Combined Carbonaceous Removal and Nitrification with Biological Aerated Filters

Abstract

This paper describes the use of a submerged biological aerated filter (BAFs), on a pilot plant scale, in the secondary nitrification of low strength domestic wastewater. The results, obtained throughout three months of tests, confirmed the ability of BAFs to obtain simultaneous carbonaceous removal and nitrification. In fact, after a start-up period of 5 weeks, a remarkable steady state condition in the removal of suspended solids (TSS), chemical oxygen demand (COD) and nitrification was reached. For a hydraulic loading rate of 1.6 m3 m−2 h−1, the mean efficiency of the process in the removal of TSS and COD was 85% and 83% respectively. Mean concentrations in the influent flow of around 114 mgTSS/L and 140 mgCOD/L were reduced to average values of below 17 mgTSS/L and 25 mgCOD/L. Secondary nitrification was achieved with a mean efficiency of 85% for a mean volumetric loads of 0.45 kgN-Namm m−3 d−1 (25°C). Through an intensive activity of nitrification, in the steady state condition, mean influent concentrations of around 12 mgN-Namm/L were reduced to average values of below 2 mgN-Namm/L. The removal loading rate increased linearly with the applied loading rate for volumetric loads of up to 0.7 kgN-Namm m−3 d−1. The nitrification was not sensitive to the applied COD loads because of the low level of carbon substrate.