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.

Swine manure treatment technologies as drivers for circular economy in agribusiness: A techno-economic and life cycle assessment approach.

Anaerobic digestion has been employed as a technology capable of adding value to waste coupled with environmental impact mitigation. However, many issues need to be elucidated to ensure the systems viability based on this technology. In this sense, the present study evaluated technically, environmentally, and economically, four configurations of swine waste treatment systems focused on the promotion of decarbonization and circularity of the swine chain. For this, a reference plant, based on a compact treatment process named SISTRATES® (Portuguese acronym for swine effluent treatment system) was adopted to serve as a model for comparison and validation. The results showed the importance of prioritization of the energy recuperation routes through anaerobic digestion, providing increased economic benefits and minimizing environmental damage. Thus, the SISTRATES® configuration was the one that presented the best designs in a circular context, maximizing the recovery of energy and nutrients, along with the reduction of greenhouse gas emissions, ensuring the sustainability of the pig production chain.

The potential of animal manure management pathways toward a circular economy: a bibliometric analysis.

Improper disposal of animal waste is responsible for several environmental problems, causing eutrophication of lakes and rivers, nutrient overload in the soil, and the spread of pathogenic organisms. Despite the potential to cause adverse ecological damage, animal waste can be a valuable source of resources if incorporated into a circular concept. In this sense, new approaches focused on recovery and reuse as substitutes for traditional processes based on removing contaminants in animal manure have gained attention from the scientific community. Based on this, the present work reviewed the literature on the subject, performing a bibliometric and scientometric analysis of articles published in peer-reviewed journals between 1991 and 2021. Of the articles analyzed, the main issues addressed were nitrogen and phosphorus recovery, energy generation, high-value-added products, and water reuse. The energy use of livestock waste stands out since it is characterized as a consolidated solution, unlike other routes still being developed, presenting the economic barrier as the main limiting factor. Analyzing the trend of technological development through the S curve, it was possible to verify that the circular economy in the management of animal waste will enter the maturation phase as of 2036 and decline in 2056, which demonstrates opportunities for the sector's development, where animal waste can be an economic agent, promoting a cleaner and more viable product for a sustainable future.

Integration of swine manure anaerobic digestion and digestate nutrients removal/recovery under a circular economy concept.

The application of the circular economy concept should utilize the cycles of nature to preserve materials, energy and nutrients for economic use. A full-scale pig farm plant was developed and validated, showing how it is possible to integrate a circular economy concept into a wastewater treatment system capable of recovering energy, nutrients and enabling water reuse. A low-cost swine wastewater treatment system consisting of several treatment modules such as solid-liquid separation, anaerobic digestion, biological nitrogen removal by nitrification/denitrification and physicochemical phosphorus removal and recovery was able to generate 1880.6 ± 1858.5 kWh d-1 of energy, remove 98.6% of nitrogen and 89.7% of phosphorus present in the swine manure. In addition, it was possible to produce enough fertilizer to fertilize 350 ha per year, considering phosphorus and potassium. In addition, the effluent after the chemical phosphorus removal can be safely used in farm cleaning processes or disposed of in water bodies. Thus, the proposed process has proven to be an environmentally superior swine waste management technology, with a positive impact on water quality and ensuring environmental sustainability in intensive swine production.

Comparação entre tecnologias de aproveitamento energético de resíduos sólidos urbanos e balanço de emissões de gases de efeito estufa no município do Rio de Janeiro, RJ, Brasil / Comparison between energy recovery technologies for municipal solid waste and greenhouse gas emissions balance in the city of Rio de Janeiro, RJ, Brazil

