Statistical analysis for the quality assessment of digestates from separately collected organic fraction of municipal solid waste (OFMSW) and agro-industrial feedstock. Should input feedstock to anaerobic digestion determine the legal status of digestate?

Short term effects of digestate and composted digestate on soil health and crop yield: Implications for sustainable biowaste management in the bioenergy sector

Composting mitigates environmental risks associated with using solid digestate as fertilizer. However, evidence is lacking on benefits of using composted digestate as fertilizer in enhancing soil health and increasing agronomic yield compared to non-composted digestate (hereafter, digestate). A field study was conducted consisting of digestate, composted digestate, co-composted digestate with biogas feedstocks (corn [Zea mays L.] silage, poultry litter, corn silage + poultry litter or food processing by-product), inorganic nitrogen fertilizer, and control (no treatment applied) on soil microbial biomass, enzyme activities (EA), soil organic carbon (SOC), bioavailable P (P), total nitrogen (TN), soil health index (SHI), and sunflower (Helianthus annuus L.) yield. The Partial Least Square Path Model (PLS-PM) was used to predict: 1) nutrient cycling in response to changes in microbial growth and EA and 2) agronomic yield in response to SHI and soil nutrients dynamics. Composted digestate had equivalent soil health benefits with most of co-composted materials and digestate, albeit agronomic yield was greatest with composted digestate, which was 40 % and 100 % greater than with inorganic nitrogen fertilizer and digestate, respectively, indicating composted digestate's potential to replace the synthetic N fertilizer. Moreover, composts from a sole digestate, rather than the ones from co-composted with fresh feedsstocks, can be promising organic amendments and fertilizers for growing sunflower. The PLS-PM model identified that triggered microbial biomass growth and EA, following digestate and composted digestate applications, catalyzed organic matter decomposition, resulting in enhanced nutrients contents and soil health. However, the model revealed that improved SHI did not predict agronomic yield, as opposed to P and TN, suggesting agronomic performance may have been more sensitive to changes in specific soil nutrients status than the overall soil health condition. We conclude that the benefits of composted digestate as fertilizer hint the significance of digestate valorization via post-digestate composting and compost utilization for sustainability of the bioenergy sector.

Cobalt oxide nanoparticles as a new strategy for enhancing methane production from anaerobic digestion of noxious aquatic weeds

This study investigated the effect of cobalt oxide nanoparticles (Co₃O₄-NPs) supplementation on anaerobic microbial population changes and anaerobic digestion (AD) performance and production. Co₃O₄-NPs (3 mg/L) showed the maximum enhancement of biogas yield over the cow dung (CD) as control and the co-digestion process of CD with water hyacinth (WH) by 58.9 and 27.2 %, respectively. Furthermore, methane (CH₄) yield was enhanced by 89.96 and 43.4 % over CD and co-digestion processes, respectively. Additionally, the microbiological assessment analysis using VIT® gene probe technology showed that Co₃O₄-NPs enhance the viability of total bacterial cells by 9 %. The techno-economic analysis reflects the revenue of this strategy on the highest net energy content of biogas, which was achieved with 3 mg/L Co₃O₄-NPs and was 428.05 kWh with a net profit of 67.66 USD/m³ of the substrate. Therefore, nanoparticle supplementation to the AD process can be considered a promising approach to enhance biogas and CH₄.

Recent advances in biogas production using Agro-Industrial Waste: A comprehensive review outlook of Techno-Economic analysis

Agrowaste sources can be utilized to produce biogas by anaerobic digestion reaction. Fossil fuels have damaged the environment, while the biogas rectifies the issues related to the environment and climate change problems. Techno-economic analysis of biogas production is followed by nutrient recycling, reducing the greenhouse gas level, biorefinery purpose, and global warming effect. In addition, biogas production is mediated by different metabolic reactions, the usage of different microorganisms, purification process, upgrading process and removal of CO₂ from the gas mixture techniques. This review focuses on pre-treatment, usage of waste, production methods and application besides summarizing recent advancements in biogas production. Economical, technical, environmental properties and factors affecting biogas production as well as the future perspective of bioenergy are highlighted in the review. Among all agro-industrial wastes, sugarcane straw produced 94% of the biogas. In the future, to overcome all the problems related to biogas production and modify the production process.

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.

