The most probable number (MPN) measurement showed that the overwhelming quantity of nitrosobacteria immobilized on biofilm was the main reason for stable and high nitrite accumulation in the reactor.

• 最大可能计数法（MPN）测定发现，亚硝化菌在数量上的绝对优势是反应器能始终保持高效稳定的亚硝氮积累的主要原因。