Comparative study of the combustion, pyrolysis and gasification processes of Leucaena leucocephala: Kinetics and gases obtained

Leucaena leucocephala is a fast-growing leguminous biomass with great energetical and valueadded chemical compounds potential (saccharides, biogas, bio-oil, etc.). Using the thermogravimetric and derivative thermogravimetric curves, the different trends followed by L. leucocephala during pyrolysis, 0.25 equivalence ratio (ER) of gasification, 0.50 equivalence ratio of gasification and combustion were analyzed, and the activation energies were obtained by Distributed Activation Energy Model (DAEM) method. Gas samples were collected through adsorption tubes during the gasification at 0.25 ER and 0.50 ER to observe the distribution of the main chemical products in this process by gas chromatography/mass spectrometry and were compared with pyrolysis products. It was found that small amounts of oxygen have changes in the kinetics of the process, leading to significant decreases in the activation energy at the beginning of the degradation of components such as cellulose (from 170 to 135 kJ mol-1 at 0.25 conversion at 0.50 ER gasification). The activation energy of lignin disintegration was also reduced (342 kJ mol-1), assimilating the beginnings of gasification processes such as the Boudouard reaction. 0.50 ER gasification is potentially an interesting process to obtain quality bio-oil, since a large amount of hexane is detected (44.96%), and value-added oxygenated intermediates such as alcohols and glycols. Gasification at 0.25 ER, on the other hand, is much more similar to pyrolysis, obtaining a wide variety of short-chain compounds resulting from the disintegration of the main lignocellulosic components, especially ketones such as 1-hydroxypropan-2-one (19.48%), and notable amount of furans and anhydrosugars like d-allose (5.50%).This study was supported by the Ministry of Economy and Competitiveness (Spain), as well as by the National Research Program Oriented to the Challenges of Society (Project PID2020-112875RB-C21 funded by MCIN/AEI 10.13039/501100011033, t)he Ministry of Innovation, Science and Business of the Government of the Junta of Andalusia (Spain), the Operative Program is framed within FEDER Andalusia 2014–2020 with Project number UHU-125540, and the CEPSA Foundation Chair. Funding for open access charge: Universidad de Huelva / CBUA

Ultrasound extraction optimization for bioactive molecules from Eucalyptus globulus leaves through antioxidant activity

Antioxidant products present a very high added value and are demanded in the market. The optimization of their extraction is a high-stakes matter for both economic and environmental points of view. Ultrasound extraction has been considered one of the most promising methods, so the relative importance of key parameters may have decisive economic significance. For this reason, different parameters that have influence on the extraction capacity such as ultrasound power, time, temperature, pH and % ethanol in water have been studied to know the relationships between the independent parameters and their influence on the extraction from Eucalyptus globulus leaves. An experimental Box-Behnken factorial design and subsequent analysis by neural networks have been used. The relative influence of each parameter varies according to the nature of the extracted compound. In this regard, the higher capacity of extraction of the selected antioxidant compounds by means of the variation of the operation conditions can be facilitated. For all the studied compounds, temperature has been the most important parameter for their extraction. The relative content (%) of bioactive compounds (terpenes) in the optimized Eucalyptus globulus extract has been performed by GC–MS analysis

Optimization of bioactive compounds by ultrasound extraction and gas chromatography - mass spectrometry in fast-growing leaves

Fast-growing crops are of great economic importance in the production of paper pulp and energy. The commercialization of the bioactive components from underutilized parts could provide additional value to these crops. In the present study, chromatography gas coupled to mass spectrometry triple quadrupole (GC–MS/MS) and ultrasound extraction technique was used in the bioactive compounds determination in fast-growing crops leaves. Twenty-one terpenes and eight polyphenolic bioactive compounds were studied. Prior to GC–MS/MS, polydimethylsiloxane (PDMS) - stir bars preconcentration and trimethylsilane (TMS) derivatization steps were used for terpenes and polyphenolic compounds, respectively. Several parameters (pH, temperature, ethanol–water mixtures, ultrasound power, and ultrasound time) of the extraction step were optimized by central composite experimental design. Ethanol content, ultrasound power, and ultrasound time were the parameters that most influence the extraction efficiency of terpenes in biomass residues, while for polyphenolic compounds it was temperature and ultrasound time. The optimal ultrasound extraction conditions for terpenes were 60% ethanol, pH 4, 80 W, 40 ºC, and 15 min, whereas for polyphenolic compounds they were 60% ethanol, pH 4, 120 W, 50 ºC, and 15 min. The detection limits (LOD) were in the range of 0.200–3.02 µg kg−1 and 7.9–540 µg kg−1 for terpenes and polyphenolic compounds, respectively. The developed analytical method was applied to twelve fast-growing leaves (Leucaene (diversifolia and leucocephala), Eucalyptus (globulus and urograndis), Populus (I214 and AF2), Prosopis (alba and juliflora), Robinia, Tagasaste, Ulmus pumila, and Paulownia). Eucalyptol was the mayor terpene present in all the plants studied, while chlorogenic and quinic acid were the mayor phenolic compounds.This study was supported by the Ministry of Economy and Competitiveness (Spain), as well as by the National Research Program Oriented to the Challenges of Society (Project PID2020-112875RB-C21 funded by MCIN/AEI /10.13039/501100011033), and the Ministry of Innovation, Science and Business of the Government of the Junta of Andalusia (Spain), the Operative Program is framed within FEDER Andalusia 2014–2020 (Project UHU-125540). Funding for open access charge: Universidad de Huelva / CBUA

