Six bioreactors with different additives of nanoscale zero valent iron (nZVI), zeolite, nZVI and zeolite mixture (IMZ), and nZVI coated zeolite (ICZ) particles were tested to evaluate the overall anaerobic digestion performance of domestic sludge under 37 °C. For 14 days' long, the daily biogas production, methane content, pH, soluble chemical oxygen demand (soluble COD), total alkalinity and total ammonia nitrogen variations were measured, and the overall performance of anaerobic digestion was assessed. The results showed that ICZ addition caused a lag period before starting to generate a significant biogas volume then the cumulative production increased more than the other bioreactors, and the higher the iron particles coated zeolite were added the more the biogas generated. Compared to the control bioreactor, the two highest methane contents were depicted with the addition of the only nZVI and the IMZ mixture and the methane content was stimulated up to 88 and 74%, respectively. However, the maximum cumulative methane volume was obtained with supplementing of ICZ particles with a loading of 1000 mg/L of iron nanoparticles. These results might be attributed to the high reactivity of nanoparticles, which can be assigned to the anaerobic corrosion of nZVI and electrons generation that could be utilized effectively the methanogens utilization and methane production. Considering its high efficiency and good performance, the iron zeolite system can be extended to practical engineering application for biomethane production.
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