(613d) Wet Biomass Waste Valorization through Hydrothermal Liquefaction and Integrated Post-Treatment Measures

Wet biomass wastes such as food waste and dairy waste have very high water content over 90%. They can cause severe environmental and public health issues if left untreated including surface/groundwater pollution, water eutrophication, greenhouse gas emissions, etc. Traditional thermochemical treatments (e.g., pyrolysis or combustion) are energy inefficient for wet biomass wastes due to the higher vaporization enthalpy requirement. Hydrothermal liquefaction (HTL) hydrolyzes organics contained in wet biomass in an aqueous media at temperature ranging from 250 to 350 °C and pressures from 3 to 30 MPa for residence times of 5 to 60 minutes to produce bio-crude oil, solid hydrochar, and water-soluble chemicals in varying amounts depending on feed composition and operating conditions. Bio-crude oil can be further upgraded and used for transportation fuel. Hydrochar can act as a soil amendment due to its high nutrient (N and P) content. Water-soluble chemicals include short-chain carboxylic acids and sugar monomers that can be recovered through post-treatment measures such as anaerobic digestion (AD) to produce biogas for electricity generation or recovered as phosphorous-rich and nitrogen-rich nutrient compounds using membrane distillation (MD).

Currently, most researchers employ batch methods for HTL processing of wet biomass wastes where the feedstock(s) are loaded into the reactor and then heated to the target temperature. The heating time, depending on the target temperature and reactor size, can vary from several minutes up to an hour. However, the results obtained from batch experiments often are not quantitatively reproducible. In our studies, we have found that batch results differ significantly from continuous HTL operation on the industrial scale where the feedstock is injected into the reactor maintained at the target temperature. We examine how different experimental methods (i.e. batch vs. feed injection) affect the product distribution for a variety of different feedstocks including model compounds and mixtures representing typical wet biomass wastes. It explores methods to optimize the target product yield (i.e. bio-crude oil) in terms of mixture composition in order to maximize synergistic effects among different compounds.

In the presentation, post-treatment measures for the aqueous phase including AD and MD will also be briefly outlined to illustrate the benefits of combining HTL with other treatment methods. Along those lines, system analysis studies conducted in our group of applications of combined AD and HTL processing of dairy and food wastes will be reviewed.