Full-scale trials of external nitrifcation on plastic media nitrifying trickling filter

Abstract

The full-scale single-stage tertiary nitrifying trickling flter (NTF) at the Citrusdal Wastewater Treatment Plant provides for external nitrifcation of unclarifed effuent from the facultative aerobic lagoon in order to meet standard effuent ammonia concentration requirements. The apparent ammonia nitrifcation rate (ApANR, gN/m2 media surfaced) of the NTF was sensitive to particulate organic loading rates which were predominantly in the form of algae, and the soluble COD removal rates increased under cold climates. Installation of forced-air ventilation fans improved the nitrifcation effciency from 15% to 43%. An increase in hydraulic loading rate (HLR) by effuent recirculation signifcantly improved the ApANR, eradicated flter fies and decreased the prevalence of worms. Maximum ApANR of ∼1.0 gN/m2·d was achieved yielding an ammonia-removal effciency of approximately 71%. Profle samples collected along the NTF media depth indicated poor media wetting at low HLR resulting in low ApANR (<0.5 gN/m2·d). Also during the cold and rainy winter period, poor bioflm activity and prevalence of motile algae were observed, and under low hydraulic loading rates and warmer temperatures, a dominance of flter fies and fy larvae were observed. In contrast, in controlled laboratory studies, ApANRs up to 1.72 gN/m2.d (22.1 mgN/l removal) were attained, which, in conformity with full-scale, was also found to be sensitive to hydraulic loading conditions.