Short-cut enhanced nutrient removal from anaerobic supernatants: pilot scale results and full scale development of the S.C.E.N.A. process

The feasibility of the Short-Cut Enhanced Nutrients Abatement (SCENA) system was for the first time validated at pilot scale in the real environment of the municipal wastewater treatment plant of Carbonera (Veneto Region, Italy). The system was integrated in the sewage sludge treatment line for the short-cut nitrogen and via-nitrite phosphorus removal from the reject water. Ammonia and phosphorus concentration in the reject water were around 500 mgN/L and 60 mgP/L. Compared to municipal wastewater, this stream overloaded the mainstream treatment train of 26% and 12% total nitrogen and phosphorus, respectively. The sewage sludge (alkaline) fermentation liquid (SFL) was used as best available carbon source to enhance the nutrients removal via-nitrite. These contained the following mixture of short-chain fatty acids: 41% acetic, 29% propionic, 16% butyric. After 20 days of start-up operation, the specific ammonium utilization rate (sAUR) increased up to 10 mgN/gVSSh at 20°C. Under steady state conditions, the SCENA system was stably fed with a volumetric nitrogen loading rate (vNLR) of 0.55 kgN/(m3 d) and biologically removed up to 85% of nitrogen and 65% of phosphorus. The BioP dry sludge showed P content of 55 mgP/gTS which has enhanced agrovalorisation potential after composting. Relevant residues of polyelectrolyte in the anaerobic supernatant caused strong overnight decrease of mixed liquor suspended solids in the bioreactor, which soon recovered its stability without affecting the specific removal performances.