The valorization of the anaerobic digestate from the organic fractions of municipal solid waste: Challenges and perspectives

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.

Integration of Digestate-Derived Biochar into the Anaerobic Digestion Process through Circular Economic and Environmental Approaches-A Review

The growing energy consumption and the need for a circular economy have driven considerable interest in the anaerobic digestion (AD) of organic waste, offering potential solutions through biogas and digestate production. AD processes not only have the capability to reduce greenhouse gas emissions but also contribute to the production of renewable methane. This comprehensive review aims to consolidate prior research on AD involving different feedstocks. The principles of AD are explored and discussed, including both chemical and biological pathways and the microorganisms involved at each stage. Additionally, key variables influencing system performance, such as temperature, pH, and C/N ratio are also discussed. Various pretreatment strategies applied to enhance biogas generation from organic waste in AD are also reviewed. Furthermore, this review examines the conversion of generated digestate into biochar through pyrolysis and its utilization to improve AD performance. The addition of biochar has demonstrated its efficacy in enhancing metabolic processes, microorganisms (activity and community), and buffering capacity, facilitating Direct Interspecies Electron Transfer (DIET), and boosting CH4 production. Biochar also exhibits the ability to capture undesirable components, including CO2, H2S, NH3, and siloxanes. The integration of digestate-derived biochar into the circular economy framework emerges as a vital role in closing the material flow loop. Additionally, the review discusses the environmental benefits derived from coupling AD with pyrolysis processes, drawing on life cycle assessment investigations. Techno-economic assessment (TEA) studies of the integrated processes are also discussed, with an acknowledgment of the need for further TEA to validate the viability of integrating the biochar industry. Furthermore, this survey examines the techno-economic and environmental impacts of biochar production itself and its potential application in AD for biogas generation, aiming to establish a more cost-effective and sustainable integrated system.

A Low-Cost Ecofriendly Oxidation Process to Manufacture High-Performance Polymeric Biosurfactants Derived from Municipal Biowaste

Biosurfactants account for about 12% of the global value of the surfactant market, which is currently dominated by synthetic surfactants obtained from fossil sources. Yet, the production of biosurfactants from renewable feedstock is bound to increase, driven by the increasing pressure from both society and governments for chemistry-based industries to become more ecofriendly and economically sustainable. A photo-chemical oxidation process is reported here, yielding new biosurfactants from urban biowaste in water that perform as a solvent and terminal oxidant reagent at room temperature without the addition of conventional oxidants and catalysts. Products with 200-500 kDa molecular weight are obtained. They lower the surface tension of water down to 34 mN/m at 0.5-2 g/L concentration. The estimated cost is rather low (0.1-1.5 EUR/kg), which is competitive with the cost of synthetic surfactants but much lower than the cost of the best-performing bacterial surfactants. For the implementation of the photo-chemical oxidation process at the industrial level, the results suggest that the new biosurfactants obtained in the present work may not reach the performance level of the best-performing bacterial surfactants capable of lowering the surface tension of water down to 28 mN/m. Yet, the biosurfactants produced by the photo-chemical process have a greater chance of being marketed on large scales.

Lutein Production by Halophilic Microalgae Using Anaerobic Digestate as the Substrate and Its Potential Application as a Biopesticide

Production of value-added products from waste anaerobic digestate is economically and environmentally important for sustainable development of industrial process and products. In this study halophilic microalgae, Chlorella vulgaris 92001, Chlorella vulgaris 50291, Chlorella vulgaris 10241 and Tetraselmis indica, were initially screened for lutein production using synthetic dairy digestate (DD), municipal digestate (MD) and poultry digestate (PD) as no-cost substrates. Screening and optimization of parameters, such as dilution, pH, MgCl2, NaCl, NaHCO3 and inoculum concentration for maximum lutein production were further performed employing statistically designed Plackett-Burman and response surface methodology. Cultivation of C. vulgaris 92001 in a split column photobioreactor under optimum culture condition showed increase in lutein production by 2.36-fold in batch mode. The influence of different hydraulic retention time (HRT) values of 150, 130, 100 and 90 h on lutein production was evaluated in continuous mode with the split column photobioreactor. Lutein produced using the synthetic poultry digestate showed good potential biopesticide activity against Spodoptera litura (fall armyworm). Overall, this study demonstrated bioprocess development to produce lutein using synthetic anaerobic digestate from marine algae and its potential application as a biopesticide.

