RESUMO
Fly ash is a significant pollutant in thermal power stations. Although this waste harms the environment and humans, it is badly removed and managed, and only a few studies are interested in this waste. For that, this study aims to valorise fly ash into potential adsorbents to treat tannery effluents for the first time. The physicochemical characterisation showed that fly ash has a pHpzc of 9.78, a very porous structure, a high specific surface area of 3127.2 m2/g with a total pore volume of 3.27 cm3/g, and a high silica and aluminium percentage. SEM showed that the fly ash studied has a small particle size ranging between 32 nm and 100 µm. Batch adsorption experiments were done, and the effects of adsorption parameters were investigated. The kinetics and isotherms models indicate that the equilibriums were achieved in 30 min, where the maximum uptake capacity was 2496, 223.7 and 106.8 mg/g for Chemical Oxygen Demand (COD), chromium (VI) and sulfide ions, respectively. The kinetic data were well fitted to the pseudo-second-order model and showed that adsorption onto fly ash may be chemical and physical simultaneously. Freundlich's model gave a better fit for the experimental adsorption equilibrium data and displayed multilayer adsorption. The thermodynamic isotherm showed that the adsorption onto fly ash is thermodynamically spontaneous (ΔG° < 0) and endothermic (ΔH° > 0). In conclusion, fly ash, which is a free material, has a more robust adsorption capacity than other expensive materials. Thus, it can be a promising, eco-friendly, attractive adsorbent for industrial wastewater treatment.
RESUMO
Effects of the extract of Nigella arvensis (NA) seeds on transepithelial Na(+) transport were studied in cultured A6 toad kidney cells by recording short-circuit current (I(sc)), transepithelial conductance (G(T)), transepithelial capacitance (C(T)) and fluctuation in I(sc). Apical application of NA extract had merely a small stimulatory effect on Na(+) transport, whereas basolateral administration markedly increased I(sc), G(T) and C(T). A maximal effect was obtained at 500 microll(-1) of lyophilized NA extract. The increase in C(T) suggests that the activation of I(sc) occurs through the insertion of transport sites in the apical membrane. In experiments performed in the absence of Na(+) transport [apical Na(+) was replaced by N-methyl-D-glucamine (NMDG(+))], basolateral NA extract did not affect I(sc) and G(T), indicating that Cl(-) conductance was not influenced. Noise analysis of I(sc) using 6-chloro-3,5-diaminopyrazine-2-carboxamide (CDPC) showed that NA extract reduced single-channel current (i(Na)) and decreased channel open probability (P(o)) but evoked a threefold increase in channel density (N(T)), which confirms the insertion of Na(+) channels. The separation of the compounds in the crude extract of NA was performed by fast protein liquid chromatography (FPLC) on a Superdex 200 gel-filtration column and by reverse-phase high-pressure liquid chromatography (RPHPLC) on an micro RPC C2/C18 SC2.1/10 column connected to a SMART system. Analysis of the purified active fraction by mass spectrometry demonstrated the presence of adenosine as the single organic compound in the extract that had a stimulatory effect on Na(+) transport. In a separate series of experiments, we confirmed that 1 micromol l(-1) adenosine had similar effects on the parameters of Na(+) transport as did the NA extract. The action of adenosine was further identified by experiments in which NA extract was added after adenosine. In these experiments, NA extract did not affect I(sc), G(T) or C(T). These results clearly demonstrate an essential role of adenosine in the stimulatory action of NA extract.