Evaluation of Nitrification Kinetics for a 2.0 MGD IFAS Process Demonstration

Abstract

The James River Treatment Plant (JRTP) operated a 2 MGD Integrated Fixed Film Activated Sludge (IFAS) demonstration process from November 2007 to April 2009 to explore IFAS performance and investigate IFAS technology as an option for a full scale plant upgrade in response to stricter nutrient discharge limits in the James River Basin. During the study, nitrification kinetics for both ammonia and nitrite oxidizing bacteria and plastic biofilm carrier biomass content were monitored on a near-weekly basis comparing the IFAS media, the IFAS process mixed liquor, and mixed liquor from the full-scale activated sludge process. Carrier biomass content is variable with respect to temperature and process SRT and relates to the localization of nitrification activity in the IFAS basin. Similar to trends observed for carrier biomass content (Regmi, 2008), ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) activity also shifted from the fixed film to the suspended phase as water temperatures increased and vice versa as the temperature decreased. The data suggest that AOB activity occurs on the surface of the biofilm carriers, while NOB activity remains deeper in the biofilm. During the highest temperatures observed in the IFAS tank, AOB activity on the media contributed as little as 30% of the total nitrification activity in the basin, and after temperatures dropped below 20 °C, AOB activity in the fixed film phase made up 75% of the total activity in the IFAS basin. During the warmest period of the summer, the media still retained more than 60% of the total NOB activity, and more than 90% of the total NOB activity during the period of coldest water temperature. This trend also points out that some AOB and NOB activity remained in the mixed liquor, even during the coldest periods. The retention of nitrification activity in the