Unveiling the microwave heating performance of biochar as microwave absorber for microwave-assisted pyrolysis technology

Microwave (MW) heating has gained significant attention in food industries and biomass-to-biofuels through pyrolysis over conventional heating. However, constraints for promoting MW heating related to the use of different MW absorbers are still a major concern that needs to be investigated. The present study was conducted to explore the MW heating performance of biochar as a low-cost MW absorber for performing pyrolysis. Experiments were performed on biochar under different biochar dosing (25 g, 37.5 g, 50 g), MW power (400 W, 700 W, 1000 W), and particle sizes (6 mm, 8 mm, 10 mm). Results showed that MW power and biochar dosing significantly impacted average heating rate (AHR) from 17.5 to 65.4 °C/min at 400 W and 1000 W at 50 g. AHR first increased, and then no significant changes were obtained, from 37.5 to 50 g. AHR was examined by full factorial design, with 94.6% fitting actual data with predicted data. The model suggested that the particle size of biochar influenced less on AHR. Furthermore, microwave absorption efficiency and biochar weight loss were investigated, and microwave absorption efficiency decreased as MW power increased, which means 17.16% of microwave absorption efficiency was achieved at 400 W rather than 700 W and 1000 W. Biochar weight loss estimated by employing mass-balance analysis, 2-10.4% change in biochar weight loss was obtained owing to higher heating rates at higher powers and biochar dosing.

Metformin and lamotrigine sorption on a digestate amended soil in presence of trace metal contamination

The antidiabetic drug metformin and antiepileptic drug lamotrigine are contaminants of emerging concern that have been detected in biowaste-derived amendments and in the environment, and their fate must be carefully studied. This work aimed to evaluate their sorption behaviour on soil upon digestate application. Experiments were conducted on soil and digestate-amended soil as a function of time to study kinetic processes, and at equilibrium also regarding the influence of trace metals (Pb, Ni, Cr, Co, Cu, Zn) at ratio pharmaceutical/metal 1/1, 1/10, and 1/100. Pharmaceutical desorption experiments were also conducted to assess their potential mobility to groundwater. Results revealed that digestate amendment increased metformin and lamotrigine adsorbed amounts by 210% and 240%, respectively, increasing organic matter content. Metformin adsorption kinetics were best described by Langmuir model and those of lamotrigine by Elovich and intraparticle diffusion models. Trace metals did not significantly affect the adsorption of metformin in amended soil while significantly decreased that of lamotrigine by 12-39%, with exception for Cu2+ that increased both pharmaceuticals adsorbed amounts by 5 - 8%. This study highlighted the influence of digestate amendment on pharmaceutical adsorption and fate in soil, which must be considered in the circular economy scenario of waste-to-resource.

Unlocking the potential of sugarcane leaf waste for sustainable methane production: Insights from microbial pre-hydrolysis and reactor optimization

Sugarcane leaf waste, a byproduct of the growing global sugar industry, challenges agricultural waste management. This study explores its potential for methane production via anaerobic digestion. A microbial pre-hydrolysis, using lignocellulose-degrading bacteria, enhanced soluble chemical oxygen demand at an optimal initial substrate concentration of 40 g-volatile solid/L. Comparative analysis with untreated and bioaugmented leaves revealed the pre-hydrolyzed leaves achieved the highest methane production rate (MPR) at 14.0 ± 0.5 mL-CH4/L·d, surpassing others by 1.47 and 1.67 times. Two continuous stirred tank reactors were employed to assess the optimal hydraulic retention time (HRT). Results showed a stable methane production with an HRT of 25 days, yielding high MPRs: 88.70 ± 0.63 mL-CH4/L·d from pre-hydrolyzed sugarcane leaves and 82.57 ± 1.22 mL-CH4/L·d from microbial consortium-augmented leaves. A 25-day HRT fosters high microbial diversity with Bacteroidota, Firmicutes, Chloroflexi, and Verrucomicrobiota dominance, indicating favorable conditions. Conversely, a 20-day HRT results in lower diversity due to unfavorable factors like low pH during organic overloading, leading to increased concentrations of volatile fatty acids and lactic acid, with Firmicutes as the predominant phylum. This study highlights sugarcane leaf waste's potential as a valuable resource for sustainable methane production.

A review on waste biomass-to-energy: integrated thermochemical and biochemical conversion for resource recovery

Integrating thermochemical–biochemical methods overcomes the single-path limits for bioenergy production. This synergy lowers costs and enhances energy sustainability, highlighting waste-to-energy's vital role in the circular economy transition.

