Treatment of waste activated sludge with thermal hydrolysis and mesophilic anaerobic digestion

CH2M is designing two installations where the thermal hydrolysis process (THP) is being used to treat waste activated sludge (WAS) and the hydrolyzed WAS will be combined with primary sludge prior to being fed to mesophilic anaerobic digestion. The technical issues for each process has proven to be different in the two case studies which are highlighted, one in Calgary, Canada and one in Singapore.The THP plant in Singapore will treat an initial flow of up to 53 metric tons of dry solids per day and is designed to be expandable to meet the ultimate requirement of 70 metric tons of dry solids per day by adding a 4th reactor. The THP system will treat both thickened and un-thickened WAS and concentrated grease waste. The thermally hydrolyzed sludge will be cooled by primary sludge and fed to 3 existing egg-shaped digesters. The total biosolids produced from these digesters to be dewatered on existing centrifuges will be 44.5 dry metric tons per day. Construction has begun in 2015 and the plant is expected to be operational in 2017.For Calgary, CH2M teamed with Stantec and completed conceptual and preliminary designs. WAS will be thickened, dewatered, and subjected to THP prior to blending with thickened primary sludge. Pre-selection of the THP equipment is in progress after which detailed design will be completed. Construction will begin in 2017. This facility will have capacity to manage an average of about 50 metric tons dry solids from a population equivalent (PE) of 1,237,000.The manuscript provides details on the decision factors associated with each project and the expected benefits and compares the technical design and operating data for each project.