Morpho-structural and thermo-mechanical characterization of recycled polypropylene and polystyrene from mixed post-consumer plastic waste

In this work, a complete sorting and characterization of dirty non-recyclable mixed plastic (plasmix fraction) from municipal solid waste was performed. The procedure comprised a visual inspection and identification of the materials presented in the mixed plastic bales, and subsequent moisture and dirt content determination. Afterwards, both polypropylene and polystyrene fractions obtained from the sorting process were recycled and physico-mechanically and thermally characterized for the assessment of recycled material quality. The dirty nonrecyclable mixed plastic from municipal solid waste was composed of polypropylene (28.89 %), polyethylene terephthalate (22.02 %), polystyrene (9.65 %) and rigid polyethylene (4.68 %). Regarding the moisture and dirt content of the mixed plastic fraction, the results were highly variable, mainly due to the heterogeneity of the material, its origin, atmospheric conditions, etc. The average sum of both parameters (moisture and dirt) was around 15 %. The mechanical properties were within the expected range for each type of polymer, noting that polystyrene recycled materials are more brittle than recycled polypropylene. The recycling of non-food polypropylene wastes yielded a material with higher impact resistance (70 kJ/m2) and Young´s modulus (1934 MPa) as compared to that obtained from the recycling of food packages. Concerning the polystyrene recyclates, it is worth mentioning that recycled materials obtained from foamed residues (expanded polystyrene and extruded polystyrene showed approximately twice the tensile strength with respect to the recycled materials from high impact polystyrene and general-purpose polystyrene residues. In some cases, infrared and thermal analyses revealed cross-contamination with traces of other polymers

Chronic exposure to environmental temperature attenuates the thermal sensitivity of salmonids

Metabolism, the biological processing of energy and materials, scales predictably with temperature and body size. Temperature effects on metabolism are normally studied via acute exposures, which overlooks the capacity for organisms to moderate their metabolism following chronic exposure to warming. Here, we conduct respirometry assays in situ and after transplanting salmonid fish among different streams to disentangle the effects of chronic and acute thermal exposure. We find a clear temperature dependence of metabolism for the transplants, but not the in-situ assays, indicating that chronic exposure to warming can attenuate salmonid thermal sensitivity. A bioenergetic model accurately captures the presence of fish in warmer streams when accounting for chronic exposure, whereas it incorrectly predicts their local extinction with warming when incorporating the acute temperature dependence of metabolism. This highlights the need to incorporate the potential for thermal acclimation or adaptation when forecasting the consequences of global warming on ecosystems

Estudio de la degradación fotocatalítica de contaminantes emergentes: desarrollo de composites fotoactivos y aplicación en un reactor de spouted bed

Photocatalysis is currently being considered for water decontamination due to its ability to degrade organic pollutants to CO2, water and mineral acids. In TiO2 photocatalysis, UV radiation is needed to create hole-electron pairs which can be transferred to water to form oxidizing species. However, this process generally suffers low apparent quantum yield. Hence, the first goal of this work was to investigate the parameters that deactivate the catalyst in real waters such as tap, river or wastewater. In general, the removal efficiency of clofibric acid (CFA) decreased with inorganic salts, especially with sulfates and carbonates, and also in environmental waters. A general kinetic model was developed to describe the CFA photodegradation depending on the type and concentration of substances present in water. High correlation was observed between experimental CFA concentrations and those predicted by the model. After that, several strategies were tried to improve quantum yields by adding electron scavengers and powdered activated carbon (PAC). Among the e--scavengers tested, only NaIO4 showed significant effect on the degradation of the analytes (a mixture of 5 pharmaceuticals: sulfamethoxazole, carbamazepine, CFA, diclofenac and ibuprofen), especially when the assays were performed in river water. Regarding the addition of PAC, different composites prepared from titania nanoparticles and PAC were tested. In any case, depending on each pharmaceutical tested and on its competitive affinity with the others, the combined treatment of adsorption and photocatalytic degradation improved the overall removal efficiency of drugs in water. One of the main drawbacks of TiO2 photocatalysis its nanometric size that usually leads to catalyst washing out from systems. Hence, a new procedure to immobilize TiO2 nanoparticles on a larger matrix such as calcium alginate was investigated to obtain millimetric-size particles with photocatalytic activity. Two natural thickeners, xanthan gum (XG) and locust bean gum (LBG), were also added to improve the mechanical stability of the photoactive beads. Nevertheless, the presence of thickening compounds affected negatively to their photocatalytic efficiency, while the most effective ones were alginate-TiO2 (TA) beads. Furthermore, a new type of photocatalytic material based on TiO2, calcium alginate and 1.5% of PAC was tested. It was confirmed that these so formed composites (TA/PAC) combined adsorption with photolysis and, thus, were more efficient at micropollutants removal. Finally, a new spouted bed photocatalytic reactor (SBPR) was designed at bench scale. After assessing the effect of light adsorption, inlet air flow and photocatalyst load, continuous-flow experiments were performed for the mixture of pharmaceuticals. Different operational conditions were set in order to evaluate the influence of influent flow rate and pollutant concentration. On the whole, it was noticed that the SBPR worked efficiently for high inlet loadings of contaminants and that it was able to treat satisfactorily micropollutant concentrations of up to 10 mg L-1