Soil quality changes in an Iberian pyrite mine site 15 years after land reclamation

Reclamation of highly degraded mine lands to a sustainable environmental quality has become a major policy concern in many countries with a long mining tradition. This paper reports the soil quality status of a historical mine site _fteen years after its reclamation, using indicators of chemical reactivity, soil fertility and health, and discusses the progress and effectiveness of the implemented measures by a comparative analysis between pre- and post-reclamation conditions. Twenty composite surface samples (0–20 cm depth) were obtained for physical and chemical characterization from the open pit mine and waste disposal area, using a strati_ed random sam- pling approach. Additionally seven sites were selected to collect topsoil samples for microbiological testing. Re- sults showed that soil quality changed noticeably over the study period (2003–2018), with overall improvements in key properties, such as structural stability, cation exchange capacity, degree of base saturation, soil organic carbon, and available phosphorus. Prior to reclamation, the mine soil was unable to support vegetation due to hyperacidity coupled with elevated levels of toxic metals and nutrient de_ciencies. The combined use of sugar beet lime and composted biosolids as a low-cost, locally available, soil amendment was effective in neutralizing both active and exchangeable acidity, and reducing the mobility, plant uptake and human bioaccessibility of trace elements. The amendment addition also enhanced soil fertility, carbon storage, nutrient availability and microbial biomass (bacteria and fungi). Revegetation with Pinus pinea and Nerium oleander has proven to be a successful strategy to create a vegetative cover aesthetically pleasant and environmentally compatible with the surrounding undisturbed landscape, although further efforts should be made to monitor over time the phytotoxic and bioaccessible levels of residual metals, notably Cd, Cu and Zn. The insights gained from this land reclamation experience provide success criteria for assisting natural attenuation in other abandoned mining sites worldwide.The authors appreciate the support provided by the University of Huelva/CBUA Open Access Author Fee Fund

Simultaneous production of carotenoids and chemical building blocks precursors from chlorophyta microalgae

Replacement of fossil fuels has to be accompanied by the incorporation of bio-based procedures for the production of fine chemicals. With this aim, the microalga Chlamydomonas reinhardtii was selected for its ability to accumulate starch, an environmentally-friendly alternative source of chemical building blocks, such as 5′ -hydroxymethylfurfural or levulinic acid. The content of appreciated lipophilic coproducts was assessed in the selected microalga cultured at different nutritional conditions; and the parameters for the acidic hydrolysis of the algal biomass, obtained after pigments extraction, were optimized using a Central Composite Design. Response Surface Methodology predicted that the optimal hydrolysis conditions were elevated temperature, high DMSO % and short hydrolysis time for glucose. LA was favored at long times and high acid % and 5′ -HMF at lower acid % and high DMSO %. Chlamydomonas can therefore be used as a sustainable feedstock for the simultaneous production of high-added value lipophilic compounds and platform chemicals.Funding for open access charge: Universidad de Huelva / CBUA

Impact of heavy metals in the microalga Chlorella sorokiniana and assessment of its potential use in cadmium bioremediation

The chlorophyte microalga Chlorella sorokiniana was tested for the bioremediation of heavy metals pollution. It was cultured with different concentrations of Cu2+, Cd2+, As (III) and As (V), showing a significant inhibition on its growth at concentrations of 500 µM Cu2+, 250 µM Cd2+, 750 µM AsO33- and 5 mM AsO43- or higher. Moreover, the consumption of ammonium was also studied, showing significant differences for concentrations higher than 1 mM of Cu2+ and As (III), and 5 mM of As (V). The determination of intracellular heavy metals concentration revealed that Chlorella sorokiniana is an outstanding Cd accumulator organism, able to accumulate 11,232 mg kg−1 of Cd, and removing 65% of initial concentration of this heavy metal. Finally, antioxidant enzymes, such as catalase (CAT) and ascorbate peroxidase (APX), and enzymes involved in the production of glutamate and cysteine, such as glutamine syntethase (GS), glutamate dehydrogenase (GDH), O-acetylserine (thiol) lyase (OASTL) and NAD-isocitrate dehydrogenase (NAD-IDH) were studied both at gene expression and enzymatic activity levels. These enzymes exhibited different grades of upregulation, especially in response to Cd and As stress. However, GS expression was downregulated when Chlorella sorokiniana was cultured in the presence of these heavy metals.This work was supported in part by research grants from the Euro- pean governments (INTERREG VAPOCTEP-2014-2020; 0055_ALGAR- ED_PLUS_5_E), the Operative FEDER Program-Andalucía 2014-2020, the University of Huelva (UHU-1257518), and by the European Regional Development Fund through the Agencia Estatal de Investigaci ́on grant (PID 2019-110438RB-C22