Application of life cycle assessment to high quality-soil conditioner production from biowaste

The recent large-scale urbanization and industrialization resulted in an impressive growth of solid waste generation worldwide. Organic fraction generally constitutes a large fraction of municipal solid waste and its peculiar chemical properties open to various valorization strategies. On this purpose, life cycle assessment is applied to an innovative industrial system that processes 18 kt/y of agricultural and livestock waste into a high-quality soil conditioner. The high-quality soil conditioner production system consists of a series of processes, including anaerobic digestion and vermicomposting, allowing the generation of a peat-like material with high carbon content, porosity, and water-holding capacity. The presence of a photovoltaic plant and a cogeneration plant, fed with the biogas produced in the anaerobic digestion, makes the system entirely self-sufficient from the national grid and generating a surplus of electricity of 1177MWh/y. The high-quality soil conditioner showed better environmental performances in 15 out of 18 impact categories when compared to alternative scenarios. In particular, the high-quality soil conditioner and the related biowaste management resulted in a carbon saving of around 397 kg CO2 eq/ton compared with a scenario involving the employment of peat in place of the high-quality soil conditioner and a traditional biowaste management, and 165 kg CO2 eq/ton compared with a scenario where cogeneration is replaced by biomethane upgrading. This study demonstrates the possibility of using organic waste as an environmentally sustainable and renewable source for energy and carbon to soil conditioning.

Environmental and economic impacts of improper materials in the recycling of separated collected food waste through anaerobic digestion and composting

Separately collected food waste (SC-FW) is effectively recycled through industrial anaerobic digestion (AD) and composting. However, the presence of improper materials in SC-FW not only generates technical problems to AD and composting, but also lowers the quality of the outputs of the processes. As a consequence, improper materials found in SC-FW cause not negligible environmental and economic burdens. In this study, the environmental and economic impacts due to the presence of unsuitable materials in the SC-FW, determined through compositional analysis, were estimated through life cycle assessment and environmental life cycle costing approaches. Three different scenarios were analysed for both AD and composting processes: (i) the current situation (CS); (ii) the improved scenario (AS) with an amount of improper materials in SC-FW reduced to 3 % (w/w); (iii) the ideal scenario (IS) with the total absence of foreign materials. Environmental benefits were determined for the AS and IS scenarios in 17 of the 19 analysed impact categories. Considering the GHG emissions, higher savings were measured for AD in AS and IS scenarios (47 % and 79 %, respectively) than in CS scenario. Similarly, savings of -10.4 kg fossil oil eq/ton_SC-FW (AS) and - 17.1 kg fossil oil eq/ton_SC-FW (IS) for AD could be obtained with respect to the CS scenario. Greater economic benefits were calculated for AD (-76.4 €/ton_SC-FW) and composting (-52.2 €/ton_SC-FW) in the IS scenario. Savings up to € 2,249,780 and € 3,888,760 could have been obtained in 2022 by reducing to 3 % (w/w) and eliminating, respectively, the amount of improper materials in the SC-FW. The results of the compositional analyses of SC-FW allowed to identify the incorrect behaviours in FW source-sorting activity and to plan interventions to improve the current FW management system. The quantified environmental and economic benefits could further motivate citizens to correctly differentiate FW.

Valorization of Anaerobic-Fermentation Liquid Digestates-Membrane-Based Process Development

Complete valorization of various wastes and effluents, with significant organic content, remains a great challenge in the pursuit of a circular economy. The approach based on anaerobic fermentation, leading to valuable biogas production, has been broadly accepted and employed as an attractive processing scheme. However, despite notable research efforts, complete valorization of the digestates (involving recovery of nutrients/by-products and full recycling/reuse of treated water) requires additional work for sustainable process development. This study aims to make a contribution in this direction by demonstrating a systematic methodology for valorizing the liquid digestate. The proposed membrane-based processing scheme involves UF-membrane pretreatment of the liquid digestate (for sludge separation) and subsequent NF/RO membrane treatment for reuse/recycling of the permeate; the concentrate, enriched in "nutrients" (phosphate and ammonium compounds), can be utilized for soil fertilization, with further conditioning/processing. By performing targeted laboratory experiments and advanced simulations, the membrane-based process was developed to a relatively high technology-readiness level, including a pilot unit design/construction and preliminary testing with satisfactory results. Through pilot testing in industrial environment, further process development and optimization will be pursued, towards practical applications. The demonstrated methodology is also considered appropriate for systematic development of membrane-based processes to valorize/treat a variety of similar effluents.

