WERF ROSI Project – Do We Need a Revised Time-Temperature Requirement to Achieve Class A Biosolids

摘要

Sudden increase (SI) of indicator bacteria, such as E. coli, in dewatered cake has been reported inprocesses that utilize thermophilic pretreatment followed by digestion or thermophilic digestion.The SI typically occurs when centrifuge dewatering is utilized. Increases of up to 4 or 5 ordersof magnitude have been measured. The objective of this research was to investigate if increasedtime-temperature would better inactivate the indicator organisms and prevent SI. The workexamined a range of time and temperature both in the lab and full-scale systems. The resultssuggested that an increased time-temperature for thermal treatment was associated with plantsthat did not have SI. In addition, a field trial with a pre-pasteurization plant showed thatincreasing the pre-pasteurization temperature from about 68 to the mid 70s decreased the extentof SI. Overall the results are supportive of revising the time-temperature for completeinactivation of indicator bacteria. However, this increased time-temperature regime is likely notnecessary for the inactivation of Salmonella, as other research has shown that SI did not occurfor Salmonella.