Hydrochar and hydrochar co-compost from OFMSW digestate for soil application: 2. agro-environmental properties

The work concerns the study of the hydrochar from digestate and hydrochar co-compost characterization as amendments. The processes for hydrochar and co-compost production were described in Part 1 of this work (Scrinzi et al., 2022). The amendment properties of hydrochar (produced at 180-200-220 °C for 3 h) and co-composts (25%, 50%, and 75% hydrochar percentage of digestate substitution) were assessed by phytotoxicity, plant growth bioassay, and soil effect. Different seeds species (Lepidium sativum, Cucumis sativus, and Sorghum bicolor sp.) were dosed at increased concentrations using both wet raw amendments and their water extracts. The chemical characterization showed phytotoxic compounds content depending on both the initial feedstock (digestate) and the HTC process; at the same time, the analysis highlighted the reduction of these compounds by composting (organic acid, polyphenols, salt concentration). The dose-response was analyzed by the Cedergreen-Streibig-Ritz model and the half-maximal effective concentration (EC50) was calculated based on this equation. The soil properties and GHG emissions measurements (CH₄, CO₂, N₂O, and NH₃) highlighted the effect on N dynamics and on soil respiration induced by substrates. The HC200 soil application determined a significant impact on CO₂ and N₂O emission and NH₃ volatilization (10.82 mol CO₂/m²; 51.45 mmol N₂O/m²; 112 mol NH₃/m²) and a significant reduction of total N and TOC (46% of TKN and 49% of TOC). The co-compost (75%) showed specific effects after soil application compared to other samples an increase of available P (48%), a greater content of nitrogen (1626 mg/kg dry basis), and a reduction of organic carbon (17%). Our results demonstrate the good quality of co-compost and at the same time the validity of this post-treatment for addressing many issues related to hydrochar use in the soil as an amendment, confirming the suitability of HTC process integration for digestate treatment in anaerobic digestion plants.

Physical, chemical, and microbial contaminants in food waste management for soil application: A review

Currently, 1.3 billion tonnes of food are thrown away each year, most of which are incinerated or landfilled causing large environmental, social, and economic issues. Therefore, the utilisation of food waste as biofertilisers, such as composts and digestates, is a solution to reduce the problems created by incineration and landfilling whilst simultaneously amending soils. The improper disposal of food wastes and bulking materials can contribute to high levels of contaminants within the end-product. Moreover, the food waste and bulking materials, themselves, may contain trace amounts of contaminants. These contaminants tend to have long half-lives, are easily mobile within soil and plants, can accumulate within the food supply chain, and have moderate to high levels of toxicity. This review aims to examine the current and emerging contaminants of high concern that impact the quality of food-waste fertilisers. The paper presents the volume of current and emerging contaminants of plastics, other physical (particulate) contaminants, heavy metals, pesticides, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), per- and polyfluoroalkyl substances (PFAS), and pathogens within food-waste composts and digestates. Due to the large extent of organic chemical contaminants and the unknown level of toxicity and persistence, the risk assessment of organic chemical contaminants in the food-supply chain remains largely unknown. This study has presented available data from literature of various contaminants found in food waste, and composts and digestates derived from food waste, and evaluated the data with current regulations globally. Overall, to reduce contaminants in composts and digestates, more studies are required on the implementation of proper disposal separation, effective composting and digestion practices, increased screening of physical contaminants, development of compostable plastics, and increased regulatory policies on emerging, problematic contaminants. Moreover, examination of emerging contaminants in food-waste composts and digestates is needed to ensure food security and reduce future human-health risks.

Molecular diversity of liquid digestate from anaerobic digestion plants for biogenic waste

The treatment and valorization of liquid digestate (ADLD) after anaerobic digestion of biogenic waste are challenging. This study used ultra-high resolution mass spectrometry to determine the molecular characteristics of ADLD collected from different full-scale plants for food waste treatment. The results indicated that there were regular differences in the dissolved organic matter (DOM) indicators among the samples from dry and wet anaerobic processes. ADLD DOM had higher H/C and O/C, and contained more easily degradable proteins. In addition, sCOD and pH were the drivers of the molecular distribution of ADLD common compounds. The same common compounds were present in the ADLD from different anaerobic digestion plants. They had a significant correlation with physicochemical characteristics. The compounds relating to plant hormones and nutrients as well as xenobiotics were both identified, suggesting that comprehensive considerations should be taken into account for the land application of ADLD.

