Laura Azocar - Academia.edu (original) (raw)

Papers by Laura Azocar

Minerals, Aug 21, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

New Biotechnology, Sep 1, 2014

Catalysts, Apr 30, 2022

Applied Microbiology and Biotechnology, Aug 10, 2010

As biodiesel (fatty acid methyl ester (FAME)) is mainly produced from edible vegetable oils, crop... more As biodiesel (fatty acid methyl ester (FAME)) is mainly produced from edible vegetable oils, crop soils are used for its production, increasing deforestation and producing a fuel more expensive than diesel. The use of waste lipids such as waste frying oils, waste fats, and soapstock has been proposed as low-cost alternative feedstocks. Non-edible oils such as jatropha, pongamia, and rubber seed oil are also economically attractive. In addition, microalgae, bacteria, yeast, and fungi with 20% or higher lipid content are oleaginous microorganisms known as single cell oil and have been proposed as feedstocks for FAME production. Alternative feedstocks are characterized by their elevated acid value due to the high level of free fatty acid (FFA) content, causing undesirable saponification reactions when an alkaline catalyst is used in the transesterification reaction. The production of soap consumes the conventional catalyst, diminishing FAME production yield and simultaneously preventing the effective separation of the produced FAME from the glycerin phase. These problems could be solved using biological catalysts, such as lipases or whole-cell catalysts, avoiding soap production as the FFAs are esterified to FAME. In addition, by-product glycerol can be easily recovered, and the purification of FAME is simplified using biological catalysts.

World Journal of Microbiology & Biotechnology, Mar 22, 2011

Industrial Crops and Products, 2017

Cellulose nanofibrils (CNF) were isolated from agro-industrial waste (corn husks and oat hulls) a... more Cellulose nanofibrils (CNF) were isolated from agro-industrial waste (corn husks and oat hulls) and market kraft pulp fibres, and a detailed comparative study was performed. Initially, the raw materials were subjected to a conventional pulping process to remove lignin and hemicelluloses. The chemical pre-treatment was based on 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation and the mechanical treatment was carried out with a high-pressure homogenizer. An extensive characterization of the raw material and of the nanofibrillated celluloses was performed, considering structural and chemical aspects. CNF films were produced for their characterization by optical methods, laser profilometry (LP), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Considering the same pulping and chemical pre-treatment, the analyses indicated that the oxidized corn husks fibres had higher carboxylate content and thus a larger tendency to nanofibrillate compared to the oat hulls fibres. The obtained content of carboxylic acids was directly proportional to the content of cellulose in the assessed samples, confirming the selectivity of the TEMPO-mediated oxidation. The fibrillated corn husks material had a minor fraction of residual fibres (<4%) and homogeneous nanofibril width distribution (<20 nm), which is a major achievement. The homogeneous CNF morphology was confirmed by AFM analysis. Hence, this study demonstrates that the assessed agro-industrial wastes are sustainable resources for production of CNF, which may have a wide range of value-added applications.

Catalysts

A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4P... more A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4PW11V1O40 and TBA5PW10V2O40) and Mo (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS), and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)12−XO40)(3+X)− anions are the main species present in the TBA salts. Additionally, CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 at 170 °C. Independently of...

Minerals, 2021

This research focused on the evaluation of the potential use of a soil-isolated bacteria, identif... more This research focused on the evaluation of the potential use of a soil-isolated bacteria, identified as Staphylococcus equorum, for microbial-induced calcite precipitation (MICP) and copper removal. Isolated bacteria were characterized considering growth rate, urease activity, calcium carbonate precipitation, copper tolerance as minimum inhibitory concentration (MIC) and copper precipitation. Results were compared with Sporosarcina pasteurii, which is considered a model bacteria strain for MICP processes. The results indicated that the S. equorum strain had lower urease activity, calcium removal capacity and copper tolerance than the S. pasteurii strain. However, the culture conditions tested in this study did not consider the halophilic feature of the S. equorum, which could make it a promising bacterial strain to be applied in process water from mining operations when seawater is used as process water. On the other hand, copper removal was insufficient when applying any of the bac...

