SMART-Plant_Optimization of the Short-Cut Enhanced Nutrient Abatement (SCENA) system using fermented cellulosic primary sludge as carbon source

Anaerobic sewage sludge digestion results in the release of soluble organic nitrogen-containing compounds, ammonium and orthophosphate from the sludge mass into the bulk liquid, so that the reject water generated by the dewatering of the digested sludge has elevated nutrients concentrations. This nutrient rich stream is commonly recycled to the wastewater treatment plant (WWTP) influent or directly to secondary biological treatment, resulting in increased nutrient loadings to the mainstream wastewater treatment processes. Although the sidestream accounts for only about 1 % of daily average influent flow, it can increase the nitrogen load to the mainstream biological treatment by 20-25 % {Inc. Metcalf & Eddy, 2014} and the phosphorus loading by up to 40-65% in case of application of mainstream BioP processes (Destison, 2006). The sidestream inflow may lead to an increase in air supply, and thus the energy demand, and chemical requirements for biological nutrient removal (BNR) processes. To minimize these negative impacts and reduce plant operating costs in terms of energy, chemicals and maintenance, the reject water from anaerobic digester should be treated separately before it is recycled to the headworks of the WWTPs. Short-cut nitrogen removal (SCNR) through the ammonium oxidation to nitrite and its subsequent reduction to gaseous nitrogen has gained increasing attention over the last years. The completely autotrophic nitrogen removal process is considered more economically attractive as it further reduces energy demand and has no external carbon source requirements. However, its operational and environmental sensitivity, especially to variability and shock loadings, and the facts that neither enhanced biological phosphorus removal can be achieved nor nitrogen is completely removed are major concerns for its wide implementation (Malamis et al., 2014). On the other hand, SCNR can be conveniently coupled with suitable bioprocesses for phosphorus removal through its accumulation in biomass and can be a sustainable option resulting in the production of high added value products. In fact, the mechanism of phosphorus uptake can be realized under aerobic and anoxic conditions by phosphorus accumulating organisms (PAOs) that can utilize oxygen and/or nitrite as electron acceptors (Carvalho et al., 2007), which compete with glycogen accumulating organisms (GAOs) for the available carbon source. Indeed, to achieve an effective nitrogen and phosphorus removal via-nitrite, readily biodegradable COD should be provided and cellulosic primary sludge from sieved municipal wastewater (Ruiken et al., 2013) represents a valuable substrate to produce Volatile Fatty Acids (VFAs) by acidogenic fermentation. In this work, the enrichment of PAOs from activated sludge were carried out in a lab scale Sequencing Batch Reactor (SBR) using the fermentation liquid from cellulosic primary sludge for nitrogen and phosphorus removal from anaerobic supernatant. Moreover, the competition between PAOs and GAOs were deeply investigated by FISH analyse