No abstract

No abstract

No abstract

The main challenge in implementing shortcut nitrogen removal processes for mainstream wastewater treatment is the out-selection of nitrite oxidizing bacteria (NOB) to limit nitrate production. A model-based approach was utilized to simulate the impact of individual features of process control strategies to achieve NO(-)(2)-N shunt via NOB out-selection. Simulations were conducted using a two-step nitrogen removal model from the literature. Nitrogen shortcut removal processes from two case studies were modeled to illustrate the contribution of NOB out-selection mechanisms. The paper highlights a comparison between two control schemes; one was based on online measured ammonia and the other was based on a target ratio of 1 for ammonia vs. NOx (nitrate + nitrite) (AVN). Results indicated that the AVN controller possesses unique features to nitrify only that amount of nitrogen that can be denitrified, which promotes better management of incoming organics and bicarbonate for a more efficient NOB out-selection. Finally, the model was used in a scenario analysis, simulating hypothetical optimized performance of the pilot process. An estimated potential saving of 60% in carbon addition for nitrogen removal by implementing full-scale mainstream deammonification was predicted.

This paper deals with an almost 1-year long pilot study of a nitritation-denitritation process that was followed by anammox polishing. The pilot plant treated real municipal wastewater at ambient temperatures. The effluent of high-rate activated sludge process (hydraulic retention time, HRT=30 min, solids retention time=0.25 d) was fed to the pilot plant described in this paper, where a constant temperature of 23 °C was maintained. The nitritation-denitritation process was operated to promote nitrite oxidizing bacteria out-selection in an intermittently aerated reactor. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia and nitrate+nitrite concentrations. The unique feature of this aeration control was that fixed dissolved oxygen set-point was used and the length of aerobic and anoxic durations were changed based on the effluent ammonia and nitrate+nitrite concentrations. The anaerobic ammonia oxidation (anammox) bacteria were adapted in mainstream conditions by allowing the growth on the moving bed bioreactor plastic media in a fully anoxic reactor. The total inorganic nitrogen (TIN) removal performance of the entire system was 75±15% during the study at a modest influent chemical oxygen demand (COD)/NH4+-N ratio of 8.9±1.8 within the HRT range of 3.1-9.4 h. Anammox polishing contributed 11% of overall TIN removal. Therefore, this pilot-scale study demonstrates that application of the proposed nitritation-denitritation system followed by anammox polishing is capable of relatively high nitrogen removal without supplemental carbon and alkalinity at a low HRT.