Enhanced Sewage Sludge Disintegration and Hydrogen Production by Ionizing Radiation Pretreatment in the Presence of Fe2+

The effect of ferrous ion (Fe2+) on sludge disintegration by ionizing radiation and subsequent hydrogen production was studied. Sludge was pretreated with 20 kGy ionizing radiation at three pH levels (pH 3, 5, and 7) with 0-1000 mg/L Fe2+ dosages. Results showed that the sludge disruption was better promoted by Fe2+ at pH 5. The highest soluble chemical oxygen demand of 5.01 g/L (4.66 times that of control) was achieved with 800 mg/L Fe2+ addition at pH 5. Cumulative hydrogen production (CHP) was also enhanced in subsequent dark fermentation; a CHP of 26 mL H-2/100 mL was 2 times and 1.73 times that of the control and sole radiation pretreated groups, respectively. Change of dissolved organics showed that ionizing radiation pretreatment mainly induced the release of protein-like organics, and the addition of Fe2+ further induced the solubilization of microbial byproduct-like organics. Sludge degradation was also promoted by Fe2+ addition. Microbial analysis showed that CHP had a significant positive correlation with Paraclostridium sp. and Clostridium tertium, and the addition of Fe2+ suppressed species that are negatively related to CHP. This study suggested that Fe2+ could significantly enhance the hydrogen production from sewage sludge by promoting sludge disintegration and affecting the microbial distribution.