Environmental assessments of biological treatments of biowaste in life cycle perspective: A critical review

Assessment of the environmental sustainability of municipal solid waste valorization by anaerobic digestion and by composting in Sri Lanka

Municipal solid waste management (MSWM) remains a major concern in Sri Lanka, and various treatment methods have been deployed. Though both composting and anaerobic digestion have been effective in environmental decontamination, there are other environmental issues that should be assessed. This study aimed to evaluate the environmental impacts of a full-scale composting plant and an anaerobic digestion plant for managing the organic fraction of municipal solid waste (OFMSW) in Sri Lanka using life cycle assessment (LCA). The results show that OFMSW composting causes unfavourable environmental impacts on damage categories such as human health (6.77 × 10-4 disability-adjusted life years (DALY) tonne-1 OFMSW), ecosystem quality (1.90 × 10-6 species.year tonne-1 OFMSW), and resource scarcity (3.66 × 10-1 United States Dollar (USD) tonne-1 OFMSW). Anaerobic digestion also leads to unfavourable impacts on human health (2.13 × 10-4 DALY tonne-1 OFMSW) and ecosystem quality (6.46 × 10-7 species.year tonne-1 OFMSW). However, the impact on resource scarcity (-3.85 × 10-2 USD tonne-1 OFMSW) was avoided due to electricity production via anaerobic digestion. Specifically, the treatment of OFMSW by anaerobic digestion resulted in a reduction by 68.3% in the total environmental load as compared to composting. It can be concluded that out of the two existing systems investigated, anaerobic digestion has a more favourable environmental impact than composting.

Closing the Carbon Loop in the Circular Plastics Economy

Today, plastics are ubiquitous in everyday life, problem solvers of modern technologies, and crucial for sustainable development. Yet the surge in global demand for plastics of the growing world population has triggered a tidal wave of plastic debris in the environment. Moving from a linear to a zero-waste and carbon-neutral circular plastic economy is vital for the future of the planet. Taming the plastic waste flood requires closing the carbon loop through plastic reuse, mechanical and molecular recycling, carbon capture, and use of the greenhouse gas carbon dioxide. In the quest for eco-friendly products, plastics do not need to be reinvented but tuned for reuse and recycling. Their full potential must be exploited regarding energy, resource, and eco efficiency, waste prevention, circular economy, climate change mitigation, and lowering environmental pollution. Biodegradation holds promise for composting and bio-feedstock recovery, but it is neither the Holy Grail of circular plastics economy nor a panacea for plastic littering. As an alternative to mechanical downcycling, molecular recycling enables both closed-loop recovery of virgin plastics and open-loop valorization, producing hydrogen, fuels, refinery feeds, lubricants, chemicals, and carbonaceous materials. Closing the carbon loop does not create a Perpetuum Mobile and requires renewable energy to achieve sustainability. This article is protected by copyright. All rights reserved.

Environmental sustainability of an integrate anaerobic digestion-composting treatment of food waste: Analysis of an Italian plant in the circular bioeconomy strategy

In light of the adoption of recent global policies and strategies for a more sustainable food waste management system and a greater control of environmental impacts, this study describes a circular bioeconomy plant model, currently operating in South Italy, for treatment and enhancement of organic fraction of municipal solid waste. The key basis for plant activity is dry anaerobic digestion of separately collected organic fraction of municipal solid waste (SC-OFMSW) followed by digestate composting process. Biomethane for use in the transport sector is obtained by biogas cleaning and upgrading, while high-quality compost for organic farming is produced by digestate composting. Plant activities are completed by the transformation of part of the produced waste into refuse derived fuel (RDF) to be allocated to waste-to-energy plants and the treatment of odour emissions which allows the recovery of ammonium sulphate as a fertilizer. A rooftop photovoltaic system supplies most of electric energy needed by the plant. For plant activities relative to 2020, carbon footprint was equal to -112 kg CO₂eq. for Mg of organic waste, while depletion of fossil resources was estimated at -89.6 kg oil eq. Mg^-1 of waste. Primary energy demand of food waste treatment system was -2.66 GJ Mg^-1 of input waste. Replacement of natural gas with biomethane for transport sector provided the greatest improvement contribution for all the examined categories.

Environmental impact assessment of organic fraction of municipal solid waste treatment by anaerobic digestion in Sri Lanka

The management of organic fraction of municipal solid waste (OFMSW) has continued to be a significant challenge in Sri Lanka. Anaerobic digestion is one of the management options of OFMSW. However, it generates unavoidable environmental impacts that should be addressed. The present study focuses to assess the environmental impact of a full-scale anaerobic digestion plant in Sri Lanka from a life cycle perspective. The inventory data were obtained from direct interviews and field measurements. Environmental burdens were found to be in terms of global warming potential (230 kg CO₂ eq) ozone formation on human health (6.15 × 10^-6 kg NO_x eq), freshwater eutrophication (2.92 × 10^-3 kg P eq), freshwater ecotoxicity (9.27 × 10^-5 kg 1,4 DCB eq), human carcinogenic toxicity (3.98 × 10^-4 kg 1,4 DCB eq), land use (1.32 × 10^-4 m² a crop eq) and water consumption (2.23 × 10^-2 m³). The stratospheric ozone depletion, fine particulate matter formation, ozone formation on terrestrial ecosystems, terrestrial acidification, marine eutrophication, ecotoxicity (terrestrial and marine), human non-carcinogenic toxicity, mineral resource scarcity and fossil resource scarcity, were avoided due to electricity production. Results show that the direct gaseous emissions and digestate generation should be addressed in order to reduce the burdens from the anaerobic digestion plant. Finally, the results of the study could help in policy formation and decision-making in selecting future waste management systems in Sri Lanka.

