Kinetics of Indigenous Nitrate Reducing Sulfide Oxidizing Activity in Microaerophilic Wastewater Biofilms

23 páginas.-- 10 figuras.-- 2 tablas.-- 74 referencias.-- Supporting Information: Dataset. in http://dx.doi.org/10.1371/journal.pone.0149096Nitrate decreases sulfide release in wastewater treatment plants (WWTP), but little is known on how it affects the microzonation and kinetics of related microbial processes within the biofilm. The effect of nitrate addition on these properties for sulfate reduction, sulfide oxidation, and oxygen respiration were studied with the use of microelectrodes in microaerophilic wastewater biofilms. Mass balance calaculations and community composition analysis were also performed. At basal WWTP conditions, the biofilm presented a double-layer system. The upper microaerophilic layer (~300 μm) showed low sulfide production (0.31 μmol cm-3 h-1) and oxygen consumption rates (0.01 μmol cm-3 h-1). The anoxic lower layer showed high sulfide production (2.7 μmol cm-3 h-1). Nitrate addition decreased net sulfide production rates, caused by an increase in sulfide oxidation rates (SOR) in the upper layer, rather than an inhibition of sulfate reducing bacteria (SRB). This suggests that the indigenous nitrate reducing-sulfide oxidizing bacteria (NR-SOB) were immediately activated by nitrate. The functional vertical structure of the biofilm changed to a triple-layer system, where the previously upper sulfide-producing layer in the absence of nitrate split into two new layers: 1) an upper sulfide-consuming layer, whose thickness is probably determined by the nitrate penetration depth within the biofilm, and 2) a middle layer producing sulfide at an even higher rate than in the absence of nitrate in some cases. Below these layers, the lower net sulfide-producing layer remained unaffected. Net SOR varied from 0.05 to 0.72 μmol cm-3 h-1 depending on nitrate and sulfate availability. Addition of low nitrate concentrations likely increased sulfate availability within the biofilm and resulted in an increase of both net sulfate reduction and net sulfide oxidation by overcoming sulfate diffusional limitation from the water phase and the strong coupling between SRB and NR-SOB syntrophic relationshipAC was funded by projects P06-RNM-01787, P11-RNM-7199, the PAI group RNM-214 from Consejería de Innovación, Ciencia y Empresa, Junta de Andalucía and CTM2013-43857-R from the Spanish Ministry of Economy and Competitiveness. JMG was funded by the PAI group BIO-288 from Consejería de Innovación, Ciencia y Empresa, Junta de Andalucía. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewe

Net sulfide oxidation rate (nSOR) <i>vs</i>. added nitrate concentration kinetics in wastewater biofilms amended with different concentrations of sulfate and nitrate.

<p>(a) Net sulfide oxidation rate (nSOR) <i>vs</i>. added nitrate concentration at fixed concentration of 2 mM and 10 mM sulfate. (b) nSOR was calculated according to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149096#pone.0149096.e004" target="_blank">Eq. 4</a>. Solid lines are the modeled values calculated from kinetic parameters determined from double inverse plots. Kinetic parameters for the 2 mM sulfate experiment were: K_s = 0.58 mM NO₃^-, V_max = 0.15 mM H₂S cm^-2 h^-1 and for 10 mM sulfate were: K_s = 0.55 mM NO₃^-, V_max = 0.55 mM H₂S cm^-2 h^-1.). Inserted in plot b are the slopes of the regression lines (a), the intercepts (b) and determination coefficients (R²).</p