Heavy metals uptake on Malpighia emarginata D.C. seed fiber microparticles: Physicochemical characterization, modeling and application in landfill leachate.

Environmental heavy-metals contamination is a worldwide concern and the treatment of their sources constitutes a sustainable and efficient alternative. This work investigated the performance of Malpighia emarginataD.C. seed fibers microparticles (Me-SFMp) as biosorption platform for heavy metal ions. Integrated physicochemical analyses (FAAS, FTIR, SEM/EDS and XRF) showed that such ability was associated with the high microstructural porosity, wide surface area and diversity of functional groups on Me-SFMp structures, which favored the high and fast uptake of the target-substances (Cd, Zn, Cr, Pb, Cu and Ni ions). In terms of reactional kinetics, the pseudo-second order model showed better data correlation (R2 from 0.9992 to 0.9998) and suggested the chemisorption as limiting step of the reaction mechanisms. From the Langmuir isotherms (R2 from 0.9993 to 0.9998), it was observed that these phenomena occurred non-linearly on a homogeneous biosorbent monolayer. Me-SFMp can also be reused after desorption processes conducted in acid medium and, under ideal conditions (0.8 g biosorbent dosage; 100 mL of 1.00 mg L-1 multi-metal solution adjusted to pH = 8.0; 300 rpm stirring speed; and 60 min contact time), the following maximum removal percentages order was observed for the first cycle: Cd (100%) = Zn (100%) > Cr (95.1%) > Pb (86.8%) > Cu (84.2%) > Ni (81.0%). The procedure was successfully applied to remove the studied heavy metal ions from raw landfill leachate, even in the presence of several (in)organic interferers, reinforcing the strong biosorbent-adsorbate interaction and the viability of this proposal.

Inactivation, lysis and degradation by-products of Saccharomyces cerevisiae by electrooxidation using DSA.

The yeast Saccharomyces cerevisiae, a microorganism with cell walls resistant to many types of treatments, was chosen as a model to study electrochemical disinfection process using dimensionally stable anodes (DSA). DSA electrodes with nominal composition of Ti/RuO2TiO2 and Ti/RuO2TiO2IrO2 were evaluated in 0.05 mol L-1 Na2SO4 containing yeast. The results showed inactivation about of 100 % of the microorganisms at Ti/RuO2TiO2 by applying 20 and 60 mA cm-2 after 120 min of electrolysis, while a complete inactivation at Ti/RuO2IrO2TiO2 electrode was achieved after 180 min at 60 mA cm-2. When chloride ions were added in the electrolyte solution, 100 % of the yeast was inactivated at 20 mA cm-2 after 120 min of electrolysis, independent of the anode used. In the absence of chloride, the energy consumption (EC) was of 34.80 kWh m-3, at 20 mA cm-2 by using Ti/RuO2TiO2 anode. Meanwhile, in the presence of chloride, EC was reduced, requiring 30.24 and 30.99 kWh m-3 at 20 mA cm-2, for Ti/RuO2TiO2 and Ti/RuO2IrO2TiO2 electrodes, respectively, The best performance for cell lysis was obtained in the presence of chloride with EC of 88.80 kWh m-3 (Ti/RuO2TiO2) and 91.85 kWh m-3 (Ti/RuO2IrO2TiO2) to remove, respectively, 92 and 95 % of density yeast. The results clearly showed that yeast, as a model adopted, was efficiently inactivated and lysed by electrolysis disinfection using DSA-type electrodes.

Influence of NO2 and metal ions on oxidation of aqueous-phase S(IV) in atmospheric concentrations

An investigation was made of the influence of atmospheric concentrations (15 or 130 ppbv) of NO2 on the aqueous-phase oxidation rate of S(IV) in the presence and absence of Fe(III), Mn(II) and Cr(VI) metal ions under controlled experimental conditions (pH, T, concentration of reactants, etc.). The reaction rate in the presence of the NO2 flow was slower than the reaction rate using only clean air with an initial S(IV) concentration of 10-4 mol/L. NO2 appears to react with S(IV), producing a kind of inhibitor that slows down the reaction. Conversely, tenfold lower concentrations of S(IV) ([S(IV)]º = 10-5 mol/L) caused a faster reaction in the presence of NO2 than the reaction using purified air. Under these conditions, therefore, the equilibrium shifts to sulfate formation. With the addition of Fe(III), Mn(II) or Cr(VI) in the presence of a NO2 flow, the reaction occurred faster under all the conditions in which S(IV) oxidation was investigated.

A reação de oxidação de S(IV) em fase aquosa foi estudada em laboratório em presença de NO2 dos íons metálicos Fe(III), Mn(II), e Cr(VI) sob condições experimentais controladas (pH, T, concentração dos reagentes, etc.). Na presença de corrente de ar com NO2 (15 ou 130 ppbv) a reação de oxidação de S(IV) ocorreu mais lentamente do que na presença de ar purificado, para uma concentração inicial de S(IV) de 10-4 mol/L. Ao contrário, para concentração inicial de S(IV) dez vezes menor ([S(IV)]° = 10-5 mol/L) a reação ocorreu mais rapidamente na presença de NO2. A explicação está relacionada com o equilíbrio envolvendo a formação de espécies intermediárias de longa vida, que impedem o prosseguimento da reação, porém a depender das concentrações relativas de S(IV) e NO2, essas espécies se decompõem deslocando o equilíbrio no sentido de formação de sulfato. A adição dos íons Fe(III), Mn(II) ou Cr(VI) em presença de corrente de ar com NO2 indicou atividade catalítica para esses íons, em todas as condições nas quais a oxidação de S(IV) foi investigada.

Influence of NO2 and metal ions on oxidation of aqueous-phase S(IV) in atmospheric concentrations.

An investigation was made of the influence of atmospheric concentrations (15 or 130 ppbv) of NO2 on the aqueous-phase oxidation rate of S(IV) in the presence and absence of Fe(III), Mn(II) and Cr(VI) metal ions under controlled experimental conditions (pH, T, concentration of reactants, etc.). The reaction rate in the presence of the NO2 flow was slower than the reaction rate using only clean air with an initial S(IV) concentration of 10(-4) mol/L. NO2 appears to react with S(IV), producing a kind of inhibitor that slows down the reaction. Conversely, tenfold lower concentrations of S(IV) ([S(IV)]o masculine=10(-5) mol/L) caused a faster reaction in the presence of NO2 than the reaction using purified air. Under these conditions, therefore, the equilibrium shifts to sulfate formation. With the addition of Fe(III), Mn(II) or Cr(VI) in the presence of a NO2 flow, the reaction occurred faster under all the conditions in which S(IV) oxidation was investigated.