Denitrification and biofilm growth in a pilot-scale biofilter packed with suspended carriers for biological nitrogen removal from secondary effluent

Abstract

Tertiary denitrification is an effective method for nitrogen removal from wastewater. A pilot-scale biofilter packed with suspended carriers was operated for tertiary denitrification with ethanol as the organic carbon source. Long-term performance, biokinetics of denitrification and biofilm growth were evaluated under filtration velocities of 6, 10 and 14m/hr. The pilot-scale biofilter removed nitrate from the secondary effluent effectively, and the nitrate nitrogen (NO3-N) removal percentage was 82%, 78% and 55% at the filtration velocities of 6, 10 and 14m/hr, respectively. At the filtration velocities of 6 and 10m/hr, the nitrate removal loading rate increased with increasing influent nitrate loading rates, while at the filtration velocity of 14m/hr, the removal loading rate and the influent loading rate were uncorrelated. During denitrification, the ratio of consumed chemical oxygen demand to removed NO3-N was 3.99–4.52mg/mg. Under the filtration velocities of 6, 10 and 14m/hr, the maximum denitrification rate was 3.12, 4.86 and 4.42gN/(m2·day), the half-saturation constant was 2.61, 1.05 and 1.17mg/L, and the half-order coefficient was 0.22, 0.32 and 0.24(mg/L)1/2/min, respectively. The biofilm biomass increased with increasing filtration velocity and was 2845, 5124 and 7324mg VSS/m2 at filtration velocities of 6, 10 and 14m/hr, respectively. The highest biofilm density was 44mg/cm3 at the filtration velocity of 14m/hr. Due to the low influent loading rate, biofilm biomass and thickness were lowest at the filtration velocity of 6m/hr.