No abstract

No abstract

Most biogas plants in the world run under psychrophilic conditions and are operated by small and medium farmers. There is a gap of knowledge on the performance of these systems after several years of operation. The aim of this research is to provide a complete evaluation of a psychrophilic, low-cost, tubular digester operated for eight years. The thermal performance was monitored for 50 days, and parameters such as pH, total volatile fatty acid (tVFA), chemical oxygen demand (COD) and volatile solids (VS) were measured every week for the influent and effluent. The digester operated at a stabilized slurry temperature of around 17.7 °C, with a mean organic load rate (OLR) equal to 0.52 kg VS/m3digester *d and an estimated hydraulic retention time (HRT) of 25 days. The VS reduction in the digester was around 77.58% and the COD reduction was 67 ± 3%, with a mean value for the effluent of 3.31 ± 1.20 g COD/Lt, while the tVFA decreased by 83.6 ± 15.5% and the presence of coliforms decreased 10.5%. A BioMethane potential test (BMP) for the influent and effluent showed that the digester reached a specific methane production of 0.40 Nm3CH4/kg VS and a 0.21 Nm3CH4/m3digester d with 63.1% CH4 in the biogas. These results, together with a microbiological analysis, show stabilized anaerobic digestion and a biogas production that was higher than expected for the psychrophilic range and the short HRT; this may have been due to the presence of an anaerobic digestion microorganism consortium which was extremely well-adapted to psychrophilic conditions over the eight-year study period.

Cocoa is a product of natural origin rich in polyphenols, mainly procyanidins and flavan-3-ols, which has a high antioxidant power. Its regular consumption brings positive health effects. The objective of the present study was to evaluate the effects of diameter of particle, extraction time, temperature, pressure and ethanol concentration in the supercritical fluid extraction (SFE) of bioactive compounds from cocoa husk. This work was developed in two stages. The first stage was aimed to study the impact of the particle size and extraction time. Extractions were carried out under constant conditions. Once particle size and extraction time were defined, it gave way to the second stage, where the effect of three levels of temperature (308.15, 313.15 and 318.15 K), pressure (10, 15 and 20 MPa) and concentration of ethanol (2, 11, and 20% ethanol) were evaluated. The results of this study suggest that particle sizes less than 0.26mm and extraction times exceeding 147min could increase the total polyphenol content (TPC). Finally, a multivariate statistical analysis was developed, showing that the most favorable conditions for obtaining extracts rich in polyphenols corresponded to 308.15K, 20MPa and 20% ethanol, under which the TPC was 35.11(±1.57)EAGmg/LEg, a total flavan-3-oles content (TFC) of 12.89 (±0.51)EEPmg/gLE and total carotenoids content (TCC) of 64.35(±1.54)EBC mg/gLE. The results obtained suggest that SFE favors the extraction of apolar compounds (carotenoids) from cocoa husk. Likewise, for the optimal extraction point, husk cocoa showed antioxidant capacity of 489.58μmol ET/LEg.

No abstract