From waste to wealth: Innovations in organic solid waste composting

Biochar and pyroligneous acid contributed to the sustainable reduction of ammonia emissions: From compost process to soil application

Aerobic composting is vital for resource recycling but struggles with high ammonia (NH3) emissions. Biochar (BC) and pyroligneous acid (PA), products of waste pyrolysis, have great potential for reducing NH3 emissions. However, the effective utilization of BC and PA to reduce NH3 emissions in both compost process and product application remains unclear. In this study, different amounts of BC and PA were incorporated into the composting process. The evaluation indexes of compost products were systematically assessed and compared through the cultivation of amaranth. Results demonstrated that rational use of BC and PA could enhance compost quality and effectively reduce NH3 emissions. The addition of 15 %BC+ 3 %PA resulted in a 92.31 % increase in NH4+-N content while reducing NH3 emission by 39.94 % during composting. The synergistic effect achieved by maintaining NH4+-N, enhancing NO3--N, and regulating pH. The compost products in 15 %BC+ 3 %PA complied with the requirements of China's National organic fertilizer standard. Moreover, these compost products demonstrated soil sustained fertility effects, reducing NH3 emission by 41.05 %-69.66 % and increasing total weight of amaranth by 4.62 % by a dosage of 4 %. This study is highly significant for addressing the issue of NH3 emission in both the compost process and soil application.

Metagenomic Analysis of Microbial Community Associated with Food Waste Composting

Food waste is an increasing cause of concern in India. Its management through composting plays a vital role in managing the biodegradable fraction of municipal solid waste. However, the existing composting process has many challenges, such as the lack of optimum microenvironment and microbiome knowledge, which limits efficient outcomes. Therefore, the present study aims to bridge the gap by applying metagenomics to study microbial community dynamicity during different stages of composting. The bacterial community analysis showed that genus Marionobacter (9.4%) and Halomonas (7.4%) were prevalent during the mesophilic stage, whereas the Bacillus (12.2%) and Cellulomonas (0.1%) were prevalent during the thermophilic and maturation stage of composting. The functional profiling of metagenome indicated the abundance of genes involved in degradation of polymeric compounds such as carbohydrates, lipids, and proteins. The relative abundance of arginine and proline metabolisms increased during the thermophilic stage. Whereas the relative abundance of genes involved in fatty acid, tryptophan, galactose, and propanoate metabolisms declined. Similarly, the CAZyme tool predicted that the genes encoding for glycoside hydrolase (GH) families were higher during the mesophilic and thermophilic stages of composting. These enzymes play an important role in degradation of complex polysaccharides such as cellulose and hemicellulose. The data obtained from the present study could be utilized for the optimization and improving the composting process.

Simulation of greenhouse gas emission during sewage-sludge composting with high-concentration oxygen aeration

Continuous emission of greenhouse gases (CH4, N2O) is still one of key issues inhibiting the sustainability of the composting industry, which is regulated by aeration combined with porosity of the matrix via varying dissolved-oxygen (DO) distribution of in compost particles. Numerical simulation is considered to be an emerging tool for optimizing oxygen supply and porosity of the matrix. Therefore, in this study, a novel numerical simulation approach was developed, which includes a DO distribution model and fitting equations of GHG based on DO distribution. The parameters (porosity distribution, coefficients) were obtained from pilot experiments of sewage-sludge composting at aeration of two oxygen concentrations (20.9 %, OC20.9; 40.0 %, OC40.0) respectively. As a result, when the air-immobile region ranged from 0.2 to 0.5 and the O2 concentration was increased from 20.9 % (OC20.9) to 100.0 % (OC100.0), the CH4 emission rate decreased by a range of 53 %-96 %, while the N2O emission rate varied from a decrease of 7 % to an increase of 59 %. The developed simulation approach can be used to assist in establishing novel technologies to reduce GHGs emission in composting via optimizing oxygen supply combined with matrix's porosity.

