Sewage sludge production poses a significant global challenge, with anaerobic digestion (AD) being the most widely employed method to manage this issue. However, since hydrolysis is the rate-limiting step in AD, pretreatment of sludge can aid in enhancing the process.
The current study aimed to evaluate sludge solubilization and gas production—particularly bio-hydrogen (bio-H₂) production—following low-temperature thermal pretreatment (LTTP) at 55°C. This thesis replicates the full-scale setup of the Themista® system, which employs a two-stage thermal pretreatment process with 55°C and 70°C as the heating stages, operating in a semi-continuous mode. Four distinct pretreatment experiments were conducted to assess sludge solubilization and gas production: LTTP , LTTP with H₂O₂ at 55°C, LTTP with FeCl₂ at 55°C, and LTTP with both H₂O₂ and FeCl₂ at 55°C.
The results demonstrated that both thermo-chemical and thermal pretreatments exhibited similar soluble chemical oxygen demand(sCOD) release patterns. A shift from tightly bound to more soluble fractions of extracellular polymeric substances (EPS) was observed post-pretreatment. Gas production was noted only at 55°C across all conditions, with bio-H₂ being produced under each pretreatment. Notably, thermal pretreatment with FeCl₂ resulted in an average H₂ COD/tCOD ratio that was 24 times higher than that of thermal pretreatment alone. However, the average sludge to gas COD percentage for all pretreatments remained below 0.06%, with the highest of 0.1% observed in the thermal treatment with FeCl₂. Additionally, significant increases in BMP and a sludge COD to CH₄ conversion percentage of 75% were observed post-treatment with thermal pretreatment combined with FeCl₂