suspended solids (SS) will provide the possible strategy for the control of co-precipitation. In this study, SS was divided into high-density SS (separated by centrifugation) and low-density SS (further separated by filtration), and the role of SS on the co-precipitation of FIB, PAdV and ARGs was investigated. The distribution analysis showed that 35.5-73.0% FIB, 79.6% PAdV and 64.5-94.8% ARGs existed in high-density SS, while the corresponding values were 26.9-64.4%, 11.7% and 3.5-24.3% in low-density SS. During struvite generation, 82.7-96.9% FIB, 75.5% PAdV and 56.3-86.5% ARGs were co-precipitated into struvite. High-density SS contributed 20.7-68.5% FIB, 63.9% PAdV and 38.7-87.2% ARGs co-precipitation, and the corresponding contribution of low-density SS was 31.4-79.2%, 3.9% and 6.2-54.7%. Moreover, the precipitated SS in struvite obviously decreased inactivation efficiency of FIB and ARGs in drying process. These results provide a potential way to control the co-precipitation and inactivation of FIB, PAdV and ARGs in struvite through removing high-density SS prior to struvite recovery.

Identification of livestock farms with potential risk of environmental pollution by using a model for returning livestock manure to cultivated land

Livestock farms produce a large amount of livestock manure, which, if not disposed of properly, will become an environmental pollution source. However, limited research has been conducted on identifying livestock farms with a potential risk of environmental pollution. In this study, a model for returning livestock manure to cultivated land was constructed. Livestock manure was returned to cultivated land, and the amount of surplus livestock manure nutrients, including nitrogen and phosphorus, in livestock farms was calculated with pig manure as an example. Then, livestock farms with a potential risk of environmental pollution in Shanggan Town and part of Xiangqian Town in Fuzhou City were identified using phosphorus as an index. Results showed that the spatial distributions of nitrogen and phosphorus from pig manure in the cultivated land varied. All cultivated lands exhibited the maximum carrying capacity for phosphorus, and 1811 cultivated lands exhibited potential nitrogen carrying capacity. A total of 13,958.997 kg of phosphorus from pig manure in 144 livestock farms could not be disposed to cultivated lands. In all, 144 livestock farms with surplus phosphorus from pig manure were identified as potential environmental pollution sources. These findings can serve as a scientific basis for the utilization of livestock manure, prevention of environmental pollution caused by livestock farms, and layout planning of livestock farms.

Treatment and utilization of swine wastewater - A review on technologies in full-scale application

The management of swine wastewater has become the focus of attention in the farming industry. The disposal mode of swine wastewater can be classified as field application of treated waste and treatment to meet discharge standards. The status of investigation and application of unit technology in treatment and utilization such as solid-liquid separation, aerobic treatment, anaerobic treatment, digestate utilization, natural treatment, anaerobic-aerobic combined treatment, advanced treatment, are reviewed from the full-scale application perspective. The technologies of anaerobic digestion-land application is most appropriate for small and medium-sized pig farms or large pig farms with enough land around for digestate application. The process of "solid-liquid separation-anaerobic-aerobic-advanced treatment" to meet the discharge standard is most suitable for large and extra-large pig farms without enough land. Poor operation of anaerobic digestion unit in winter, hard to completely utilize liquid digestate and high treatment cost of digested effluent for meeting discharge standard are established as the main difficulties.

Rice straw for energy and value-added products in China: a review

The rise of global waste and the decline of fossil fuels are calling for recycling waste into energy and materials. For example, rice straw, a by-product of rice cultivation, can be converted into biogas and by-products with added value, e.g., biofertilizer, yet processing rice straw is limited by the low energy content, high ash and silica, low nitrogen, high moisture, and high-quality variability. Here, we review the recycling of rice straw with focus on the global and Chinese energy situations, conversion of rice straw into energy and gas, biogas digestate management, cogeneration, biogas upgrading, bioeconomy, and life cycle assessment. The quality of rice straw can be improved by pretreatments, such as baling, ensiling, and co-digestion of rice straw with other feedstocks. The biogas digestate can be used to fertilize soils. The average annual potential energy of collectable rice straw, with a lower heating value of 15.35 megajoule/kilogram, over the past ten years (2013-2022) could reach 2.41 × 109 megajoule.

