Optimization of Thermal Hydrolysis Process for Co-digestion of Fermented Primary Sludge and Waste Activated Sludge

• Author / Creator

  Zhou, Peijun

• This study focused on the optimization of the thermal hydrolysis process (THP) for co- digestion of fermented primary sludge (FPS) and thickened waste activated sludge (TWAS). For this purpose, lab-scale experiments were conducted under two different schemes with different combinations of pretreatment temperatures (140, 160, and 180oC) and exposure times (15, 30, and 60 minutes); severity indices were ranged from 2.4 to 4.1. In scheme-1, a mixture of FPS and TWAS was subjected to THP, while in scheme-2, only TWAS was pretreated with THP. The biochemical methane potential (BMP) test was conducted for the evaluation of methane yields from sludge pretreated under different conditions. In scheme- 1, the highest soluble chemical oxygen demand to total chemical oxygen demand (SCOD/TCOD) ratio of ~ 46% was achieved for FPS+TWAS pretreated at 180oC for 15 minutes; volatile suspended solids (VSS) removal efficiency was 53%. In scheme-2, the maximum SCOD/TCOD ratio of ~ 58% was attained for TWAS pretreated at 180oC for 30 minutes; VSS removal efficiency was 68%. Thus, 180oC was the most effective temperature for sludge solubilization under both conditions. Severity indices showed a positive correlation with COD solubilization and VSS reduction efficiencies in scheme-2, while such relationships were not found in scheme-1. The increase in methane yields did not correlate with aggressive solubilization efficiencies achieved at 180oC. In scheme-1, the maximum biomethane yield of 272  24 mL/g COD was achieved for FPS+TWAS pretreated at 160oC for 60 minutes, which was 161% higher than the control. In scheme-2,
  II
  the highest biomethane yield of 182  155 mL/g COD was achieved for TWAS pretreated at 140oC for 30 minutes, which was 75% higher than the control. For both schemes, increases in severity indices negatively affected biomethane yields. Thus, the results suggested that higher severity indices could lead to solubilization of certain inhibitory or refractory organics.

• Subjects / Keywords

  • Anaerobic digestion (AD); biomethane; thermal hydrolysis process (THP); solubilization; fermented primary sludge (FPS); thickened waste activated sludge (TWAS)

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-hq3c-5h92

• License

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