Preservation Methods Of Quality Bacteria For Nitrogen Removal

Microorganisms are a kind of important national resource, and their preservation is a means of storing good strain and meeting application requirements. In the field of wastewater treatment, a lot of novel biotechnologies such as short-cut nitrification and anammox (anaerobic ammonium oxidation) process for nitrogen removal were developed over the past decades, so a large amount of quality microorganisms for nitrogen removal are needed to promote the application of novel biotechnologies. Compared with other microorganisms, it is difficult to obtain and store quality nitrifying bacteria and anammox bacteria because of their slow growth and high sensitivity to environment. Therefore, the preservation methods of nitrifying bacteria and anammox bacteria were studied, and main results are as follows:1. The preservation characteristics were studied and some efficient preservation methods were suggested for mixed nitrifying culture.â‘ As preservation evaluation index, nitrifying activity is better than total biomass. After preservation for 5 months, the survival biomass percentage was 2.5 to 3.9 times larger than the survival activity percentage with different preservation methods, so it is easy to mislead the evaluation results by using total biomass as evaluation index.â‘¡The content of heme c and ATP could qualitatively describe nitrifying activity, but the color had no correlation with nitrifying activity. Under anaerobic conditions, the color of preserved mixed nitrifying culture was changed from orange yellow to black due to sulfate reduction, but low temperature and nitrite/nitrate could decrease the sulfide formation and the color change.â‘¢Anaerobic preservation was better than aerobic preservation for mixed nitrifying culture. Under anaerobic and aerobic conditions, the half decay times of survival activity were 1.71 months and 1.60 months, and the survival activity percentages were 15.9% and 5.6% respectively after preservation for five months.â‘£Nitrite could improve the preservation of mixed nitrifying culture, and could decrease the decay rate of nitrifying activity. Under anaerobic conditions, the decay rates of nitrifying activity were 0.010 d^-1, 0.020 d^-1 and 0.021 d^-1, the half decay times of survival activity were 2.41, 1.13 and 1.09 months, and the survival activity percentages were 13.1%, 14.4% and 13.9% after preservation for 5 months by means of 4℃with 5 mmol·L^-1 nitrite, 4℃with 5 mmol·L^-1 nitrate and 4°C, respectively.⑤Natural temperature was suitable for storing mixed nitrifying culture. Under anaerobic conditions, the activity decay rates were 0.012 d^-1, 0.021 d^-1, 0.019 d^-1, 0.013 d^-1, the half decay times of survival activity were 1.71, 1.09, 1.22 , 1.62 months, and the survival activity percentages were 16.0%, 13.9%, 20.8%, 20.4% after preservation for 5 months by means of natural temperature, 4℃, -20℃and -20℃with 15% glycerol respectively. The survival activity percentage at natural temperature was not the highest, but the cost was the lowest of all preservation methods.2. The preservation characteristics of anaerobic ammonium oxidation were studied, and some efficient preservation methods were suggested for mixed anammox culture.â‘ The content of heme c could qualitatively describe anammox activity, but the color had no correlation with anammox activity because of sulfide production which led to the change of color from red to black during the preservation of mixed anammox culture.â‘¡Intermittent starvation was worse than persistent starvation during the preservation of mixed anammox culture. Under anaerobic conditions, three preservation methods, 4℃with substrate of (NH₄)₂SO₄, 4℃with addition of substrate (NO₂^--N/NH₄⁺-N ratio of 1.32) every ten days and 4℃with addition of substrate (NO₂^--N/NH₄⁺-N ratio of 1.63) every ten days, were carried out. After preservation for 5 months, their survival activity percentages were 74.7%, 68.0% and 60.3% respectively.â‘¢The preservation at 4℃with (NH₄)₂SO₄ was the best, but that at natural temperature with (NH₄)₂SO₄ was the cheapest. Under anaerobic conditions, the survival activity 4℃with (NH₄)₂SO₄, 4℃with NH₄Cl and natural temperature with (NH₄)₂SO₄ were 74.7%, 45.0% and 64.2% respectively after preservation for 5 months.