Anaerobic digestate management, environmental impacts, and techno-economic challenges

Digestate is a nutrient-rich by-product from organic waste anaerobic digestion but can contribute to nutrient pollution without comprehensive management strategies. Some nutrient pollution impacts include harmful algal blooms, hypoxia, and eutrophication. This contribution explores current productive uses of digestate by analyzing its feedstocks, processing technologies, economics, product quality, impurities, incentive policies, and regulations. The analyzed studies found that feedstock, processing technology, and process operating conditions highly influence the digestate product characteristics. Also, incentive policies and regulations for managing organic waste by anaerobic digestion and producing digestate as a valuable product promote economic benefits. However, there are not many governmental and industry-led quality assurance certification systems for supporting commercializing digestate products. The sustainable and safe use of digestate in different applications needs further development of technologies and processes. Also, incentives for digestate use, quality regulation, and social awareness are essential to promote digestate product commercialization as part of the organic waste circular economy paradigm. Therefore, future studies about circular business models and standardized international regulations for digestate products are needed.

The Current Status and Future Potential of Biogas Production from Canada’s Organic Fraction Municipal Solid Waste

With the implementation of new policies supporting renewable natural gas production from organic wastes, Canada began replacing traditional disposal methods with highly integrated biogas production strategies. Herein, data from published papers, Canadian Biogas Association, Canada’s national statistical agency, and energy companies’ websites were gathered to gain insight into the current status of anaerobic digestion plants in recovering energy and resource from organic wastes. The availability of materials prepared for recycling by companies and local waste management organizations and existing infrastructures for municipal solid waste management were examined. Governmental incentives and discouragements in Canada and world anaerobic digestion leaders regarding organic fraction municipal solid waste management were comprehensively reviewed to identify the opportunities for developing large-scale anaerobic digestion in Canada. A range of anaerobic digestion facilities, including water resource recovery facilities, standalone digesters, and on-farm digesters throughout Ontario, were compared in terms of digestion type, digester volume, feedstock (s), and electricity capacity to better understand the current role of biogas plants in this province. Finally, technology perspectives, solutions, and roadmaps were discussed to shape the future in terms of organic fraction municipal solid waste management. The findings suggested that the biogas industry growth in Canada relies on provincial energy and waste management policies, advanced technologies for diverting organic waste from landfills, improving biogas yield using existing pretreatment methods, and educating farmers regarding digester operations.

Agricultural application of digestates derived from agricultural and municipal organic wastes: a health risk-assessment for heavy metals

A Human-health Risk Assessment was performed for an agricultural site in North-East Italy undergone digestate application to (i) check the compliance of digestate land spreading with the Italian and European regulations on contaminated agricultural soils and (ii) evaluate how resulting risk estimations can be influenced by the applied modeling assumptions. The assessment estimated the risk related to adults and children intake of Heavy Metals (HM) contained in crops at concentrations estimated by a soil-plant transfer model based on the substance-specific soil-water partition coefficients. Eight different scenarios were investigated, according to different digestate type (from biowaste and agro-industrial byproducts), digestate application techniques and soil background concentrations. Non-risky situations resulted in all scenarios involving digestate application. The totality of calculated non-carcinogenic Hazard Indexes (HI) and carcinogenic total risk (RTOTC) resulted below 0.02 and 3E10^-9, respectively. In contrast with the definition, non-carcinogenic risks were associated with the considered soil background concentrations, with HI s up to 1.7 for child receptors, while carcinogenic risk was calculated below the concern threshold (i.e., RTOTC < 10^-5). Accordingly, this study highlighted (i) non-concerning situations related with lawful application of digestates and (ii) the need to improve the modeling of bioavailability to plant of HMs background content of soil.

Processes and prospects on valorizing solid waste for the production of valuable products employing bio-routes: A systematic review

Humanity is struggling against a major problem for a proper management of generated municipal solid waste. The collected waste causes natural issues like uncontrollable emission of greenhouse gases and others. Even though, escalation of waste results in minimizing the areas accessible for disposing the waste. Creating awareness in the society to use organic products like biofuels, biofertilizers and biogas is a need of an hour. Biochemical processes such as composting, vermicomposting, anaerobic digestion, and landfilling play important role in valorizing biomass and solid waste for production of biofuels, biosurfactants and biopolymer. This paper covers the details of biomass and solid waste characteristics and its composition. It is also focused to provide updated information about reutilization of biomass for value creation. Technologies and products obtained through bio-routes are discussed in current review paper together with the integrated system of solid waste management. It also covers challenges, innovations and perspectives in this field.