Confirming the presence of selected antibiotics and steroids in Norwegian biogas digestate

Farms utilizing sewage sludge and manure in their agronomic plant production are recognized as potential hotspots for environmental release of antibiotics and the resulting promotion of antibiotic resistance. As part of the circular economy, the use of biogas digestates for soil fertilizing is steadily increasing, but their potential contribution to the spreading of pharmaceutical residues is largely unknown. Digestates can be produced from a variety of biowaste resources, including sewage sludge, manure, food waste, and fish ensilage. We developed a method for the detection of 17 antibiotics and 2 steroid hormones and applied the method to detect pharmaceutical residues in digestates from most municipal biogas plants in Norway, covering a variety of feedstocks. The detection frequency and measured levels were overall low for most compounds, except a few incidents which cause concern. Specifically, relatively high levels of amoxicillin, penicillin G, ciprofloxacin, and prednisolone were detected in different digestates. Further, ipronidazole was detected in four digestates, although no commercial pharmaceutical products containing ipronidazole are currently registered in Norway. A simplified risk assessment showed a high risk for soil microorganisms and indicates the tendency for antibiotic-resistant bacteria for penicillin G and amoxicillin. For prednisolone and ipronidazole; however, no toxicity data is available for reliable risk assessments.

Environmental implications, potential value, and future of food-waste anaerobic digestate management: A review

Globally, the valorisation of food waste into digestate through the process of anaerobic digestion is becoming increasingly popular. As a result, a large amount of food-waste digestate will need to be properly utilised. The utilisation of anaerobic digestion for fertiliser and alternative uses is essential to obtain a circular bioeconomy. The review aims to examine the environmental management of food-waste digestate, the value of digestate as a fertiliser and soil conditioner, and the emerging uses and improvements for post-anaerobic digestion reuse of digestate. Odour emissions, contaminants in food waste, emission and leaching of nutrients into the environment, and the regulations, policies, and voluntary initiatives of anaerobic digestion are evaluated in the review. Food-waste digestate can provide essential nutrients, carbon, and bio-stimulants to soils and increase yield. Recently, promising research has shown that digestates can be used in hydroponic systems and potentially replace the use of synthetic fertilisers. The integration of anaerobic digestion with emerging uses, such as extraction of value-added products, algae cultivation, biochar and hydrochar production, can further reduce inhibitory sources of digestate and provide additional economic opportunities for businesses. Moreover, the end-product digestate from these technologies can also be more suitable for use in soil application and hydroponic use.

Current Trends in Biological Valorization of Waste-Derived Biomass: The Critical Role of VFAs to Fuel A Biorefinery

The looming climate and energy crises, exacerbated by increased waste generation, are driving research and development of sustainable resource management systems. Research suggests that organic materials, such as food waste, grass, and manure, have potential for biotransformation into a range of products, including: high-value volatile fatty acids (VFAs); various carboxylic acids; bioenergy; and bioplastics. Valorizing these organic residues would additionally reduce the increasing burden on waste management systems. Here, we review the valorization potential of various sustainably sourced feedstocks, particularly food wastes and agricultural and animal residues. Such feedstocks are often micro-organism-rich and well-suited to mixed culture fermentations. Additionally, we touch on the technologies, mainly biological systems including anaerobic digestion, that are being developed for this purpose. In particular, we provide a synthesis of VFA recovery techniques, which remain a significant technological barrier. Furthermore, we highlight a range of challenges and opportunities which will continue to drive research and discovery within the field. Analysis of the literature reveals growing interest in the development of a circular bioeconomy, built upon a biorefinery framework, which utilizes biogenic VFAs for chemical, material, and energy applications.

Bioreactor-scale production of rhamnolipids from food waste digestate and its recirculation into anaerobic digestion for enhanced process performance: Creating closed-loop integrated biorefinery framework

Reaching industrially relevant productivities in bioprocesses and their efficient integration in the existing industrial infrastructure remain as important challenges in the circular economy to create closed loop sustainability framework. Using anaerobic digestion (AD) biorefinery as a model, the present work addressed these problems via integration of next-generation rhamnolipids production with AD. A high rhamnolipids concentration of 10.25 ± 1.34 g/L was obtained by fed-batch fermentation using food waste digestate as medium. Digestate-derived rhamnolipids contained Rha-C₁₀-C₁₀ and Rha-Rha-C₁₀-C₁₀ as the predominant congeners. These were used back in single-phase AD to demonstrate their effect on sludge solubilization and digestion efficiency. A dosage of 0.02 g rhamnolipids/g total suspended solids was found to be optimal which enhanced the hydrolysis-acidogenesis reactions to up to 27% over control. It however retarded methane production which could be overcome by the prolongation of digestion time. Finally, the value chain appreciation by the proposed process was demonstrated by a feasibility analysis.

