Nitrate removal efficiency and bacterial community dynamics in denitrification processes using poly (L-lactic acid) as the solid substrate.
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Laboratory-scale solid-phase denitrification (SPD) reactors for nitrate removal were constructed by acclimating activated sludge with poly (L-lactic acid) (PLLA) having weight-average molecular weights (M(w)) of 9,900, 12,000, and 45,100 g mol(-1). A good nitrate removal rate (3.5-5.3 mg NO(3)(-)-N g [dry wt](-1) h(-1)) was found in the reactor containing PLLA of 9,900 g mol(-1), whereas the other two reactors with the higher M(w) PLLA showed low nitrate removal efficiency. Microbial community dynamics in the low M(w) PLLA-acclimated reactor were studied by 16S rRNA gene-targeted PCR-denaturing gradient gel electrophoresis and quinone profiling. Nonmetric multidimensional scaling analyses of these data sets revealed a marked population shift during acclimation of the SPD reactor with low M(w) PLLA. The 16S rRNA gene clone library and culture-dependent analyses showed that bacteria belonging to the family Comamonadaceae predominated and played the primary role in denitrification in the PLLA-using reactor; however, none of the bacterial isolates from the reactor degraded PLLA. These results suggest that the nitrate removal property of the PLLA-using SPD reactor is attained through the bioavailability of hydrolysates released abiotically from the solid substrate. (+info)
nirK-harboring denitrifiers are more responsive to denitrification- inducing conditions in rice paddy soil than nirS-harboring bacteria.
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We analyzed the quantity and diversity of nitrite reductase genes (nirS and nirK) in rice paddy soil before and after inducing denitrification. A quantitative PCR analysis showed that the copy number of nirK, but not nirS, increased significantly in response to the denitrification-inducing conditions. Diverse nirS and nirK clones were identified by clone library analyses. Clones related to the NirS of Burkholderiales and Rhodocyclales, and NirK distantly related to known denitrifiers increased their proportion in response to the denitrification-inducing conditions, and therefore, might be involved in denitrification in rice paddy soil. (+info)
Nitrifying granules cultivation in a sequencing batch reactor at a low organics-to-total nitrogen ratio in wastewater.
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