Analysis of biological treatment technologies, their present infrastructures and suitability for biodegradable food packaging - A review

Recently, there has been an increased demand for biodegradable plastics in the food packaging industry, especially for highly food soiled packaging items containing food/beverage solids that will not be recycled using a non-biological process. However, the increased usage of those materials have also raised concerns and confusion, as a major part of these biodegradable plastics are not effectively separated nor recycled. The lack of acceptance in recycling facilities, related to confusion with their conventional polymers counterparts, as well as short retention times of recycling facilities, often incompatible with the degradation kinetics of biodegradable plastics, stand as the major drawbacks for bioplastics treatment. Additionally, the presence of incompletely biodegraded bioplastics during biological treatments or in the final products i.e. compost or digestate, could lead to process failure or limit the commercialization of the compost. This work critically reviews the fundamentals of the biological treatments, anaerobic digestion and composting processes, and discusses the current strategies to improve their performance. In addition, this work summarizes the state-of-the-art knowledge and the impact of bioplastics on full-scale treatment plants. Finally, an overview of the current installed treatment capacity is given to show the areas of opportunity that can be improved and exploited to achieve a better waste management of biodegradable plastics.

Harnessing the potential of exogenous microbial agents: a comprehensive review on enhancing lignocellulose degradation in agricultural waste composting

Composting converts organic agricultural wastes into value-added products, yet the presence of significant non-biodegradable lignocelluloses hinders its efficiency. The introduction of various exogenous microbial agents has been shown to effectively addresses this challenge. In this context, basing on the microbial enzymatic mechanism for lignocellulose degradation, this paper synthesizes the latest research advancements and practical applications of exogenous microbial agents in agricultural waste composting. Given that the effectiveness of lignocellulose degradation is highly dependent on the waste's inherent characteristics, it is crucial to carefully consider the composition of fungi and bacteria, the dosage of microbial agents, and the composting process operation, tailored to the specific type of agricultural waste. Moreover, the combination of additives with exogenous microbial agents can further enhance the degradation of lignocelluloses and the humification of organic matters. Furthermore, insights into the future research and application trends of exogenous microbial agents in agricultural waste composting was prospected.

Spent mushroom substrate: A review on present and future of green applications

The cultivation of edible mushrooms plays a significant role in revitalizing numerous rural regions in China. However, this process generates a large amount of spent mushroom substrate (SMS). Traditional methods for handling SMS, such as random stacking and incineration, lead to resource waste and environmental pollution. The content of organic matter in SMS can range from 40% to 60%, and it also contains various beneficial elements such as trace minerals, making it a valuable resource for biomass. This review initially explores the unique characteristics of SMS and then summarizes the main methods of utilizing its resources. Presently, common resource utilization techniques for SMS include using it as a second-generation cultivation substrate, preparing animal feed and soil fertilizer, producing methane, bioethanol, hydrogen, bio-oil, and electrodes of energy storage devices, extracting enzymes and polysaccharides, and creating bioremediation materials for heavy metals and organic pollutants removal. While research has been conducted on these utilization methods, there are still relatively few large-scale industrial applications. This review also highlights existing challenges and potential solutions in the SMS utilization. Upcycling SMS via innovative and practical technologies presents a promising approach to transforming organic waste into economic value.

Adsorption mechanism and remediation of heavy metals from soil amended with hyperthermophilic composting products: Exploration of waste utilization

Due to high humification, hyperthermophilic composting products (HP) show potential for remediating heavy metal pollution. However, the interaction between HP and heavy metals remains unclear. This study investigated the adsorption mechanism and soil remediation effect of HP on heavy metals. The results showed that the maximum adsorption capacity of HP increased by an average of 30.74 % compared to conventional composting products. HP transformed 34.87 % of copper, 42.55 % of zinc, and 35.63 % of lead from exchangeable and reducible forms into residual and oxidizable forms, thus reducing the soil risk level. In conclusion, HP significantly enhanced the adsorption of heavy metals and their transformation from unstable to stable forms, primarily due to the higher content of hydroxyl and carboxyl groups. This study aims to demonstrate the effectiveness of HP for remediating heavy metal pollution and to enhance the understanding of the underlying mechanism, which lays a foundation for waste utilization.

