A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1992

Batch experiments were conducted to optimize the conditions of t hermal. alkali. and thermochemical pretreatments of waste activated sludge from the standpoints of improved particulate solubilization and increased methane production. These three types of pretreatment methods were then compared u sing the same criteria of increased solubilization a nd methane production in anaerobic digestion. Alkali. thermal. and thermochemical pretreatments improved the solubilization of waste activated sludge and en hanced the methane production in the subsequent digestion. Alkali pretreatment at 0.3 gNaOH/gVSS dose for 30 min contact time solubilized 9% of raw sludge VSS. and increased the methane conversion rate at 8 clays HRT by 30% over the unpretreatecl WAS (control). On the other hand, thermal pretreatment at 11 5°C temperature for 15 min contact time solubilized 18% of raw sludge VSS. In crease in methane conversion rate over the control at 8 days HRT was 1603. Thermochemical pretreatment at J 15°C temperature. 0.3 gNaOH/gVSS dose for 5 min contact bme solubilized more raw slu dge VSS (36% solubilization rate) than that attained from either alkali or thermal pretreatment. Digestion at 8 days HRT increased. the methane conversion rate by only 1153 over t h e control. a value lower than that obtained from thermal pretreatment. However, digestion performance of the the1·mochemically pretreated slu dge improved at low F(COD)/M(VSS) loading. and at 0.25 gCOD/gVSSseed. methane conversion rate at 8 days HRT was increased by as much as 220% over the control. an improvement of 74% and 20% over alkali pretreatment and heat pretreatment, respectively.