<p>This research represents a continuation of our earlier investigations into the impact of sea salt and sodium carbonate (Na₂CO₃) on biocrude production through hydrothermal liquefaction (HTL). In this study, we employed three distinct types of feedstocks: lipid-rich Camelina, an energy crop cultivated on marginal lands; protein-rich microalgae, a marine species; and carbohydrate-rich sawdust from forestry residues, to thoroughly explore the sea salt effect on these feedstocks, with the outcomes compared to results achieved using Na₂CO₃, a conventional additive in HTL processes. Notably, the introduction of 5% sea salt markedly elevated the biocrude yield from 59.5 wt% to 66.8 wt% for HTL of Camelina at 270&#xa0;°C. Na₂CO₃, however, proved not to be a suitable additive for lipid-rich Camelina HTL, especially at a relatively high temperature (320&#xa0;°C). Sea salt facilitated the formation of esters over fatty amides, increasing biocrude yield. In the case of protein-rich microalgae HTL, the presence of sea salt was not influential for biocrude yield, whereas the addition of Na₂CO₃ reduced the biocrude yield. For sawdust HTL, sea salt had a negative effect, but 5% Na₂CO₃ addition improved biocrude formation. These experimental findings underscore the complexity of selecting the right additive for HTL biocrude production, we thus developed a machine learning-based predictive tool with an R² value greater than 0.94, showcasing a substantial advancement over conventional methods. This research contributes to the cleaner biocrude production from diverse biomass sources by demonstrating the potential of using sea salt, a more environmentally benign additive compared to traditional Na₂CO₃, as well as through machine learning-aided prediction.</p> Graphical Abstract <p></p>