Valorizing waste iron powder in biogas production: Hydrogen sulfide control and process performances

Biogas is composed of different gases including hydrogen sulfide (H₂S), which is a hazardous gas that damages pipes and generators in anaerobic digestion system. The objective of this study was to control H₂S by waste iron powder produced by laser cutting machine in a steel and iron industry. Waste iron powder was mixed with dairy manure at a concentration between 2.0 and 20.0 g/L in batch experiments, while the concentration was varied between 1.0 and 4.0 g/L in bench experiment. In batch experiment, a reduction of up to 93% of H₂S was observed at waste iron powder of 2.0 g/L (T1), while the reduction was of more than 99% at waste iron powder beyond 8.0 g/L (T4 ∼ T6). The total sulfide concentration (S_T) increased together with waste iron powder concentration and was fitted with a quadratic equation with a maximum S_T of 208.0 mg/L at waste iron powder of 20.2 g/L. Waste iron powder did not have significant effect on methane yield in batch and bench experiments. However, hydrolysis rate constant was increased by almost 100%, while the lag-phase period was reduced to half in test digesters compared to that in control digester. In bench experiment, H₂S concentration was reduced by 89% at 2.0 g/L, while 50% at 1.0 g/L. Therefore, waste iron powder was effectively removed H₂S and did not affect negatively anaerobic digestion process.