The biorefinery concept goes beyond the compliance with environmental legislation for wastewater treatment, by adding value to the by-products of the process. In this context, the use of acidogenic reactors is encouraging due to the possibility of recovering intermediate products of anaerobic digestion. In acidogenic reactors, the fermentative reactions are predominant, transforming the complex organic matter of the effluents into organic acids, alcohols, hydrogen gas and carbon dioxide. Depending on the yields of these products, their recovery is of great interest. In addition, several studies show that the use of acidogenic reactors may lead to higher efficiency of methanogenic reactors, fed with previously acidified effluent, in terms of methane production and effluent quality. However, the application of acidogenic reactors faces limitations, which must be overcome by the advantages offered to the process. Due to the constant production of organic acids, alkalization is a common practice, but it has a negative impact on the environmental and economic balance. In this sense, in our previous research, we studied the operation of several acidogenic reactors to produce hydrogen without the addition of alkalis, using sucrose-based synthetic effluent. Relatively high H2 yield and production were achieved, continuously and in the long-term, under extreme acid conditions (pH <3.0). Effluent fermentation was also satisfactory, and the main products of the liquid phase were acetate and ethanol. Considering that these results are promising, but at the same time there is still much to be investigated about how this occurred and how to propose general rules on acidogenesis under these conditions, it is proposed in the present project a detailed metagenomic analysis of the microbiota of acidogenic reactors, without alkalization and fed with different types of effluents; more precisely, sucrose and sugarcane vinasse. In a complementary way, metatranscriptomic approach is proposed to verify which genes are actually being expressed. The use of a multiomics approach aims to evaluate the genomic potential for biohydrogen production by the established microbial communities, to elucidate the metabolic routes of interest and, mainly, to provide scientific support for the optimization of the operational conditions to obtain the desired products.
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