Anaerobic Digestion of Cassava Pulp with Sewage Sludge Inocula

The effectiveness of sludge inocula from a municipal carrousel oxidation ditch wastewater treatment plant was studied for both batch and semi-continuous anaerobic digestion (AD) of cassava pulp. In 1.25-L batch experiments, the following sludge inocula were used: I1 sludge from the hydrolysis acidification tank pre-acclimated with cassava pulp; I2, predigested sludge from the hydrolysis acidification tank; and I3, predigested sludge from the gravity thickening tank. In 1.0-L semi-continuous tests, mesophilic AD of cassava pulp inoculated with I3 was carried out at organic matter loading rates (OLRs) of 1.5 to 12.5 kg volatile solids (VS)/(m(3) d), whereas 1.5 to 18.0 kgVS/(m(3) d) was used for thermophilic AD. For batch operations, all sludge types could be used as the inoculum for the mesophilic AD of cassava pulp, whereas only I1 was used for thermophilic AD. The maximum specific methane yields were 0.333 and 0.395 m(3)/kgVS(added), respectively, for mesophilic and thermophilic batch digestion with I1. During semi-continuous AD of cassava pulp inoculated with I3, high specific methane yields of 0.334 to 0.336 m(3)/kgVS(added) were obtained under both mesophilic and thermophilic conditions. For thermophilic AD of cassava pulp with sludge inocula, the range of optimum OLR was 2.5 to 15.0 kgVS/(m(3) d), and that was 2.5 to 8.7 kgVS/(m(3) d) for mesophilic AD.