Pilot-scale membrane-covered composting of food waste: Initial moisture, mature compost addition, aeration time and rate

The impact of different operational parameters on the composting efficiency and compost quality during pilot-scale membrane-covered composting (MCC) of food waste (FW) was evaluated. Four factors were assessed in an orthogonal experiment at three different levels: initial mixture moisture (IMM, 55 %, 60 %, and 65 %), aeration time (AT, 6, 9, and 12 h/d), aeration rate (AR, 0.2, 0.4, and 0.6 m3/h) and mature compost addition ratio (MC, 2 %, 4 %, and 6 %). Results indicated that 55 % IMM, 6 h/d AT, 0.4 m3/h AR, and 4 % MC addition ratio simultaneously provided the compost with the maximum cumulative temperature and the minimum moisture. It was shown that the IMM was the driving factor of this optimum composting process. On contrary, the optimal parameters for reducing carbon and nitrogen loss were 65 % IMM, 6 h/d AT, 0.4 m3/h AR, and 2 % MC addition ratio. The AR had the most influence on reducing carbon and nitrogen losses compared to all other factors. The optimal conditions for compost maturity were 55 % IMM, 9 h/d AT, 0.2 m3/h AR, and 6 % MC addition ratio. The primary element influencing the pH and electrical conductivity values was the AR, while the germination index was influenced by IMM. Protein was the main organic matter limiting the composting efficiency. The results of this study will provide guidance for the promotion and application of food waste MCC technology, and contribute to a better understanding of the mechanisms involved in MCC for organic solid waste treatment.

Preparation of high-temperature and low-temperature-resistant solid microbial agent for cattle manure fermentation and effect on composting

We used microbiology and molecular biology techniques to screen out high-temperature and low-temperature-resistant saprobiotics for compost and prepared a compound fermentation bacteria agent to rapidly ferment cattle manure into high-quality organic fertilizer in low-temperature season. Conventional composting and high-throughput techniques were used to analyze the changes of physical and chemical indexes and biodiversity in the process of composting, from which high and low-temperature-resistant strains were obtained, and high-temperature and low-temperature-resistant solid composite bactericides were prepared and added to composting to verify the effects of composite bactericides on composting. The conventional composting cycle took 22 days, and the diversity of microflora increased first and then decreased. Composting temperature and microbial population were the key factors for the success or failure of composting. Two strains of high-temperature-resistant bacteria and six strains of low-temperature-resistant bacteria were screened out, and they were efficient in degrading starch, cellulose, and protein. The high-temperature and low-temperature-resistant solid bacterial agent was successfully prepared with adjuvant. The preparation could make the compost temperature rise quickly at low temperature, the high temperature lasted for a long time, the water content, C/N, and organic matter fell quickly, the contents of total phosphorus and total potassium were increased, and the seed germination index was significantly improved. Improve the composting effect. The solid composite bacterial agent can shorten the composting time at low temperature and improve the composting efficiency and quality.

From organic fertilizer to the soils: What happens to the microplastics? A critical review

