Enhanced propionic acid degradation (EPAD) system: Proof of principle and feasibility

Full-scale anaerobic single-phase digesters can be confronted with process instabilities, which often result in the accumulation of propionic acid (HPr). As a solution, an enhanced propionic acid degradation (EPAD) system has been conceptually designed and experimentally tested at lab-scale. The system consisted of two components: a liquid/solid separator containing a microfiltration membrane and an up-flow anaerobic sludge bed (UASB) reactor specialized in HPr degradation. Two lab-scale continuous stirred tank reactors (CSTR) were used, i.e. the CSTRcontrol and the CSTRtreatment Firstly, the CSTRs were stressed by organic overloading to obtain high HPr levels. During the recovery period, besides stop feeding, no actions were taken to decrease the residual HPr concentration in the CSTRcontrol, while the CSTRtreatment was connected to EPAD system in order to accelerate its recovery. By the end of the experiment, the CSTRtreatment completely recovered from HPr accumulation, while no significant decrease of the HPr level in the CSTRcontrol was observed. Based on the experimental results, the up-scaling of EPAD system was evaluated and it would only account for about 2% of the volume of the full-scale digester, thus suggesting that the implementation of a mobile EPAD system in full-scale practice should be feasible. (C) 2009 Elsevier Ltd. All rights reserved.