Long term experiences in a pilot-scale high-rate activated sludge system with lamella clarifier: Effluent quality and carbon capture

The limited available area for treatment plants in population-dense settlements increases the need for technologies with smaller footprints. The high-rate activated sludge (HRAS) process aims to capture carbon from wastewater by limiting biological assimilation with a high loading rate which enables occupying a smaller footprint. The footprint of the HRAS system can be further reduced by using lamella clarifiers instead of conventional ones. Conventional clarifiers were used in previous studies on the operational parameters of the HRAS system. This study aims to determine the optimum operational conditions in terms of hydraulic retention time (HRT) (75 and 50 min) and dissolved oxygen (DO) concentration (0.2, 0.5, and 0.8 mg/L) of a HRAS system including a lamella clarifier using 124 days data. The best effluent quality and carbon capture were observed at HRT of 75 min and DO concentration of 0.5 mg/L, which was considered the optimum condition with the highest extracellular polymeric substances (EPS) production in the reactor. The high EPS production helped flocs come together and settle faster with the highest carbon capture compared to other operational conditions. Based on the mass balance, 41.7 % of chemical oxygen demand (COD), 34 % of total nitrogen (TN), and 60 % of total phosphorus (TP) in the influent were captured into the sludge stream at the optimum condition. Lower HRT and DO concentration decreased EPS production and led to particulate COD loss through effluent and hampered carbon capture. Furthermore, higher DO concentration caused more carbon loss through oxidation.