Effects Of Iron Oxides On The Anaerobic Methanogenic Degradation Of Organic Matters

Under anaerobic environments, the degradation of organic pollutants might be more effective. Benzoate and acetate are significance intermediate products of various organic pollutants. In consequence, the degratd rates and extents of benzoate and acetate affect thedegradation of organic pollutants. The special anaerobic environment in paddy soil induces that its methanogenesis cannot be ignored. The anaerobic methanogenic degradation of benzoate and methanogenesis in paddy soil are the coactions results of multiple microbes, in which iron oxides played a particular role. This work study the effect of differentconductivity (magnetite and hematite) on anaerobic methanogenic degradation of benzoate,and the effect different crystalline iron oxides(ferrihydrite and hematite) on methane emission in paddy soil as related to drying/wetting cycles, which benefits to prviding the experiment basis for effects of iron oxides on the degradation of organic pollutants.Effects of different iron oxides on methane emission in paddy soil as related to drying/wetting cycles:This study investigated the effects of iron oxides with different crystallinity, ferrihydrite and hematite, on the methane emission in paddy soil of South China under different water conditions, alternative drying/wetting cycles(DW) and continuous flooding. The rates of methane emission, methane production potential were determined. Results showed:(1) As alternative drying/wetting cycles facilitated the Fe(Ⅲ)/Fe(Ⅱ) cycle, ensuring Fe(Ⅲ) respiration proceed in the wetting cycles and Fe(Ⅲ)-reducing microbes constantly consuming methane-producing substrate (H2and acetate) in the soil, the coupled suppression effect of DW and iron oxides is more obvious than the single effect caused by DW or iron oxides.(2) Under the circumstance of DW and iron oxides addition, as the Eh of ferrihydrite is apparently higher than the Eh of producing CH4, moreover compared hematite, ferrihydrite is more easily reduced by microbes, DW coupling poorly crystalline ferrihydrite posed a more significantly inhibitory effect on the methane emission from paddy soil than coupling crystalline hematite. In the experiment of anaerobic methanogenic degradation of benzoate accelerated by (semi)conductive iron oxides:To measure the effects of (semi)conductive iron oxides on anaerobic methanogenic degradation of benzoate, paddy soil of South China samples were served as the inoculation under anaerobicthermostatic cultivation. Molecular biological techniques (real-time quantitative PCR, T-RFLP and clone libraries) were chosen as assessment methods to evaluate the abundance of the structure of microbial communities. Results showed:(1) adding (semi)conductive iron oxides accelerated the rate of anaerobic methanogenic degradation of benzoate. Interestingly, compared with semiconductive hematite, conductive magnetite posed a more significantly promoting effect on this degradation process.(2) adding (semi)conductive iron oxides increased the numbers of methanogen, and higher abundance of methanogenunder the circumstance ofmagnetite.(3) The Clostridia bacteria, the potential importance driving force for electron transport in direct interspecies, enriched by the addition of (semi)conductive iron oxides. The results implied that electron transfer reactions in syntrophism ans methanogens might be facilitated by (semi)conductive iron oxides, which accelerated the rate of anaerobic methanogenic degradation of benzoate under (semi)conductive iron oxides condtions.