RESUMO O presente estudo analisou o potencial de recuperação energética dos resíduos sólidos urbanos (RSU) e o balanço de emissões de gases de efeito estufa (GEE) resultante no município do Rio de Janeiro, Rio de Janeiro, com base em três cenários tecnológicos alternativos. Os potenciais de geração foram calculados para a recuperação de gás de lixo (GDL) em 363,98 GWhe.ano-1 e 0,181 MWhe.t-1, para a biodigestão anaeróbica em 367,27 GWhe.ano-1 e 0,247 MWhe.t-1; e para a incineração em 1.139,33 GWhe.ano-1 e 0,459 MWhe.t-1. Os indicadores de intensidade de carbono mostram que, ao se considerar somente as emissões de GEE de combustão, a recuperação de GDL e a biodigestão anaeróbica apresentam os menores valores (7,488.10-4 tCO2eq.MWhe-1), enquanto a incineração apresenta o valor de 1,248 tCO2eq.MWhe-1. Por outro lado, ao se considerar também as emissões de aterro associadas, os indicadores dos dois primeiros cenários correspondem a 8,191 e 3,552 tCO2eq.MWhe-1, respectivamente.

ABSTRACT The present study analyzes the energy recovery potential of municipal solid waste (MSW) and the resulting greenhouse gas (GHG) emission balance in the city of Rio de Janeiro, Rio de Janeiro, Brazil, based on three alternative technological scenarios. The generation potentials were calculated for waste gas recovery (WGR) to be 363.98 GWhe.year-1 and 0.181 MWhe.t-1, 367.27 GWhe.year-1 and 0.247 MWhe.t-1 for anaerobic biodigestion, and 1.139.33 GWhe.year-1 and 0.459 MWhe.t-1 for incineration. Carbon intensity indicators show that, when only considering GHG emissions from the combustion process, WGR recovery and anaerobic biodigestion present the lowest values, of 7.488.10-4 tCO2eq.MWhe-1, while the value for incineration corresponds to 1.248 tCO2eq.MWhe-1. On the other hand, when considering associated landfill GHG emissions, the indicators in the first two scenarios correspond to 8.191 and 3.552 tCO2eq.MWhe-1, respectively.

Análise do potencial de aproveitamento energético de biogás de aterro e simulação de emissões de gases do efeito estufa em diferentes cenários de gestão de resíduos sólidos urbanos em Varginha (MG) / Analysis of the potential use of landfill biogas energy and simulation of greenhouse gas emissions of different municipal solid waste management scenarios in Varginha, MG, Brazil

RESUMO O presente trabalho propõe avaliar a viabilidade econômica e ambiental de aproveitamento energético do biogás do aterro sanitário do município de Varginha (MG), além de analisar as emissões de gases de efeito estufa (GEE) e o uso de energia em diferentes cenários hipotéticos de gerenciamento de resíduos sólidos urbanos (RSU). Considerou-se uma projeção de geração de RSU em 20 anos de funcionamento do aterro, cuja produção de biogás foi estimada por meio do software LandGEM©. A análise de viabilidade econômica foi realizada por meio dos indicadores de valor presente líquido (VPL) e taxa interna de retorno (TIR). As emissões de GEE foram estimadas aplicando-se o modelo Waste Reduction Model (WARM©), considerando o cenário atual e três cenários alternativos de gerenciamento de RSU. Os cenários diversificaram em estratégias de reciclagem, digestão anaeróbia, incineração e disposição em aterro, com recuperação energética. Somente o aproveitamento energético com potência de 150 kW resultou em viabilidade econômica. Já os maiores benefícios ambientais foram obtidos pelo cenário 3, baseado na recuperação de materiais recicláveis, digestão anaeróbia e incineração dos RSU, reduzindo consideravelmente o volume de RSU destinados ao aterro. Dentre as práticas de gerenciamento dos cenários propostos, a reciclagem obteve os maiores ganhos energéticos e remoção de emissões de GEE.

