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Cannibalism is a behavior that different species of fish exhibit in the early stages of their life, and it has been widely reported. In Tabasco, Mexico, the ancestral species Atractosteus tropicus is farmed, which is a freshwater fish with a high nutritional and economic value. This species exhibits high cannibalistic behavior both in its larval and juvenile stages, which considerably decreases its production. Therefore, strategies have been developed to mitigate the effects of this behavior. One of them is the placement of shelters (rocks and artificial vegetation), which allow the vulnerable population to protect themselves from cannibals. The goal of this work is to study the effect of shelters on the cannibalistic behavior of the A. tropicus population through a mathematical model. The population is divided into two classes, the vulnerable population (prey) and the cannibal population (predator). Moreover, a system of ordinary differential equations is established, which is analyzed, and sufficient conditions for the coexistence of the two species are shown. Numerical simulations show coexistence by varying levels of refuge. The results obtained in this work can be applied to other populations that exhibit cannibalistic behavior. [ABSTRACT FROM AUTHOR]

In many countries, whey from the dairy industry is an abundant waste that generates an important environmental impact. Alternative processes to use the whey and minimize the environmental impact are needed. This work considered six formulations with different ammonium sulfate and L-phenylalanine (L-Phe) concentrations to produce bioethanol in sweet whey fermentation by Kluyveromyces marxianus. The results showed a maximum bioethanol concentration equal to 25.13 ± 0.37 g L−1 (p < 0.05) for formulation F6, with 1 g L−1 of L-Phe and 1.350 g L−1 of ammonium sulfate (96 h). For these conditions, the chemical oxygen demand removal percentage (CODR%) was 67%. The maximum CODR% obtained was 97.5% for formulation F3 (1 g L−1 of L-Phe) at 96 h; however, a significant decrease in bioethanol concentration (14.33 ± 2.58 g L−1) was observed. On the other hand, for formulation, F3, at 48 h of fermentation time, a bioethanol concentration of 23.71 ± 1.26 g L−1 was observed, with 76.5% CODR%. Based on these results, we suggest that the best conditions to obtain a significant bioethanol concentration and CODR% value are those used on the configuration F3 at 48 h. [ABSTRACT FROM AUTHOR]

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In some fermentation systems, whey components (lactose, proteins and minerals) can produce isopentyl acetate (IA). An analysis of the best conditions for IA production with Kluyveromyces marxianus was developed in this work. The experiment design was two-factor and three-level design based on a response surface methodology (RSM) using Design-Expert® software. The analysis of anomeric protons by nuclear magnetic resonance (1H-NMR) showed 81.25% of β lactose content. This characteristic favored the production of IA. The maximum output (Mp) of IA, determined by gas chromatography, was 9.52 g/L (p < 0.05). The central composite design (CCD) was used to perform the factor analysis. Results showed that concentrations of 0.03 (g/L) ammonium sulphate and 0.3 (v/v) of isoamyl alcohol are the best conditions for a maximum rate of IA production. The production of IA can reduce the discharge of whey, allowing its reuse and revaluation. [ABSTRACT FROM AUTHOR]

Energy integration is a tool which allows reducing the heating and cooling requirements for production processes. This is particularly important in the processes for production of biofuels, since such processes are expected to have low environmental impact, which can be achieved by reducing the need for steam and cooling water. It is common to perform energy integration by making use of all the available streams. This approach may allow reducing as much as possible utilities' requirements, but other indicators may be affected, such as capital costs, since the number of required equipment is increased. Thus, in this work the effect of performing partial integration is assessed, i.e., selecting only a few streams to perform the energy integration. The effect of increasing the number of integrated streams is assessed in terms of sustainability indicators based on the green chemistry principles. The studied indicators are utilities' requirements, total annual cost, environmental impact (assessed through CO2 emissions) and safety (assessed through the HPS1 index). The study is applied to the energy integration of a supercritical biodiesel production process and a lignocellulosic bioethanol production process. [ABSTRACT FROM AUTHOR]