Waste management optimization with NLP modeling and waste-to-energy in a circular economy.

This work presents a methodology integrating Non-Linear Programming (NLP) for multi-objective and multi-period optimization, addressing sustainable waste management and energy conversion challenges. It integrates waste-to-energy (WtE) technologies such as Anaerobic Digestion (AD), Incineration (Inc), Gasification (Gsf), and Pyrolysis (Py), and considers thermochemical, technical, economic, and environmental considerations through rigorous non-linear functions. Using Mexico City as a case study, the model develops waste management strategies that balance environmental and economic aims, considering social impacts. A trade-off solution is proposed to address the conflict between objectives. The economical optimal solution generates 1.79M$ with 954 tons of CO2 emissions while the environmental one generates 0.91M$ and reduces emissions by 54%, where 40% is due to gasification technology. Moreover, the environmentally optimal solution, with incineration and gasification generates 9500 MWh/day and 5960 MWh/day, respectively, demonstrates the capacity of the model to support sustainable energy strategies. Finally, this work presents an adaptable framework for sustainable waste management decision-making.

Use of life cycle assessment for estimating impacts of waste-to-energy technologies in solid waste management systems: the case of Buenos Aires, Argentina.

Analysing municipal solid waste (MSW) management scenarios is relevant for planning future policies and actions toward a circular economy. Life cycle assessment (LCA) is appropriate for evaluating technologies of MSW treatment and their environmental impacts. However, in developing countries, advanced assessments are difficult to introduce due to the lack of technical knowledge, data and financial support. This research aims to assess the main potentialities of the introduction of waste-to-energy (WtE) systems in a developing Argentinean urban area considering the existing regulations about MSW recycling goals. The study was conducted with WRATE software and the proposed scenarios were current management, grate incineration of raw MSW and incineration of solid recovered fuel (SRF). In addition, a sensitivity analysis on the energy matrix was included. It was found that the production of SRF allows increasing the energy generation from waste by 200% and reducing the environmental impact of about 10% regarding the current MSW management system. Acidification Potential and Abiotic Depletion Potential were sensitive to changes in electricity mix. Results showed that if MSW reduction goals are achieved, changes in MSW composition will affect the performance of WtE plants and, in some cases, they will be not technically feasible. The outcomes of this study can be of interest for developing countries stakeholders and practitioners interested in LCA and sustainable MSW management.

Social acceptance, emissions analysis and potential applications of paper-waste briquettes in Andean areas.

The research assessed waste-based briquettes consumption compared to conventional fuels in the Andes. Laboratory tests were conducted together with on-field analysis in Colquencha (Bolivia). The laboratory study shows that the performances of briquettes are better in terms of PM2.5 (933.4 ± 50.8 mg kg-1) and CO emissions (22.89 ± 2.40 g kg-1) compared to animal dung (6265.7 ± 1273.5 mgPM2.5 kg-1 and 48.10 ± 12.50 gCO kg-1), although the boiling time increased due to the lower fuel consumption rate and firepower compared to shrubs. The social survey organized with 150 Bolivian citizens suggested that low-income households are not able to pay for an alternative fuel: about 40% would pay less than 4 USD per month, while methane use for cooking is positively correlated with the income level (r = 0.244, p < 0.05). On field analysis suggested that local cookstoves are not appropriate for briquettes combustion since indoor air pollution overcomes 30 ppm of CO and 10 mgPM2.5 m-3. On balance, local small manufactures can be the main target for selling waste-based briquettes to reduce shrubs and wood consumption. However, briquettes production costs seem not yet competitive to natural easy-to-obtain fuels (i.e., animal dung). The research encourages the use of cellulosic and biomass waste-based briquettes in the Andean area for cooking, heating, or manufacturing and strongly advises policy-makers to introduce economic incentives for the recovery of secondary raw materials.

Livestock waste management for energy recovery in Brazil: a life cycle assessment approach.