Soil Contaminated with Hazardous Waste Materials at Rio Tinto Mine (Spain) Is a Persistent Secondary Source of Acid and Heavy Metals to the Environment

Mineralogical analysis and laboratory-based leaching tests coupled with speciation modeling were undertaken to quantify the potential for short-term acid generation and the release of trace elements from soils heavily contaminated with mine waste at Rio Tinto. Three different waste materials were considered as case studies: roasted pyrite, copper slags, and leached sulfide ores. The results showed elevated values of net acid generation (up to 663 mmol H+/kg), the major pools being potential sulfidic acidity and acidity retained in jarosite. Remarkable contents of As and toxic heavy metals were found especially in the slag-contaminated soil. Copper, Zn, and Pb were the most abundant metals in the acid leach solutions resulting from mine soil-water interaction, with peak values of 55.6 mg L−1, 2.77 mg L−1, and 2.62 mg L−1, respectively. Despite the high total contents of trace elements occurring in soil, the mobile fraction was limited to maximum release values of 12.60% for Cd and 10.27% for Cu, according to the test leaching. Speciation calculations indicated that free metal ions (M2+) and sulfate species (MSO40) accounted for most of the dissolved load. Acid soil drainage is a secondary source of acid and heavy metals in the mine site and, therefore, an effective land reclamation program should ensure that acidity and metal mobility are reduced to environmentally sustainable levels.This research was supported by the Regional Government of Andalusia (Spain) and the European Regional Development Fund Andalusia 2014–2020 through Project P-18-TP-3503, in collaboration with DSM Soluciones Medioambientales

Amino acids profile of 56 species of microalgae reveals that free amino acids allow to distinguish between phylogenetic groups

Microalgae represent a phototrophic resource with a high protein content, whose nutritional value is very high as a result of its amino acid profile. Although the total amino acid profile has been repeatedly described to change little among phylogenetic groups of microalgae, some variability has occasionally been reported. Part of this uncertainty is associated with the low phylogenetic diversity encompassed in the work to date and the high methodological variability between studies. Among these studies, very few have differentiated between total and free amino acid content for common microalgae samples. Thus, in the present work, the profile of total and free amino acids has been determined in a diverse group composed of 56 species of microalgae belonging to 7 phyla. A multivariate analysis of the total amino acid profile in the studied microalgae group revealed close amino acid patterns throughout microalgae phylogeny and agreed with results obtained from similar analysis performed with published data. Conversely, the free amino acid profile strongly differentiated between phylogenetic groups. On the one hand, species of Cyanobacteria, Plantae, Cryptophyta, and Bacillariophyta showed close free amino acid patterns, characterized by the highest abundance of free glutamic acid. Ochrophyta species were particularly rich in free proline, while the free amino acid profile of Miozoa and Haptophyta species stood out from the rest of the phylogenetic groups for their outstanding levels of the two essential amino acids phenylalanine and lysine. Haptophyta species were also characterized by their much higher free tyrosine content.This work was supported by the European Union Cooperation Program INTERREG VA POCTEP-055 ALGARED PLUS5E Spain-Portugal (2014–2020). The authors are grateful to the Fertinagro Biotech Foundation (C´atedra Fertinagro Biotech Universidad de Huelva). Funding for open access charge: Universidad de Huelva / CBUA is acknowledged

Assessment of elemental composition in commercial fish of the Bay of Cádiz, Southern Iberian Peninsula

The assessment of trace metal content in our fish diet is important due to the adverse effect on human health. Despite the increasing interest about the fish quality, little information is available for Southern Spain, a region characterized by high seafood intake. Nine species from the Bay of Cádiz with high commercial value were selected. Similar values were measured in the nine studied species for most of the elements, except for the macroelements Ca and S, and the microelements Fe, Mn and As, which showed significant differences among species. Metal Pollution Index (MPI) did not differ among species, and it was similar to those obtained for other Atlantic and Mediterranean locations. The values measured for the nine species were below the health limits provided by World, European and Spanish legislations, indicating that, in general terms, consumption of these species is safe in the study area.We are very grateful to Dr. P. Burgos for chemical analysis conducted in IRNAS-CSIC (Instituto de Recursos Naturales y Agrobiología, Consejo Superior de Investigaciones Científicas, Sevilla). During the study, ID-A enjoyed a grant "Margarita Salas" financed by the European Union (Next Generation EU) and the Ministerio de Universidades of Spain