(30d) Batch to Continuous: Scale-up of Hydrothermal Processing of Food Waste

Waste-to-fuel technologies have the potential to reduce reliance on non-renewable resources and address environmental concerns related to waste disposal. Mainstream and WPI have adopted a two-pronged approach utilizing hydrothermal liquefaction (HTL) and hydrothermal gasification (HTG) to convert food waste into a biocrude product. This approach is able to reduce wet wastes, generate renewable energy, and produce only clean water for disposal. A heterogeneous catalyst is used during HTL to improve the biocrude yield and energy recovery and a sequential catalytic HTG cleans the aqueous fraction by converting soluble organics to permanent gases.

A continuous HTL/HTG food waste processing system was developed to test and demonstrate the viability of processing large-scale food waste. The continuous system can process up to two liters of food waste slurry per hour. The HTL reaction converts food waste to biocrude, char, gases, and water-soluble compounds in a catalytic continuous stirred-tank reactor (CSTR). As the products exit the CSTR, the char is removed immediately to prevent clogging downstream before the biocrude and the aqueous phase are separated using a gravity separation unit. The resulting biocrude is collected, but the aqueous phase dissolved organics must be removed to safely dispose of the water. The aqueous phase is passed to a catalytic packed bed reactor where the dissolved organics are converted to permanent gases (i.e., hydrogen, methane, and carbon dioxide) via catalytic HTG. Between 93%-98% of the dissolved organics are converted and the resulting permanent gases can be recycled into the HTL reactor to improve biocrude yield and reduce the residence time. The continuous system is fully automated using a central control unit constructed in LabVIEW. The performance of the continuous system to process a variety of waste streams was evaluated by the biocrude yield and composition, in addition to total organic content (TOC) of the aqueous phase.