Formation of Carbohydrates, Proteins and Melanoidins during LowTemperature Thermal Hydrolysis of Primary and Secondary Sewage Sludge

The effects of low to medium temperature (44-121°C) Thermal Hydrolysis (THP) treatment of Primary (PS) and Secondary (WAS) municipal Wastewater Sludge on formation of carbohydrates, proteins, Melanoidins and methane generation potential were evaluated. Results show that between 1.5 and 12% of Volatile Solids (VS) was hydrolyzed into Filtered Dissolved Solids (FDS), with 55-100% represented as carbohydrates and proteins depending on sludge type and THP temperature. Proteins are produced at 160 to 350% of the values for carbohydrates in terms of g gVS-1, and WAS values are 4 to 5 times as large as PS values. Much more Low Molecular Weight (LMW) proteins are formed than High MW (HMW) proteins at all temperatures for both PS and WAS. The same is true for carbohydrates from PS, but the quantities of LWM and HWM produced are similar for WAS. Low-medium temperature THP increased BMP of WAS from 145 ml CH4 gVS-1 in untreated WAS to up to 230 ml CH4 gVS-1 (44 to 57% increase depending on temperature), and only nominally increased BMP of PS (by 0 to 7.5%). THP caused the formation of much more Melanoidins in WAS than PS and showed little dependence on temperature in the range evaluated herein. There was a nearly 20-fold increase in supernatant color for both PS and WAS that was well correlated with increases in THP temperature. Overall, the effects of low-medium temperature THP are significant for WAS and limited for PS.