Single-stage, single-sludge nitrogen removal by an activated sludge process with cross-flow filtration

Nitrogen removal by a single-stage, single-sludge activated sludge process with cross-flow filtration was qualitatively studied. Artificial wastewater had a BOD/TKN ratio from 1.8 to 24.5. The BOD loading to the process ranged from 0.33 to 1.66 g l−1 d−1, the TKN loading from 0.032 to 0.268 g l−1 d−1 and the sludge retention time (SRT) was quite long (54–4200 d). In each experiment, more than 97% of organic carbon was removed. The sludge biomass concentration (MLVSS) was high at a high volumetric BOD loading. Total Kjeldahl nitrogen (TKN) was successfully nitrified and higher than 29% of the TKN which was loaded to the reactor was removed in many of the experimental runs. The nitrogen balance of each unit was calculated. Denitrification was estimated to be responsible for 39–86% of the removed nitrogen in an aeration vessel. Although denitrification was not observed up to 0.438 g l−1 d−1 of BOD loading, the denitrification rate increased as the BOD loading increased. The percentage of nitrogen removal was a function of the BOD/TKN ratio of the influent. Lower DO concentration did not increase the denitrification rate, but intermittent aeration-BOD loading did increase it; TKN was completely removed up to 0.21 TKN g l−1 d−1, and the denitrification rate reached 0.0074 gN VSS−1 d−1.