Ni impact on denitrification was revealed in two continuous FBRs. Denitrification tolerated solub... more Ni impact on denitrification was revealed in two continuous FBRs. Denitrification tolerated soluble Ni concentrations as high as 500 mg/L. Ni speciation was investigated by using both modeling and XRD analysis. Ni 3 (PO 4 ) 2 precipitates were detected by XRD on activated carbon at FBR termination. The high tolerance of Dechloromonas to Ni successfully maintained denitrification.
Arsenic effects on nitrification were revealed using FBR enriched cultures. Nitrification was not... more Arsenic effects on nitrification were revealed using FBR enriched cultures. Nitrification was not affected by 100 mg As TOT /L at neutral pH. 150-200 mg As TOT /L inhibited ammonium oxidation by 25%. As(III) oxidation to As(V) decreased arsenic toxicity to nitrification. FBR enrichment consisted of C. Nitrospira defluvii and other nitrifying species.
The effect of the sulfide concentration on the location of the metal precipitates within sulfate-... more The effect of the sulfide concentration on the location of the metal precipitates within sulfate-reducing inversed fluidized bed (IFB) reactors was evaluated. Two mesophilic IFB reactors were operated for over 100 days at the same operational conditions, but with different chemical oxygen demand (COD) to SO(4)(2-) ratio (5 and 1, respectively). After a start up phase, 10mg/L of Cu, Pb, Cd and Zn each were added to the influent. The sulfide concentration in one IFB reactor reached 648 mg/L, while it reached only 59 mg/L in the other one. In the high sulfide IFB reactor, the precipitated metals were mainly located in the bulk liquid (as fines), whereas in the low sulfide IFB reactor the metal preciptiates were mainly present in the biofilm. The latter can be explained by local supersaturation due to sulfide production in the biofilm. This paper demonstrates that the sulfide concentration needs to be controlled in sulfate reducing IFB reactors to steer the location of the metal precipitates for recovery.
Purity and settling properties determine metal sulfide recovery from bioreactors. The influence o... more Purity and settling properties determine metal sulfide recovery from bioreactors. The influence of macronutrients commonly present in mineral media and wastewaters on Cu, Pb, Cd and Zn depletion kinetics and characteristics was evaluated in batch experiments with chemically produced sulfide at different concentrations. The metal depletion kinetics showed that metals with slower depletion rates (Zn and Cd) are susceptible to other removal mechanisms such as biosorption onto the sulfate reducing biofilm and precipitation with macronutrients when sulfide is below the stoichiometric metal to sulfide ratio. For Zn, the main mechanism of removal is its sorption onto apatite (Ca(5)(PO(4)))(3)(+)(OH(-)), a compound formed due to the presence of CaCl(2)·2H(2)O and KH(2)PO(4) in the mineral medium. All precipitates were 8.1-10.0μm regardless the sulfide concentration demonstrating that this parameter is less relevant for particle growth and settling, compared to the agglomeration of the precipitates.
The dispersion of nitrogenous compounds and heavy metals into the environment is frequent during ... more The dispersion of nitrogenous compounds and heavy metals into the environment is frequent during mining activities. The effects of nickel (Ni) and cobalt (Co) on denitrification of simulated mine waters were investigated in batch bioassays and fluidized-bed reactors (FBRs). At pH 7, batch tests revealed that Co did not exhibit inhibition on denitrification even at 86.6 mg/L. Ni showed to be inhibitory at 50 and 100 mg/L by decreasing nitrate removal efficiencies of 18 and 65 %, respectively. In two FBRs, operated at 7-8 and 22°C, 5.5 mg/L Ni did not affect nitrate and nitrite removals because of FBR potential of diluting soluble Ni feed concentration. On the contrary, the effluent pH clearly decreased in both FBR1 and FBR2 because of nickel sulfide precipitation and Ni inhibition of the last two steps of denitrification. When Ni injection was stopped, the process recovered more slowly at 22 than 7-8°C. This is the first study reporting the effect of Ni on denitrification in biological FBRs.