Post-digestate composting benefits and the role of enzyme activity to predict trace element immobilization and compost maturity

The current study evaluated the quality of agricultural waste digestate by composting or co-composting with biogas feedstock (maize silage, food processing waste, or poultry litter). Temperature, phytotoxicity, C/N ratio, water extractable trace elements, and 14 enzyme activities were monitored. Temperature dropped earlier in digestate and maize silage co-composting pile, reducing time to maturity by 20 days. Composting and co-composting reduced phytotoxicity and C/N ratio, but increased immobilization of Al, Ba, Fe, Zn, and Mn at least by 40% in all piles. All the enzyme activities, except arylsulfatase and α-glucosidase, increased at the maturity phase and negatively correlated with organic matter content and most of trace elements. Post-digestate composting or co-composting with biogas feedstock is a promising strategy to improve digestate quality for fertilizer use, and selected enzyme activities can be indicators of compost maturity and immobilization of trace elements.

Industrial-Scale Hydrothermal Carbonization of Agro-Industrial Digested Sludge: Filterability Enhancement and Phosphorus Recovery

Hydrothermal carbonization (HTC) provides an attractive alternative method for the treatment of high-moisture waste and, in particular, digested sludge. HTC could reduce the costs and environmental risks associated with sludge handling and management. Although it is recognized that the dewaterability of hydrochars produced from digested sludge, even at mild temperatures (180–190 °C), is highly improved with respect to the starting material, the filterability of HTC slurries for the recovery of the solid material (hydrochar) still represents a challenge. This study presents the results of an investigation into the filterability of agro-industrial digested sludge HTC slurries produced by a C-700 CarboremTM HTC industrial-scale plant. The filterability of HTC slurries, produced at 190 °C for 1 h, with the use of acid solutions of hydrochloric acid, sulfuric acid or citric acids, was investigated by using a semi-industrial filter press. The use of sulfuric acid or citric acid solutions, in particular, significantly improved the filterability of HTC slurries, reducing the time of filtration and residual moisture content. The acid treatment also promoted the migration of heavy metals and phosphorus (P) in the HTC filtrate solution. This study demonstrates that P can be recovered via the precipitation of struvite in high yields, recovering up to 85 wt% by mass of its initial P content.

A review on nitrogen dynamics and mitigation strategies of food waste digestate composting

Food waste digestate is a by-product of the anaerobic digestion of food waste. Presence of high ammonium nitrogen content significantly increase the nitrogen loss upon direct application on soil or by conventional composting. In this review, a comprehensive discussion regarding the effective management of food waste digestate is outlined, in which global food waste digestate production, characteristics, and composting are discussed. The nitrogen dynamics cycle considering high ammonium nitrogen content in the digestate is also evaluated, including ammonification, nitrification, denitrification, and other possible mechanisms based on the current literature. Mitigation strategies for reducing nitrogen loss via C/N ratio adjustment and the addition of physical, chemical, and microbial amendments were evaluated and estimated for 15 countries based on the available data on food waste anaerobic digestion plants. Reduced nitrogen loss and high quality compost could be produced from food waste digestate by adapting mitigation strategies.

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

The anaerobic digestion is a well-established process for the treatment of organic solid waste, pursuing its conversion into a methane rich gas destined to energy generation. Research has largely dealt with the enhancement of the overall bioconversion yields, providing several strategies to maximize the production of bio-methane from the anaerobic processing of a wide variety of substrates. Nevertheless, the valorization of the process effluents should be pursued as well, especially if the anaerobic digestion is regarded in the light of the circular economy principles. Aim of this work is in identifying the state of the art of the strategies to manage the digestate from the anaerobic processing of the organic fractions of municipal solid waste. Conventional approaches are described and novel solutions are figured out in order to highlight their potential scale up as well as to address future research perspectives.