Livestock farming has exerted intense environmental pressure on our planet. The high emissions to the environment and the high demands of resources for the production process have encouraged the search for decarbonization and circularity in the livestock sector. In this context, the objective of this study was to evaluate and compare the environmental performance of two different uses for biogas generated in the anaerobic digestion of animal waste, either for electricity generation or biomethane. For this purpose, a life cycle assessment approach was applied to evaluate the potential of anaerobic digestion as a management technology for three different livestock wastes, related to beef cattle, dairy, and sheep in the Brazilian animal production context. The results suggest that the treatment scenarios focusing on biomethane generation were able to mitigate the highest percentage of damages (77 to 108%) in the global warming category when compared to the scenarios without the use of anaerobic digestion (3.00·102 to 3.71·103 kgCO2 eq) or in the perspective of electricity generation (mitigation of 74 to 96%). In terms of freshwater eutrophication, the generation of electricity (- 2.17·10-2 to 2.31·10-3 kg P eq) is more favorable than the purification of biogas to biomethane (- 1.73·10-2 to 2.44·10-3 kg P eq), due to the loss of methane in the upgrading process. In terms of terrestrial ecotoxicity, all scenarios are very similar, with negative values (- 1.19·101 to - 7.17·102 kg 1,4-DCB) due to the benefit of nutrient recovery, especially nitrogen, associated with the use of digestate as fertilizer, which was one of the critical points in all scenarios. Based on these results, it is evident that proper management of all stages of the treatment life cycle is the key to decarbonization and circularity in livestock waste management. The biogas use does not present different effects on the environmental performance of the scenarios studied, demonstrating that the purpose should be chosen according to the needs of each plant or management system.

Development of waste-to-energy through integrated sustainable waste management: the case of ABREN WtERT Brazil towards changing status quo in Brazil.

In the context of circular economy, it is known that once waste is generated, it should be subject to proper treatment for recovering material or energy before being disposed. Many countries worldwide, especially developing countries such as Brazil, have been struggling to effectively apply sustainable waste management in municipalities and still rely on dumpsites and unsuitable landfills. Misinformation, a weak legal framework, lack of financial resources and poor infra-structure as well as pressure from organizations profiting from the expansion of landfills are some factors contributing to the preservation of the negative status quo: the "landfill culture". Material recovery, i.e., recycling and composting, is applied to less than 5% of Brazilian municipal waste, while 95% is disposed of in landfills or dumpsites. In this context, ABREN WtERT (Waste-to-Energy Research and Technology Council) Brazil was created in 2019 as the first permanent organization formed to promote the development of energy and material recovery from waste focused on the waste-to-energy (WTE) market. In this paper, the strategy proposed and implemented by the organization towards changing the status quo in Brazil through an integrated sustainable waste management approach is described. The proposed strategy integrates the concepts of Sustainability and Circular Economy for minimizing landfill disposal (avoiding methane emissions) and maximizing material/energy recovery. Among others, the approach focuses on changing the public opinion regarding thermal treatment facilities, mainly incinerators, which has been wrongly linked to pollution, excessive public expenditures and considered a harm to the recycling industry. The activities performed by ABREN include engaging public and private institutions, enhancing education, leading the publication of research and business studies, gathering industry members and academy experts, as well as creating strategic alliances with players around the globe. As a result, within a few years, major outcomes were achieved in Brazil, such as: (i) changes in the legal framework, (ii) launching of a specific public auction category for sponsoring electricity production from WTE facilities, and (iii) establishment of official targets for municipalities to decrease landfill disposal and increase recycling/biological treatment and energy recovery from thermal treatment. Among the national goals, it should be highlighted the target regarding the increase from zero to 994 MW of electricity production from municipal solid waste, which will require building dozens of new WTE facilities. Global outcomes are expected as well since Brazil is the seventh largest country of the globe and the most influential in Latin America. International and national business deals should thrive due to the need of operational skills and technology imports, and the avoidance of carbon emissions will positively reflect the world climate. In parallel, there is also potential for the academy to benefit from research projects and investments if the WTE national industry is to be developed in the long term.

To dream or not to dream in Havana: multi-criteria decision-making for material and energy recovery from municipal solid wastes.

