Zero valent iron enhances methane production from primary sludge in anaerobic digestion

This study proposed a novel zero valent iron (ZVI) technology to enhance anaerobic methane production from primary sludge in the anaerobic digester and to improve the dewaterability of digested sludge for the first time. Compared to the control test without ZVI, the anaerobic digester with ZVI at all levels (1, 4 and 20 g/L) played a driving role in anaerobic methane production from primary sludge. The maximal biochemical methane production of 439 ± 5 L CH₄/kg VS was achieved at ZVI of 4 g/L, while only 345 ± 2 L CH₄/kg VS (volatile solids) was produced in the case of no-ZVI dosage, representing a relative increase of 26.9 ± 0.1%. It was also found that ZVI addition would produce an anaerobically digested sludge with a better dewaterability, as indicated by the decrease of the normalized capillary suction time from 100 to 63 ∼ 89 s, respectively. Model based analysis revealed that the enhanced methane production from primary sludge was due to an increase in both hydrolysis rate and biochemical methane potential of primary sludge. Economic analysis demonstrated that ZVI technology was economically favorable.