Alternating pure oxygen and air cycles for the biostabilization of unsorted fraction of municipal solid waste

Hydrothermal liquefaction of composite household waste to biocrude: the effect of liquefaction solvents on product yield and quality

The hydrothermal liquefaction (HTL) of composite household waste (CHW) was investigated at different temperatures in the range of 240-360 °C, residence times in the range of 30-90 min, and co-solvent ratios of 2-8 ml/g, by utilising ethanol, glycerol, and produced aqueous phase as liquefaction solvents. Maximum biocrude yield of 46.19% was obtained at 340 °C and 75 min, with aqueous phase recirculation ratio (RR) of 5 ml/g. The chemical solvents such as glycerol and ethanol yielded a biocrude percentage of 45.18% and 42.16% at a ratio of 6 ml/g and 8 ml/g, respectively, for 340 °C and 75 min. The usage of co-solvents as hydrothermal medium increased the biocrude yield by 35.30% and decreased the formation of solid residue and gaseous products by 19.82% and 18.74% respectively. Also, the solid residue and biocrude obtained from co-solvent HTL possessed higher carbon and hydrogen content, thus having a H/C ratio and HHV that is 1.01 and 1.23 times higher than that of water as hydrothermal medium. Among the co-solvents, HTL with aqueous phase recirculation resulted in higher carbon and energy recovery percentages of 9.36% and 9.78% for solid residue and 52.09% and 56.75% for biocrude respectively. Further qualitatively, co-solvent HTL in the presence of obtained aqueous phase yielded 33.43% higher fraction of hydrocarbons than the pure water HTL and 7.70-17.01% higher hydrocarbons when compared with ethanol and glycerol HTL respectively. Nitrogen containing compounds, such as phenols and furfurals, for biocrudes obtained from all HTL processes, were found to be present in the range of 8.30-14.40%.

Cooperative environmental governance in urban South Asia: implications for municipal waste management and waste-to-energy

This paper critically discusses the importance of cooperative environmental governance (CEG) for efficient waste management and waste-to-energy (WtE) generation in the context of growing urban South Asia. Focusing on Bangladesh, India and Pakistan experiences, the paper reveals that even though much progress has been done in the urbanisation in the selected countries, the process of waste management (mainly municipal solid waste) has not been effective due to low level of local inclusion. As a result, the WtE generation potential has not been realised to its fullest. In addition, it has been argued that institutional and social reforms are extremely important for strengthening the CEG, and it will eventually lead to effective and optimal WtE generation in the urban cities of the selected South Asian countries for green transition and urban sustainability. Finally, an integrated solid waste management framework has been formulated for policy implications in South Asia.

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.

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

The role of Mechanical–Biological Treatment (MBT) is still of the utmost importance in the management of residual Municipal Solid Waste (MSW). These plants can cover a wide range of objectives, combining several types of processes and elements. The aim of this work is to assess and compare, from an environmental point of view, the performance of seven selected MBT plants currently operating in different countries, which represent the main MBT layout and processes. For the scope, a combined Life Cycle Assessment (LCA) and Material Flow Analysis (MFA) approach has been adopted to assess plant-specific efficiencies in materials and energy recovery. Metals recovery was a common and high-efficiency practice in MBT; further recovery of other types of waste was often performed. Each assessed MBT plant achieved environmental benefits: among them, the highest environmental benefit was achieved when the highest amount of waste was recovered (not only with material recycling). Environmental results were strongly affected by the recycling processes and the energy production, with a little contribution from the energy requirement. The impacts achieved by the MBT process were, on average, 14% of the total one. The main condition for a suitable MBT process is a combination of materials recovery for the production of new raw materials, avoiding disposal in landfill, and refuse-derived fuel production for energy recovery. This work can be of help to operators and planners when they are asked to define MBT schemes.

