Waste activated sludge high‐rate treatment of septage: Stabilization phase trials and comparison with winery wastewater treatment

Abstract

The waste‐activated sludge high‐rate (WASHR) process is evaluated as a batch‐mode pre‐treatment for actual septage using a high‐rate contact stabilization (HRCS) approach. Designed to reduce organic loadings on downstream processes, the WASHR process features a relatively short aerobic contact phase (1–6 h) that promotes the adsorption of organics onto the activated sludge biomass followed by settling and decanting, and a longer stabilization phase (8–56 h) that provides aerobic stabilization of the settled biomass. This study investigated the stabilization phase performance at a contact phase loading rate of 2.0 mg COD/mg MLVSS, focusing on maximizing chemical oxygen demand (COD) removal, volatile solids (VS) removal, and observed biomass yield. Two sets of trials using different septage samples were conducted, with hydraulic retention time (HRT) and operating temperature as independent variables. For the first trial set, a contact phase COD removal of 83.1% was observed after 5 h. During the subsequent stabilization phase, maximum COD and VS removals of 36.8% and 20.1%, respectively, were observed at an HRT of 56 h, while the highest observed biomass yield of 0.205 mg VSS/mg COD _removed occurred at 24 h. In the second trial, peak COD and VS removals were 34.8% and 16.5%, respectively, at 52 h, with a maximum observed biomass yield of 0.257 mg VSS/mg COD _removed at 28 h. These results are compared to those from a previous WASHR study regarding the treatment of winery wastewater, with the aim of highlighting the potential in HRCS processes for enhancing organics oxidation in high‐strength wastewater treatment, rather than maximizing energy recovery.