Nitrogen fixation in the activated sludge treatment of thermomechanical pulping wastewater: effect of dissolved oxygen

N-ViroTech, a novel technology which selects for nitrogen-fixing bacteria as the bacteria primarily responsible for carbon removal, has been developed to treat nutrient limited wastewaters to a high quality without the addition of nitrogen, and only minimal addition of phosphorus. Selection of the o...

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Bibliographic Details
Published in:Water Science & Technology 2003-01, Vol.48 (8), p.1-8
Main Authors: Slade, A H, Anderson, S M, Evans, B G
Format: Article
Language:English
Subjects:
Acetylene
Acetylene reduction
Activated sludge
Activated Sludge Process
Ammonium
Bacteria
Biochemical oxygen demand
Bioreactors
Discharge
Dissolved oxygen
Hydraulic retention time
Mechanics
Nitrogen
Nitrogen fixation
Nitrogen Fixation - physiology
Organic carbon
Organic loading
Oxygen
Oxygen - chemistry
Phases
Phosphorus
Phosphorus - analysis
Pulping
Retention
Retention time
Sewage - chemistry
Sewage - microbiology
Sludge treatment
Solubility
Suspended solids
Technology
Temperature
Thermomechanical treatment
Total oxygen demand
Waste Disposal, Fluid - methods
Wastewater treatment
Water Purification - methods
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Summary:N-ViroTech, a novel technology which selects for nitrogen-fixing bacteria as the bacteria primarily responsible for carbon removal, has been developed to treat nutrient limited wastewaters to a high quality without the addition of nitrogen, and only minimal addition of phosphorus. Selection of the operating dissolved oxygen level to maximise nitrogen fixation forms a key component of the technology. Pilot scale activated sludge treatment of a thermomechanical pulping wastewater was carried out in nitrogen-fixing mode over a 15 month period. The effect of dissolved oxygen was studied at three levels: 14% (Phase 1), 5% (Phase 2) and 30% (Phase 3). The plant was operated at an organic loading of 0.7-1.1 kg BOD5/m3/d, a solids retention time of approximately 10 d, a hydraulic retention time of 1.4 d and a F:M ratio of 0.17-0.23 mg BOD5/mg VSS/d. Treatment performance was very stable over the three dissolved oxygen operating levels. The plant achieved 94-96% BOD removal, 82-87% total COD removal, 79-87% soluble COD removal, and >99% total extractives removal. The lowest organic carbon removals were observed during operation at 30% DO but were more likely to be due to phosphorus limitation than operation at high dissolved oxygen, as there was a significant decrease in phosphorus entering the plant during Phase 3. Discharge of dissolved nitrogen, ammonium and oxidised nitrogen were consistently low (1.1-1.6 mg/L DKN, 0.1-0.2 mg/L NH4+-N and 0.0 mg/L oxidised nitrogen). Discharge of dissolved phosphorus was 2.8 mg/L, 0.1 mg/L and 0.6 mg/L DRP in Phases 1, 2 and 3 respectively. It was postulated that a population of polyphosphate accumulating bacteria developed during Phase 1. Operation at low dissolved oxygen during Phase 2 appeared to promote biological phosphorus uptake which may have been affected by raising the dissolved oxygen to 30% in Phase 3. Total nitrogen and phosphorus discharge was dependent on efficient secondary clarification, and improved over the course of the study as suspended solids discharge improved. Nitrogen fixation was demonstrated throughout the study using an acetylene reduction assay. Based on nitrogen balances around the plant, there was a 55, 354 and 98% increase in nitrogen during Phases 1, 2 and 3 respectively. There was a significant decrease in phosphorus between Phases 1 and 2, and Phase 3 of the study, as well as a significant increase in nitrogen between Phases 2 and 3 which masked the effect of changing the dissolved oxygen. Op
ISSN:0273-1223
1996-9732
DOI:10.2166/wst.2003.0446