• Energy Research

The use of bio-plastic-based packaging as an alternative to conventional plastic packaging is increasing. Among the plethora of different bio-based plastics, the most relevant ones are those that, at the end of their life, can be treated with the organic fraction of municipal solid waste. Even in these cases, their impact on the waste processing and recycling is not always positive. This study aim to assess on a laboratory scale the influence on combined anaerobic digestion and composting industrial processes of a bio-based plastic film, namely cellulose acetate (CA), in pure and modified (additions of additive) forms. CA films were mixed with organic waste and subjected to: (i) anaerobic digestion; (ii) active composting and (iii) two stages of curing composting. Anaerobic digestion and composting were monitored through methane yield and oxygen uptake respectively; additionally, the bio-plastics degree of disintegration was assessed during all the processes. The final disintegration of pure and modified CA was 73.82% and 54.66%, respectively. Anaerobic digestion contributes to the disintegration of the material, while aerobic treatment appears to be nearly ineffective, especially for modified CA. The presence of cellulose acetate during anaerobic digestion of food waste increased the methane yield by about 4.5%. Bioassay confirmed the absence of possible toxic effects on the final compost from the bio-plastic treatment. Although bio-based materials are not the only solution to plastic pollution, the findings confirm the need to upgrade the organic waste treatment plants and the necessity to revise the requirements for the use of compost in agriculture.

The incomplete degradation of bio-plastics waste is undermining the suitability of current anaerobic digestion (AD) and composting, opening up the exploration of new treatment routes, including mixed waste. Bio-plastics are treated with mixed waste in a mechanical-biological treatment (MBT) plant with the production of a dry fraction for incineration and a biologically stable one for landfill. An alternative post-treatment of the bio-stabilised waste based on AD is possible. It follows that the main goal of this study is to verify the feasibility of managing cellulose-based bio-plastics with mixed municipal waste, comparing the AD of the MBT plant outputs with the possible solution of incineration. Experimental lab tests have been carried out to describe the two processes, whose results were the basis for an economic analysis. The values of biochemical methane po-tential (BMP) and higher heating value (HHV) are used as an index for AD and incineration, respectively. Samples with and without bio-plastics were created; fresh and processed (7 and 14 days of biostabilization) samples were, thus, analysed. For AD, the fresh waste averaged 177 NmL CH4/gVS and a 22% and 33% decrease in BMP value was achieved after 7 and 14 days of biostabilization, respectively. Samples with and without bio-plastics revealed a similar trend. 7 and 14 days of biostabilization increased the HHV of fresh waste (18.01 J/kg) of 16.1% and 19.7%, respectively. Bio-plastics did not significantly change the HHV. The economic analysis revealed the suitability of both AD and incineration, irrespective of the presence of bioplastics.

The population growth of South-Asian countries is contributing significantly to the escalating volume of municipal solid waste (MSW). Presently, waste management in this region predominantly relies on landfilling, necessitating a shift towards a more sustainable paradigm. To address this imperative, this study explores the feasibility of extending the European-based waste management system for treating MSW in Cambodia, Thailand, and Vietnam. Assuming as current scenario the direct disposal in landfill, the environmental and technical performances of five other proposed scenarios based on the following technologies were assessed: mechanical–biological treatment; incineration; their combination; mechanical recycling; composting and anaerobic digestion. As expected, all alternative technologies showed potential for improving the current scenario. However, from an environmental point of view, incineration of mixed MSW emerged as the sole option that yielded a discernible environmental benefit for all the countries involved in the study (achieving a carbon footprint of about −0.111 t-CO2-Eq./FU). Recycling-based scenarios achieved higher benefits for Thailand and Vietnam (−0.145 and −0.186 t-CO2-Eq./FU, respectively), but not Cambodia (0.072 t-CO2-Eq./FU) due to the lack of valuable materials to recycle. Technical findings showed how separate collection remains the system generating the least amount of waste for disposal (about 0.185 t), having a synergic effect on the combined approach of mechanical–biological treatment and incineration, which boasts the highest specific energy yield (about 0.339 and 1.183 kW/t, for electric and thermal energy, respectively). These results underscore the imperative to extend the analysis to the economic domain, combining diverse criteria to identify the most sustainable solution.

Anaerobic digestion (AD) of organic fraction of municipal solid waste (OFMSW) is considered an excellent solution for both waste management and energy generation, although the impacts of waste collection and transportation on the whole management system are not negligible. AD is often regarded as a centralized solution for an entire community, although recently, there has been some debate on the adoption of decentralized, smaller facilities. This study aims to evaluate the techno-economic feasibility of an AD plant at the local scale for the treatment of organic waste generated from urban districts. Depending on the type of feedstock, two scenarios were evaluated and compared with the reference scenario, based on composting treatment: (1) mono-AD of OFMSW and (2) co-AD of OFMSW and sewage sludge (SS). Furthermore, different district extensions of the metropolitan area were considered with the goal of determining the optimal size. Results showed the advantage of the two scenarios over the reference one. Scenario 1 proved to be the most suitable solution, because the introduction of SS in Scenario 2 increased costs and payback time, rather than generating a higher waste amount and lower biogas yield. The preferred district extension was the medium-sized one. Capital cost strongly affected the economic analysis, but revenue from the city for the management operation of the organic waste could significantly decrease costs. Further studies about the differences in the type of feedstock or the introduction of other criteria of analysis (such as environmental) are considered necessary.

To face the ongoing issues related to global warming, a circular economy approach should be pursued, rethinking the waste management system and the recovery of organic waste. The main organic waste streams are Food Waste (FW) and municipal Sewage Sludge (SS). In the spirit of circularity, a commingled treatment of FW and SS could be a viable solution. To this end, the present work aims to review the technical and environmental aspects of the co-treatment of FW and SS through biological and thermal processes. Firstly, a detailed characterization of the two substrates is presented as well as the current and future treatment technologies. Then, the technical feasibility and the environmental impacts of conventional biological co-treatments of FW and SS (i.e., composting, anaerobic digestion, and a combination of them), as well as innovative thermal ones (i.e., incineration, gasification, pyrolysis, and hydrothermal carbonization), is summarized. The outcomes of this work could contribute to achieving a more sustainable way to approach organic waste treatment and to help policy-making authorities move toward sustainable planning.