Selection of in-situ desulfurizers for chicken manure biogas and prediction of dosage

The hydrogen sulfide (H₂ S) in biogas is poisonous and corrosive, so it is usually removed in the early stage of biogas upgrading. Dosing iron compounds directly into the anaerobic fermenter is an in-situ method for rough desulphurization. But it is difficult to estimate the appropriate amount of iron compound to add and overdosing is usually inevitable. Five kinds of iron compounds (FeCl₂, FeCl₃, Fe(OH)₃, Fe₂ O₃, and FeSO₄) were applied as in-situ desulfurizers in chicken manure fermentation to reduce H₂ S emissions. Biogas yield, CH₄ concentration, and H₂ S concentration were examined to evaluate the performance of these desulfurizers. Among these five desulfurizers, FeCl₂, FeCl₃, and Fe(OH)₃ showed better performance; the desulfurization rates were all above 98.5% when the addition was 16 mmol L^-1. In order to establish the prediction model of the required amount for in-situ desulfurizer, it is assumed that the dosage of desulfurizer could be simply divided into two parts: one part for consumption of released H₂ S, and the other part for guaranteeing a certain desulfurizing level. Under this assumption, the prediction formulas were fitted based on the bottle experiments and applied in a 5 L fermentation system. The required desulfurization levels (H₂ S concentration) when adding FeCl₂, FeCl₃, and Fe(OH)₃ were set to 120, 200, and 100 ppmv, respectively. After adding the calculated dosage of the three in-situ desulfurizers, the actual H₂ S concentrations were 163.0, 180.3, and 89.4 ppmv, respectively, which were relatively closed to the required desulfurization levels.