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A Novel Bioreactor for High Density Cultivation of Diverse Microbial Communities
Published on: December 25, 2015
Nitrate removal efficiency and bacterial community dynamics in denitrification processes using poly (L-lactic acid)
Masaaki Takahashi1, Takeshi Yamada, Motohiro Tanno
1Department of Environmental and Life Sciences, Toyohashi University of Technology, Aichi, Japan.
Microbes and Environments
|May 12, 2011
Summary
Low molecular weight poly (L-lactic acid) (PLLA) enhanced solid-phase denitrification (SPD) reactors for nitrate removal. Bacteria, primarily Comamonadaceae, thrived on PLLA hydrolysates, not PLLA itself, driving efficient nitrate reduction.
Area of Science:
- Environmental Microbiology
- Biotechnology
- Water Treatment
Background:
- Nitrate contamination in water bodies poses significant environmental and health risks.
- Solid-phase denitrification (SPD) offers a promising approach for nitrate removal.
- The role of polymer properties and microbial communities in SPD efficiency requires further investigation.
Purpose of the Study:
- To investigate the impact of poly (L-lactic acid) (PLLA) molecular weight on the performance of laboratory-scale SPD reactors for nitrate removal.
- To analyze the microbial community dynamics in PLLA-acclimated SPD reactors.
- To elucidate the mechanism of nitrate removal in PLLA-based SPD systems.
Main Methods:
- Construction and operation of laboratory-scale SPD reactors using activated sludge acclimated with PLLA of varying molecular weights (9,900, 12,000, and 45,100 g mol(-1)).
- Assessment of nitrate removal rates.
- Microbial community analysis using 16S rRNA gene-targeted PCR-denaturing gradient gel electrophoresis, quinone profiling, and 16S rRNA gene clone library sequencing.
- Culture-dependent analyses of bacterial isolates for PLLA degradation.
Main Results:
- The SPD reactor with low molecular weight PLLA (9,900 g mol(-1)) exhibited a high nitrate removal rate (3.5–5.3 mg NO(3)(-)-N g [dry wt](-1) h(-1)).
- Reactors with higher molecular weight PLLA showed significantly lower nitrate removal efficiency.
- Microbial analysis revealed a distinct population shift during acclimation, with Comamonadaceae bacteria predominating and playing a key role in denitrification.
- No bacterial isolates were found to degrade PLLA, suggesting abiotic hydrolysis as the source of nutrients.
Conclusions:
- The molecular weight of PLLA is a critical factor influencing SPD reactor efficiency for nitrate removal.
- Low molecular weight PLLA supports a more effective microbial community for denitrification.
- Nitrate removal in PLLA-based SPD reactors is primarily driven by the bioavailability of abiotically released PLLA hydrolysates, rather than direct bacterial degradation of PLLA.
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