Currently, solid waste management strategies in Havana are outdated. This paper aimed to select the most suitable alternative for integrating material recovery facilities (MRF) with waste-to-energy technologies in the city of Havana, Cuba. Seven scenarios were considered: combustion, gasification, and hydrothermal carbonization (HTC) with and without carbon capture, and anaerobic digestion (AD). The selection was based on environmental, techno-economic, and social parameters using an analytic hierarchy process (AHP) as a multi-criteria decision-making tool (MCDM). The MCDM-AHP accounted for qualitative criteria (based on experts' judgments) and quantitative (based on Aspen Plus simulation models). From the MRF, 63% of the input recyclable materials were recovered, representing an energy saving of 256 kW-h/tMSW. The AHP results showed that environmental criteria had the highest priority, resulting in ~63% and ~73% higher than social and techno-economic criteria, respectively. Likewise, from the techno-economic, environmental, and social sub-criteria analysis, investment risk, pollution, and work safety had the major concern compared with the other sub-criteria levels. Overall, MRF+AD was the most suitable scenario (21% preference) for treating Havana's municipal solid waste (MSW), followed by combustion and gasification with carbon capture, respectively. This study confirms that AD is a preference option for emerging economies like Cuba, mainly due to low environmental pollution, high social acceptance, and financial stability in the long term.

A comparison assessment of landfill waste incineration and methane capture in the central region of Mexico.

This article aims to conduct a techno-economic feasibility assessment of producing energy by waste incineration and methane capture in the central region of Mexico. Three scenarios at different efficiency rates were considered: 50, 80 and 100%. For the methane project, yields and power capacity were determined using the potential generation rate and the degradable organic carbon content through the LandGEM model. For incineration, the waste calorific potential and the average moisture content were used to estimate the achievable electrical performance. The estimated annual energy was 35,018 GWh for methane, compared to 537.71 GWh for incineration. Both projects reported financial economic feasibilities when evaluated at a discount rate of 12%. Incineration reported an net present value of US$49,942,534 and an internal rate of return of 26% in contrast to US$4,054,109 and 17% for the methane project. Although the payback period for incineration was lower than for methane, its levelized cost of energy was significantly higher. These results are intended to assist the decision-making process when planning and developing waste management strategies under principles of circular economy in Mexico and similar regions worldwide.

Perspectives in solid recovered fuel production in Bolivia: Analysis of characteristics and potential benefits.

Solid recovered fuels (SRF) can provide another treatment option to the solid waste management (SWM) sector. However, in developing countries, to date, this system approach has not found considerable application. In Bolivia, SRF is not deemed within the national regulation and the final disposal in open dumping areas is still a reality. This research article provides the first attempt in evaluating the SRF characteristics and its potentialities in Bolivia, taking La Paz as a case study. Laboratory analysis of the rejects produced after selective collection and sorting has been conducted, focusing on non-hazardous and non-recyclable waste fractions. The international standards related to EN 15359:2011 for the classification of the SRF were employed, assessing the most feasible mix of materials to provide the highest classification of SRF in terms of low calorific value (LCV), chlorine, and mercury concentration. Results reported that the SRF made of 80% plastics (85% PE and 15% PP) and 20% cellulosic (blend 2), as well as 30% plastics (50% PP and 50% PE) and 70% cellulosic (blend 1), can be considered an alternative fuel in Bolivia. On balance, it has been estimated that the use of non-recyclable plastics and cardboard from municipal solid waste can provide, on average, about 0.9-2.7 billion MJ of energy for cement kilns, solving about 1.4-5.3% of the SWM issues and covering about 8-23.4% of the energy demand for cement production in Bolivia. These results are novel for the scientific literature for estimating the potentialities of SRF in Latin America.

Impacts of a large-scale model of Municipal Solid Waste: An Input-Output analysis for the largest Brazilian metropolitan region.

This article presents socio-economic, energetic and CO2 emissions' impact by considering a large-scale integrated plant to treat Municipal Solid Waste (MSW) in the Metropolitan Region of São Paulo (MRSP); the most important Brazilian macro-region. As an alternative to landfills, this plant offers a source of renewable energy and a good assessment of benefits the circular economy provides. Based on the most recent interregional economic transactions data, the proposed Input-Output model has shown reductions in the local energy demand (-0.31%), carbon emissions (-3.40%). On the other hand, it has suggested gains in the GDP (+0.21%) and formal job positions (+0.08% or 10.6k) when recyclables are introduced massively in the economy.

