This work assessed the energy potential and alternative usages of biogas and sludge generated in upflow anaerobic sludge blanket reactors at the Laboreaux sewage treatment plant (STP), Brazil. Two scenarios were considered: (i) priority use of biogas for the thermal drying of dehydrated sludge and the use of the excess biogas for electricity generation in an ICE (internal combustion engine); and (ii) priority use of biogas for electricity generation and the use of the heat of the engine exhaust gases for the thermal drying of the sludge. Scenario 1 showed that the electricity generated is able to supply 22.2% of the STP power demand, but the thermal drying process enables a greater reduction or even elimination of the final volume of sludge to be disposed. In Scenario 2, the electricity generated is able to supply 57.6% of the STP power demand; however, the heat in the exhaust gases is not enough to dry the total amount of dehydrated sludge.

The production of dairy products generates several environmental impacts, and life cycle assessment (LCA) is a useful methodology to quantify and understand those impacts. In Brazil, some traditional dairy products have not yet been evaluated using the LCA methodology. Based on this gap, we conducted a cradle-to-gate LCA of six dairy products from a plant in Minas Gerais, Brazil. We also performed two sensitivity analyses. The first analysis was on how the environmental profiles of the products changed depending on how the multifunctional processes were allocated. The second analysis evaluated how these changes in environmental profiles occurred depending on the way that the impacts were allocated to products and by-products (whey and buttermilk) produced within the dairy factory. Among the dairy products studied, the impacts of mozzarella cheese and butter substantially surpassed those of other products; cheese spread and dulce de leche had a similar impact; and yoghurt and milk had the lowest values for the impact categories that were assessed. The inclusion of by-products in the analysis proved to be an effective way to reduce the environmental impacts attributed to the dairy products, especially for cheese and cheese spread, the impact values of which decreased by 56% and 46%, respectively. Additionally, the use of different strategies to deal with the multifunctional processes significantly affected the impact results of the dairy products. The subdivision of processes combined with causal allocation was the best alternative as opposed to the allocation by milk solids. These results could offer a better understanding of the environmental profiles of dairy products from Brazil, especially the traditional products, such as dulce de leche and cheese spread. Other contributions of this study include the proposal of alternatives that could improve the environmental profiles of products (such as the processing of by-products and the questioning of the use of allocation according to milk solids, which have been commonly used in other life cycle assessment studies) and the proposal of a better method for assessing the environmental impacts of dairy products.

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).

Online approaches for monitoring water quality can be an alternative aid to rapid decision-making in watershed management, especially reservoirs, given their vulnerability to the process of eutrophication. In this study, a modified water quality index (WQI) was developed using parameters that are easily measured with sensors, which would allow for the online monitoring of reservoirs. The modified WQI was based on WQI_CETESB and we used regression models to obtain values for the parameters: total phosphorus (TP), total nitrogen (TN), biochemical oxygen demand (BOD) and total solids (TS). Water quality data from reservoirs from 2003 to 2020 were used, which were provided by the Environmental Company of the State of São Paulo (CETESB), Brazil. The adjusted modified WQI employing weight redistribution (WQI_RWAdj or WQI_SOL) presented the most promising results, with a Pearson correlation of 0.92 and a success rate of 72.6% and 97.0% for the CETESB and simplified classifications, respectively. WQI_SOL, which was proposed in the present study, exhibited a satisfactory performance, allowing the water quality of reservoirs to be monitored remotely and in real-time.