Effects of Iron Compounds on Batch Anaerobic Digestion of Primary Sludge: Control of Hydrogen Sulfide and Phosphate

This study evaluated the effectiveness of using iron (Fe) powder and ferrous chloride (FeCl2) to decrease hydrogen sulfide (H2S) concentration ([H2S]) from biogas production by anaerobic digestion (AD) of primary sludge, and to decrease phosphate (PO4-P) concentration ([PO4-P]) in the sludge. [H2S] and [PO4-P] removal increased as doses of Fe powder and FeCl2 increased to a certain point. Optimal supplementation was 5 g/L for Fe powder (H2S reduction=98%, PO4-P removal=95%) and 0.5 g/L for FeCl2 (H2S reduction=98%, PO4-P removal=97%). Appropriate dosage of Fe powder or FeCl2 can control [H2S] in biogas and decrease [PO4-P] in AD effluent, but excessive dosage can inhibit the digestion. The biogas production and methane content were higher with Fe powder compared with FeCl2, but neither treatment had a significant effect on methane yield. The measured biogas production was accurately captured by the first-order kinetic model, as evidenced by a strong fit with high R2 values (0.957–0.980), and the deviations between the measured and predicted biogas production using the first-order kinetic model were <10%.