Second-Generation Lignocellulosic Supportive Material Improves Atomic Ratios of C:O and H:O and Thermomechanical Behavior of Hybrid Non-Woody Pellets.

Pellets refer to solid biofuels for heating and power. The pellet's integrity is of great relevant to ensure safe and effective transportation and storage, and comfort to stakeholders. Several materials that are supportive, whether organic and inorganic, to pellets exist. However, no work in the literature is linking making hybrid non-wood pellets with addition of residual biomass from distillation of cellulosic bioethanol, and this requires further investigations. Figuring out how effective this challenging agro-industrial residue could be for reinforcing non-wood pellets is accordingly the scientific point of this study focusing on management of waste and valorization of biomass. The pilot-scale manufacturing of hybrid pellets consisted of systematically pressing sugarcane bagasse with the lignocellulosic reinforcement at the mass ratios of 3:1, 1:1, and 1:3 on an automatic pelletizer machine at 200 MPa and 125 °C. Elemental contents of C and H, durability, and energy density all increased significantly from 50.05 to 53.50%, 5.95 to 7.80%, 95.90 to 99.55%, and 28.20 to 31.20 MJ kg-1, respectively, with blending the starting material with the reinforcement at 1:3. Preliminary evidence of residual biomass from distillation of second-generation bioethanol capable of highly improving molecular flammable/combustible properties, mechanical stability, and fuel power of composite non-wood pellets exist.

Pretreatment using Opuntia cochenillifera followed by household slow sand filters: technological alternatives for supplying isolated communities.

Household slow sand filter (HSSF) performance in continuous and intermittent flows was evaluated when influent water was treated with a natural coagulant extracted from Opuntia cochenillifera. The water under study, used as influent, had a turbidity of 111 ± 17.3 NTU. When clarifying the water with O. cochenillifera, the best condition obtained was 30  mg L-1 in natural pH (without correction), generating clarified water with turbidity satisfactory to filters operation (7.83 ± 2.32 NTU). The results indicated a better performance of continuous flow HSSF in turbidity removal (79.2% ± 8.39%) and higher efficiency of intermittent flow HSSF in the removal of E. coli (2.86 log ± 0.79 log for 12  h pause period and 2.41 log ± 0.42 log for 4  h pause period). For the sake of comparison, the evaluated HSSFs had the same production (60 L day-1). The impact on the interruption of the 96-h feed into the HSSFs was analysed and the results indicated a significant change in the quality of the filtered water after resuming the operation. This fragility of technology must be considered when it is implemented as lack of water can be a reality in the target communities. Acute toxicological assays with C. xanthus larvae showed no toxicity for pretreated and filtered water; however, more testing should be performed.

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

Municipal biowaste is a major environmental issue. Life-cycle assessment is a valuable tool to assess recycling options, and anaerobic digestion and composting have performed adequately. However, reviews indicate several discrepancies between studies. Thus, we critically review 25 life-cycle assessments of the composting and anaerobic digestion of municipal biowaste. Our objective is to identify decisive factors, methodological gaps and processes that affect environmental performance. We generally identified methodological gaps in expanding systems borders. In energy systems, the replaced energy source did not consider power generation or dynamic regulation. All studies adopted mixed energy sources or marginal approaches. Agroecosystems included the carbon sequestration potential and compensation for the production of synthetic fertilizers only. A limited range of scientifically proven benefits of compost use has been reported. In general, studies provided a limited account of the effects of use on land emissions, but contradictory assumptions emerged, mainly in modelling synthetic fertilizer compensation. Only three studies compensated direct emissions from the use of synthetic fertilizers, and none included indirect emissions. Further studies should include an analysis of the additional benefits of compost use, compensate for the effects of emissions from synthetic fertilizer use on land and mix attributional and consequential approaches in energy system expansion.

Energy recovery from municipal solid waste of intermunicipal public consortia identified in São Paulo State.

