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Genifuel Hydrothermal Processing Bench Scale Technology Evaluation Project (WE&RF Report LIFT6T14)
Citation:
Marrone, P. Genifuel Hydrothermal Processing Bench Scale Technology Evaluation Project (WE&RF Report LIFT6T14). Water Environment & Reuse Foundation, Alexandria, VA, 2016.
Impact/Purpose:
Benefits of this study: • Demonstrates that biocrude can be generated from HTL of all three major types of wastewater sludge (primary, secondary, and digested solids) at reasonable yields (i.e., 25-37%) and of comparable quality to that of other biocrudes generated from other high water content biomass feeds. • Shows that secondary sludge is more difficult to dewater than either primary sludge or digested solids, and results in a biocrude that may be difficult to recover, though the latter may have been at least partially a result of test equipment problems. • Demonstrates that CHG gas product is capable of meeting siloxane limits for use as an internal combustion engine fuel, and CHG aqueous product is capable of meeting water discharge requirements except for nitrogen for some wastewater treatment facilities. • Provides a fully characterized set of feed and effluent data for each sludge feed type tested.
Description:
Hydrothermal Liquefaction (HTL) and Catalytic Hydrothermal Gasification (CHG) proof-of-concept bench-scale tests were performed to assess the potential of the Genifuel hydrothermal process technology for handling municipal wastewater sludge. HTL tests were conducted at 300-350◦C and 2900 psig on three different feeds: primary sludge (11.9 wt% solids), secondary sludge (9.7 wt% solids), and post-digester sludge (also referred to as digested solids) (16.0 wt% solids). Corresponding CHG tests were conducted at 350◦C and 2900 psig on the HTL aqueous phase product using a ruthenium based catalyst. A comprehensive analysis of all feed and effluent phases was also performed. Total mass and carbon balances closed to within ± 15% in all but one case. Biocrude yields from HTL tests were 37%, 25%, and 34% for primary sludge, secondary sludge, and digested solids feeds, respectively. The biocrude yields accounted for 59%, 39%, and 49% of the carbon in the feed for primary sludge, secondary sludge, and digested solids feeds, respectively. It should be noted that HTL test results for secondary sludge may have been affected by equipment problems. Biocrude composition and quality were comparable to that seen with biocrudes generated from algae feeds. CHG product gas consisted primarily of methane, with methane yields (relative to CHG input) on a carbon basis of 47%, 61%, and 64% for aqueous feeds that were the product of HTL tests with primary sludge, secondary sludge, and digested solids, respectively. Siloxane concentrations in the CHG product gas were below the detection limit and well below fuel input composition limits set by several engine manufacturers. Relative to that of the sludge feeds, the HTL-CHG process resulted in a reduction in chemical oxygen demand (COD) of greater than 99.9% and a reduction in residual solids for disposal of 94-99%. The test results, as a whole, support further long term testing in a larger scale integrated system that is representative of what would be installed at a water resource recovery facility (WRRF) in order to fully assess the technical and economic viability of this technology for wastewater sludge treatment. [NOTE: The link below connects to a WE&RF site where the Final Report can be downloaded for free, after registering at the WE&RF site. For some projects the Executive Summary is available and can be downloaded for free without registering on the WE&RF site.]
