Development of a mathematical model for a microbial denitrification co-culture system comprising acetogenic bacterium Sporomusa ovata and denitrifying bacterium Pseudomonas stutzeri.

Previous study has shown that co-culturing acetogenic bacterium Sporomusa ovata (SO), with denitrifying bacterium Pseudomonas stutzeri (PS), is a promising strategy to enhance the microbial denitrification for nitrate-contaminated groundwater remediation. However, the mutual effects and reaction kinetics of these two bacteria in the co-culture system are poorly understood. In this study, a mathematical model for this co-culture system was established to fill this knowledge gap. Model simulation demonstrated that SO had a significant effect on the kinetics of denitrification by PS, while PS slightly affected the kinetics of acetate production by SO. The optimal initial HCO3-/NO3- ratio and SO/PS inoculation ratio were 0.77-1.48 and 67 for the co-culture system to achieve satisfied denitrification performance with less acetate accumulation. Finally, the minimum hydrogen supply was recommended when the initial bicarbonate and nitrate concentrations were assigned in the range of 2-20 mM and 2-4 mM for simulating the natural nitrate-contaminated groundwater treatment. These findings could provide useful insights to guide the operation and optimization of the denitrification co-culture system.

Batch study for Pb2+ removal by polyvinyl alcohol-biochar macroporous hydrogel bead.

In this paper, a novel adsorbent which used polyvinyl alcohol, alginate and biochar was successfully made and been used to remove lead from aqueous solutions. Batch experiments were carried out to evaluate the adsorption capacities of Pb (II) on this bead. Experimental data were analysed by the model equations like Langmuir and Freundlich and adsorption kinetic constants were determined using pseudo-first-order (PFO) and pseudo-second-order (PSO). In this study, the adsorption characteristics of Pb (II) were well fitted by the Langmuir isotherm model and pseudo-second-order (PSO) kinetic model. The adsorption of Pb (II) onto PVA-biochar beads are spontaneous and exothermic at 303-333 K by the evidence of the changes in standard Gibbs free energy, standard enthalpy and standard entropy. The maximum adsorption capacity for Pb (II) was estimated to be 176.40 mg/g, which is comparable with other adsorbents. While the maximum adsorption increased varying the pH of initial solution from 2 to 6, the effect on the adsorption amount by the sodium ion concentration is not very large. The results of EDS spectra indicated that the existence of lead in polyvinyl alcohol (PVA)-biochar bead after adsorption, which proving the adsorption of lead. In XPS spectrum, the observed Pb elements also demonstrated that the lead was adsorbed by PVA-biochar bead.