Fuel, 2021

Abstract The carbonization of Nannochloropsis gaditana microalgae biomass was found to produce bi... more Abstract The carbonization of Nannochloropsis gaditana microalgae biomass was found to produce bio-coal that is similar to bituminous coal used in thermal power plants. Currently, microalgae that capture CO2 while they are in the growth stage are considered a source for the production of biofuels. The carbonization of biomass for producing bio-coal has received attention for its ability to improve the biomass quality for producing solid biofuels. The research was focused on optimizing a fixed carbon index (FCindex), which allows finding operational conditions of carbonization to favor the fixed carbon content without significantly affecting the bio-coal yield. The optimization carried out by response surface methodology in a thermogravimetric analyzer allowed the prediction of optimal carbonization conditions to achieve an FCindex of 191% at 403 °C, 71 °C/min, and 60 min of residence time. The bio-coal produced under optimized conditions was characterized by 59% of fixed carbon and 41% of volatiles on a dry and ash-free basis, which is similar to bituminous coal. The promising results of dry carbonization producing bio-coal similar to bituminous coal could promote this technology, avoiding the necessity of hydrothermal carbonization. Because a high ash content was detected in the final product, further studies using the optimized conditions and a washing step should be conducted.

Fuel, 2020

A Biomass Quality Index (BQI) developed using a previously reported tool was shown to be a promis... more A Biomass Quality Index (BQI) developed using a previously reported tool was shown to be a promising method to rank biomass suitable for solid biofuel production. The BQI was developed by selecting 12 chemical parameters to be analyzed among ten available biomasses produced in the north, central and south of Chile. Furthermore, a Parameter Quality Index (PQI) was calculated to estimate the contribution of each parameter in the BQI. The sum of all PQIs for each biomass allowed the BQI to be determined, and biomasses with lower BQIs were more highly ranked. The results showed that the first 3 ranks were dominated by biomasses collected in central Chile, hazelnut shell, cherry pits and corn cobs (BQI ≤ 16.1). Furthermore, a promising candidate that was ranked fourth place was wheat straw (BQI = 17.7), which may be able to be used the highly polluted southern zone. Meanwhile, grass and the microalgae N. gaditana were ranked last (BQI ≥ 69.5). The low BQI obtained for the studied biomasses were related to their low PQIs regarding moisture content, low trace element content, low ash percentage and high carbon content and HHV. By contrast, high BQI values were related to high PQIs for moisture, Cl, Na and K content. K had a high contribution and Cu had a low contribution in the index. Due to the difficulty of milling the top ranked biomass, further studies should include a grindability analysis or other physical parameters to complete the BQI methodology.

Fuel, 2019

In this study, the torrefaction process was optimized to improve the energy yield (Y energy) in w... more In this study, the torrefaction process was optimized to improve the energy yield (Y energy) in wheat straw pellet production. Wheat is the main agricultural product of Chile and cultivated in approximately 262 000 ha of land. Additionally, solid biofuel alternatives are necessary in the southern cities of Chile to reduce the pollution produced by low-quality firewood used as fuel. That being the case, it appears that wheat straw is a feasible raw material for solid biofuel production. In the current study, the torrefaction of wheat straw was optimized in a thermogravimetric analyzer using the response surface methodology (RSM). The polynomial model generated from the RSM study showed that heating rate and temperature were significant variables on the response variable, Y energy ; time was insignificant. It was shown that a decrease in temperature of up to 130°C resulted in an enhancement of the Y energy value, and at the aforementioned temperature, a low heating rate improved Y energy. Following the conditions predicted by the model, torrefaction assays were conducted in a bench scale reactor under light torrefaction conditions: a torrefaction temperature of 145°C, heating rate of 3°C/min, and final torrefaction time of 50 min. The torrefied biomass was employed in a pellet production process that was performed in a pilot plant facility. The pellet produced from the torrefied biomass under light torrefaction conditions was named "brown pellet" because of its color. Most of the pellet properties satisfy the Standards for Industrial pellets (ISO 17225-6). This showed that light torrefaction temperature can be a potential pretreatment to achieve a commercial production process. Finally, an interesting result was obtained-the bulk density of brown pellets (568 ± 8 kg/m 3) was considerably higher compared to that of wheat straw pellets (469 ± 8 kg/ m 3). This was probably caused by an increment in grinding characteristics. Further studies that focus on identifying the effects of light torrefaction conditions on the mechanical properties of wheat straw pellets should be conducted.

Crystals, 2018

Microbially induced calcite precipitation (MICP) through a ureolytic pathway is a process that pr... more Microbially induced calcite precipitation (MICP) through a ureolytic pathway is a process that promotes calcite precipitation as a result of the urease enzymatic activity of several microorganisms. It has been studied for different technological applications, such as soil bio-consolidation, bio-cementation, CO2 sequestration, among others. Recently, this process has been proposed as a possible process for removing heavy metals from contaminated soils. However, no research has been reported dealing with the MICP process for heavy metal removal from wastewater/waters. This (re)view proposes to consider to such possibility. The main characteristics of MICP are presented and discussed. The precipitation of heavy metals contained in wastewaters/waters via MICP is exanimated based on process characteristics. Moreover, challenges for its successful implementation are discussed, such as the heavy metal tolerance of inoculum, ammonium release as product of urea hydrolysis, and so on. A semi-...

