Performance of anaerobic membrane bioreactor for sewage sludge treatment: Mesophilic and thermophilic processes

• Anaerobic MBR technology for sewage sludge treatment was studied experimentally
• Digestion and filtration was compared in mesophilic and thermophilic conditions
• Membrane decoupled SRT and HRT, and higher OLRs compared to CSRT process were treated
• High temperature improved filtration and influenced sludge rheological properties
• Fouling by struvite was enhanced at higher temperature due to high N–NH4 concentration

The viability of the anaerobic membrane bioreactor (AnMBR) technology for the treatment of sewage sludge has been studied under mesophilic and thermophilic conditions. Coupling membrane filtration with the digestion process allows the digestion to be operated with longer solids retention time (SRT), and the volumetric load can be increased considerably compared to the conventional completely stirred reactor process. Maximum SRT is conditioned by the total solids concentration and the viscosity of the digested sludge. Values of 50 and 30 days for 55 and 35 °C were obtained in the experimental platforms. Organic loads of 6.4 and 4.6 gCOD/(L·d) were successfully treated at 55 and 35 °C, respectively, representing a significant digester volume reduction compared to conventional systems. The performance of thermophilic and mesophilic AnMBRs were compared, and the same sludge biodegradability was measured. The difference was the distribution of the inert COD among the soluble and particulate fractions. Better filtration performance was observed in the thermophilic system, where a larger flow could be attained and the lower viscosity enabled operation with higher SRT. However, increased irreversible fouling at higher temperature was shown to require optimised chemical cleaning strategies to extend membrane lifetime. In conclusion, AnMBR offers an extensive opportunity for the treatment of waste streams with high-solids content waste streams, where membrane filtration is one of the most promising technologies for decoupling solids and hydraulic retention times.