(407f) Understanding the Effects of Mixed Municipal Solid Waste Streams on HTL Product Characteristics

In 2018, each person in the United States was responsible for the production of nearly five pounds of municipal solid waste (MSW) per day.¹ Co-HTL of food and green waste components of MSW can help reduce waste and achieve economies of scale and the interactions between these feeds must be understood.

This work aims to understand the effect of mixing food and green waste on oil yield and product composition. Real food waste obtained from a veteran’s affairs hospital resulted in 35.9% oil yield non-catalytically, in contrast to 12.13% for green waste. Current studies have revealed sustained oil yield (34.1%) with addition of up to 25% lignocellulosic waste (Figure 1). Additionally, results show increasing char yields (21 – 33.5%) with increased green waste content, due in part to its high (up to 13%) ash content.

Despite a drastic difference in carbon content in the feeds, 52% for food waste and 19% for green waste, FTIR indicates minimal differences between oil phase functional groups and vibrations. The primary difference occurs at 3400 cm^-1 where the addition of green waste increases the OH stretching band. Solid phase FTIR mirrors the observed similarities, however, pure green waste solid phase which contains a significant OH stretch band. The similarities observed via FTIR are not sustained with GC/MS, as food waste oil contains large fatty acid peaks that decrease with the addition of green waste, only to be replaced by the presence of ketones and aromatics.

Qualitative observations also show improved homogeneity of food waste oil, noting that it is less sticky. Green waste oil, on the other hand appears to contain two distinct phases, a free-flowing liquid, and a sticky residue. This works provides useful insight into the feasibility of mixed MSW feeds for use in hydrothermal liquefaction.