ABSTRACT The present work proposes to evaluate the economic and environmental viability of energy recovery from biogas in the landfill of Varginha-MG, as well to analyze greenhouse gas emissions (GHG) and energy consumption in different scenarios of municipal solid waste (MSW) management. A 20-year projection of MSW generation and landfill operation were considered, whose biogas production was estimated through LandGEM software. The economic feasibility analysis was performed using the net present value (NPV), and the internal rate of return (IRR) as indicators. GHG emissions were estimated by applying the WARM model (Waste Reduction Model) considering the current MSW management scenario and three alternative ones. The scenarios diversified into recycling strategies, anaerobic digestion, landfill disposal and incineration with energy recovery. Only the energy recovery with a power of 150 kW resulted in economic viability. Moreover, the largest environmental benefits were obtained by scenario 3, based on the recovery of recyclable materials, anaerobic digestion and incineration of MSW, considerably reducing the volume of MSW landfilled. Among all management practices of the proposed scenarios, recycling resulted in greater energy gains and GHG emission removal.

Statistical model for heating value of municipal solid waste in Brazil based on gravimetric composition.

Municipal solid waste (MSW) management is a serious problem for public administrations, especially in terms of treatment and final disposal. These wastes have a high energy content and one of the possibilities of treatment is the recovery of energy through thermochemical processes. The parameter used to measure the amount of useful energy available in collected waste when submitted to thermochemical processes is called the lower heating value (LHV), which is usually determined in the laboratory or through empirical models from the literature. To this end, this paper aims to present two models for prediction of the LHV in the municipal solid waste of the municipality of Santo André. Samples were collected from 36 garbage trucks in the above-mentioned city, from September 2015 to January 2016. The models were developed based on the results of the gravimetric composition and laboratory analysis. The technique used to develop the models was the multiple linear regression by least squares method. As a result, the models obtained mean absolute percentage error (MAPE) indexes of 5.09% and 5.52%, considered excellent according to the literature classification. In addition, the calculated LHV of the Santo André municipal waste was 7.03 MJ/kg, which indicates a great potential for energy recovery using thermochemical processes. These are the first LHV prediction models developed in Brazil, which has been a significant accomplishment in Brazil. The proposed models were developed using empirical measurements of moisture in the solid waste and the LHV on samples collected with a statistically representative sampling method.

Three municipal solid waste gasification technologies analysis for electrical energy generation in Brazil.

In Brazil, in 2016, 196,050 tonnes day-1 of municipal solid waste (MSW) were collected, which means a waste generation of 1.035 kg per capita per day. Only 59.1% of the waste has adequate destination in sanitary landfills, whereas the remaining 40.9% has inadequate destination in controlled landfills and open dumps (ABRELPE, 2018). Among all the states in the country, the State of São Paulo has the biggest per capita generation: 2.290 kg. Today, the only waste destination practiced in the country is deposition in landfills, but other possibilities can be considered. Among thermal treatment routes, the gasification of MSW is an interesting alternative to be studied, because of its versatility and relatively low emissions. The aim of this work is to evaluate the potential of electricity generation through MSW gasification in Santo André city, Brazil, comparing three waste gasification technologies: TPS Termiska Processer AB, Carbogas and Energos. These alternatives have operated commercially for a few years, and data are available. Specific characteristics of each technology were taken into account, such as the reactor type and fuel properties. For the electricity production scheme, two energy conversion systems were assumed: an internal combustion engine and a steam power cycle. From the process parameters adopted, the results showed that Carbogas technology, coupled to internal combustion engines, presents the highest efficiency of electricity generation (30%) and also the lowest cost of electrical energy produced (US$65.22 MWh-1) when Santo André's gate fee is applied.

Thermal drying of industrial sludge using forced aeration.

This study investigated an industrial biosludge drying system using hot gases from a coal furnace, seeking to increase the solids content of the biosludge above 50% (w.b.), considered suitable for combustion in biomass boilers. Biosludge was collected from a paper mill activated sludge plant. Biosludge mixtures with eucalyptus chips and eucalyptus bark in two different proportions (15% and 25%) were placed into a drying chamber. Hot gases generated by the furnace, with a flowrate of 0.64 ± 0.02 m3 s-1 at 100 ± 20°C, were applied to the piles through a blowing system. The results demonstrated that the 75% biosludge/25% eucalyptus bark mixture achieved the best drying ratio, increasing the total solids content from 31% to 72%, over a 5-h drying period. Nevertheless, all other treatments involving the addition of a bulking agent achieved solids content above 50%, confirming the positive effect of adding dried material to the sludge. These results indicate a potential use of hot gases that are currently available and released into the atmosphere by paper mills.

