Lessons learnt from different inoculation strategies for pilot-scale start-up of partial nitritation for landfill leachate treatment

Conventional biological processes are not enough to achieve desired removal efficiencies from N-rich waste streams such as landfill leachate. In this aspect, start-up phase of a sequencing batch reactor was monitored that treated landfill leachate through a nitritation (LPN) process. The reactor was inoculated from two different sources with distinctive microbial compositions. The acclimatized sludge, taken from a leachate intermittent aeration reactor, failed to establish nitritation but instead developed a nitrification process initially (N-NO3 > 500 mg/l and N-NO2 almost null) and showed no biological activity afterwards. The latter non-acclimatized sludge taken from a conventional activated sludge (CAS) reactor achieved N-NH4 removal up to 96%. Although the nitrite oxidizing genus Nitrospira was abundant in the CAS, it was not further detected in the LPN system. Moreover, the enrichment of ammonia oxidizing genus Nitrosomonas in the LPN was consistent with the establishment of an efficient nitritation process.