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Coliform bacteria and nitrogen fixation in pulp and paper mill effluent treatment systems
F Gauthier1, J D Neufeld, B T Driscoll
1Pulp and Paper Research Institute of Canada (PAPRICAN), Pointe-Claire, Québec, Canada, H9R 3J9.
Applied and Environmental Microbiology
|December 1, 2000
Summary
Pulp and paper mills often add nitrogen to wastewater treatment, but nitrogen fixation occurs in primary clarifiers, not bioreactors. This nitrogen fixation is primarily carried out by Klebsiella bacteria, suggesting a reassessment of nitrogen supplementation needs.
Area of Science:
- Environmental microbiology
- Industrial wastewater treatment
- Nitrogen cycling
Background:
- Pulp and paper mills commonly use activated sludge for biotreatment of effluents.
- Nitrogen (N) is often supplemented with ammonia or urea, assuming negligible N fixation in treatment systems.
- This practice incurs significant costs for mills.
Purpose of the Study:
- To investigate nitrogen (N2) fixation in pulp and paper mill effluent treatment systems.
- To identify the microorganisms responsible for N2 fixation.
- To evaluate the significance of N2 fixation in primary clarifiers versus activated sludge bioreactors.
Main Methods:
- Acetylene reduction assays were used to measure N2 fixation rates.
- Quantitative nitrogenase (nifH) gene probing identified N2-fixing bacteria.
- Bacterial isolations and identification (including coliforms) were performed.
Main Results:
- In situ N2 fixation was undetectable in activated sludge bioreactors.
- Significant N2 fixation was detected in six of seven primary clarifiers.
- Klebsiella strains, possessing the nifH gene, dominated culturable cells in primary clarifiers and were responsible for N2 fixation.
Conclusions:
- Pulp and paper mill primary clarifiers are active sites of N2 fixation, contrary to assumptions.
- The microbial community in primary clarifiers is biased towards N2 fixation, mainly by Klebsiella.
- This finding may explain the prevalence of Klebsiella in mill water systems and suggests potential for reducing supplemental nitrogen addition.