Generating electrical energy through urban solid waste in Brazil: An economic and energy comparative analysis.

The search for alternative energy sources and increasing concerns over the generation of municipal solid waste are two widely discussed themes in contemporary academic literature. A possible alternative for solving both of these problems is through electrical energy generation through the use of this waste material. Although this practice is encouraged by the Brazilian National Solid Waste Policy, energy production through such methods still requires improvement. Given these considerations, this study aims to evaluate the generation of electric energy from solid waste in three different systems (biogas from sanitary landfills; methanization of organic fraction in anaerobic digesters; and combustion in incinerators) through economic and energy analysis. Economic analysis was performed with the parameters Net Present Value and Levelized Cost of Electricity. Economic viability was only seen in the cases which considered landfill biogas energy recovery, demonstrating a need for incentives and support policies to enable technologies that are environmentally more advantageous than landfills.

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.

Potencial energético de resíduos sólidos domiciliares do município de Ponta Grossa, Paraná, Brasil / Energy potencial of household solid waste (HSW) in the city of Ponta Grossa, Paraná, Brazil

RESUMO A disposição dos resíduos sólidos domiciliares (RSD) é um desafio na maior parte dos municípios brasileiros, pois é realizada sem tratamento prévio, trazendo inúmeros impactos. A utilização de incineração com recuperação energética possibilita a redução dos impactos. O objetivo deste estudo foi analisar o potencial energético dos RSD do município de Ponta Grossa, Paraná, Brasil. Para isso, foram coletadas amostras no aterro do município para a realização das análises. A caracterização gravimétrica apresentou valores de 0,28 kg kg-1 para os recicláveis, 0,44 kg kg-1 para a matéria orgânica e 0,28kg kg-1 para os rejeitos. Os conteúdos de carbono fixo variaram de 0,06 a 0,09 kg kg-1, os de materiais voláteis de 0,75 a 0,81 kg kg-1 e os de cinzas de 0,10 a 0,18 kg kg-1. E o poder calorífico superior médio apresentou valor elevado, 19.807 kJ kg-1, se comparado com o de resíduos de outras cidades do mundo.

ABSTRACT Household solid waste (HSW) disposition is a challenge for the majority of the Brazilian cities, most held without pretreatment, which causes impacts. Incineration with recovery energy is an alternative to reduce impacts. In this study we analyzed the energy potential of HSW in the city of Ponta Grossa, Paraná, Brazil. Samples were collected at the municipal landfill for the analysis. Waste gravimetric characterization showed value 0.28 kg kg-1for recyclables, 0.44 kg kg-1for organic matter and 0.28 kg kg-1 for rejects. The fixed carbon content ranged from 0.06 to 0.09 kg kg-1, the volatile materials from 0.75 to 0.81 kg kg-1 and ashes from 0.10 to 0.18 kg kg-1. The average gross calorific value showed high value, 19,807 kJ kg-1, compared to the waste of other cities in the world.

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.

Influence of carbon electrode material on energy recovery from winery wastewater using a dual-chamber microbial fuel cell.

The aim of this work was to evaluate three carbon materials as anodes in microbial fuel cells (MFCs), clarifying their influence on the generation of electricity and on the treatability of winery wastewater, a highly organic-loaded waste. The electrode materials tested were carbon felt, carbon cloth and carbon paper and they were used at the same time as anode and cathode in the tests. The MFC equipped with carbon felt reached the highest voltage and power (72 mV and 420 mW m-2, respectively), while the lowest values were observed when carbon paper was used as electrode (0.2 mV and 8.37·10-6 mW m-2, respectively). Chemical oxygen demand (COD) removal from the wastewater was observed to depend on the electrode material, as well. When carbon felt was used, the MFC showed the highest average organic matter consumption rate (650 mg COD L-1 d-1), whereas by using carbon paper the rate decreased to 270 mg COD L-1 d-1. Therefore, both electricity generation and organic matter removal are strongly related not to the chemical composition of the electrode (which was graphite carbon in the three electrodes), but to its surface features and, consequently, to the amount of biomass adhered to the electrode surface.

