Solution pH is among the most important parameters that influence heavy metal biosorption. This work presents a kinetic study of the effects of pH on chromium biosorption onto Cupressus lusitanica Mill bark from aqueous Cr(VI) or Cr(III) solutions and proposes a mechanism of adsorption. At all assayed contact times, the optimum pH for chromium biosorption from the Cr(III) solution was 5.0; in contrast, optimum pH for chromium biosorption from the Cr(VI) solution varied depending on contact time. The kinetic models that satisfactorily described the chromium biosorption processes from the Cr(III) and Cr (VI) solutions were the Elovich and pseudo secondorder models, respectively. Diffuse reflectance infrared Fourier transform spectroscopy studies suggest that phenolic compounds present on C. lusitanica Mill bark play an important role in chromium biosorption from the Cr(III) solution. On the other hand, chromium biosorption from the Cr(VI) solution involved carboxyl groups produced on the bark by redox reactions between oxygen-containing groups and Cr(VI), and these were in turn responsible for the biosorption of Cr (III) produced by Cr(VI) reduction.

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Abstract:Microalgae are an alternative and sustainable source of lipids that can be used as a feedstock for biodiesel production. Nitrate is a good nitrogen source for many microalgae and affects biomass and lipid yields of microalgae. In this study, the effect of nitrate on cell growth and lipid production and composition in Monoraphidium contortum, Tetraselmis suecica, and Chlorella minutissima was investigated. Nitrate affected the production of biomass and the production and composition of lipids of the three microalgae tested. Increasing the nitrate concentration in the culture medium resulted in increased biomass production and higher biomass productivity. Furthermore, increasing the nitrate concentration resulted in a reduction in lipid content and productivity in M. contortum; however, the opposite effect was observed in T. suecica and C. minutissima cultures. diesel infrastructure for storage and distribution. Biodiesel offers several advantages over petroleumbased diesel. For example, biodiesel is a renewable and biodegradable energy resource, it produces fewer toxic emissions (carbon monoxide, aromatic compounds, hydrocarbons, particulate matter, sulfur oxides, nitrogen oxides, and metals), it is less volatile and safer to transport, store and handle, and it increases efficiency, reduces wear, and extends engine life [2,3].Currently, biodiesel is produced from vegetable oils (edible or inedible), waste oils, and animal fats. However, this practice has raised serious concerns in the international community regarding the production, price, and availability of food. Other concerns include the deforestation of large areas of land that could be used to grow oleaginous vegetables, the huge amounts of water needed for irrigation, and the inability of these biodiesel sources to meet current and future fuel demands [4,5]. A sustainable biodiesel industry needs alternative raw materials that can be obtained easily from alternative renewable and biodegradable sources, allowing continuous operation and avoiding the limitations described [6].Currently, there is a consensus that microalgae are an alternative and sustainable source of lipids that can be used as a feedstock for biodiesel production. Microalgae are suitable for this purpose because they are photosynthetic microorganisms with a simple cellular structure and are easy to culture. Furthermore, microalgae grow in a variety of environments, their growth rate is 20 to 30 times faster than other sources of biofuels, they exhibit high photosynthetic efficiency, contribute greatly to the sequestration of atmospheric CO 2 , thereby mitigating climate change, can be harvested 365 days a year, can be grown in areas unsuitable for agriculture, livestock, industry, or tourism, require smaller volumes of water than oleaginous plants and can use water unsuitable for human consumption, their intracellular lipid content is high and the productivity of lipids per unit area is considerably higher than that of oleaginous plants [7][8][9][10].Several studies have shown that...

Perezone, a sesquiterpenic benzoquinone with diverse medicinal properties, accumulates in the roots of Acourtia species. In this time-dependent study, the production of perezone was followed in A. cordata culture systems of plants kept in vitro or acclimated and grown in pots. Perezone was characterized by several analytical methods, using the crystallized compound isolated from roots of wild plants as standard. A procedure was developed for its selective quantification, which considers the specific bathochromic shift of the absorbance band in the visible region between the spectra of perezone in its non-ionic and ionic forms, with intensity directly proportional to concentration. In vitro, perezone was recovered from A. cordata roots in average amounts of 5.21 mg g−1 dry weight. Contrastingly, in plants under ex vitro conditions, perezone in roots increased logarithmically, rising from an average of 2.4 mg g−1 dry weight at the 12th week, to 43.6 mg g−1 dry weight at the 31st week, an amount comparable to wild plants. These findings show the feasibility of in vitro and ex vitro culture systems to propagate and conserve the germplasm of perezone-producing Acourtia plants, and a fast and reliable method for the quantification of this valuable compound.