Nitrogen Fixation in the Activated Sludge Treatment of Thermomechanical Pulping Wastewater, 2001 Environmental Conference Proceedings

Alison Slade, Sheree Anderson, Bridget Blackwell, Peter Dare, Hamish Pearson--Nitrogen supplementation is often practised to ensure effective biological treatment of nutrient limited wastewaters. A novel technology, which selects for nitrogen-fixing bacteria as the bacteria primarily responsible for carbon removal, has been developed. Pilot scale activated sludge treatment of a thermomechanical pulping wastewater was carried out in nitrogen-fixing mode. The plant was operated at an organic loading of 1.05 kg BOD5/m 3 /d, a solids retention time of 8.9 d, a hydraulic retention time of 1.4 d and a F:M ratio of 0.23 mg BOD5/mg VSS/d. The dissolved oxygen concentration was controlled at 14%, at a temperature of 30ºC. Very good organic substrate removals were achieved, with 87% total COD removal, 85% soluble COD removal, 85% dissolved organic carbon removal and 95% BOD5 removal. Discharge of soluble nitrogen was low (1.3 mg/L DKN, 0.1 mg/L NH4 + -N and 0.0 mg/L oxidised nitrogen). Low total nitrogen discharge was dependent on efficient secondary clarification. There was a 55% increase in nitrogen in the system, resulting in a nitrogen fixation rate of 4046 mg N/d and 0.0151 mg N/mg VSS/d. The nitrogen-fixing system operated at a BOD:N:P ratio of 100:0.7:0.5, and proved to be very robust, able to accommodate considerable variation in wastewater composition.