A Tale of Two Pilots: Comparing a WAS-only Thermal Hydrolysis Process to Conventional THP

WAS-only thermal hydrolysis (TH) has been implemented in at least six facilities throughout the world—none to date in North America. There have been some recent publications regarding the benefits and installation experience of WAS-only TH, and the process can be easily approximated using a theoretical mass balance. However, the authors are unaware of any empirical study that compared a WAS-only TH process side-by-side with a conventional* TH process using the same feed solids. WAS-only TH is one of the short-listed alternatives for the ongoing Comprehensive Biosolids Plan for Baltimore City, Maryland. In response to the aforementioned observed gap in research, the authors conducted a pilot study with the purpose of quantifying differences in digester performance, such as biogas production and volatile solids reduction (VSR), as well as the characteristics of the digested solids, such as dewaterability, odor, energy content (an important criteria for beneficial use as an alternative fuel), and recalcitrant dissolved organic nitrogen (rDON).