Potencial energético e alternativas para o aproveitamento do biogás e lodo de reatores UASB: estudo de caso Estação de tratamento de efluentes Laboreaux (Itabira) / Energy potential and alternative usages of biogas and sludge from UASB reactors: case study of the Laboreaux wastewater treatment plant (Itabira)

RESUMO: Este trabalho estuda o potencial de aproveitamento energético dos subprodutos biogás e lodo gerados na estação de tratamento de efluentes (ETE) Laboreaux em Itabira (MG), composta de reatores UASB, filtros biológicos percoladores e unidade de desaguamento do lodo por filtro prensa. Os subprodutos biogás e lodo foram caracterizados em termos quantitativos (produção) e qualitativos (composição e poder calorífico) durante 12 meses de monitoramento. Foram estudados dois cenários de aproveitamento energético dos subprodutos: (i) uso prioritário do biogás para a secagem térmica do lodo e o excedente de biogás para geração de eletricidade em motor de combustão interna; e (ii) uso prioritário do biogás visando à geração de eletricidade e ao aproveitamento do calor dos gases de exaustão para a secagem térmica de lodo. Para a análise desses cenários, utilizou-se o software CHEMCAD(r) a fim de determinar as condições de queima do biogás em câmara de combustão e em motor de combustão interna, assim como na determinação dos balanços de massa e energia. O estudo analisou o potencial de aproveitamento dos subprodutos do tratamento como fonte de energia renovável para uso na própria ETE e para fornecimento a terceiros. No cenário 1, a geração de eletricidade é menor (atendendo 22,2% da demanda de energia da ETE), mas a secagem térmica possibilita maior redução no volume final de lodo a ser disposto ou a eliminação completa de disposição final se o lodo seco final (com 10% de umidade) for utilizado como combustível por terceiros. No cenário 2, a geração de eletricidade é capaz de suprir 57,6% da demanda de energia da ETE, todavia o calor contido nos gases de exaustão não é suficiente para a secagem de todo o lodo desaguado, configurando uma menor redução na quantidade de lodo a ser disposto (13,5 ou 24,9% de redução em massa, conforme a alternativa de remoção de umidade selecionada).

ABSTRACT: This work assesses the potential of energy recovery of the byproducts biogas and sludge produced at the Laboreaux wastewater treatment plant (WWTP), in Itabira (MG), which is integrated by UASB reactors, trickling filters and sludge dehydration unit (filter press). The byproducts biogas and sludge were quantitatively (production) and qualitatively (composition and calorific value) characterized during a monitoring period of 12 months. Two scenarios for energy recovery from the byproducts were considered: (i) priority use of biogas for sludge thermal drying and the excess of biogas being used for power generation in an internal combustion engine (ICE); and (ii) primary use of biogas for power generation and the heat of the engine exhaustion gases being used for sludge thermal drying. Biogas burning conditions into a combustion chamber and in an internal combustion engine, as well as mass and energy balances for each scenario, were assessed with the CHEMCAD(r) software. The study analysed the potential use of the byproducts as sources of renewable energy for use in the WWTP itself and to be offered to third party. In scenario 1, the electricity generation is lower (fulfilling 22.2% of the WWTP energy demand), but thermal drying allows greater reduction of sludge volume to be disposed of, or the entire elimination of final disposal if the dry sludge (with 10% moisture content) is used as fuel by the third party. As for scenario 2, the electricity generation is sufficient to supply 57.6% of the WWTP energy demand, nevertheless the heat contained in exhausted gases is not enough to dry the whole dehydrated sludge, configuring a lower reduction of sludge amount to be disposed of (13.5 or 24.9% of mass reduction, depending on the moisture reduction alternative chosen).

