Effect of La2 O3 and CeO2 on anaerobic methanogenesis process: Kinetics analysis and process mechanism study.

La2 O3 and CeO2 , as main rare earth oxides, with unique physical and chemical properties have been widely used in catalyst and grinding industry. In this study, the effects of La2 O3 and CeO2 on the anaerobic process were investigated. The biological methane production tests showed that 0-0.05 g/L La2 O3 and 0-0.05 g/L CeO2 enhanced anaerobic methanogenesis process. The result showed maximum specific methanogenic rates of La2 O3 and CeO2 were 56.26 mL/(h·gVSS) and 49.43 mL/(h·gVSS) and, compared with the control, increased 4% and 3%, respectively. La2 O3 significantly reduced the accumulation of volatile fatty acids (VFAs), whereas CeO2 had no similar effect. Dissolution experiments demonstrated that the content of extracellular La in the anaerobic granular sludge reached 404 µg-La/g volatile suspended solid (VSS), which was 134 times higher than that of extracellular Ce (3 µg-Ce/gVSS). The content of intracellular La reached 206 µg-La/gVSS, which was 19 times higher than that of intracellular Ce (11 µg-Ce/gVSS). The different stimulation between La3+ and Ce3+ could be attributed to the different dissolution of La2 O3 and CeO2 . The result of this work is helpful to optimize anaerobic processes and to develop novel additives. PRACTITIONER POINTS: Novel anaerobic additives were developed. La2O3 and CeO2 in 0-0.05 g/L enhanced organics degradation and methane production. The addition of La2O3 significantly reduced the accumulation of volatile fatty acids. The solubilization of La2O3 was stronger than CeO2. The promoting effects of low concentrations of La2O3 and CeO2 were derived from dissolved La and Ce.

Mechanism of vanadium(IV) resistance of the strains isolated from a vanadium titanomagnetite mining region.

Microbial treatment for vanadium contamination of soils is a favorable and environment-friendly method. However, information of the resistant mechanism of the strains in soils to vanadium, especially to tetravalent vanadium [vanadium(IV)], is still limited. Herein, potential of the vanadium(IV) biosorption and biotransformation of the strains (4K1, 4K2, 4K3 and 4K4) which were capable of tolerating vanadium(IV) was determined. For biosorption, the bioadsorption and the bioabsorption of vanadium(IV) occur on the bacterial cell wall and within the cell, respectively, were taken into consideration. Comparison of the vanadium(IV) adsorbed on the bacterial cell walls and remained in the cells after sorption indicated the major bacterial vanadium(IV) sorption role of the bioadsorption which was at least one order of magnitude higher than the bioabsorption amount. Isotherm study using various isotherm models revealed a monolayer and a multilayer vanadium(IV) biosorption by 4K2 and the others (4K1, 4K3 and 4K4), respectively. Higher biosorption was observed in acidic conditions than in alkaline conditions, and the maximum biosorption was 2.41, 9.35, 7.76 and 8.44 mg g-1 observed at pH 6 for 4K1, at pH 3 for 4K2, and at pH 4 for 4K3 and 4K4, respectively. At the present experimental range of the initial vanadium(IV) concentration, optimal biosorption capacity of the bacteria was observed at the vanadium(IV) level of 100-250 mg L-1. Different biotransformation level of vanadium(IV) in soils by the stains was observed during a 28-d pot incubation of the soils mixed with the strains, which can be attributed to the discrepancy of both soil properties and bacterial species. Present study can help to fill up the gaps of the insufficient knowledge of the vanadium(IV) resistant mechanism of the strains in soils.