Operation of a nitrifying activated sludge airlift (NASA) reactor without biomass carrier

An ammonia loading rate of 4.1 kg N-NH4+/m(3)d was fully oxidized to nitrat e using a nitrifying airlift without biomass carrier. The developed sludge, with a concentration of 12 gVSS/L and high density (100 gVSS/L-particle) a llowed particles to be retained with small diameter, having very low concen trations of solids in the effluent (5-10 mg VSS/L). The mean diameter of pa rticles containing the majority of total biomass increased from 220 to 360 m during the operation time. The particle size analysis showed that the per centage of flocs with smalt diameter (1-3 m) is very high but the biomass c ontent of these flocs is negligible with respect to the total biomass value . The oxygen transfer coefficient (K-La) was measured operating at differen t air flow rates, obtaining similar values during the overall operational p eriod. The use of activated sludge without support gives high nitrifying ra tes with an easier fluidization and a lower critical air flow rate than in a biofilm airlift reactor.