Sludge reduction via biodegradation of the endogenous residue (XE): experimental verification and modeling

Abstract

The feasibility of sludge reduction via the XE biodegradation process was explored both experimentally and through modeling, where the main focus was on determining the value of the bE parameter (first order degradation of XE) from a continuous process. Two activated sludge systems (30 L) were operated in parallel with synthetic wastewater during 16 months: a conventional activated system (CAS) and a modified low-sludge production activated sludge (LSP-AS) process equipped with a side-stream digester unit (DU). First, the long term data of the CAS reactor (1 year) was used to calibrate the ASM model and to estimate the heterotrophic decay constant of the cultivated sludge (bH=0.29 d-1, death-regeneration basis). Second, pre-simulations were performed to design the LSP-AS system and to estimate the DU volume required (40 L), to avoid XE accumulation in the process. Third, the LSP-AS process was built, put in operation and monitored for more than 9 months. This allowed to assess the actual behavior of the quasi-complete solids retention system. Once calibrated, the modified AS model estimated the value of the bE parameter to be in the range of 0.003-0.006 d-1, satisfactorily describing the overall sludge yield reduction of up to 49% observed in the experiments.