Utilization of nitrogen fixing organisms in biological treatment of nitrogen deficient wastewaters

IV ABSTRACT Biological treatment of nitrogen deficient wastewaters are usually accomplished by external addition of nitrogen sources to the wastewater. The operational costs increase with the external addition of nitrogenous compounds such as ammonium, urea and nitrate salts. Also, externally added nitrogen may partly end up in the effluent of the wastewater treatment plants, which reduces the effluent quality. As an alternative for effective biological treatment of nitrogen deficient and carbon rich wastewaters, nitrogen fixing bacteria can be used along with activated sludge culture. When nitrogen fixing bacteria was mixed with other activated sludge organisms, the performance of the system treating the nitrogen deficient wastewater may improve. The major objective of this thesis is to improve the treatment performance of nitrogen deficient wastewaters by using nitrogen fixing bacteria in an activated sludge unit. Azotobacter vinelandii was used as the nitrogen fixing bacteria since those organisms are obligate aerobes and can easily be adapted to an activated sludge system. Biological TOC and COD removal efficiencies of nitrogen deficient synthetic wastewater were investigated in batch and continuous systems by using Azotobacter vmetofc/H-supplemented activated sludge culture. Performance of Azotobacter added and free cultures of activated sludge were compared at different initial TN/ COD ratio in batch experiments. The results indicated clear advantage of using Azotobacter in the activated sludge culture to improve TOC removal performance at low TN/ COD ratios. More than 90 % TOC removal efficiencies were obtained withpure Azotobacter or Azotobacter added activated sludge culture from nitrogen deficient wastewaters. Azotobacter vinelandii was used with activated sludge culture for treatment of nitrogen deficient wastewater in a continuously operating activated sludge unit. COD removal performance of Azotobacter-sapplemeated activated sludge was compared with Azotobacter-fxee activated sludge culture for biological treatment of nitrogen deficient synthetic wastewater. Effects of important process variables such as TN/COD ratio, sludge age, hydraulic residence time, feed COD concentration and the COD loading rate on the COD removal performance were investigated. Kinetic constants of the system were determined by using the experimental data. It was proven that Azotobacter addition to the activated sludge in biological treatment of nitrogen deficient wastewater (TN/ COD < 0.06 ) has improved the COD removal performance significantly. Nearly, 90% COD removal efficiency was obtained from nitrogen deficient wastewater (TN/COD< 3%) by using Azotobacter supplemented activated sludge culture at HRT of 14 hours and SRT of 10 days.