The effect of calcium on the anaerobic digestion treating swine wastewater

A series of experiments with 0, 1, 3, 5, and 7 g Ca2+/l using calcium chloride were performed to evaluate the effect of various calcium concentrations on anaerobic digestion of swine wastewater. The addition of 3 g/l gave the best performance. On the other hand, the calcium concentrations of 5–7 g/l had an inhibitory effect on anaerobiosis. The lag phase durations expected in biogas production were 28–31 days with the addition of 0–3 g/l of calcium, and 43–52 days for calcium concentrations of 5 g/l or more. The concentrations of total volatile fatty acids decreased to less than 100 mg/l with calcium concentrations of 3–7 g/l. On the other hand, propionate and i-valerate concentrations remained over 4 and 0.8 g/l, respectively, when 1 g/l or less of calcium was added.