Anaerobic co-digestion of paper sludge: Feasibility of additional methane generation in mechanical-biological treatment plants

In this work, the feasibility of the anaerobic digestion of paper sludge as a co-substrate in anaerobic digestion mechanical-biological treatment (MBT) plants is investigated. In the first phase, the biochemical properties, biomethane potential (BMP), and pollutant contents of 20 different industrial paper sludges are determined. Following the general evaluation in the BMP tests, the second phase of the project involves the semi-continuous co-digestion of six paper sludges in continuous stirred reactors (CSTR). Paper sludges are categorized according to their origin within the pulp and paper mills: Deinking Sludge (DS), Primary Sludge (PS) and Biological Sludge (BS). The analysis of potentially inhibiting elements shows that the concentrations of chlororganic compounds, mineral oil and some heavy metals are highest in DS, while the mean heavy metal loads in all paper sludges are relatively low compared to other industrial sludges. Large differences in total solids (TS) and volatile solids (VS) contents are observed among the different paper sludges investigated, with DS having the highest TS due to the high inorganic contents. The BMP of the investigated sludges ranges from 90 to 355 NL CH₄ kg^-1 VS. In subsequent semi-continuous co-digestion experiments simulating MBT conditions, three DS and two fiber sludges (a mixture of PS and BS) show good methane generation rates, while one fiber sludge causes inhibition and indicates an increase in viscosity. In general, co-digestion of paper sludge in anaerobic digestion MBT plants can be a viable option for energy production and also facilitates a safe disposal of the paper sludge digestates.

Impact of Biochar Addition and Air-Flow Rate on Ammonia and Carbon Dioxide Concentration in the Emitted Gases from Aerobic Biostabilization of Waste

Application of additives to waste may influence the course of the biostabilization process and contribute to its higher effectiveness, as well as to a reduction in greenhouse gas and ammonia (NH₃) emission from this process. This paper presents research on the impact of biochar addition on the course of the biostabilization process of an undersized fraction from municipal solid waste (UFMSW) in terms of temperature changes, CO₂ concentration in the exhaust gases, NH₃ emission from the process, as well as changes in the carbon and nitrogen content in the processed waste. Six different biochar additives and three different air-flow rates were investigated for 21 days. It was found that biochar addition contributes to extending the thermophilic phase duration (observed in the case of the addition of 3% and 5% of biochar). The concentration of CO₂ in exhaust gases was closely related to the course of temperature changes. The highest concentration of CO₂ in the process gases (approx. 18–19%) was recorded for the addition of 10% and 20% of biochar at the lowest air-flow rate applied. It was found that the addition of 3% or a higher amount of biochar reduces nitrogen losses in the processed UFMSW and reduces NH₃ emission by over 90% compared to the control.

Impact of digestate addition on the biostabilization of undersized fraction from municipal solid waste

Biostabilization is a commonly applied method in mechanical-biological treatment (MBT) plants to process municipal solid waste. In many ways, e.g. by applying additives to waste, MBT plant operators strive to enhance the effectiveness of biostabilization, which leads to reducing the time and energy outlays necessary for the process, as well as to minimizing the amount of final stabilized waste directed to landfills. This paper deals with the impact of digestate waste from agricultural biogas plants used as additive to the biostabilization process of undersized fraction from municipal solid waste (UFMSW) on the intensive phase of the process and properties of stabilized waste. The aim of this study was to assess whether, and if so to what extent, the application of digestate waste affects the process. Five different input compositions were tested (without digestate and with the addition of digestate at: 2.5; 5; 7.5 and 10 wt%). Waste treatment time was 2 weeks. Changes in moisture content, organic matter (OM), respiration activity (AT4), bulk density, air-filled porosity, heavy metal content, pH, carbon to nitrogen ratio, as well as composition of process gases emitted were evaluated. Additionally, microorganisms (including pathogens) inhabiting the processed waste in the aspect of waste sanitation were analyzed. It was found that the addition of digestate at 2.5, 5 and 7.5 wt% extended the duration of the thermophilic phase and decreased the CO₂ content in process gases. The addition of digestate at 2.5 wt% and 5 wt%, decreased also OM by approx. 25% of the initial value and AT4 by approx. 30%. It was also proved that the addition of digestate favors the limited sanitation of UFMSW. As a result of the research, it was found that the addition of digestate at 2.5 wt% and 5 wt% is sufficient to accelerate the aerobic biological degradation of UFMSW.