STUDY OF ULTRA-COMPACT BIOFILM REACTORS FOR NITROGEN REMOVAL

Abstract

In this project, the feasibility, performance and operational characteristics of Ultra Compact Biofilm Reactor (UCBR) for nitrification, denitrification and nitrogen removal were investigated. The entire study was divided into four phases: namely nitrification, denitrification, integrated nitrogen removal in a single UCBR and sequential nitrogen removal in two UCBRs. From the results obtained in this study it was found that the performance of UCBRs was very much affectcd by the quality of biofilm developed within the reactors.

ln the nitrification UCBR, when proper support medium (sand pm1iclcs with average diameter of 0.265 mm) and start-up strategies were applied, biofilm with a density of 95 g/l could be formed and quickly developed to a biomass concentration of 17 g/l within a period of three months. The efficiency of nitrification reached over 95% at a loading rate of 10.5 kg ammonium-N/m3 .d. This type of UCBR was robust and flexible with respect to environmental and operational changes.

In the denitrification UCBR, biofilm with a density of around 25 g/l could be formed, The conversion rate of the nitrate-N could reach a maximum value of 10.5 kg/m3 ·d when biomass concentration was 3 g/l. Start-up was easier and quicker than the nitrification UCBR. However, the denitrifier biofilm was not as dense and robust as the nitrifier biofilm. In particular, the denitrifier biofilm was sensitive to pH changes which suggested that operational control in a denitrification UCBR would be more critical.

Integrated nitrogen removal in a single UCBR was not efficient due to the adverse impact of anoxic environment on nitrifier biofilm while sequential nitrogen removal in two UCBR.s was successfully carried out with a removal efficiency of 95% and a removal rate of 6 kg N/m3 .d. The capacities of UCBRs for nitrification, denitrification and nitrogen removal were all rather high comparing with other types of reactors commonly reported in the literature.