Carbon footprint of anaerobic digestion combined with ultrasonic post-treatment of agro-industrial organic residues

Modelling of technical, environmental, and economic evaluations of the effect of the organic loading rate in semi-continuous anaerobic digestion of pre-treated organic fraction municipal solid waste

The study concerned technical feasibility, economic profitability, and carbon footprint (CF) analysis of semi-continuous anaerobic digestion (sAD) of organic fraction of municipal solid waste (OFMSW). The research assessed the pre-treatment effect on sAD by varying organic loading rates (OLR) from 3.38 to 6.75 kgvs/m3d. Three sAD configurations were investigated: hydrodynamic-cavitated (HC-OFMSW), enzymatically pre-treated (EN-OFMSW), and non-pre-treated (AD-OFMSW). Principal Component Analysis and Supervised Kohonen's Self-Organizing Maps combined the experimental, economic, and environmental evaluations. The sAD configurations were grouped predominantly according to the OLR however, within each OLR group the configurations were clustered according to the pre-treatments. The finding highlighted that pre-treatments offset inhibition in sAD of OFMSW due to the OLR increase, being economically profitable and CF negative up to 4.50 kgvs/m3d for EN-OFMSW and to 5.40 kgvs/m3d for HC-OFMSW. Whereas sAD-OFMSW remained economically and environmentally viable only up to 3.87 kgvs/m3d. HC-OFMSW reached the highest performance. In detail, for HC-OFMSW the NPV and CF ranged from 17679.30 to 43827.12 euros and from -51.08 to -407.210 kg CO2eq/1 MWh daily produced, by decreasing the OLR from 5.40 to 3.87 kgvs/m3d. These results are fundamental since pre-treatment is usually expensive due to additional energy or chemical requirements.

Development of lignocellulosic biorefineries for the sustainable production of biofuels: Towards circular bioeconomy

The idea of environment friendly and affordable renewable energy resources has prompted the industry to focus on the set up of biorefineries for sustainable bioeconomy. Lignocellulosic biomass (LCB) is considered as an abundantly available renewable feedstock for the production of biofuels which can potentially reduce the dependence on petrochemical refineries. By utilizing various conversion technologies, an integrated biorefinery platform of LCB can be created, embracing the idea of the 'circular bioeconomy'. The development of effective pretreatment methods and biocatalytic systems by various bioengineering and machine learning approaches could reduce the bioprocessing costs, thereby making biomass-based biorefinery more sustainable. This review summarizes the development and advances in the lignocellulosic biorefineries from the LCB to the final product stage using various different state-of-the-art approaches for the progress of circular bioeconomy. The life cycle assessment which generates knowledge on the environmental impacts related to biofuel production chains is also summarized.

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.

The Use of a Simplified Carbon Footprint Tool for Organic Waste Managers: Pros and Cons

Given that the pressure of climate change action on companies is increasing, it is recommended to measure the improvement of mitigation activities in terms of GHG emissions. This paper aims to highlight the still-open aspects that characterise simplified GHG accounting tools, starting from the outcomes of a case study. This study was performed using a simplified Italian software for the CO2 eq accounting of composting and anaerobic digestion, two mitigation activities that contribute an important share of global GHG emissions reduction. The tool is based on the life-cycle thinking approach. It has been applied to an Italian company that treats the organic fraction of municipal solid waste. The tool analysis has made it possible to stress several issues that are currently the object of debate in the literature, for example, the trade-off between the flexibility of the software and its user friendliness or the multifunctionality issues and their different interpretations. However, focusing on just one impact category, i.e., climate change, may lead to an incomplete picture of the overall environmental performance of the process analysed. Therefore, this tool could be improved by including other impact categories, such as eutrophication and acidification, which may be affected by the studied activities.

Bioconversion of organic wastes into value-added products: A review

Rapid urbanization has increased the demand for food, feed, and chemicals that have in turn augmented the use of fossil-based resources and generation of organic waste. Owning to the characteristics like high abundance, renewability, and ease of accessibility, valorization of organic wastes serves as a potential solution for waste management issues. Several industrial wastes, due to their organic and nutrient-rich composition, have been utilized as a resource for the production of value-added products such as biofuels, biopesticides, biohydrogen, enzymes, and bioplastics via microbial fermentation processes. The process consists of pre-treatment of the waste biomass, production of value-added product in reactors and downstream processing for product's recovery. The integration of new comprehensive technologies for organic waste utilization will also stimulate the transition towards a circular economy. Therefore, the feasibility and sustainability of the production of various value-added products from biowastes and byproduct streams will be discussed in the present review.

Supporting decision making to achieve circularity via a biodegradable waste-to-bioenergy and compost facility

Bioproducts, such as energy and fertilizers, are strongly interrelated with the biodegradable waste treatment processes, within a holistic management strategy. Although different forms of biological treatment technologies are available, anaerobic digestion represents a process of major importance in the overall management strategy of biodegradable waste. This paper presents a methodology to support decision making for efficient management of biodegradable waste. The decision support framework provides the background towards the selection and design of a biodegradable waste installation with emphasis on the recovery of energy and organic fertilizer. The discrete steps are analytically defined and illustrated to assist managers and policy makers to organize their decision making in the whole spectrum of procedures required to promote sustainable biodegradable waste management programs. The methodological approach developed can be generically applied by public authorities, producers and stakeholders following essential basic steps regarding safe and environmentally friendly production of high-quality final product. Moreover, a demonstration is performed for a real-case study for the Region of Serres, Greece. The proposed installation is expected to manage 3,285 t of biodegradable waste and generate approximately 160,000 m³/a of biogas, 400 MWh_el/a and 450 MWh_thermal/a. The final bioproduct exceeds 3 kt of digestate that will be valorized in arable land close to the installation. Crucial interactions and managerial insights are also highlighted. The decision support framework aims to assist the research community, the private sector and decision makers to produce affordable and sustainable compost/digestate recovered from waste, also supporting the transition to a low carbon future and sustainable -circular- development.