Mesophilic Anaerobic Co-digestion of Manure and Thickened Waste Activated Sludge at Different Mixture Ratios

Anaerobic digestion (AD) has attracted attention for its ability to produce biogas as a renewable energy source and for its impact on the economy. Recent studies have indicated that anaerobic co-digestion (AcoD) is more advantageous than conventional mono-digestion. The benefits of improved energy production and solids reduction using multiple substrates has encouraged researchers to study co-digestion technology and to further understand the effect of adding co-substrates on the digestion process. A proper mixture ratio of the co-substrates is required to obtain larger quantities of biomethane, optimal hydrolysis rate and shorter lag phase. This study was aimed to study the influence of mixture ratio in co-digestion of manure and thickened waste activated sludge (TWAS) in mesophilic condition. Manure and TWAS at different mixture ratios of 9:1, 7:3, 1:1, 3:7, and 1:9 on a volumetric basis were used to determine the effect of the mixture ratios on methane production in biomethane potential assay (BMP). Results showed that co-digestion of TWAS and manure at the ratio of 1:9 (V/V) resulted in the highest ultimate biomethane production of 378 mL CH4 /g VSAdded. In comparison, anaerobic digestion of TWAS alone yielded 195.48 mL CH4 /g VSAdded and manure alone 325 mL CH4 /g VSAdded. This research also verified the advantages of co-digestion over mono-digestion.