Reuse of Digestate from Anaerobic Digestion of Organic Waste: Enhancement of Biogas Production Using Ozonation

Anaerobic digestion of organic waste generates nutrient-rich digestate, which poses challenges for effective utilization due to its complex structure. Ozonation has emerged as an environmentally friendly treatment method for breaking down recalcitrant organic materials. In addition, co-digestion has been found to enhance methane production. This study employed ozone treatment on digestate, followed by mixing it with primary and excess sludge in sequencing batch tests. Results showed that methane production from ozone treated anaerobic digestate (ODI) (83.20 mL/g VSS) was 101.2% higher compared with untreated digestate (41.34 mL/g VSS). Co-digestion further improved methane production, with ODI combined with primary and excess sludge producing 180.51 mL/g VSS and 152.64 mL/g VSS, respectively, exceeding that of ODI alone (83.20 mL/g VSS). In addition, combining ODI with excess sludge (152.64 mL/g VSS) resulted in 6.5% higher methane production compared with excess sludge alone (143.29 mL/g VSS). Microbial community structure analysis revealed the enrichment of key flora facilitating organic matter to methane conversion during anaerobic digestion. In conclusion, integrating ozone pretreatment and co-digestion presents an environmentally-friendly approach for digestate reuse.