Simultaneous nitrification and autotrophic denitrification in fluidized bed reactors using pyrite and elemental sulfur as electron donors

In this study, simultaneous nitrification and autotrophic denitrification (SNAD) with either elemental sulfur or pyrite were investigated in fluidized bed reactors in mesophilic conditions. The reactor performance was evaluated at different ammonium (12-40 mg/L of NH4+-N), nitrate (35-45 mg/L of NO3--N), and dissolved oxygen (DO) (0.1-1.5 mg/L) concentrations, with a hydraulic retention time of 12 h. The pyrite reactor supported the SNAD process with a maximum nitrogen removal efficiency of 139.5 mg/(L·d) when the DO concentration was in the range of 0.8-1.5 mg/L. This range, however, limited the denitrification efficiency of the reactor, which decreased from 90.0% ± 5.3% in phases II-V to 67.9% ± 7.2% in phases VI and VII. Sulfate precipitated as iron sulfate (FeSO4/Fe2(SO4)3) and sodium sulfate (Na2SO4) minerals during the experiment. The sulfur reactor did not respond well to nitrification with a low and unstable ammonium removal efficiency, while denitrification occurred with a nitrate removal efficiency of 97.8%. In the pyrite system, the nitrifying bacterium Nitrosomonas sp. was present, and its relative abundance increased from 0.1% to 1.1%, while the autotrophic denitrifying genera Terrimonas, Ferruginibacter, and Denitratimonas dominated the community. Thiobacillus, Sulfurovum, and Trichlorobacter were the most abundant genera in the sulfur reactor during the entire experiment.

Response of bioaerosol cells to photocatalytic inactivation with ZnO and TiO_(2)impregnated onto Perlite and Poraver carriers

Bioaerosols are airborne microorganisms that cause infectious sickness,respiratory and chronic health issues.They have become a latent threat,particularly in indoor environment.Photocatalysis is a promising process to inactivate completely bioaerosols from air.However,in systems treating a continuous air flow,catalysts can be partially lost in the gaseous effluent.To avoid such phenomenon,supporting materials can be used to fix catalysts.In the present work,four photocatalytic systems using Perlite or Poraver glass beads impregnated with ZnO or TiO_(2)were tested.The inactivation mechanism of bioaerosols and the cytotoxic effect of the catalysts to^bioaeros^ls were studied.The plug flow photocatalytic reactor treated a bioaerosol flow of 460×10^(6)cells/m^(3)_(air)with a residence time of 5.7 s.Flow Cytometry(FC)was used to quantify and characterize bioaerosols in terms of dead,injured and live cells.The most efficient system was ZnO/Perlite with 72%inactivation of bioaerosols,maintaining such inactivation during 7.5 h due to the higher water retention capacity of Perlite(2.8 mL/gpcriite)in comparison with Poraver(1.5 mL/gperiite).However,a global balance showed that Ti0_(2)/Poraver system triggered the highest level of cytotoxicity to bioaerosols retained on the support after 96 h with 95%of dead cells.SEM and FC analyses showed that the mechanism of inactivation with ZnO was based on membrane damage,morphological cell changes and cell lysis;whereas only membrane damage and cell lysis were involved with Ti0_(2).Overall,results highlighted that photocatalytic technologies can completely inactivate bioaerosols in indoor environments.