Potential of Sustainable Concept for Handling Organic Waste in Tunisia

Nowadays, Tunisia is seeking to implement cost-efficient and sustainable solutions in relation to the treatment of organic waste which, at up to 65%, makes up the largest proportion of total waste generated in the country. Therefore, an efficient tool for decision makers is needed to provide a clear approach about the potential of organic waste as well as the treatment concept, which can be adapted based on technical requirements and local conditions. Results revealed that there is a high variation in terms of the nature of the collected biowaste, which affects the selection of the adopted bioprocess for each geographical zone of the study area. Three main categories of biowaste are produced along the coastline of Tunisia: food waste (FW) (102.543 t/a); green waste (GW) (1.326.930 t/a); and cattle manure (CM) (1.548.350 t/a). Based on the results of similar projects and laboratory-scale research work, anaerobic and aerobic digestion were examined. Regarding aerobic digestion, the monitoring of several physicochemical parameters ascertained that the co-composting of FW and GW at different ratios (GW: FW = 100:0, 75:25, 50:50, and 25:75) allowed the production of a stable and mature compost. A highly qualified end-product was generated from each trial categorized as a finished compost of class V with reference to German Standards of compost. Regarding the anaerobic process, different feedstock mixtures (FW:CM = 0:1, 1:1, 2:1, and 3:1) were prepared to feed semi-continuous anaerobic reactors. However, a significant improvement in the process development was recorded for digesters including a higher fraction of FW, which produced 0.846 LN/kg VSin as the maximum biogas production. Therefore, biological treatments of food waste and different co-substrates seems to be a suitable technique for Tunisia in terms of waste management, environmental, and energy aspects. However, the evaluation of the efficiency of the proposed biological treatments was also verified by a draw-up of a technical and economic feasibility analysis. Although the cost–benefit estimations proved that the profits from both the compost and biogas plants would be very modest, the feasibility of such sustainable projects should not only be evaluated on an economic basis, but also by taking into account socio-environmental considerations including decreasing environmental threats, providing work opportunities, increasing incomes, stimulating public awareness as well as reducing the operating costs linked to landfilling.

Anaerobic Digestion Performance: Separate Collected vs. Mechanical Segregated Organic Fractions of Municipal Solid Waste as Feedstock

The replacement of fossil fuel with renewable energy sources seems as though it will be crucial in the future. On the other hand, waste generation increases year by year. Thus, waste-to-energy technologies fit in with the actual trends, such as the circular economy. The crucial type of generated waste is municipal solid waste, which is in the research area. Regarding the organic fraction of municipal solid waste (OFMSW), anaerobic digestion (AD) allows the recovery of biogas and energy. Furthermore, if it is supported by source segregation, it should allow the recovery of material as fertilizer. The AD process performance (biogas yield and stability) comparison of source-segregated OFMSW (ss-OFMWS) and mechanically sorted OFMSW (ms-OFMSW) as feedstocks was performed in full-scale conditions. The daily biogas volume and methane content were measured to assess AD efficiency. To verify the process stability, the volatile fatty acid (VFA) content, pH value, acidity, alkalinity, and dry matter were determined. The obtained biogas yield per ton was slightly higher in the case of ss-OFMSW (111.1 m3/ton), compared to ms-OFMSW (105.3 m3/ton), together with a higher methane concentration: 58–60% and 51–53%, respectively, and followed by a higher electricity production capacity of almost 700 MWh for ss-OFMSW digestion. The obtained VFA concentrations, at levels around 1.1 g/kg, pH values (slightly above 8.0), acidity, and alkalinity indicate the possibilities of the digester feeding and no-risk exploitation of either as feedstock.

Bromatological, Proximate and Ultimate Analysis of OFMSW for Different Seasons and Collection Systems

In order to study the quality of organic fractions of municipal solid waste (OFMSW), five different municipalities in Tuscany were chosen for sampling according to the peculiarities of their collection systems. The five collection systems selected were sampled four times: during March, June, September and December, for a total of 20 picking analyses. In addition, emphasis was also given to the study of the variability of OFMSW composition related to ultimate, proximate and bromatological analyses. Road container collection systems proved to have a higher content of non-compostable and undesirable fractions (22%±1%) when compared to door-to-door systems (6% ± 1%). During months with lower temperature (March and December), the garden waste content in the OFMSW was negligible, with kitchen waste prevailing. This altered the physical chemical composition of OFMSW, which had a lower lignin content and higher methane production in the months with lower temperatures (272 ± 23 NLCH4 kgTVS−1) compared to June and September (238 ± 14 NLCH4 kgTVS−1). In general, the Tuscan OFMSW had a higher dry matter content (42%) than observed in previous studies. In conclusion, the result could direct possible future operators of anaerobic digestion plants towards the choice of dry and semi-dry technologies.