Integrated system of anaerobic digestion and pyrolysis for valorization of agricultural and food waste towards circular bioeconomy: Review

Agricultural and food waste have become major issue affecting the environment and climate owing to growing population. However, such wastes have potential to produce renewable fuels which will help to meet energy demands. Numerous valorization pathways like anaerobic digestion, pyrolysis, composting and landfilling have been employed for treating such wastes. However, it requires integrated system that could utilize waste and promote circular bioeconomy. This review explores integration of anaerobic digestion and pyrolysis for treating agricultural and food waste. Proposed system examines the production of biochar and pyro-oil by pyrolysis of digestate. The use of this biochar for stabilizing anaerobic digestion process, biogas purification and soil amendment will promote the circular bioeconomy. Kinetic models and framework of techno-economic analysis of system were discussed and knowledge gaps have been identified for future research. This system will provide sustainable approach and offer carbon capture and storage in form of biochar in soil.

Biochar and hydrochar in the context of anaerobic digestion for a circular approach: An overview

Biochar and hydrochar are carbonaceous materials with valuable applications. They can be synthesized from a wide range of organic wastes, including digestate. Digestate is the byproduct of anaerobic digestion (AD), which is performed for bioenergy (biogas) production from organic residues. Through a thermochemical process, such as pyrolysis, gasification, and hydrothermal carbonization - HTC, digestate can be converted into biochar or hydrochar. The addition of either biochar or hydrochar in AD has been reported to improve biochemical reactions and microbial growth, increasing the buffer capacity, and facilitating direct interspecies electrons transfer (DIET), resulting in higher methane (CH₄) yields. Both biochar and hydrochar can adsorb undesired compounds present in biogas, such as carbon dioxide (CO₂), hydrogen sulfide (H₂S), ammonia (NH₃), and even siloxanes. However, an integrated understanding of biochar and hydrochar produced from digestate through their return to the AD process, as additives or as adsorbents for biogas purification, is yet to be attained to close the material flow loop in a circular economy model. Therefore, this overview aimed at addressing the integration of biochar and hydrochar production from digestate, their utilization as additives and effects on AD, and their potential to adsorb biogas contaminants. This integration is supported by life cycle assessment (LCA) studies, showing positive results when combining AD and the aforementioned thermochemical processes, although more LCA is still necessary. Techno-economic assessment (TEA) studies of the processes considered are also presented, and despite an expanding market of biochar and hydrochar, further TEA is required to verify the profitability of the proposed integration, given the specificities of each process design. Overall, the synthesis of biochar and hydrochar from digestate can contribute to improving the AD process, establishing a cyclic process that is in agreement with the circular economy concept.

Recent Advances on Innovative Materials from Biowaste Recycling for the Removal of Environmental Estrogens from Water and Soil

New technologies have been developed around the world to tackle current emergencies such as biowaste recycling, renewable energy production and reduction of environmental pollution. The thermochemical and biological conversions of waste biomass for bioenergy production release solid coproducts and byproducts, namely biochar (BC), hydrochar (HC) and digestate (DG), which can have important environmental and agricultural applications. Due to their physicochemical properties, these carbon-rich materials can behave as biosorbents of contaminants and be used for both wastewater treatment and soil remediation, representing a valid alternative to more expensive products and sophisticated strategies. The alkylphenols bisphenol A, octylphenol and nonylphenol possess estrogenic activity comparable to that of the human steroid hormones estrone, 17β-estradiol (and synthetic analog 17α-ethinyl estradiol) and estriol. Their ubiquitous presence in ecosystems poses a serious threat to wildlife and humans. Conventional wastewater treatment plants often fail to remove environmental estrogens (EEs). This review aims to focus attention on the urgent need to limit the presence of EEs in the environment through a modern and sustainable approach based on the use of recycled biowaste. Materials such as BC, HC and DG, the last being examined here for the first time as a biosorbent, appear appropriate for the removal of EEs both for their negligible cost and continuously improving performance and because their production contributes to solving other emergencies, such as virtuous management of organic waste, carbon sequestration, bioenergy production and implementation of the circular economy. Characterization of biosorbents, qualitative and quantitative aspects of the adsorption/desorption process and data modeling are examined.