Evaluation of composting parameters, technologies and maturity indexes for aerobic manure composting: A meta-analysis

Aerobic composting is an efficient method to recover nutrients from animal manure. However, there is considerable variability in the management and maturity criteria used across studies, and a systematic meta-analysis focused on compost maturity is currently lacking. This study investigated the optimal range of startup parameters and practical criteria for manure composting maturity, as well as the effectiveness of in situ technologies in enhancing composting maturity. Most maturity indexes were associated with composting GI, making it an ideal tool for evaluating the maturity of manure composts. GI increased with declined final C/N and (Final C/N)/(Initial C/N) (P < 0.01), and therefore a maturity assessment standard for animal manure composting was proposed: a mature compost has a C/N ratio ≤23 and a GI ≥70, while a highly mature compost has a GI ≥90 and preferably (Final C/N)/(Initial C/N) ≤0.8. Meta-analysis demonstrated that C/N ratio regulation, microbial inoculation and adding biochar and magnesium-phosphate salts are effective strategies for improving compost maturity. Specifically, a greater reduction in the C/N ratio during the composting process is beneficial for improving the maturity of compost product. The optimal startup parameters for composting have been determined, recommending an initial C/N ratio of 20-30 and an initial pH of 6.5-8.5. An initial C/N ratio of 26 was identified as the most suitable for promoting compost degradation and microorganism activity. The present results promoted a composting strategy for producing high-quality compost.

Urban mining from biomass, brine, sewage sludge, phosphogypsum and e-waste for reducing the environmental pollution: Current status of availability, potential, and technologies with a focus on LCA and TEA

Rapid industrialization, improved standards of living, growing economies and ever-increasing population has led to the unprecedented exploitation of the finite and non-renewable resources of minerals in past years. It was observed that out of 100 BMT of raw materials processed annually only 10% is recycled back. This has resulted in a strenuous burden on natural or primary resources of minerals (such as ores) having limited availability. Moreover, severe environmental concerns have been raised by the huge piles of waste generated at landfill sites. To resolve these issues, 'Urban Mining' from waste or secondary resources in a Circular Economy' concept is the only sustainable solution. The objective of this review is to critically examine the availability, elemental composition, and the market potential of the selected secondary resources such as lignocellulosic/algal biomass, desalination water, sewage sludge, phosphogypsum, and e-waste for minerals sequestration. This review showed that, secondary resources have potential to partially replace the minerals required in different sectors such as macro and microelements in agriculture, rare earth elements (REEs) in electrical and electronics industry, metals in manufacturing sector and precious elements such as gold and platinum in ornamental industry. Further, inputs from the selected life cycle analysis (LCA) & techno economic analysis (TEA) were discussed which showed that although, urban mining has a potential to reduce the greenhouse gaseous (GHG) emissions in a sustainable manner however, process improvements through innovative, novel and cost-effective pathways are essentially required for its large-scale deployment at industrial scale in future.

Effects of different gasification biochar grain size on greenhouse gases and ammonia emissions in municipal aerated composting processes

This work is aimed at investigating the effects derived from the application of minimum amounts of two different sized biochars, obtained through biomass gasification, on the greenhouse gases and ammonia emissions from a co-composting process of the organic fraction of municipal solid waste. The chosen biochar-to-organic waste share is set to 3% w/w dry, and the results obtained are compared with a conventional composting process without biochar. Nine aerated static pilot-scale bins with a volume of 1.3 m³ were prototyped and run, three per thesis and three for the control. The trial lasted 63 days, following the same approach used in full-scale composting facilities. The testing period was divided into a forced aeration phase followed by a static phase. In terms of global warming potential, the use of fine biochar and coarse biochar resulted in 13 and 11 kg CO₂eq ton-1 emitted respectively. These values are 36% and 45% lower than the 20 kg of CO₂eq ton-1 emitted by the control theses. Specifically, the chosen minimum amounts of biochar produced a reduction of CH₄ and N₂O, while a significant reduction in NH₃ emissions was not detected. Carbon dioxide showed a slight increase in biochar theses. This work has proven that fine and coarse gasification-derived biochars improve the bio-oxidative phenomena and reduce greenhouse gases emissions of the composters, regardless of the biochar particle size and regardless of the modest 3% w/w biochar-to-organic waste share used.

Resourcelized conversion of livestock manure to porous cage microsphere for eliminating emerging contaminants under peroxymonosulfate trigger

Pollution and resource waste caused by the improper disposal of livestock manure, and the threat from the release of emerging contaminants (ECs), are global challenges. Herein, we address the both problems simultaneously by the resourcelized conversion of chicken manure into porous Co@CM cage microspheres (CCM-CMSs) for ECs degradation through the graphitization process and Co-doping modification step. CCM-CMSs exhibit excellent performance for ECs degradation and actual wastewater purification under peroxymonosulfate (PMS) initiation, and show adaptability to complex water environments. The ultra-high activity can maintain after continuous operation over 2160 cycles. The formation of C-O-Co bond bridge structure on the catalyst surface caused an unbalanced electron distribution, which allows PMS to trigger the sustainable electron donation of ECs and electron gain of dissolved oxygen processes, becoming the key to the excellent performance of CCM-CMSs. This process significantly reduces the resource and energy consumption of the catalyst throughout the life cycle of production and application.

