Dark Fermentation Process Response to the Use of Undiluted Tequila Vinasse without Nutrient Supplementation

The technical feasibility of valorizing tequila vinasse (TV), a wastewater with high pollution potential, through the production of biogenic hydrogen via dark fermentation, has long been proven in diverse lab-scale reactors that were operated either in batch or continuous mode. However, such systems have mainly been tested with diluted streams and nutrient supplementation, hindering the techno-economic attractiveness of the TV-to-hydrogen concept at large scale. In this study, the feasibility of producing hydrogen from high-strength undiluted TV with no added extra nutrients was evaluated under batch mesophilic conditions. Additionally, the use of two different acidogenic inocula obtained either by heat or heat-aeration pretreatment was investigated to get a greater understanding of the effect of inoculum type on the process. The results obtained showed that the TV utilized herein contained macro- and micro-nutrients high enough to support the hydrogenogenic activity of both cultures, entailing average hydrogen yields of 2.4–2.6 NL H2/L vinasse and maximum hydrogen production rates of 1.4–1.9 NL H2/L-d. Interestingly, the consumption of lactate and acetate with the concomitant production of butyrate was observed as the main hydrogen-producing route regardless of the inoculum, pointing out the relevance of the lactate-driven dark fermentative process. Clostridium beijerinckii was ascertained as key bacteria, but only in association with microorganisms belonging to the genera Enterobacter and Klebsiella, as revealed by phylogenetic analyses.

Impact of Inoculum Type on the Microbial Community and Power Performance of Urine-Fed Microbial Fuel Cells

Bacteria are the driving force of the microbial fuel cell (MFC) technology, which benefits from their natural ability to degrade organic matter and generate electricity. The development of an efficient anodic biofilm has a significant impact on the power performance of this technology so it is essential to understand the effects of the inoculum nature on the anodic bacterial diversity and establish its relationship with the power performance of the system. Thus, this work aims at analysing the impact of 3 different types of inoculum: (i) stored urine, (ii) sludge and (iii) effluent from a working MFC, on the microbial community of the anodic biofilm and therefore on the power performance of urine-fed ceramic MFCs. The results showed that MFCs inoculated with sludge outperformed the rest and reached a maximum power output of 40.38 mW·m−2anode (1.21 mW). The power performance of these systems increased over time whereas the power output by MFCs inoculated either with stored urine or effluent decreased after day 30. These results are directly related to the establishment and adaptation of the microbial community on the anode during the assay. Results showed the direct relationship between the bacterial community composition, originating from the different inocula, and power generation within the MFCs.

Infectivity and effectivity of commercial and native arbuscular mycorrhizal biofertilizers in seedlings of maize (Zea mays)

<p class="Body"><strong>Background: </strong>Nowadays there is a need to implement novel and effective methods in sustainable agriculture. Arbuscular mycorrhizal (AM) fungi are an alternative that benefits crop productivity and reduces the use of chemical inputs.<strong></strong></p><p class="Body"><strong>Question: </strong>Have commercial and native mycorrhizal inoculants the same infectivity? Is the performance of maize seedlings affected by commercial and native inoculum type?</p><p class="Body"><strong>Study species:</strong> Maize (<em>Zea mays</em>).<strong></strong></p><p class="Body"><strong>Study site and dates: </strong>Greenhouse experiment, March 2016.<strong></strong></p><p class="Body"><strong>Methods: </strong>The experimental design was unifactorial (five levels) and completely randomized: four mycorrhizal inocula (liquid, liquid mix, solid, and native AM spores), and one control (NM- inoculum). After a month of inoculating the seedlings, we harvested the plants, and the biomass and AM colonization were evaluated.<strong></strong></p><p class="Body"><strong>Results: </strong>The seedlings without AM fungi had greater total above- and belowground biomass compared with the inoculated seedlings. Only native and solid fungus treatments showed AM colonization in their roots. Our results are discussed in terms of soil mineral nutrient concentrations, cost-benefit of mycorrhizal symbiosis, edaphic origin of AM-native and contained of commercial inocula.<strong> </strong><strong></strong></p><p class="Body"><strong>Conclusions: </strong>The infectivity and effectiveness observed in the maize seedlings depends of mycorrhizal inoculum type.</p>