Legal requirements for digestate as fertilizer in Austria and the European Union compared to actual technical parameters

Biogas is mainly discussed in the context of renewable energy, digestate is playing a minor role. However, in the upcoming EU Fertilizer Product Regulation digestate as eligible component material is in line with the circular economy action plan. This article discusses the quality of raw digestate based on analysis data from Austrian biogas plants regarding to the current Austrian as well as the European fertilizer regulatory framework. Therefore, a survey among Austrian biogas plant operators for results of digestate analysis and substrate input and energy output is used. The results show, that the legislative framework applies to a minimum of 1.5 million tonnes of digestate. Austrian digestate is of high quality with regards to the nutrient content, required limit values for heavy metals and is also safe with respect to their hygienic parameters. The following European fertilizer product function categories are available for international trade of digestate: "organic soil improver", "growing medium", and "organic, non-microbial plant biostimulant". Establishing legal criteria determining End-of-Waste and subsequently the product status for digestate is another important step in the European circular economy.

Fertilizing potential and CO2 emissions following the utilization of fresh and composted food-waste anaerobic digestates

Wet and dry-batch anaerobic digestion, and composting are common technologies in food waste (FW) management, resulting in different outputs. However, the effects of composting on carbon dioxide (CO₂) emissions, nitrogen (N) and phosphorus (P) fertilizing capacity in view of closing nutrient cycle are still poorly investigated. In this work, two FW anaerobic digestates from the wet (D₁) and dry-batch process (D₂), and their respective composts (C₁ and C₂) were tested in a soil incubation (84 days at 25 °C) to assess CO₂ emissions in comparison with a mixed (animal slurry/energy crop) digestate (BD) and a reference municipal solid waste compost (MSWC). The same products were also tested for the relative P efficiency (RPE) in soil, in comparison with a chemical-P source (30 mg P kg^-1). Lastly, the apparent recovery fraction of N (N-ARF) from the five organic products was determined in a pot test with ryegrass (84 days; 300 kg available N ha^-1), compared to a chemical fertilizer (NPK). Composting strongly reduced net-CO₂ emissions compared to the two digestates (625 vs. 2850 mg CO₂ kg^-1 soil). Oppositely, composting very modestly influenced RPE that ranged around 100-90% in D₁ and C₁, and ≈30% in D₂ and C₂. Moreover, composting did not significantly reduce N-ARF that ranked in descending order as follows: NPK (77.5%) > D₁ = BD (17.7%) ≥ C₁ (14.7%) > MSWC (3.6%) > D₂ (1.2%) > C₂ (-3.1%). Composting was shown a reliable strategy for FW digestate management, as it reduces potential CO₂ emission without affecting these products' N- and P-fertilizing capacity.

Energy and Nutrients’ Recovery in Anaerobic Digestion of Agricultural Biomass: An Italian Perspective for Future Applications

Anaerobic digestion (AD) is the most adopted biotechnology for the valorization of agricultural biomass into valuable products like biogas and digestate, a renewable fertilizer. This paper illustrates in the first part the actual situation of the anaerobic digestion sector in Italy, including the number of plants, their geographical distribution, the installed power and the typical feedstock used. In the second part, a future perspective, independent of the actual incentive scheme, is presented. It emerged that Italy is the second European country for the number of anaerobic digestion plants with more than 1500 units for a total electricity production of about 1400 MWel. More than 60% of them are in the range of 200 kW–1 MW installed power. Almost 70% of the plants are located in the northern part of the Country where intensive agriculture and husbandry are applied. Most of the plants are now using energy crops in the feedstock. The future perspectives of the biogas sector in Italy will necessarily consider a shift from power generation to biomethane production, and an enlargement of the portfolio of possible feedstocks, the recovery of nutrients from digestate in a concentrated form, and the expansion of the AD sector to southern regions. Power to gas and biobased products will complete the future scenario.