Biomass and Bioenergy, 2015

The use of photosynthetic CO 2 reduction capacity of microalgae can be used for biogas upgrading.... more The use of photosynthetic CO 2 reduction capacity of microalgae can be used for biogas upgrading. Such process would convert CO 2 contained in the biogas into microalgal biomass, generating two products: upgraded biogas and biomass. Growth rate of Nannochloropsis gaditana was determined in atmospheres containing different levels of CH 4 and CO 2. Results showed no effect of CH 4 rich atmosphere over microalgal development. CO 2 inhibition was observed only when microalgae culture was exposed to atmospheres containing 9% of CO 2. Direct contact of the biogas and the microalgal culture is not a feasible way to upgrade biogas, due to oxygen desorption to the gas phase. A two-stage process, involving a photobioreactor connected with a gas/liquid mass transfer unit showed to be an efficient way to remove CO 2 from the biogas, keeping low levels of oxygen in the upgraded biogas.

Water Science and Technology, 2014

Biomass retention, required for high rate anaerobic wastewater treatment, can be accomplished cou... more Biomass retention, required for high rate anaerobic wastewater treatment, can be accomplished coupling an anaerobic bioreactor with membrane filtration. However, low flux seems to be a common factor when operating anaerobic membrane bioreactors (AnMBRs). Modification of biomass properties may represent a strategy for improving membrane flux. The addition of flocculants was tested as a tool for flux increase. Six different products were tested in dead-end filtration experiments. Based on the results, two products were selected for cross-flow tests. The one presenting better performance (Nalco MPE50) was tested in a laboratory-scale continuous AnMBR. Results show that the flocculant was able to substantially increase flux. Indeed, the flux-increasing effect was observed for several weeks after flocculant addition. Therefore, the use of flocculants seems to be an interesting tool to cope with temporary increases in required flux.

Fuel, Mar 1, 2015

h i g h l i g h t s Feasible whole cell catalysis process to produce FAAE from microalgae lipids.... more h i g h l i g h t s Feasible whole cell catalysis process to produce FAAE from microalgae lipids. The efficiency of the process is related to the complexity of carbon source used (lipids). The hyphae have an important role in mass transfer since they may acts as pipeline. Temperature affected the quantity of alcohol added, not the fungi activity.

Renewable Energy, 2020

Abstract The production of fatty acid methyl esters (FAME) from waste frying oil (WFO) was studie... more Abstract The production of fatty acid methyl esters (FAME) from waste frying oil (WFO) was studied using fly ash as received as a heterogeneous catalyst. The fly ash used in this research had a high content of both CaO and SO3, two compounds that have been previously proposed as catalysts in FAME production. The study was carried out on the basis of a response surface methodology (RSM). The model generated by RSM predicted as optimal conditions to obtain a 100% FAME yield at a methanol-to-oil molar ratio of 3.1:1, 11.2 (wt.% based on oil weight) fly ash and a temperature of 59 °C with agitation at 245 rpm and 6 h of reaction time. Additional experiments comparing anhydrous with aqueous medium showed that fly ash presented a high catalytic capacity to transform free fatty acids (FFA) into FAME through consecutive hydrolysis and esterification processes (hydroesterification) compared with that associated with the transesterification mechanism. According to the results, the fly ash used in this study would act as a multipurpose or “versatile” catalyst due to its chemical composition with constituents that act as acidic and basic catalysts, therefore, catalyzing the transesterification and hydroesterification reactions simultaneously and increasing the conversion yields of FAME.

Journal of Environmental Management, 2020

Copper contamination in watercourses is a recent issue in countries where mining operations are p... more Copper contamination in watercourses is a recent issue in countries where mining operations are prevalent. In this study, the application of copper precipitation through microbe-induced carbonate precipitation (MICP) was analyzed using urea hydrolysis by bacteria to evaluate precipitated copper carbonates. This article demonstrates the application of a copper precipitation assay involving Sporosarcina pasteurii (in 0.5 mM Cu 2þ and 333 mM urea) and analyzes the resultant low removal (10%). The analysis indicates that the low removal was a consequence of Cu 2þ complexation with the ammonia resulting from the hydrolysis of urea. However, the results indicate that there should be a positive correlation between the initial urea concentration and the bacterial tolerance to copper. This identifies a challenge in the industrial application of the process, wherein a minimum consumption of urea represents an economic advantage. Therefore, it is necessary to design a sequential process that decouples bacterial growth and copper precipitation, thereby decreasing the urea requirement.