C. Escapa

Nutrients and pharmaceuticals removal from wastewater by culture and harvesting of Chlorella sorokiniana.

This work aimed to study both the removal of nutrients and pharmaceuticals, namely salicylic acid or paracetamol, from water by the culture of Chlorella sorokiniana. The removal of nutrients was nearly complete at the end of the batch culture; above 70% for nitrates and 89% for phosphates in the semicontinuous culture. The pharmaceuticals removal kinetics were 2.3 times greater for the salicylic acid than paracetamol, reaching volumetric efficiencies above 93% for salicylic acid in the semicontinuous culture. Finally, to separate the microalgae biomass from treated water, metal salts, synthetic polyelectrolytes and a biopolymer were tested as coagulants-flocculants. The best flocculation results were achieved with AlCl3 (95.23% with 200mgg(-1), 1min incubation time). However, given that resulting flocs had different characteristics, flocculants must be chosen on the basis of the subsequent use of the biomass.

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 25,000 μg l-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 80 h 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.

Adsorption Separation of Analgesic Pharmaceuticals from Ultrapure and Waste Water: Batch Studies Using a Polymeric Resin and an Activated Carbon

The performance of a polymeric resin (Sepabeads SP207, from Resindion, Binasco, Italy) was compared with that of an activated carbon (GPP20, from Chemviron Carbon, Feluy, Belgium) in the adsorption of acetaminophen and ibuprofen from either ultrapure or waste water. Kinetic and equilibrium adsorption experiments were carried out under batch operation conditions, and fittings of the obtained results to different models were determined. The kinetic experimental results fitted the pseudo-first and -second order equations, and the corresponding kinetic rates evidenced that the pharmaceuticals adsorption was faster onto GPP20 than onto Sepabeads SP207, but was mostly unaffected by the aqueous matrix. The equilibrium results fitted the Langmuir-Freundlich isotherm model. The corresponding maximum adsorption capacity (Qm, mg−1) was larger onto GPP20 (202 mg g−1 ≤ Qm ≤ 273 mg g−1) than onto the polymeric resin (7 mg g−1 ≤ Qm ≤ 18 mg g−1). With respect to the parameter KLF (mg g−1 (mg L−1)−1/n), which points to the adsorbent-adsorbate affinity, greater values were determined for the pharmaceuticals adsorption onto GPP20 than onto Sepabeads SP207. For both adsorbents and pharmaceuticals, neither Qm or KLF were affected by the aqueous matrix.

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.