Contributions of available substrates and activities of trophic microbial community to methanogenesis in vegetative and reproductive rice rhizospheric soil.

Potential of methane production and trophic microbial activities at rhizospheric soil during rice cv. Supanburi 1 cultivation were determined by laboratory anaerobic diluents vials. The methane production was higher from rhizospheric than non-rhizospheric soil, with the noticeable peaks during reproductive phase (RP) than vegetative phase (VP). Glucose, ethanol and acetate were the dominant available substrates found in rhizospheric soil during methane production at both phases. The predominance activities of trophic microbial consortium in methanogenesis, namely fermentative bacteria (FB), acetogenic bacteria (AGB), acetate utilizing bacteria (AB) and acetoclastic methanogens (AM) were also determined. At RP, these microbial groups were enhanced in the higher of methane production than VP. This correlates with our finding that methane production was greater at the rhizospheric soil with the noticeable peaks during RP (1,150 ± 60 nmol g dw-1 d-1) compared with VP (510 ± 30 nmol g dw-1 d-1). The high number of AM showed the abundant (1.1x104 cell g dw-1) with its high activity at RP, compared to the less activity with AM number at VP (9.8x102 cell g dw-1). Levels of AM are low in the total microbial population, being less than 1% of AB. These evidences revealed that the microbial consortium of these two phases were different.

Anaerobic degradation kinetics of reactive dye with different carbon sources.

This study aims to investigate the anaerobic degradation kinetics of reactive dye, C.I. Reactive Red 141 (Evercion Red H-E7B) by partially granulated anaerobic mixed culture using three carbon sources, namely modified starch (MS), polyvinyl alcohol (PVA) and acrylic size (AS) during batch incubation. There is a first-order kinetics reaction in the decolorization processes using MS and PVA as carbon sources, while a zero-order kinetics relationship describes the decolorization process for the AS carbon source. The k values and color removal rate of decolorization with MS carbon source was higher than those of PVA and AS carbon sources. This is because the MS carbon source was well degraded in comparison to AS and PVA, respectively This study also found dye reduction could be enhanced through the addition of MS as a carbon source. The decolorization rates increased with decrease in dye concentrations of RR 141. In contrast, the decolorization rates increased with increase in COD concentration.