The main reasons, which this research is based on, are evidenced by the need of technical, political, economic and socioenvironmental coordination for the municipal solid waste management in Brazil and in the State of São Paulo. Most of the counties do not have adequate size to promote the management of MSW, so it's necessary to perform a consortia to do it. Therefore, it was necessary to characterize the current State of Sao Paulo consortial arrangements considering the environment (including sanitation, waste, water resources, among others). The scale of waste generation and the total population involved in these consortia were also considered. The energy potential of municipal solid waste was evaluated considering two possible technologies: The burning of landfill biogas in engines and the incineration in plants with Rankine cycle. It was identified that the sum of consortia energy potential was 1,454,336 MWh y-1 (landfill biogas), and 2,715,925 MWh y-1 (incineration). It is intended that such results provide significant information and encourage interaction between the different agents involved in the intermunicipal arrangements. It is expected that the characterisation and calculation of energy potential will stimulate future studies about new consortia approaches that consider energy recovery in their projects.

Comparative analysis of waste-to-energy alternatives for a low-capacity power plant in Brazil.

The Brazilian National Solid Waste Policy has been implemented with some difficulty, especially in convincing the different actors of society about the importance of conscious awareness among every citizen and businesses concerning adequate solid waste disposal and recycling. Technologies for recovering energy from municipal solid waste were considered in National Solid Waste Policy (NSWP), given that their technical and environmental viability is ensured, being the landfill biogas burning in internal combustion engines and solid waste incineration suggested options. In the present work, an analysis of current technologies and a collection of basic data on electricity generation using biogas from waste/liquid effluents is presented, as well as an assessment of the installation of a facility that harnesses biogas from waste or liquid effluents for producing electricity. Two combined cycle concepts were evaluated with capacity in the range 4-11 MW, gas turbine burning landfill biogas and an incinerator that burns solid waste hybrid cycle, and a solid waste gasification system to burn syngas in gas turbines. A comparative analysis of them demonstrated that the cycle with gasification from solid waste has proved to be technically more appealing than the hybrid cycle integrated with incineration because of its greater efficiency and considering the initially defined guidelines for electricity generation. The economic analysis does not reveal significant attractive values; however, this is not a significant penalty to the project given the fact that this is a pilot low-capacity facility, which is intended to be constructed to demonstrate appropriate technologies of energy recovery from solid waste.

Evaluation of two different alternatives of energy recovery from municipal solid waste in Brazil.

Brazil has a large population with a high waste generation. The municipal solid waste (MSW) generated is deposited mainly in landfills. However, a considerable fraction of the waste is still improperly disposed of in dumpsters. In order to overcome this inadequate deposition, it is necessary to seek alternative routes. Between these alternatives, it is possible to quote gasification and incineration. The objective of this study is to compare, from an energetic and economic point of view, these technologies, aiming at their possible implementation in Brazilian cities. A total of two configurations were evaluated: (i) waste incineration with energy recovery and electricity production in a steam cycle; and (ii) waste gasification, where the syngas produced is used as fuel in a boiler of a steam cycle for electricity production. Simulations were performed assuming the same amount of available waste for both configurations, with a composition corresponding to the MSW from Santo André, Brazil. The thermal efficiencies of the gasification and incineration configurations were 19.3% and 25.1%, respectively. The difference in the efficiencies was caused by the irreversibilities associated with the gasification process, and the additional electricity consumption in the waste treatment step. The economic analysis presented a cost of electrical energy produced of 0.113 (US$ kWh-1) and 0.139 (US$ kWh-1) for the incineration and gasification plants respectively.

Municipal wastewater sludge as a sustainable bioresource in the United States.

Within the United States and Puerto Rico, publicly owned treatment works (POTWs) process 130.5 Gl/d (34.5 Bgal/d) of wastewater, producing sludge as a waste product. Emerging technologies offer novel waste-to-energy pathways through whole sludge conversion into biofuels. Assessing the feasibility, scalability and tradeoffs of various energy conversion pathways is difficult in the absence of highly spatially resolved estimates of sludge production. In this study, average wastewater solids concentrations and removal rates, and site specific daily average influent flow are used to estimate site specific annual sludge production on a dry weight basis for >15,000 POTWs. Current beneficial uses, regional production hotspots and feedstock aggregation potential are also assessed. Analyses indicate 1) POTWs capture 12.56 Tg/y (13.84 MT/y) of dry solids; 2) 50% are not beneficially utilized, and 3) POTWs can support seven regions that aggregate >910 Mg/d (1000 T/d) of sludge within a travel distance of 100 km.

