Cultivation and maintenance of nitrite-oxidizing bacteria granular sludge in SBR process

A SBR inoculated with nitrifying activated sludge was employed to cultivate granular sludge. Under the selective pressure of settling time, the formation of nitrite oxidizing bacteria granules were achieved by increasing NO₂^--N concentration from 25 mg/L to 75 mg/L within 120 cycles. The granules were shaped like sphere with diameter ranging from 0.5 to 0.9 mm, an average settling velocity of 2.4 cm/s, and the sludge volume index was 46.5 ml/g. As the granules was operated stably, the nitrite oxidization rate was around 0.119 mg NO₂^--N/mg MLSS·h. The enrichment of nitrite oxidization granules was quantified by FISH which indicated that nitrite oxidizing bacteria was 16.1% of the total bacteria. It is indicated that the oxidizing nitrite granules was cultured successfully.