Ni impact on denitrification was revealed in two continuous FBRs. Denitrification tolerated solub... more Ni impact on denitrification was revealed in two continuous FBRs. Denitrification tolerated soluble Ni concentrations as high as 500 mg/L. Ni speciation was investigated by using both modeling and XRD analysis. Ni 3 (PO 4 ) 2 precipitates were detected by XRD on activated carbon at FBR termination. The high tolerance of Dechloromonas to Ni successfully maintained denitrification.
Arsenic effects on nitrification were revealed using FBR enriched cultures. Nitrification was not... more Arsenic effects on nitrification were revealed using FBR enriched cultures. Nitrification was not affected by 100 mg As TOT /L at neutral pH. 150-200 mg As TOT /L inhibited ammonium oxidation by 25%. As(III) oxidation to As(V) decreased arsenic toxicity to nitrification. FBR enrichment consisted of C. Nitrospira defluvii and other nitrifying species.
The effect of the sulfide concentration on the location of the metal precipitates within sulfate-... more The effect of the sulfide concentration on the location of the metal precipitates within sulfate-reducing inversed fluidized bed (IFB) reactors was evaluated. Two mesophilic IFB reactors were operated for over 100 days at the same operational conditions, but with different chemical oxygen demand (COD) to SO(4)(2-) ratio (5 and 1, respectively). After a start up phase, 10mg/L of Cu, Pb, Cd and Zn each were added to the influent. The sulfide concentration in one IFB reactor reached 648 mg/L, while it reached only 59 mg/L in the other one. In the high sulfide IFB reactor, the precipitated metals were mainly located in the bulk liquid (as fines), whereas in the low sulfide IFB reactor the metal preciptiates were mainly present in the biofilm. The latter can be explained by local supersaturation due to sulfide production in the biofilm. This paper demonstrates that the sulfide concentration needs to be controlled in sulfate reducing IFB reactors to steer the location of the metal precipitates for recovery.
Purity and settling properties determine metal sulfide recovery from bioreactors. The influence o... more Purity and settling properties determine metal sulfide recovery from bioreactors. The influence of macronutrients commonly present in mineral media and wastewaters on Cu, Pb, Cd and Zn depletion kinetics and characteristics was evaluated in batch experiments with chemically produced sulfide at different concentrations. The metal depletion kinetics showed that metals with slower depletion rates (Zn and Cd) are susceptible to other removal mechanisms such as biosorption onto the sulfate reducing biofilm and precipitation with macronutrients when sulfide is below the stoichiometric metal to sulfide ratio. For Zn, the main mechanism of removal is its sorption onto apatite (Ca(5)(PO(4)))(3)(+)(OH(-)), a compound formed due to the presence of CaCl(2)·2H(2)O and KH(2)PO(4) in the mineral medium. All precipitates were 8.1-10.0μm regardless the sulfide concentration demonstrating that this parameter is less relevant for particle growth and settling, compared to the agglomeration of the precipitates.
The dispersion of nitrogenous compounds and heavy metals into the environment is frequent during ... more The dispersion of nitrogenous compounds and heavy metals into the environment is frequent during mining activities. The effects of nickel (Ni) and cobalt (Co) on denitrification of simulated mine waters were investigated in batch bioassays and fluidized-bed reactors (FBRs). At pH 7, batch tests revealed that Co did not exhibit inhibition on denitrification even at 86.6 mg/L. Ni showed to be inhibitory at 50 and 100 mg/L by decreasing nitrate removal efficiencies of 18 and 65 %, respectively. In two FBRs, operated at 7-8 and 22°C, 5.5 mg/L Ni did not affect nitrate and nitrite removals because of FBR potential of diluting soluble Ni feed concentration. On the contrary, the effluent pH clearly decreased in both FBR1 and FBR2 because of nickel sulfide precipitation and Ni inhibition of the last two steps of denitrification. When Ni injection was stopped, the process recovered more slowly at 22 than 7-8°C. This is the first study reporting the effect of Ni on denitrification in biological FBRs.
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Papers by S. Papirio