Influence of sludge age on the performance of MFC treating winery wastewater.

The objective of this paper was to determine the influence of sludge age on microbial fuel cell (MFC) performance for generating electricity and removing organic matter from winery wastewater. Six Solid Retention Times (SRT) were used: 1.2, 1.4, 1.8, 2.3, 3.5 and 7.0 d. Results demonstrate that the electricity generation increases by decreasing the SRT, selecting electrogenic microorganisms, once the specific organic loading rate (SOLR) increased and the competition for substrate was reduced. Decreasing the SRT, coulombic efficiency can be increased from 3.4% to almost 42.2% and maximum power density from 58 to 890 mW m(-2). However the SRT did not influence on organic matter removal in biological treatment, because only a small part of COD was removed oscillating around 600 mg L(-1) d(-1)and it was very similar at all SRT studied.

Bioenergy from stillage anaerobic digestion to enhance the energy balance ratio of ethanol production.

The challenges associated with the availability of fossil fuels in the past decades intensified the search for alternative energy sources, based on an ever-increasing demand for energy. In this context, the application of anaerobic digestion (AD) as a core treatment technology in industrial plants should be highlighted, since this process combines the pollution control of wastewaters and the generation of bioenergy, based on the conversion of the organic fraction to biogas, a methane-rich gaseous mixture that may supply the energetic demands in industrial plants. In this context, this work aimed at assessing the energetic potential of AD applied to the treatment of stillage, the main wastewater from ethanol production, in an attempt to highlight the improvements in the energy balance ratio of ethanol by inserting the heating value of methane as a bioenergy source. At least 5-15% of the global energy consumption in the ethanol industry could be supplied by the energetic potential of stillage, regardless the feedstock (i.e. sugarcane, corn or cassava). The association between bagasse combustion and stillage anaerobic digestion in sugarcane-based distilleries could provide a bioenergy surplus of at least 130% of the total fossil fuel input into the ethanol plant, considering only the energy from methane. In terms of financial aspects, the economic gains could reach US$ 0.1901 and US$ 0.0512 per liter of produced ethanol, respectively for molasses- (Brazil) and corn-based (EUA) production chains. For large-scale (∼1000 m(3)EtOH per day) Brazilian molasses-based plants, an annual economic gain of up to US$ 70 million could be observed. Considering the association between anaerobic and aerobic digestion, for the scenarios analyzed, at least 25% of the energetic potential of stillage would be required to supply the energy consumption with aeration, however, more suitable effluents for agricultural application could be produced. The main conclusion from this work indicates that anaerobic processes should be considered the core technology to treat stillage, based mainly on the attractive relation energy generation-financial return and on the possibility to keep the advantages inherent to the common fertigation when using the treated effluent in agriculture.

Characterization of Printed Circuit Boards for Metal and Energy Recovery after Milling and Mechanical Separation.

The proper disposal of electrical and electronic waste is currently a concern of researchers and environmental managers not only because of the large volume of such waste generated, but also because of the heavy metals and toxic substances it contains. This study analyzed printed circuit boards (PCBs) from discarded computers to determine their metal content and characterized them as solid waste and fuel. The analysis showed that PCBs consist of approximately 26% metal, made up mainly of copper, lead, aluminum, iron and tin, as well as other heavy metals such as cadmium and nickel. Comparison with the results of other studies indicated that the concentration of precious metals (gold and silver) has declined over time. Analysis of the leachate revealed high concentrations of cadmium and lead, giving the residue the characteristics of hazardous waste. After milling the PCBs, we found that larger amounts of metal were concentrated in smaller fractions, while the lightest fraction, obtained by density separation, had a gross calorific value of approximately 11 MJ/kg, although with a high ash content. Milling followed by density separation proved potentially useful for recovery of metals and energy-rich fractions.