In recent, soil microplastic pollution arising from organic fertilizers has been of a great increasing concern. In response to this concern, this review presents a comprehensive analysis of the occurrence and evolution of microplastics in organic fertilizers, their ingress into the soil, and the subsequent impacts. Organic fertilizers are primarily derived from solid organic waste generated by anthropocentric activities including urban (daily-life, municipal wastes and sludge), agricultural (manure, straw), and industrial (like food industrial waste etc.) processes. In order to produce organic fertilizer, the organic solid wastes are generally treated by aerobic composting or anaerobic digestion. Currently, microplastics have been widely detected in the raw materials and products of organic fertilizer. During the process of converting organic solid waste materials into fertilizer, intense oxidation, hydrolysis, and microbial actions significantly alter the physical, chemical, and surface biofilm properties of the plastics. After the organic fertilizer application, the abundances of microplastics significantly increased in the soil. Additionally, the degradation of these microplastics often promotes the adsorption of organic pollutants and affects their retention time in the soil. These microplastics, covered by biofilms, also significantly alter soil ecology due to the unique properties of the biofilm. Furthermore, the biofilms also play a role in the degradation of microplastics in the soil environment. This review offers a new perspective on the soil environmental processes involving microplastics from organic fertilizer sources and highlights the challenges associated with further research on organic fertilizers and microplastics.

Biodiversity and core microbiota of key-stone ecological clusters regulate compost maturity during cow-dung-driven composting

The primary objectives of this study were to explore the community-level succession of bacteria, fungi, and protists during cow-dung-driven composting and to elucidate the contribution of the biodiversity and core microbiota of key-stone microbial clusters on compost maturity. Herein, we used high-throughput sequencing, polytrophic ecological networks, and statistical models to visualize our hypothesis. The results showed significant differences in the richness, phylogenetic diversity, and community composition of bacteria, fungi, and eukaryotes at different composting stages. The ASV191 (Sphingobacterium), ASV2243 (Galibacter), ASV206 (Galibacter), and ASV62 (Firmicutes) were the core microbiota of key-stone bacterial clusters relating to compost maturity; And the ASV356 (Chytridiomycota), ASV470 (Basidiomycota), and ASV299 (Ciliophora) were the core microbiota of key-stone eukaryotic clusters relating to compost maturity based on the data of this study. Compared with the fungal taxa, the biodiversity and core microbiota of key-stone bacterial and eukaryotic clusters contributed more to compost maturity and could largely predict the change in the compost maturity. Structural equation modeling revealed that the biodiversity of total microbial communities and the biodiversity and core microbiota of the key-stone microbial clusters in the compost directly and indirectly regulated compost maturity by influencing nutrient availability (e.g., NH4+-N and NO3--N), hemicellulose, humic acid content, and fulvic acid content, respectively. These results contribute to our understanding of the biodiversity and core microbiota of key-stone microbial clusters in compost to improve the performance and efficiency of cow-dung-driven composting.

Ore improver additions alter livestock manure compost ecosystem C:N:P stoichiometry

Deciphering the pivotal components of nutrient metabolism in compost is of paramount importance. To this end, ecoenzymatic stoichiometry, enzyme vector modeling, and statistical analysis were employed to explore the impact of exogenous ore improver on nutrient changes throughout the livestock composting process. The total phosphorus increased from 12.86 to 18.72 g kg-1, accompanied by a marked neutralized pH with ore improver, resulting in the Carbon-, nitrogen-, and phosphorus-related enzyme activities decreases. However, the potential C:P and N:P acquisition activities represented by ln(βG + CB): ln(ALP) and ln(NAG): ln(ALP), were increased with ore improver addition. Based on the ecoenzymatic stoiometry theory, these changes reflect a decreasing trend in the relative P/N limitation, with pH and total phosphorus as the decisive factors. Our study showed that the practical employment of eco stoichiometry could benefit the manure composting process. Moreover, we should also consider the ecological effects from pH for the waste material utilization in sustainable agriculture.

