Enhancing Biogas Production Using Ultrasound-Assisted Thermal Pre-Treatment Technology for Anaerobic Co-Digestion of Sewage Sludge and Microalgae Substrates

Document Type : Research Paper


1 Department of Renewable Energies Engineering, Faculty of Mechanical and Energy Engineering, Shahid Beheshti University, Tehran, Iran

2 Department of Energy Systems Engineering, Faculty of Mechanical and Energy Engineering, Shahid Beheshti University, Tehran, Iran


The study aimed to assess the effects of ultrasound-assisted thermal pre-treatment on biogas production by co-digesting stress-adapted microalgae (Synechocystis sp.) with a combination of mixed municipal and industrial sewage sludge under anaerobic conditions. The pre-treatment process involved subjecting the microalgae biomass to thermal pre-treatment at temperatures of 70, 90, and 110 oC, while utilizing ultrasound pre-treatment for the sludge (with an average solids content of 16.7 g.L-1) at a frequency of 25 kHz and power output of 400 W for durations of 3, 9, and 15 minutes before the main digestion process. The experiment was designed by response surface methodology with a central composite design. The results revealed that the model exhibited statistical significance, with a probability value (Prob > F) of less than 0.05. Pre-treated samples demonstrated a substantial increase in biogas production compared to untreated samples, showing an average 1.4 to 5.6-fold enhancement. Optimization analysis indicated that the highest cumulative biogas production, amounting to 706 NmL, could be achieved after 2 weeks by pre-heating the microalgae cells at 110 oC for 1 hour and subjecting the sewage sludge to ultrasound pre-treatment for 3 minutes. These findings highlight the potential of ultrasound-assisted thermal pre-treatment technology as a strategy to enhance biogas production through the co-digestion of stress-resilient microalgae and sewage sludge.


Main Subjects

Articles in Press, Accepted Manuscript
Available Online from 18 June 2024
  • Receive Date: 07 January 2024
  • Revise Date: 17 June 2024
  • Accept Date: 18 June 2024