Evaluating the Impact of Thermal Dose on Sludge Rheology of the Thermal Hydrolysis Pretreatment Process
Open AccessThe gel formation potential of the sludge in function of the thermal hydrolysis pretreatment (THP) conditions were quantified as well as its impact on digestibility and dewatering at DC Water’s Blue Plains Advanced Wastewater Treatment Plant (AWTP). First, a method named gelation method was developed to represent the gel behavior of THP sludge with different sieve sizes. After the method development, initial observations of THP sludge showed promising results. Waste activated sludge showed increased gel behavior over primary sludge, indicating the application of the method in quantifying gelation behavior of sludge. The Full Scale THP at different thermal dose showed increased thermal dose results in increased gelation, and as a result of that having a negative impact on soluble COD concentration of THP sludge after an optimum thermal dose of 4950 min-°C (equivalent to 30 min at 165 °C). When the high gelated sludge from THP went into the anaerobic digesters, hydrolysis and biogas efficiency were negatively impacted. Both Pilot and Full Scale THP and AD operations showed a similar trend. The optimal range for maximized anaerobic digestion (AD) kinetics was found at 3900 to 4950 min-°C or 25 to 30 min at 165 ◦C temperature. This small optimal range would indicate the need for operating at more controlled reaction time, than achieved at this moment in practice. Finally, in dewaterability, increased gelation factor in anaerobic digested sludge didn’t show strong relationship with cake solids due to small change of cake solids in full scale operation. In summary, both pilot and full scale THP results indicated the potential use of gelation factor as a sensitive parameter for optimizing THP conditions.
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