Catalyst development for tar reduction in biomass gasification: Recent progress and the way forward

Biomass valorization via catalytic gasification is a potential technology for commercizalization to industrial scale. However, the generated tar during biomass valorization posing numerous problems to the overall reaction process. Thus, catalytic tar removal via reforming, cracking and allied processes was among the priority areas to researchers in the recent decades. This paper reports new updates on the areas of catalyst development for tar reduction. The catalyst survey include metallic and metal-promoted materials, nano-structured systems, mesoporous supports like zeolites and oxides, group IA and IIA compounds and natural catalysts based on dolomite, palygorskite, olivine, ilmenite, goethite and their modified derivatives. The influence of catalyst properties and parameters such as reaction conditions, catalyst preparation procedures and feedstock nature on the overall activity/selectivity/stability properties were simultaneously discussed. This paper not only cover to model compounds, but also explore to real biomass-derived tar for consistency. The area that require further investigation was identified in the last part of this review.

Assessment of the Possibilities for the Use of Selected Waste in Terms of Biogas Yield and Further Use of Its Digestate in Agriculture

The utilization of municipal waste and sewage sludge as a source of energy is technically very difficult due to high variability of their physical and chemical properties. The aim of this study was to evaluate the efficiency of the conversion of biomass contained in the whitewater fraction of municipal waste and sewage sludge by means of methanogenesis. The second objective was to assess the chemical composition of the digestate in the context of its use for fertilizer purposes. The whitewater fraction of municipal waste and sewage sludge was subjected to methanogenesis under static experimental conditions, according to DIM DIN 38414 methodology. The methanogenesis of concentrated substrates used in agricultural biogas plants was taken as a reference to evaluate the efficiency of the process. The organic fraction of the municipal waste was characterized by approximately 30% lower value of the soluble COD, with a comparable level of total COD compared to other materials. The total biogas yield, i.e., 404 dm³ per 1 kg of dry weight of the batch, was measured in the facility with sewage sludge. In COD value, this is 0.232 dm³·g O₂ COD. In the case of corn, these values were, respectively, 324 dm³ and 0.193, and for the organic sub-sieve fraction of municipal waste, 287 dm³·kg⁻¹ dw or 0.178 dm³·g O₂ COD, respectively. The type of fermented material did not affect the intensity of biogas production. The maximum level of biogas production occurred between the 13th and 15th day of the process. The digestate obtained in the process of methanogenesis of corn silage and the organic fraction of municipal waste was characterized by good parameters in terms of possible use for fertilization purposes.

Possibilities of Using Organic Waste after Biological and Physical Processing—An Overview

With a rapidly increasing amount of waste, waste management is an extremely important issue. Utilising processes such as combustion and biological processing significantly decreases the accumulation and volume of waste. Despite this, huge volumes of resulting waste that still need to be managed remain. This paper identifies various methods of processing organic waste, discussing both thermal and biological techniques for waste management. Additionally, this paper demonstrates that the end products remaining after processing waste are oftentimes functional for agricultural use. These materials are excellent byproducts used to produce various organic, mineral and organomineral fertilisers. For instance, it appears that the production of fertilisers is the most promising method of utilising fly ash that results from the combustion of waste. In order to minimise the environmental risk of polluting soil with heavy metals, waste, as well as ashes resulting from combustion, must meet the criteria for the limit of contaminants.

Hyperthermophilic Composting Technology for Organic Solid Waste Treatment: Recent Research Advances and Trends

Organic solid waste is considered a renewable resource that can be converted by various technologies into valuable products. Conventional thermophilic composting (TC), a well-studied and mature technology, can be applied to organic solid waste treatment to achieve waste reduction, mineralization, and humification simultaneously. However, poor efficiency, a long processing period, as well as low compost quality have always limited its wide application. In order to overcome these shortages, hyperthermophilic composting (HTC) has been recently put forward. This paper reviews the basic principle, process flow, operation parameters, research advances, and application status of HTC. Compared with the TC process, the shorter composting period and higher temperature and treatment efficiency, as well as more desirable compost quality, can be achieved during HTC by inoculating the waste with hyperthermophilic microbes. Additionally, HTC can reduce greenhouse gas emission, increase the removal rate of microplastics and antibiotic residues, and achieve in-situ remediation of heavy metal-polluted soils, which greatly improve its application potential for organic solid waste treatment. This paper also proposes the limitations and future prospects of HTC technology for a wider application. As a result, this review advances our understanding of the HTC process, which promotes its further investigation and application.