Sustainability assessment of organic waste management in three EU Cities: Analysing stakeholder-based solutions

This study focuses on a comprehensive sustainability assessment of the management of the organic fraction of municipal solid waste in Ghent (Belgium), Hamburg (Germany) and Pécs (Hungary). A sustainability assessment framework has been applied to analyse social, environmental, and economic consequences at the midpoint level (25 impact categories) and at the endpoint level (5 areas-of-protection). For each case study, the reference scenario was analysed, along with three solutions to improve the sustainability performance, which were selected and developed with the collaboration of local stakeholders. The solutions focus on food waste prevention, collection (increasing separate collection and household composting) and/or valorisation treatment (insect breeding, bioplastic production and improvement of centralised treatment). The results show that food waste prevention results in substantial improvements in all areas of protection when a significant quantity of food is saved. Solutions proposing innovative treatments such as insect breeding do not show clear improvements at the endpoint level, given current technology development level, but appear promising for some categories such as Revenues, Ecotoxicity, Land Use or Particulate Matter if the substituted products compensate the impact of the treatment (e.g., energy and water use). Enhancing the separate collection of organic waste can improve sustainability, but trade-offs may arise, e.g., decreased environmental savings from energy recovery at incineration. For this, the influence of the electricity mix (more or less decarbonised) should be carefully considered in future studies. The application of the solutions proposed to other cities should also consider potential bottlenecks such as legislation barriers, public acceptance, or management costs.

A review of circularity and sustainability in anaerobic digestion processes

The debate on the relationship between the long-established concept of sustainability, and the relatively novel one of circularity in constantly increasing biogas production remains. In this study, additional discussion elements to such an open debate are provided. With its role in the bioeconomy and ongoing ambiguity, a bibliographic review of anaerobic digestion is provided. In particular, this study aims to i) verify whether sustainability assessments and circularity measurements are performed in different ways in anaerobic digestion projects and ii) understand which indicators have been utilized for each pillar of sustainability. Initially, 152 scientific documents from the Scopus and Web of Science scholarly journal databases were selected. Specific eligibility criteria that were any type of measurement of circularity and/or assessment of sustainability, were used for screening. Fifty-eight articles met these criteria and were analyzed in depth. The results show that the terms circularity and sustainability are not always univocal concepts in the reviewed scientific contributions. Consequently, the relative criteria or measurements for their analysis are not the same. As a result, a different interpretation of the two concepts is suggested. Circularity should be considered as one of the ways to achieve the broadest objective of sustainability.

Comparison of local and centralized biowaste management strategies - A spatially-sensitive approach for the region of Porto

The increasing concern with greenhouse gas emissions and nutrients cycling creates a need for cost-effective, practical and environmentally sensible biowaste management strategies. Centralized systems have struggled to comply with those needs. Decentralized systems, treating waste at source, promise local nutrient circularity and increased resource sovereignty. The large-scale performance of decentralized systems remains unclear, especially concerning the local sink capacity to assimilate the treatment products. This study aimed to compare centralized and decentralized systems for the region of Porto and assess whether creating additional urban farms could reduce costs and environmental impacts. Spatial analysis was used to assess waste generation, potential compost bin locations, peri-urban and potential urban farmland available, and collection and transport requirements. The carbon footprint of different scenarios was determined using life-cycle assessment. The results show that local composting led to cost savings over centralized systems. However, this system encompassed positive carbon emissions and most districts evidenced limited sink capacity for compost application. Additional urban farms added significant sink capacity, however, their impact on cost and carbon footprint was insignificant. The carbon footprint of centralized systems was heavily dependent on factors influencing collection such as population density, and affected by the renewable content of the electricity grid. Anaerobic digestion was the most climate-friendly option in the urban center and local composting in remote and less dense districts. Municipalities may benefit from tailoring the treatment systems to specific districts, creating additional jobs while reducing cost and climate impacts overall.

Development of sustainable approaches for converting the organic waste to bioenergy

Dependence on fossil fuels such as oil, coal and natural gas are on alarming increase, thereby causing such resources to be in a depletion mode and a novel sustainable approach for bioenergy production are in demand. Successful implementation of zero waste discharge policy is one such way to attain a sustainable development of bioenergy. Zero waste discharge can be induced only through the conversion of organic wastes into bioenergy. Waste management is pivotal and considering its importance of minimizing the issue and menace of wastes, conversion strategy of organic waste is effectively recommended. Present review is concentrated on providing a keen view on the potential organic waste sources and the way in which the bioenergy is produced through efficient conversion processes. Biogas, bioethanol, biocoal, biohydrogen and biodiesel are the principal renewable energy sources. Different types of organic wastes used for bioenergy generation and its sources, anaerobic digestion-biogas production and its related process affecting parameters including fermentation, photosynthetic process and novel nano-inspired techniques are discussed. Bioenergy production from organic waste is associated with mitigation of lump waste generation and its dumping into land, specifically reducing all hazards and negativities in all sectors during waste disposal. A sustainable bioenergy sector with upgraded security for fuels, tackles the challenging climatic change problem also. Thus, intensification of organic waste conversion strategies to bioenergy, specially, biogas and biohydrogen production is elaborated and analyzed in the present article. Predominantly, persistent drawbacks of the existing organic waste conversion methods have been noted, providing consideration to economic, environmental and social development.