Abstract This study aimed to evaluate the effects of variables on the process of lipases production by Aspergillus niger C by submerged fermentation (SmF). The production assays were performed in shake flasks for 72 hours at 150 rpm and 32°C. First, a fractional factorial design 25-1 (FFD) was carried out to evaluate the effect of the following process variables: sucrose, ammonium sulphate, soybean oil, yeast extract concentration and pH. After the selection of the variables that significantly influenced the lipase production, a central composite rotational design 22 (CCRD) was used, aiming to find the most favorable operational conditions. The selected assay condition (15.0 g.L-1 sucrose, 4.0 g.L-1 ammonium sulphate, 4.0 g.L-1 soybean oil and 1.0 g.L-1 yeast extract at pH 5.0) was the one that presented a lipase activity of 27.46 U.mL-1. It was very close to that best assay (30.76 U.mL-1), but using half of the inducer concentration, consequently reducing process cost. The kinetics of lipase production showed that the highest specific activity was 57.17 U.mg-1. The pH and temperature effects on lipase activity produced in this study was investigated. The optimum activity was found in a more acidic pH (5.0-6.0) and 55°C.

This work aims evaluate the use of biocides in the microbiologically-influenced corrosion (MIC) of AISI 1020 carbon steel by sulfate-reducing bacteria (SRB) in artificial seawater. A natural biocide (garlic oil) and a commercial biocide (glutaraldehyde) were used to control the corrosion caused by these bacteria in artificial seawater. Microbial growth on the steel surface was evaluated by quantifying the sessile SRB using the most probable number (MPN) method. The action of biocides in the biocorrosion process was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The biofilm formation and the corrosion products on the steel surface were observed by scanning electron microscopy (SEM). The results showed that, although it was not able to inhibit the growth of sessile SRB completely, garlic oil showed a greater reduction in the corrosion process when compared to glutaraldehyde, indicating its possible application as a natural biocide under these conditions.

ABSTRACT The aim of this study was to produce bioethanol from enzymatic hydrolysates of cassava pulp, a by-product of cassava flour manufacturing, using an alcohol-tolerant Saccharomyces cerevisiae strain. First, the best operational condition of the starch hydrolysis process was determined through a complete factorial design (24), with triplicates at the central point. The independent variables evaluated were: the concentrations of α-amylase (Termamyl 2X) and glucoamylase (AMG 300L) and both liquefaction and saccharification times. The most favorable hydrolysis condition in the assay was achieved using 0.517 mL AMG.g starch-1 and 0.270 mL Termamyl.g starch-1, with liquefaction and saccharification times of 1 and 2 h, respectively. The broth obtained at this hydrolysis condition contained a high glucose concentration (160 g.L-1). Once the best reaction conditions were determined, fermentation tests were carried out in a 3 L bioreactor, in a batch system, at 30 °C, 100 rpm and pH 5.5, using 3 g.L-1 (dry biomass) of yeast as inoculum. After 24 h of fermentation, an ethanol concentration of 68 g.L-1 was obtained, with 0.48 ethanol yield and 2.83 g.L-1.h-1 productivity. These results indicate the potential use of cassava pulp, a by-product of cassava flour industries in Brazil, as a raw material for bioethanol production.

ABSTRACT In this work, the corrosion behavior of carbon steel AISI 1020 was evaluated in artificial seawater in the presence of mixed sulfate-reducing bacteria (SRB) culture isolated from the rust of a pipeline. The corrosion evaluation was performed by electrochemical techniques (open circuit potential (Eocp), polarization curves and electrochemical impedance spectroscopy (EIS)), while the formation of a biofilm and corrosion products were observed by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). The presence of SRB in the medium shifted the open circuit potential to more positive values and increased the corrosion rate of the steel. Electrochemical and morphological techniques confirmed the presence of a biofilm on the steel surface. EDS spectra data showed the presence of sulfur in the corrosion products. After removing the biofilm, localized corrosion was observed on the surface, confirming that localized corrosion had occurred. The biogenic sulfide may lead to the formation of galvanic cells and contributes to cathodic depolarization.