Investigation into the effects of different recycled magnetic additives on anaerobic co-digestion of sludge and straw.

• Effects of different recycled magnetic additives on the AD was investigated. • Methane production increased by 79.81% with addition of recycled Fe 3 O 4. • The predominant aceticlastic pathway was consolidated with recycled Fe 3 O 4. • Recycled Fe 3 O 4 enriched more Methanosarcina that broadened the methanogenic pathway. The addition of magnetic additives has been found to enhance the anaerobic co-digestion of sludge and straw. Due to strong magnetic properties, these additives can be easily separated from the digestate, allowing for recycling during the continuous anaerobic digestion process. This study aimed to investigate the impact of different recycled magnetic additives (specifically, magnetic biochar and Fe 3 O 4) on the anaerobic co-digestion of sewage sludge with corn straw. The results showed that the addition of recycled Fe 3 O 4 with an initial amount of 10 g/kg resulted in the highest cumulative methane yield of 295.70 mL/g VS added , which increased by 79.81% as compared to the control. The results suggest that magnetic biochar with higher carbon content exerts a more noticeable impact on shortening the digestion lag phase time, as indicated by kinetic analysis. With the addition of recycled Fe 3 O 4 , the Methanosaeta and Methanosarcina enhanced significantly. Especially Methanosarcina , which was increased from 3.85% to 6.28%, resulting in a 2.43% increase. Furthermore, the predominant aceticlastic pathway of digestion process was consolidated, and the enriched Methanosarcina broadened the pathways of methanogenesis. This research provides a potential utilization strategy of recycling Fe 3 O 4 for accelerating the anaerobic degradation of urban and rural areas solid waste. [ABSTRACT FROM AUTHOR]