Emergent Chemical Behavior in Mixed Food and Lignocellulosic Green Waste Hydrothermal Liquefaction

Abstract

Hydrothermal liquefaction (HTL) is a promising strategy for the conversion of energy-dense waste streams to fuels. Mixed-feed HTL aggregates multiple feed streams to achieve greater scales that capitalize on local resources, hence lowering costs. The potential for new pathways and products upon feedstock blending becomes a compounding level of complexity when unlocking emergent chemistries. Food and green waste streams were evaluated under HTL conditions (300 °C, 1 h) to understand the effect of feed molecular composition on product distributions and mechanisms. Thousands of emergent chemical compounds were detected via Fourier transform ion cyclotron resonance mass spectrometry, ultimately leading to the emergence of two dominant outcomes. First, the presence of small amounts of food waste into green waste results in substantial decarboxylation and subsequent polymerization to biocrude than chars. Second, in the other limit, small amounts of green waste promote the capping of oxygenates into the biodiesel range, such as with the emergence of fatty acid methyl esters.

Characterizing the Opportunity Space for Sustainable Hydrothermal Valorization of Wet Organic Wastes

“…In practice, cotreatment of different organic wastes could achieve greater economic scale and help mitigate the costs and CIs of carbohydrate-rich feedstocks. 31 For example, existing waste management infrastructure could serve as intermediate destinations for carbohydrate-rich feedstocks with later transport to an HTL-based system, where they can be comanaged A constant moisture content (80%) and a constant ash content (15%, on a dry weight basis) were assumed for each biochemical composition. Carbohydrate, lipid, and protein are reported on an ash-free dry weight basis.…”

“…As a result, for waste streams comprised entirely of protein, the carbon intensity could reach a minimum value of 14.7 [−280 to 280] kg CO 2 eq·tonne –1 . In practice, cotreatment of different organic wastes could achieve greater economic scale and help mitigate the costs and CIs of carbohydrate-rich feedstocks . For example, existing waste management infrastructure could serve as intermediate destinations for carbohydrate-rich feedstocks with later transport to an HTL-based system, where they can be comanaged with locally produced feedstocks with higher lipid or protein content.…”

“…In practice, cotreatment of different organic wastes could achieve greater economic scale and help mitigate the costs and CIs of carbohydrate-rich feedstocks. 31 For example, existing waste management infrastructure could serve as intermediate destinations for carbohydrate-rich feedstocks with later transport to an HTL-based system, where they can be comanaged with locally produced feedstocks with higher lipid or protein content. Ultimately, HTL-based systems could be deployed to manage regionally relevant combinations of waste resources.…”

“…HTL has been applied to multiple organic wastes including wastewater sludge, − FOG, , food waste, − animal manure, − green waste, and their mixtures. ,, These feedstocks have different biochemical (carbohydrate, protein, lipid) compositions and macrostructures, leading to variabilities in product yields and characteristics (e.g., the energy content of biocrude). For example, FOG (which are nearly 100% lipids) has a high biocrude yield of more than 80% but very low nutrient recovery potential, while gases and hydrochar have been reported to be the main products from carbohydrate-rich feedstocks such as green waste .…”