Anaerobic co-digestion of algal sludge and waste paper to produce methane

The unbalanced nutrients of algal sludge (low C/N ratio) were regarded as an important limitation factor to anaerobic digestion process. Adding high carbon content of waste paper in algal sludge feedstock to have a balanced C/N ratio was undertaken in this study. The results showed adding 50% (based on volatile solid) of waste paper in algal sludge feedstock increased the methane production rate to 1170 ± 75 ml/l day, as compared to 573 ± 28 ml/l day of algal sludge digestion alone, both operated at 4 g VS/l day, 35 °C and 10 days HRT. The maximum methane production rate of 1607 ± 17 ml/l day was observed at a combined 5 g VS/l day loading rate with 60% (VS based) of paper adding in algal sludge feedstock. Results suggested an optimum C/N ratio for co-digestion of algal sludge and waste paper was in the range of 20–25/1.