NITRIFYING GENERA IN ACTIVATED SLUDGE MAY INFLUENCE NITRIFICATION RATES
Sequencing batch reactors acclimated under aerobic and alternating anoxic/aerobic conditions were used in the research. The reason for significantly higher nitrification rates in alternating reactor (6.16±0.34 mg NH4 +-N/gVSS h) in comparison to strictly aerobic one (2.95± 0.26 mg NH4 +-N/gVSS h) was investigated. In the strictly aerobic reactor, low nitrite accumulation occurred and oxygen was limited due to the presence of organic matter. In alternating treatment, due to incorporated denitrification, pH, alkalinity, and the concentration of nitrite in the beginning of the aerobic reaction were higher; also oxygen was more available because of organics depletion. Batch tests performed with biomass developed under aerobic and alternating conditions showed however that these factors, when investigated separately, did not influence the nitrification rates enough to explain the huge differences between the types of biomass. It was suggested that the nitrification process could be performed by different genera of nitrifiers; the two common and well-studied groups of ammonia oxidizing bacteria (Nitrosospira, Nitrosomonas) and nitrite oxidizing bacteria (Nitrospira, Nitrobacter) were taken into consideration. In aerobic treatment, population of Nitrosospira and Nitrospira with low Ks values could dominate, as it was reported that they can be adapted to low nitrite and oxygen conditions; it would explain lower nitrification rates. On the other hand, Nitrosomonas and Nitrobacter with high Ks values are better competitors in environments with high dissolved oxygen and substrate concentration, Nitrobacter have also higher nitrite tolerance, so they could proliferate in the biomass developed under alternating anoxic/aerobic conditions. This would explain the higher nitrification rates and argue in favour of using alternating treatment.
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Document Type: Research Article
Publication date: 2007-01-01
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