Ana Isabel Blanco García

Effect of light on Synechocystis sp. and modelling of its growth rate as a response to average irradiance

The growth rate and CO2 biofixation rate of a photosynthetic organism depend basically on the availability of light, all other factors being optimum. In dense cultures of cyanobacteria or micro-algae intended for biomass production, incident irradiance on the reactor surface is not the same as the intensity which is received by cells, as irradiance is attenuated by cell absorption and the self-shading effect. In a well-mixed, dense culture, only the average irradiance, Iav, can be considered responsible for the photosynthetic response. In this study, the photosynthetic response of Synechocystis sp., estimated from its specific growth rate, was measured for each Iav in batch cultures irradiated with different levels of external irradiance, Iext. The specific growth rate of Synechocystis sp. depends on Iav, in accordance with the model proposed by Muller-Feuga (J Exp Mar Biol Ecol 236:1–13, 1999). A non-linear regression analysis estimated a maximum specific growth rate of 0.108 h−1, at an Iav of 930xa0μmol photons·m−2·s−1. This reveals that Synechocystis sp. is a highly light-tolerant strain, suitable for outdoor cultures. Higher Iav levels caused photoinhibition in batch cultures. Parameters obtained from the Muller-Feuga model show that the minimum irradiance needed to start growth mechanisms becomes less as light availability decreases, i.e. cells become more efficient in the use of light when it is scarce. This observation suggests that choosing for low-light adaptation may be a good strategy to improve productivity in dense cultures, where light is a limiting factor.

Removal of Arsenic from Aqueous Solutions by Sorption onto Sewage Sludge-Based Sorbent

This study aimed at evaluating and comparing the removal of arsenic from solutions by a low-cost waste-based sorbent, produced by pyrolysing sewage sludge under appropriate conditions, and by a commercially activated carbon. Batch sorption experiments were performed under isothermal conditions (20°C), in order to evaluate the effect of pH on the arsenic sorption kinetics and on the equilibrium sorption capacity of the materials under study. Kinetic data revealed that the arsenic sorption was faster onto the activated carbon than onto the pyrolysed sludge. The sorption process was well described by both the pseudo-first and pseudo-second-order kinetics equations for both materials. Changes in the initial solution pH have distinct effects on the removal of arsenic onto pyrolysed sludge and activated carbon. While for pyrolysed sludge, pH affects essentially the equilibrium time, for activated carbon it affects the sorption capacity. Equilibrium results were well described by both Freundlich and Langmuir isotherm models, although fittings corresponding to the Langmuir isotherm were slightly better. The Langmuir maximum sorption capacity determined for the pyrolysed sludge was 71xa0μgxa0g−1, while for activated carbon was 229xa0μgxa0g−1. Despite the relative lower capacity of the pyrolysed sludge, the considerable lower cost and the valorisation of the sludge may justify further research on its use for water decontamination.

Simultaneous thermogravimetric and mass spectrometric monitoring of the pyrolysis, gasification and combustion of rice straw

Energy valorization of rice straw is possible by thermal conversion. The aim of this paper was to study the emissions throughout heating of rice straw under seven different atmospheres (simulating combustion, gasification and pyrolysis). For this purpose, combustion, gasification and pyrolysis of rice straw were studied by simultaneous TG/MS dynamic runs at 15xa0°C min−1. Results showed that a partially inert atmosphere is more advisable from an environmental point of view due to the lower emission of contaminants.

Zebrafish embryo bioassays for a comprehensive evaluation of microalgae efficiency in the removal of diclofenac from water

This work deals with a preliminary study aimed at evaluating the efficiency of three different microalgae strains, namely Chlorella sorokiniana, Chlorella vulgaris and Scenedesmus obliquus in the bioremediation of diclofenac contaminated water. For this purpose, microalgae were cultured in bubbling column photobioreactors (PBRs) under batch operation until the end of the exponential growth phase. For the three strains, the concentration of diclofenac in the PBRs aquatic medium decreased along microalgae growing, which pointed to biodegradation as the main removal mechanism. Among the three strains, S. obliquus was the most capable to reduce diclofenac concentration (99% removal from an initial concentration of 25,000u202fμgu202fl-1). However, such a large removal does not guarantee an efficient treatment since transformation products (TPs) exceeding the concentration and/or toxicity of the parent compound may be generated during biodegradation of diclofenac. Thus, for a comprehensive evaluation of the microalgae treatments efficiency, the final effluents from the PBRs were tested for their effects on the embryonic development of zebrafish. Again, the S. obliquus treatment was the most efficient in the reduction of toxicity, with the corresponding effluents having no effects on the embryos mortality or abnormalities incidence (at 80u202fh post fertilization). In any case, for the three strains, the toxicity effects of effluents were equal or lower than those determined for diclofenac solutions with the same concentration. Therefore, it may be stated that, at the end of the batch culture, the removal of diclofenac by the considered strains did not involve the generation of toxic TPs to zebrafish embryos.

Chlorella sorokiniana thermogravimetric analysis and combustion characteristic indexes estimation

This work aimed to investigate thermal decomposition of microalgae throughout the different culture stages. For this purpose, Chlorella sorokiniana was cultured in photobioreactors, and microalgae biomass was sampled at different days throughout the development of the culture. The aim was to analyze the energetic value of this biomass by thermogravimetric analysis as well as to calculate combustion characteristic indexes during the different culture stages. In all cases, thermal decomposition of microalgae biomass during combustion denoted two stages. The first one encompassed the carbohydrates and proteins decomposition and the breakdown of hydrocarbon chains of fatty acids, whereas the second step was closely related to the combustion of the formed char. Fuel composition analysis denoted a microalgae HHV value quite similar to that of Poplar (considered as an energy crop) biomass and slightly higher than published values for herbaceous biomass. In relation with the culture stages, a better combustion performance was found (higher thermal indexes as well as higher DTGmax values) for microalgae biomass sampled at days 19 and 21. These results point to the importance of the culture stage for the thermal valorization of microalgae biomass.