Contact parameters calibration of mixtures in different aerobic composting period: Focusing on establishment of particle model and its flow properties

In order to calibrate the contact parameters, particle models for mixtures of each period were established by simulation of repose angle using combined models in EDEM software, and then the flow properties of mixtures in different aerobic composting periods were clarified. Results showed that compared with the six-sphere model, the use of the double-sphere model to represent the compost mixtures of each period was not only closer to the ellipsoid of the actual particles but also simplified the calculation process. The contact parameters that mostly affected the repose angle were Poisson's ratio and shear modulus of mixture in the mesophilic period and JKR surface energy in thermophilic and cooling periods. The relative errors between the simulated repose angle using the optimal parameter combination and the actual measured value were less than 2.5% indicating the reliability of the regression models at each period representing the relationship among the repose angle and significant contact parameters. In addition, the flow properties of mixtures at the mesophilic period were better than those at the thermophilic and the cooling period of its smaller repose angle, the larger mass transformation, and the smaller Ek max value. Meanwhile, mixtures in thermophilic and cooling periods had similar flow properties. Hence, these could provide information for the further application of simulation to optimize the composting process (e.g., stirring frequency and ventilation time) to promote compost maturity.

Effects of adding lignocellulose-degrading microbial agents and biochar on nitrogen metabolism and microbial community succession during pig manure composting

This study assessed the influence of the additions of lignocellulose-degrading microbial agents and biochar on nitrogen (N) metabolism and microbial community succession during pig manure composting. Four treatments were established: CK (without additives), M (lignocellulose-degrading microbial agents), BC (biochar), and MBC (lignocellulose-degrading microbial agents and biochar). The results revealed that all treatments with additives decreased N loss compared with CK. In particular, the concentrations of total N and NO3--N were the highest in M, which were 21.87% and 188.67% higher than CK, respectively. Meanwhile, the abundance of denitrifying bacteria Flavobacterium, Enterobacter, and Devosia reduced with additives. The roles of Anseongella (nitrifying bacterium) and Nitrosomonas (ammonia-oxidizing bacterium) in NO3--N transformation were enhanced in M and BC, respectively. N metabolism pathway prediction indicated that lignocellulose-degrading microbial agents addition could enhance N retention effectively mainly by inhibiting denitrification. The addition of biochar enhanced oxidation of NH4+-N to NO2--N and N fixation, as well as inhibited denitrification. These results revealed that the addition of lignocellulose-degrading microbial agents individually was more conducive to improve N retention in pig manure compost.

Fine particles removal of pyrolysis gasification flue gas from rural domestic waste: Laboratory research, molecular dynamics simulation, and applications

Chinese rural domestic waste has increased considerably with the modernization of agriculture and urbanization. Pyrolysis gasification is a common high-temperature waste treatment method. However, this method is usually accompanied by a large amount of particle emission. In this study, a rural domestic waste pyrolysis gasification station in Gansu Province, Northwest China, was selected for research. The particle emission characteristics of this station were analyzed, and the results showed that the original particle removal technologies were inefficient in fine particles. Hence, a new method of fine particle treatment, i.e., Cloud-Air-Purifying (CAP) technology, was explored herein. In CAP, fine particles grow in size via heterogeneous condensation in a supersaturated water vapor environment and are then collected efficiently using a supergravity field. A laboratory-scale pyrolysis gasifier and CAP equipment were built. Moreover, the CAP removal efficiency for particles generated from four typical rural domestic waste categories was studied. The results showed that CAP technology considerably increased the efficiency of fine particle removal. However, the removal efficiency for particles released owing to the incineration of wood was only ∼75%. This was because the tar substances formed during wood pyrolysis were attached to the surface of escaping particles, which led to a decrease in their hydrophilicity and particle condensation growth. To address this issue, the improvement in particle hydrophilicity using different surfactants was studied via molecular dynamic simulations. When the increase in water molecule adsorption, surface polarity, and the solid-liquid interaction energy for different surfactants were compared, alkylphenol ethoxylate (OP10) proved to be the most effective surfactant. Finally, the improved CAP technology combined with OP10 was applied to the on-site pyrolysis gasification flue gas treatment. Long term monitoring of the proposed technology revealed that particle removal efficiency remained >94%, exhibiting excellent fine particle removal. The successful application of the proposed technology demonstrates its potential for further application.