Biodegradación de fenol en un reactor en régimen de spouted bed con partículas de ß-ciclodextrina

A draft-tube spouted bed bioreactor with different types of aeration was developed to study the aerobic microbial degradation of aqueous phenol using a cyclodextrin-based support material. Since oxygen is a key in aerobic bioprocesses, the influence of different types of aeration on the volumetric mass transfer coefficient, kLa, was investigated. The values of kLa increased with gas spatial velocity, and decreased with increasing solid load, air flow distribution (spout to total flow ratio) and medium viscosity (carboxymethylcellulose solutions). The proposed correlations for kLa predicted the experimental data satisfactorily. Bacteria from activated sludge were acclimated to phenol in a continuous stirred tank bioreactor, and then immobilized onto the hydrogel particles within the spouted bed bioreactor. Microorganisms from cultures obtained in both bioreactors were isolated and characterized. Microbial population distribution in bioreactors was not only affected by phenol concentration, but also by oxygen and nitrogen availability, the system configuration and the presence of intermediates formed during phenol metabolization. A maximum elimination capacity of 6.63 kg-phenol/m3d was achieved in the spouted bed bioreactor, with Burkholderia cepacia being the dominant strain during high degradation periods. Batch experiments were carried out to evaluate the biodegradation of phenol by isolated dominant strains. Higher phenol concentrations inhibited the biomass and reduced the biodegradation rate. The modeling of batch phenol biodegradation indicated that the Haldane inhibitory model provided a good fit to the experimental data. Results showed that Acinetobacter baumannii and Burkholderia cepacia yielded the maximum specific growth rates

Removal of cresols from water by packed beds of cyclodextrin-based hydrogels

A cyclodextrin-based polymer was prepared by crosslinking beta-cyclodextrin with epichlorohydrin to be assessed as a sorbent material for cresols in packed-bed columns. Both Langmuir and Freundlich isotherms were appropriate to describe the sorption equilibrium in the conditions tested, and the thermodynamic parameters obtained for this process confirmed its exothermic nature with similar enthalpies (between - 6.8 and - 8.3 kJ/mol) for the three isomers. The removal of cresols from water was carried out in nine cycles of sorption-desorption in fixed-column experiments with the cyclodextrin hydrogel, achieving sorption capacities of 6.2, 11.6, and 15.1 mg/g for o-, m-, p-cresol, respectively. These differences in sorption capacities are due to the different chemical structures of cresols, that is, the relative position of the methyl and hydroxyl groups. However, similar sorption rates were observed for each isomer, with a mean value of 0.10 mg-cresol g-CDP-1 min(-1) in all cases. The experimental data for the breakthrough and the elution curves have been successfully modeled by two effective two-parameter equations, a dose-response model for the sorption step and a pulse-peak model for the regeneration step. The cyclodextrin polymer matrix has been proven to be an effective a good sorbent material for removing cresols from water, exhibiting remarkable reusability performance and structural stability throughout the successive elution steps carried out with methanol