Environmental Comparison of Different Mechanical–Biological Treatment Plants by Combining Life Cycle Assessment and Material Flow Analysis

When solid recovered fuel (SRF) production and consumption maximize environmental benefits? A life cycle assessment

Solid recovered fuel (SRF) from non-recyclable waste obtained from source separation and mechanical treatments can replace carbon coke in cement plants, contributing to the carbon neutrality. A life cycle assessment (LCA) of the SRF production from non-recyclable and selected waste was conducted in an Italian mechanical treatment plant to estimate the potential environmental impacts per ton of SRF produced. The analysis would contribute to evaluate the benefits that can be obtained due to coke substitution in best- and worst-case scenarios. The avoided impacts achieved were assessed, together with an evaluation of the variables that can affect the environmental benefits: SRF biogenic carbon content (in percentage of paper and cardboard); transportation distances travelled from the treatment plant to the cement kiln; the renewable energy used in the mechanical facility. On average, about 35.6 kgCO2-eq are generated by the SRF transportation and production phase. These impacts are greatly compensated by coke substitution, obtaining a net value of about -1.1 tCO2-eq avoided per ton of SRF. On balance, the global warming potential due to SRF production and consumption ranges from about -542 kgCO2-eq to about -1729 kgCO2-eq. The research recommended the use of SRF to substitute coke in cement kilns also in low densely-populated areas to mitigate environmental impacts and achieve carbon neutrality at a global level.

Biodrying of municipal solid waste-correlations between moisture content, organic content, and end of the biodrying process time

Biodrying refers to the decomposition of organic municipal solid waste (MSW) under aerobic conditions. This process usually lasts 14 days and requires large amounts of air to be injected into the waste matrix. The efficiency of the biodrying process depends on several geotechnical parameters, including initial moisture content, initial organic content, bulk density, dry density, solid particle density, and porosity. To examine the potential influence of these parameters on the biodrying process, we analyzed 13 biodried MSW samples. The results revealed a strong positive linear relationship between the initial moisture content and the mass loss percentage. In the first three days of the biodrying process, the waste mass rapidly decreased; afterwards, the daily mass loss occurred at a less rapid, more constant rate. The established average mass removal ratio between the volatile solids and water was 1:6.38 with a standard deviation of 1.06. Dry and solid particle densities were preserved in all 13 experiments; thus, the corresponding void ratio remained unchanged. This finding suggests that the settlement and degradation of MSW that occur during the biodrying process did not significantly influence the airflow rate.

Efficiency of biological and mechanical-biological treatment plants for MSW: The case of Spain

Biological and mechanical biological treatment plants combine mechanical and biological treatments to recover the greatest possible amount of materials from municipal solid waste (MSW) and biostabilize the organic fraction to be landfilled or applied in land. These plants handle a high percentage of the MSW generated in Europe. This work presents an exhaustive analysis of the existing plants in Spain which evaluates their typology as well as their performance. In Spain, 137 plants, which receive 13 Mt/year of waste, provide the country with total coverage. Twenty-two types of plants have been identified and grouped into six categories. There are four categories that receive mixed MSW: 1) sorting plants; 2) recovery and composting plants; 3) biodrying and recovery plants; and 4) recovery, biomethanation and composting plants and two that receive separately collected biowaste: 5) composting plants, and 6) biomethanation and composting plants. In plants that receive mixed waste, around 5% of the total input is recovered as recyclable materials (662,182 t/year), of which 29% corresponds to plastics, 27% to metals, and 27% to paper and cardboard. In addition, biostabilized material and/or biogas, and rejects (45-77% of the input) are obtained. In the biowaste plants, high-quality compost (more than 105,000 t/year), a higher biogas yield (43.60 Nm3/t·year) and a lower proportion of rejects (around 29%) are obtained.

Life cycle assessment of end-of-life options for cellulose-based bioplastics when introduced into a municipal solid waste management system

The partial degradation of cellulose-based bioplastics in industrial treatment of organic fraction of Municipal Solid Waste (MSW) opened to the investigation of further disposal routes for bioplastics in the waste management system. For this purpose, the environmental footprint of three MSW management scenarios differing only for the bioplastics final destination (organic, plastic or mixed waste streams) was assessed through a Life Cycle Assessment (LCA) approach. Results revealed how the treatment of bioplastics with organic waste achieved the worst environmental performance (5.8 kg CO₂ eq/FU) for most impact categories. On the other hand, treatment with plastics and mixed waste achieved negative impact values (that mean avoided GHG emissions) of -9.8 and -7.7 kg CO₂ eq/FU respectively, showing comparable benefits from these scenarios. The key reason was the lower quality of compost obtained from the organic treatment route, which reduced the environmental credits achieved by the energy recovery during anaerobic digestion.

Effects of cellulose-based bio-plastics on the aerobic biological stabilization treatment of mixed municipal solid waste: A lab-scale assessment

The aim of this work is to assess how the presence of cellulose-based bio-plastics influence the biological stabilization of mixed Municipal Solid Waste (MSW). For the scope, two cellulose acetate bio-plastics have been mixed with a synthetic mixed waste to create samples with and without bio-plastics. A self-induced biostabilization has been carried out for 7 and 14 days where temperature and off-gas have been monitored continuously. Results about temperature evolution, O₂ consumption, CO₂ production and respiratory quotient did not show a substantial difference regarding both the duration of the process and the presence of cellulose-based bio-plastics on the mixture. On the average, the temperature peak and the maximum daily O₂ consumption and CO₂ production were 52.2 °C, 35.81 g O₂/kg DM *d and 48.95 g CO₂/kg DM *d respectively. Disintegration of bio-plastics samples after 7 and 14 days were comparable (on the average 23.13%). The self-induced biostabilization gave its main contribution after 4 days and resulted almost finished at the end of the day 7 of the process. Results showed that cellulose-based bio-plastics did not give a negative effect on mixed MSW biological stabilization and suggest a possible management, aiming at energy recovery of the outputs.