(361e) Hydrothermal Liquefaction of Cyanobacteria and Ocean-Bound Polyethylene Plastic Waste

Plastics are pervasive environmental contaminants polluting the planet. Microplastics are plastic particles < 5-mm in size. Due to their small size, microplastics may be ecotoxic and accumulate cyanobacterial toxins released by harmful algal bloom (HAB). Given the pervasiveness of microplastic pollution and HAB, exploring technologies that can simultaneously handle microplastics and HAB while converting them into valuable products is crucial. Therefore, in this study, model HAB (Spirulina – SP) and ocean-bound polyethylene plastic (PE) waste were coprocessing using hydrothermal liquefaction (HTL). The initial screening tests for optimizing HTL reaction conditions included reaction times (0.5, 1, and 2h), SP solid concentration (10 and 25 wt.%), and temperature (300, 350, and 400 °C). After HTL reactions, four streams of products including the biocrude oil, aqueous phase, gas, and solid residue were produced and their respective yields were quantified. The chemical composition of the biocrude oil was also analyzed by using gas chromatography mass spectrometry (GC-MS). The screening results revealed that the highest oil yield (26.67 wt.%) was achieved at 2h, 10 wt.% SP, and 400 °C, with GC-MS analysis revealing the major chemical composition of biocrude oil including alkanes, alkenes, phenols, amides, aromatics and heteroatoms of nitrogen compounds. To examine potential synergies in co-converting PE and SP, additional HTL tests will be conducted using different ratios of SP and PE (SP:PE=1:0, 3:1, 1:1, 1:3, 0:1) under the down-selected optimal condition (2h, 10 wt.% SP, and 400 °C). The compositions of the biocrude oil obtained will be analyzed by GC-MS and be used to guide follow-up studies using field samples (microplastics and HAB). Fundamental insights learned from this study will be useful to guide the design of energy-efficient microplastic and HAB co-mitigation methods in future studies.