Mainstream Partial Nitritation/Anammox Nitrogen Removal Process in the Largest Water Reclamation Plant in Singapore

This paper summarizes the results of four sampling programs in Changi Water Reclamation Plant(WRP) in Singapore,which has a treatment capacity of 800 000 m³/d of municipal wastewater.Partial nitritation(72.2% of percentage on average) and nitrite shunt(nitrite accumulation ratio,NAR of 76.0% on average) were well established in the aerobic zones.NH₄⁺ removal coupled with NO₂^- reduction(Anammox process) was observed in the anoxic zones.Mass balance showed autotrophic nitrogen removal contributed to 37.5% removal of the total nitrogen in the primary effluent,while conventional denitritation/denitrification contributed to 27.1% removal,and the rest was in wasting sludge and final effluent.Microbial and kinetic studies supported the hypothesis that suspension/free cells of Anammox bacteria were able to be retained in such a short SRT process.The comparisons between the process in Changi WRP and the MLE/LE processes in other three WRPs in Singapore with respect to nitrogen concentrations,pH,and alkalinity of the effluent,aeration energy consumption and reactor volume were presented and discussed.