An integrated biorefinery approach for the valorization of water hyacinth towards circular bioeconomy: a review

Water hyacinth (WH) has become a considerable concern for people across the globe due to its environmental and socio-economic hazards. Researchers are still trying to control this aquatic weed effectively without other environmental or economic losses. Research on WH focuses on converting this omnipresent excessive biomass into value-added products. The potential use of WH for phytoremediation and utilizing waste biomass in various industries, including agriculture, pharmaceuticals, and bioenergy, has piqued interest. The use of waste WH biomass as a feedstock for producing bioenergy and value-added chemicals has emerged as an eco-friendly step towards the circular economy concept. Here, we have discussed the extraction of bio-actives and cellulose as primary bioproducts, followed by a detailed discussion on different biomass conversion routes to obtain secondary bioproducts. The suggested multi-objective approach will lead to cost-effective and efficient utilization of waste WH biomass. Additionally, the present review includes a discussion of the SWOT analysis for WH biomass and the scope for future studies. An integrated biorefinery scheme is proposed for the holistic utilization of this feedstock in a cascading manner to promote the sustainable and zero-waste circular bio-economy concept.

Critical review of biochemical pathways to transformation of waste and biomass into bioenergy

In recent years, biofuel or biogas have become the primary source of bio-energy, providing an alternative to conventionally used energy that can meet the growing energy demand for people all over the world while reducing greenhouse gas emissions. Enzyme hydrolysis in bioethanol production is a critical step in obtaining sugars fermented during the final fermentation process. More efficient enzymes are being researched to provide a more cost-effective technique during enzymatic hydrolysis. The exploitation of microbial catabolic biochemical reactions to produce electric energy can be used for complex renewable biomasses and organic wastes in microbial fuel cells. In hydrolysis methods, a variety of diverse enzyme strategies are used to promote efficient bioethanol production from various lignocellulosic biomasses like agricultural wastes, wood feedstocks, and sea algae. This paper investigates the most recent enzyme hydrolysis pathways, microbial fermentation, microbial fuel cells, and anaerobic digestion in the manufacture of bioethanol/bioenergy from lignocellulose biomass.

Influence of anaerobic biotransformation process of agro-industrial waste with Lactobacillus acidophilus on the rheological parameters: case of study of pig manure

This study evaluated the rheological behavior of the pig waste biotransformation process to produce lactic acid (LA) and biomass with Lactobacillus acidophilus in a stirred reactor. In addition, cell growth, carbohydrate consumption, and LA production were measured at three different agitation speeds, 100, 150, and 200 rpm at 37 °C, with a reaction time of 52 h. During the development of the process, the kinetic and rheological parameters were obtained using the logistic, Gompertz, generalized Gompertz, Ostwald de Waele, and Herschel-Bulkley mathematical models, respectively. The substrate used was pig manure, to which molasses was added at 12% v/v to increase the concentration of carbohydrates. The results suggest that mass exchange is favorable at low agitation speeds. Nevertheless, the presence of molasses rich in carbohydrates as a carbon source modifies the characteristics of the fluid, dilatant (n > 1) at the beginning of the process to end up as pseudoplastic (n < 1) due to the addition of exopolysaccharides and the modification of the physical structure of the substrate. This effect was confirmed by the Herschel-Bulkley model, which presented a better fit to the data obtained, in addition to finding a direct relationship between viscosity and pH that can be used as variables for the control of bioconversion processes of pig manure into biomass rich in Lactobacillus acidophilus.

