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The anaerobic biodigestion is as an alternative treatment for vinasse that preserve and even increase its fertilization potential (phosphorus, potassium and nitrogen content), dramatic reducing the BOD, making safer the use of treated vinasse for field fertirrigation. The process also yield methane, a very convenient and eco-friendly fuel gas, so the paper deals with a methodology for the calculation of the cost of the biogas, considering also the benefits of the fertirrigation using the liquid effluents from the digester, as well as the solids residues, very rich in organic matter. An analysis of the economical feasibility of the use of the biogas, obtained from the vinasse anaerobic digestion, as fuel, is also carried out. Different scenarios are evaluated, like: electric power generation through Reciprocating Combustion Engines (RCE), gas turbines and microturbines (MT), the cofiring of the biogas and bagasse in the mill’s boilers, the sale of the substituted bagasse, its utilization for electric power generation and the use of the biogas, as fuel, in spray drying of thermal sensible bioproducts (yeasts) to be commercialized. The possibility of selling the certificates of avoided greenhouse gasses emissions (carbon credits) due to the use of the biogas in substitution to fossil fuels, is also considered.

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This study assessed the effect of hydraulic retention time (HRT) on biohydrogen production by dark fermentation using an anaerobic fluidized bed reactor fed with cheese whey synthetic wastewater. The reactor of 1.2 L was operated with an approximate carbohydrate concentration of 2800 mg L -1 , and HRTs of 6, 4, 2, 1 and 0.5 h. Acetic and butyric acids were the main metabolites produced in the reactor. The hydrogen production increased from 0.039 to 1.43 L-H 2 h -1 L -1 -reactor as the HRT decreased from 6 to 0.5 h. The best hydrogen yield (HY) (2.73 mol-H 2 mol-carbohydrate -1 ) and carbohydrate consumption (81.02%) were achieved at a HRT of 6 h (12.34 kg-COD m -3 d -1 ) followed by the HY of 2.43 mol-H 2 mol-carbohydrate -1 at a HRT of 0.5h (163.02 kg-COD m -3 .d - 1 ). An increase in the influent pH in the operational phase 05 (HRT of 0.5 h) favored hydrogen production despite the reduced carbohydrate conversion compared to phase 01 (HRT of 6 h). In both conditions, the reactor presented the highest amount of acetic acid, indicating that the acetate route favored the hydrogen yield production. The HRT reduction led to an increase in microbial diversity, as evidenced by the Shannon-Wiener coefficient of 2.586, which corresponds to the operational phase with a HRT of 2 h.

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The cassava processing chain is potentially sustainable and can actively contribute in the change towards the circular economy. The present article aimed at assessing global scientific research trends on anaerobic treatment of wastewater originating from cassava processing. In this regard, a bibliometric analysis of anaerobic digestion and biogas production of wastewater from cassava processing was carried out within the period between 1980 and 2020, using the Scopus database. The results showed that the interest of research on the subject grew exponentially from 2001, being mainly focused on the recovery of by‐products such as methane, biogas, hydrogen, bio‐oil, bioethanol, propionic acid and butyric acid. Full‐scale anaerobic wastewater treatment already is carried out in countries such as India, China and Thailand, and has been explored largely in developing countries. The studies demonstrated that wastewater bioconversion is an attractive solution, with widespread full‐scale applications. The authors of the present work expect that new publications on environmental and economic sustainability of the processing industry of cassava by‐products will contribute to the sector's development towards a green and low‐carbon economy. © 2021 Society of Chemical Industry (SCI).

Aproveitamento dos efluentes domésticos para geração de energia em condomínios residenciais de baixa renda Domestic wastewater utilization for Power Generation in low-income Residential Condominiums Resumo O estudo busca avaliar o potencial energético da estação de tratamento de esgoto de condomínios residenciais de baixa renda, realizando as seguintes estimativas: produção de biogás, produção de energia elétrica, necessidade energética do condomínio e avaliação econômica. Foram contabilizadas as perdas de metano durante o processo de tratamento anaeróbico. A produção média estimada de biogás foi de 60 m³/d, resultando em uma possível disponibilidade de energia elétrica de 189,45 kWh/d, capaz de fornecer a iluminação dos postes e da área de lazer do condomínio. Além da possibilidade de atender à população local, pode-se ganhar créditos revertendo a energia elétrica gerada na rede de distribuição por meio do sistema de compensação de energia elétrica da Aneel. A utilização do biogás como geração de energia elétrica é importante para o meio ambiente, pois evita que seja lançado gás metano na atmosfera e reduz a captação dos recursos hídricos naturais com a geração de energia.

Greenhouse Gas emissions inventories are strategic environmental management tools that estimate emissions by specific sources in a given geographical area and timeframe. Developing an inventory is the first step in creating programs to improve air quality. This research aimed to prepare a GHG inventory and propose a management of its emissions from the activities of the Sanitation Company of Alagoas (Casal) in the Capital Unit in 2018. The methodology employed involved literature analysis to identify the most appropriate method for inventory preparation, data collection in various units of the company, interviews with managers and GHG accounting. The methodology used for the estimation was that indicated by the Brazilian GHG Protocol Program, complemented by the guidelines of the Intergovernmental Panel on Climate Change (IPCC) for the case of sewage treatment. The results of the GHG emissions inventory indicate that in 2018, Casal, Capital unit emitted 31,099.33 tCO2e, of which 86.7% (26,980.70 tCO2e) came from direct emissions, while indirect ones represented 13. 3% (4,118.63 tCO2e). The company's main sources of emissions were the sewage treatment and energy consumption categories, respectively. The results form the basis for the incorporation of GHG reduction measures in the company's strategic planning.