MBR excess sludge reduction by combination of electrocoagulation and Fenton oxidation processes

• 15 min Electrolysis time triggered Fenton oxidation in electro-Fenton system.
• Electrofenton and electrofenton–Fenton systems were effective for sludge removal.
• Electrofenton–Fenton process was the best from a techno-economical viewpoint.
• Sludge electrofenton–Fenton oxidation reduced membrane fouling.
• MBR coupled with electrofenton–Fenton process removed more TN compounds.

This study investigates the disintegration of excess sludge produced in a membrane bioreactor (MBR) with electrocoagulation, electrofenton and electrofenton–Fenton processes. The optimum reaction times for electrocoagulation, electrofenton and electrofenton–Fenton processes were 120, 90 and 70 min, respectively. Technical and economical investigations showed that electrofenton–Fenton system was the best one. It was found that 15 min electrofenton oxidation process was enough to trigger Fenton oxidation process and 55 min remaining reaction time could be operated without electrolysis combination. This process had low energy consumption, and the total cost was 2.02 €/m3. After optimization, two MBRs were operated in parallel with and without the batch sludge electrofenton–Fenton oxidation process. The application of electrofenton–Fenton oxidation process to MBR was effective in terms of minimizing production of excess sludge and reducing membrane fouling. The sludge yield constant (Yobs) of the control run was approximately 0.10 g MLSS/g COD, while in MBR with the sludge oxidation process, MLSS was kept nearly stable and excess sludge production was negligible. Moreover, effluents from both systems were maintained at an acceptable level. Operation of the MBR system with sludge disintegration process led to a better total nitrogen removal than the control run.