Green conversion of municipal solid wastes into fuels and chemicals

Presently, the society is facing a serious challenge for the effective management of the increasing amount of produced municipal solid wastes. The accumulated waste has caused a series of environmental problems such as uncontrolled release of greenhouse gases. Moreover, the increasing amount of wastes has resulted in a shortage of areas available for waste disposal, resulting in a nonsustainable waste management. These problems led to serious public concerns, which in turn resulted in political actions aiming to reduce the amount of wastes reaching the environment. These actions aim to promote sustainable waste management solutions. The main objective of these policies is to promote the recycling of municipal solid waste and the conversion of waste to energy and valuable chemicals. These conversions can be performed using either biological (e.g., anaerobic digestion) or thermochemical processes (e.g., pyrolysis). Research efforts during the last years have been fruitful, and many publications demonstrated the effective conversation of municipal solid waste to energy and chemicals. These processes are discussed in the current review article together with the change of the waste policy that was implemented in the EU during the last years.

Bio-syngas production from agro-industrial biomass residues by steam gasification.

This study evaluated the steam gasification potential of three residues from Brazilian agro-industry by assessing their reaction kinetics and syngas production at temperatures from 650 to 850°C and a steam partial pressure range of 0.05 to 0.3bar. The transition temperature between kinetic control and diffusion control regimes was identified. Prior to the gasification tests, the raw biomasses, namely apple pomace, spent coffee grounds and sawdust, were pyrolyzed in a fixed-bed quartz tubular reactor under controlled conditions. Gasification tests were performed isothermally in a magnetic suspension thermobalance and the reaction products were analyzed by a gas chromatograph with TCD/FID detectors. According to the characterization results, the samples presented higher carbon and lower volatile matter contents than the biomasses. Nevertheless, all of the materials had high calorific value. Syngas production was influenced by both temperature and steam partial pressure. Higher concentrations of H2 and CO were found in the conversion range of 50-80% and higher concentrations of CO2 in conversions around 10%, for all the gasified biochars. The H2/CO decreased with increasing temperature, mainly in kinetic control regime, in the lower temperature range. The results indicate the gasification potential of Brazilian biomass residues and are an initial and important step in the development of gasification processes in Brazil.

Thermogravimetric characterization and gasification of pecan nut shells.

This study focuses on the evaluation of pecan nut shells as an alternative source of energy through pyrolysis and gasification. The physicochemical characteristics of the selected biomass that can influence the process efficiency, consumption rates, and the product yield, as well as create operational problems, were determined. In addition, the thermal decomposition kinetics necessary for prediction of consumption rates and yields were determined. Finally, the performance of a downdraft gasifier fed with pecan nut shells was analyzed in terms of process efficiency and exit gas characteristics. It was found that the pyrolytic decomposition of the nut shells can be modeled adequately using a single equation considering two independent parallel reactions. The performance of the gasification process can be influenced by the particle size and air flow rate, requiring a proper combination of these parameters for reliable operation and production of a valuable syngas.

Life cycle comparison of waste-to-energy alternatives for municipal waste treatment in Chilean Patagonia.

The energy system in the Region of Aysén, Chile, is characterized by a strong dependence on fossil fuels, which account for up to 51% of the installed capacity. Although the implementation of waste-to-energy concepts in municipal waste management systems could support the establishment of a more fossil-independent energy system for the region, previous studies have concluded that energy recovery systems are not suitable from an economic perspective in Chile. Therefore, this work intends to evaluate these technical options from an environmental perspective, using life cycle assessment as a tool for a comparative analysis, considering Coyhaique city as a case study. Three technical alternatives were evaluated: (i) landfill gas recovery and flaring without energy recovery; (ii) landfill gas recovery and energy use; and (iii) the implementation of an anaerobic digestion system for the organic waste fraction coupled with energy recovery from the biogas produced. Mass and energy balances of the three analyzed alternatives have been modeled. The comparative LCA considered global warming potential, abiotic depletion and ozone layer depletion as impact categories, as well as required raw energy and produced energy as comparative regional-specific indicators. According to the results, the use of the recovered landfill gas as an energy source can be identified as the most environmentally appropriate solution for Coyhaique, especially when taking into consideration the global impact categories.