Membrane-attached biofilm as a mean to facilitate nitrification in activated sludge process and its effect on the microfaunal population

Abstract

A membrane-attached biofilm (MAB) was incorporated into a conventional activated sludge (AS) process to facilitate the nitrification. The simultaneous carbon removal and nitrification of the MAB incorporated AS (AS + MAB) process was compared with that of the AS process. The total organic carbon (TOC) loading was varied from 0.43 to 0.68 g/(L d), and the corresponding total nitrogen (T-N) loading was varied from 0.15 to 0.24 g/(L d) with keeping the C/N ratio at 2.85. The TOC removal efficiencies were above 95% for both processes within the range of TOC loading tested. The results showed the excellent carbon removal in both processes. The volumetric nitrification rate of AS + MAB process was about 0.14 g/(L d) at the T-N loading of 0.21 g/(L d), and was about seven times higher than that of AS process at the loading of 0.22 g/(L d). The results clearly demonstrated that the MAB facilitated the nitrification in the AS process. The maximum surface nitrification rate was about 8.4 g/(m 2 d), which was based on the surface area of the biofilm module. This value was almost comparable to that of nitrifying MAB under the same T-N loading, indicating little carbon inhibition against the nitrification in the AS + MAB process. On the other hand, the presence of MAB enabled the growth of slow-growing microorganisms not only nitrifying bacteria but also microfauna. The enumeration of microfauna in bulk suspension was carried out for both processes during the treatment. The abundance in rotifers, in addition to the appearance of oligochaetes, in the AS + MAB process suggested the less sludge generation due to the enlarged food-chain. The incorporation of MAB into AS process enabled the simultaneous nitrification and carbon removal, and had high potential in less sludge generation.