Effects of different treatments of manure on mitigating methane emissions during storage and preserving the methane potential for anaerobic digestion

Current agricultural practices in regards to storage of manure come with a significant GHG contribution, due, to a big extent, to CH₄ emissions. For example, in Denmark, the agricultural sector is responsible for about 11.1 metric tons of CO₂ equivalents; only about 0.2 metric tons come directly from CO₂, while 6.0 tons come from CH₄. The present study aims at evaluating and comparing two methods based on their effect on suppressing CH₄ emissions during storage as well as on preserving and enhancing CH₄ yield in a subsequent anaerobic digestion step: the commonly applied acidification with H₂SO₄ as acidifying agent and thermal treatment at the mild temperatures of 70 and 90 °C (pasteurization). Although both treatments effectively suppressed CH₄ emissions during storage, they exhibited a significant difference in preserving and/or enhancing the CH₄ potential of manure. Specifically, thermal treatment resulted in 16-35% enhancement of CH₄ potential, while acidification resulted in decreasing the CH₄ yield by 6-23% compared to non-treated manure. Further investigation showed that storage itself positively affected the CH₄ potential of treated manure in a subsequent anaerobic digestion step; this was attributed to microbial activity other than biomethanation during storage. In overall and based on the results obtained regarding suppression of CH₄ emissions during storage as well as CH₄ potential enhancement, pasteurization at the temperatures tested is a promising alternative to the broadly applied acidification of manure.

Biorefinery and sustainability for the production of biofuels and value-added products: A trends analysis based on network and patent analysis

Biorefineries are modern mechanisms used for producing value-added products and biofuels from different biomass sources. However, a crucial challenge is to achieve a sustainable model for their adequate implementation. Challenges related to technical efficiency and economic feasibility are two of the most relevant problems. Therefore, the present study sought to determine the current trends in basic research and technological development around biorefining and sustainability. We carried out a co-occurrence analysis and a patent analysis using data obtained from the Scopus and Lens databases to provide a general overview of the current state of this area of knowledge. The co-occurrence analysis intends to provide an overview of biorefining and sustainability based on terms associated with these two concepts as a starting point to determine the progress and existing challenges of the field. The results of the patent analysis consisted in identifying the main technological sectors, applicants, and territories where inventions associated with biorefining are registered. The analysis of the information showed that bioeconomy, techno-economic aspects, circular economy, technical issues associated with biomass production, and biofuels represent the focal point of basic research in a wide range of disciplines. Technology development is focused on fermentation, enzymes, and microorganisms, among other areas, which shows the validity of these traditional techniques in addressing the problems faced by the bioeconomy. This scenario shows that developed economies are the driving force behind this area of knowledge and that the PCT system is fundamental for the protection and commercialization of these inventions in places different from where they originated. Furthermore, the challenge lies in learning to work in alternative and complementary technological sectors, beyond microbiology and enzyme applications, in pursuit of the sector's technical and economic feasibility.

The synergistic effect between biofertility properties and biological activities in vermicomposting: A comparable study of pig manure

Vermicomposting is a resource technology for managing animal excreta, whereas the internal relationships of the process are vital for its wide applications. The present study examined how macronutrient and micronutrient concentrations, microbial communities, and enzymatic activity of pig manure (PM) changed during the composting and vermicomposting processes and their internal interactions. The vermicomposting process increased macronutrients more significantly than composting (32.40% of total available nitrogen, 21.70% of total available phosphorous, and 12.70% of total available potassium). The vermicomposting reduced total organic carbon (7.91%), C/N ratio (61.35%), and humification index (56.47%) more than composting due to the quick decomposition of PM. After continual fertility optimization, the total microbial population, with the exception of total fungi, rose significantly to accelerate organics mineralization and improve macronutrients in vermicomposting compared to composting. Moreover, earthworm addition favored the stabilization of the PM containing higher concentrations of micronutrients after being catalyzed by the enhanced catalase activity and reduced sucrase activity after 90 days of vermicomposting. Principal component analysis and chord plots found that the generated vermicomposting products had higher fertility properties and biological activities induced by the synergistic effect of microorganisms and earthworms. These findings highlight vermicomposting is an eco-friendly management technology for processing PM and can be scaled up for agricultural applications.

Integrated crop-livestock-bioenergy system brings co-benefits and trade-offs in mitigating the environmental impacts of Chinese agriculture

Agricultural bioenergy utilization relies on crop and livestock production, favouring an integrated crop-livestock-bioenergy production model. Yet the integrated system's exact contribution to mitigating various environmental burdens from the crop production system and livestock production system remains unclear. Here we inventory the environmental impacts of each process in three subsystems at both national and regional scales in China, ultimately identifying key processes and impact categories. The co-benefits and trade-offs in nine impact categories are investigated by comparing the life cycle impacts in the background scenario (crop production system + livestock production system) and foreground scenario (integrated system). Freshwater eutrophication is the most serious impact category in both scenarios. Except terrestrial acidification, the mitigation effects on the other eight impact categories vary from 1.8% to 94.8%, attributed to fossil energy and chemical fertilizer offsets. Environmental trade-offs should be deliberated when expanding bioenergy utilization in the identified critical regions.