Complete Ammonia Oxidation to Nitrate in a Low-Dissolved Oxygen Nitrification Reactor. activated sludge matagenomes

Aeration for nitrification is a major energy consumer to maintain high dissolved oxygen (DO) level in aerobic tank of sewage treatment plants (STPs). Low-DO nitrification shows potential in reducing aeration and energy demand of STPs. By taking advantage of active nitrifiers’ growth in warm sewage of Malaysia, the efficiency of ammoniacal nitrogen (NH4-N) removal from sewage was investigated in a lab-scale low-DO nitrification reactor. Mechanical stirring was used for aeration with designed rotational speed of 300 rotations per minute. Around 90% of NH4-N was removed at near-zero DO condition during active nitrification. All NH4-N was oxidised into nitrate nitrogen (NO3-N), with negligible nitrite nitrogen (NO2-N) accumulation. Emission of potent nitrous oxide (N2O) gas from STPs is often associated with NO2-N accumulation. Hence, low-DO nitrification in this study did not show indication of the emission of N2O. Also, the microbial community structure was elucidated by 16S rRNA amplicon sequencing and fluorescence in-situ hybridisation. The most abundant nitrifiers were related to Nitrospira genus and Nitrosomonadaceae family, which were present in 1% to 2% of total community. Denitrifiers belong to the genera Thauera and Dechloromonas though present in the reactor denitrification was not detected. This study showed active low-DO nitrification for warm sewage, which is a sustainable process that could significantly reduce the energy footprint of STPs in line with global goal of energy efficient use.