Reducing wasted sewage sludge from wastewater treatment: Comparison of two membrane bioreactor pilot plants

This study compares two Oxic Settling Anaerobic (OSA) – Membrane Bioreactor (MBR) configurations fed with real wastewater. The novelty of the study is to consider an MBR configuration (namely, MBR-OSA II) never investigated with the OSA process. The influence of the hydraulic retention time (HRT) inside the anaerobic reactor for each configuration (namely, MBR – OSA I and MBR – OSA II) was investigated. Four experimental periods were carried out: Period I and II for MBR – OSA I, under HRT of 4 and 6 h, respectively, and Period III and IV for MBR – OSA II, under HRT of 4 and 6 h, respectively. Results showed the decay rate bH increased with the HRT, especially during Periods I and II (from 0.62 d−1 to 0.77 d−1). The anaerobic HRT influenced the total sewage sludge production. With the increase of the HRT for the same configuration, the sludge production decreased. In terms of biological sludge production, a substantial reduction occurred under MBR – OSA II operation compared to MBR – OSA I. However, despite MBR-OSA II configuration providing the highest reduction of the biological sludge production (78 %) (during Period IV), during this Period, the highest N2O (N2O emission factor till to 3.1 %) production and membrane fouling occurred. Indeed, Period IV showed the highest membrane resistance (namely, 25 · 10−13 m−1). Thus, the MBR-OSA I with anaerobic HRT equal to 6 h provided the best results.