Simultaneous biosorption of Cd(II), Ni(II) and Pb(II) onto a brown macroalgae Fucus vesiculosus: Mono- and multi-component isotherms, kinetics and thermodynamics.

Due to the anthropic activities, several heavy metal ions are introduced into the environment, impacting ecosystems and local activities. In this context, the biosorption process using algae represents an alternative form for these compounds remediation due to the advantages derived from the biosorbent and process efficiency. Thus, the present study evaluated Cadmium (Cd(II)), Nickel (Ni(II)) and Lead (Pb(II)) remediation from aqueous media in mono- and multi-component systems. The biosorbent was characterized in terms of its morphology and composition and parameters involving equilibrium, kinetics, and thermodynamics were investigated. Lastly, the sample was considered in a real surface water sample remediation impacted by a mining dam rupture. Except for Freundlich, all isotherm models tested satisfactorily adjusted to the experimental data for a mono-component system. The maximum biosorption capacities (qm) were 143.2 ±â€¯7.5, 70.1 ±â€¯1.9, 516.3 ±â€¯12.5 mg g-1 for Cd(II), Ni(II) and Pb(II) ions, respectively. When binary systems were considered, an antagonism effect was observed. The biosorption of Cd(II) was drastically affected by the presence of Ni(II), while Pb(II) biosorption in general was less affected by other metals presence. As observed for the binary system, the worst effect in the ternary system was observed for Cd(II) biosorption, being significantly affected by Ni(II) and Pb(II) presence. Overall, the biosorption order in mono- and multi-component systems was found to be Pb(II) ≫ Cd(II) > Ni(II). The affinity for the metals ions was also observed by Elovich's desorption constant, in which aPb(II)≪aCd(II)aCd(II), achieving an equilibrium passed 49 min. From the stages involved in biosorption process, film diffusion presented the greatest contribution as control-stage obtaining a lower diffusion coefficient in all cases. The process was spontaneous in all temperature range evaluated, considered exothermic for all metal ions evaluated. Iron, manganese and nickel concentrations in real surface water samples were higher than the allowed by the Brazilian National Environment Council (CONAMA). Comparing the hazard index values before and after the biosorption process, a reduction superior to 8 × was observed (HIbefore: 3.36, HIafter: 0.40), in which there was no non-carcinogenic risk imposed to the surrounding population after the treatment applied.

Comparison of commercial baker's yeast versus bacteria-based membrane bioreactors for landfill leachate treatment.

This study compares the performance of the membrane bioreactor (MBR) inoculated with commercial baker's yeast (Saccharomyces cerevisiae) (MBRy) versus one inoculated with bacterial sludge (MBRb) for treatment of landfill leachate. The MBRb and MBRy were operated with a hydraulic retention time of 48 h, solids retention time of 60 d, and specific air demand based on membrane area of 0.6 m3 h-1 m-2. The MBRy was more efficient in removing chemical oxygen demand (COD) (68 ± 12%), color (79 ± 8%), ammoniacal nitrogen (58 ± 18%), and phosphorus (62 ± 19%) compared to MBRb, which showed removal efficiencies of 44 ± 18%, 46 ± 20%, 45 ± 17%, and 29 ± 15% for COD, color, ammoniacal nitrogen, and phosphorus. Furthermore, the MBRy had lower production of soluble microbial products, which are the main cause of membrane fouling, and so a lower membrane fouling potential. The average hydraulic permeability of the MBRy (32.23 L m-2 h-1 bar-1) was about four times higher than that of the MBRb (8.34 L m-2 h-1 bar-1). Thus using commercial baker's yeasts as a MBR inoculum can enhance pollutants' removal and membrane performance.

Treatment of landfill leachate by hybrid precipitation/microfiltration/nanofiltration process.

This paper describes a promising method to treat stabilized landfill leachate. Such method consists of a combination of chemical precipitation processes, a cost-effective technique with high potential to remove contaminants with foulant nature, microfiltration aimed at removing the produced precipitate and nanofiltration (NF) for final polishing. This study was carried out on a bench unit comprising a precipitation reactor associated with a submerged hollow-fiber microfiltration membrane module and a flat NF membrane cell operated in batch and continuous mode with a treating capacity of 0.1 L h(-1). Combining these processes yielded a clear and colorless permeate and proved to be very efficient at removing organic and inorganic matter. The results showed the importance of membrane processes to ensure treated landfill leachate quality. Also the precipitation associated with microfiltration as a pretreatment process is able to guarantee low membrane fouling due to the significant retention of humic substances which are known for their high potential to cause NF membrane fouling.

Effect of phosphorylation on hydrogen-bonding interactions of the active site histidine of the phosphocarrier protein HPr of the phosphoenolpyruvate-dependent phosphotransferase system determined by 15N NMR spectroscopy.

The phosphocarrier protein HPr of the phosphoenolpyruvate-dependent sugar transport system of Escherichia coli can exist in a phosphorylated and a nonphosphorylated form. During phosphorylation, the phosphoryl group is carried on a histidine residue, His15. The hydrogen-bonding state of this histidine was examined with 15N NMR. For this purpose we selectively enriched the histidine imidazole nitrogens with 15N by supplying an E. coli histidine auxotroph with the amino acid labeled either at the N delta 1 and N epsilon 2 positions or at only the N delta 1 position. 15N NMR spectra of two synthesized model compounds, phosphoimidazole and phosphomethylimidazole, were also recorded. We show that, prior to phosphorylation, the protonated His15 N epsilon 2 is strongly hydrogen bonded, most probably to a carboxylate moiety. The H-bond should strengthen the nucleophilic character of the deprotonated N delta 1, resulting in a good acceptor for the phosphoryl group. The hydrogen bond to the His15 N delta 1 breaks upon phosphorylation of the residue. Implications of the H-bond structure for the mechanism of phosphorylation of HPr are discussed.