Interactive effect of trivalent iron on activated sludge digestion and biofilm structure in attached growth reactor of waste tire rubber

<p>Waste tire rubber (WTR) has been introduced as an alternative, novel media for biofilm development in several experimental systems including attached growth bioreactors. In this context, four laboratory-scale static batch bioreactors containing WTR as a support material for biofilm development were run under anoxic condition for 90 days using waste activated sludge as an inoculum under the influence of different concentrations (2.5, 6.5, 8.5 mg/l) of trivalent ferric iron (Fe³⁺). The data revealed that activated sludge with a Fe³⁺ concentration of 8.5 mg/l supported the maximum bacterial biomass [4.73E + 10 CFU/ml cm²]; besides, it removed 38% more Chemical oxygen demand compared to Fe³⁺ free condition from the reactor. Biochemical testing and 16S rDNA phylogenetic analysis of WTR-derived biofilm communities further suggested the role of varying concentrations of Fe³⁺ on the density and diversity of members of Enterobacteria(ceae), ammonium (AOB) and nitrite oxidizing bacteria. Furthermore, Fluorescent <i>in situ</i> hybridization with phylogenetic oligonucleotide probes and confocal laser scanning microscopy of WTR biofilms indicated a significant increase in density of eubacteria (3.00E + 01 to.05E + 02 cells/cm²) and beta proteobacteria (8.10E + 01 to 1.42E + 02 cells/cm²), respectively, with an increase in Fe³⁺ concentration in the reactors, whereas, the cell density of gamma proteobacteria in biofilms decreased.</p

Characterization of Electrical Current-Generation Capabilities from Thermophilic Bacterium Thermoanaerobacter pseudethanolicus Using Xylose, Glucose, Cellobiose, or Acetate with Fixed Anode Potentials

<i>Thermoanaerobacter pseudethanolicus</i> 39E (ATCC 33223), a thermophilic, Fe­(III)-reducing, and fermentative bacterium, was evaluated for its ability to produce current from four electron donorsxylose, glucose, cellobiose, and acetatewith a fixed anode potential (+ 0.042 V vs SHE) in a microbial electrochemical cell (MXC). Under thermophilic conditions (60 °C), <i>T. pseudethanolicus</i> produced high current densities from xylose (5.8 ± 2.4 A m^–2), glucose (4.3 ± 1.9 A m^–2), and cellobiose (5.2 ± 1.6 A m^–2). It produced insignificant current when grown with acetate, but consumed the acetate produced from sugar fermentation to produce electrical current. Low-scan cyclic voltammetry (LSCV) revealed a sigmoidal response with a midpoint potential of −0.17 V vs SHE. Coulombic efficiency (CE) varied by electron donor, with xylose at 34.8% ± 0.7%, glucose at 65.3% ± 1.0%, and cellobiose at 27.7% ± 1.5%. Anode respiration was sustained over a pH range of 5.4–8.3, with higher current densities observed at higher pH values. Scanning electron microscopy showed a well-developed biofilm of <i>T. pseudethanolicus</i> on the anode, and confocal laser scanning microscopy demonstrated a maximum biofilm thickness (<i>L</i>_f) greater than ∼150 μm for the glucose-fed biofilm