The successful operation of any type of hydrogen-producing bioreactor depends on the performance of the microorganisms present in the system. Both substrate and partial gas pressures are crucial factors affecting dark fermentation metabolic pathways. The main objective of this study was to evaluate the impact of both factors on hydrogen production using anaerobic granular sludge as inoculum and, secondly, to study the metabolic shifts of an anaerobic community subjected to low partial gas pressures. With this goal in mind, seven different wastewater (four synthetic media, two industrial wastewater, and one domestic effluent) and the effect of applying vacuum on the systems were analyzed. The application of vacuum promoted an increase in the diversity of hydrogenproducing bacteria, such as Clostridium, and promoted the dominance of acetoclastic-over hydrogenotrophic methanogens. The application of different media promoted a wide variety of metabolic pathways. Nevertheless, reduction of the hydrogen partial pressure by application of vacuum lead to further oxidation of reaction intermediates irrespective of the medium used, which resulted in higher hydrogen and methane production, and improved the COD removal. Interestingly, vacuum greatly promoted biogenic hydrogen production from a real wastewater, which opens possibilities for future application of dark fermentation systems to enhance biohydrogen yields.

Strain ZNI5, isolated from a hydrocarbon contaminated soil and identi ed as Bacillus subtilis after 16s rDNA sequence, grew and produced lipopeptides biosurfactants when cultured on glucose based media. After puri cation by anionic exchange chromatography and identi cation Reverse Phase High Performance Liquid Chromatography-Mass Spectrometry, the biosurfactant produced by ZNI5 were determined to be cyclic lipopeptides homologues. Four families of lipopeptides were identi ed by HPLC-MS analysis. They belongs to surfactin isoforms with molecular weights of 979, 993, 1007, 1021 and 1035 Da; iturin isoforms with molecular weights of 1028, 1042 and 1056 Da; Licheniformin with molecular weight of 1410 and newly identi ed isoforms named Inesfactin with molecular weights of 973 and 987 Da. Functional properties of the ZNI5 biosurfactant were studied. It was characterized as a powerful surface-active agent that decreases the surface tension of water from 72 mN/m to about 32 mN/m with a CMC value of 350 mg/L more e cient than chemical surfactants (Triton X100; CTAB and SDS). It has the capacity to disperse oil to about 80 mm at a concentration of 800 mg/L showing close e ciencies to the listed chemical surfactants. In addition, by studying the surface tension decrease capacity and the oil displacement activity, ZNI5 lipopeptide biosurfactant showed great thermal, pH and salts activity and stability enabling its use in the bioremediation elds and for diverse industrial applications.

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BACKGROUND: This work is focused on the anaerobic biodegradation of wastewater from used industrial oils (UIO) recovery using a bench-scale expanded granular sludge bed reactor (EGSB) at room temperature.