Lipid Extraction from Wet Polymer-Flocculated <i>Chlorella sorokiniana</i> Using Liquefied Dimethyl Ether without Centrifugation and Drying Pretreatment

The energy intensive nature of harvesting microalgae by centrifugation and drying results in a low energy profit ratio for biofuel production from wet microalgae. To address this, microalgal cultures can be flocculated by polymers to reduce energy consumption and avoid centrifugation. Additionally, lipids can be directly extracted from wet microalgae harvested by centrifugation using liquefied dimethyl ether (DME) to reduce energy consumption. In this study, we investigated the lipid extraction from the green alga, <i>Chlorella sorokiniana</i> (<i>C. sorokiniana</i>), flocculated with amphoteric and cationic polymers using liquefied DME, without centrifugation and drying pretreatment. Although the addition of amphoteric polymer did not interfere with lipid extraction by liquefied DME, the amount of lipids extracted by ethanol from flocculated <i>C. sorokiniana</i> decreased. The addition of cationic polymers also interferes with lipid extraction using liquefied DME, chloroform-methanol mixtures, and ethanol. Surface functional group measurements revealed that the amphoteric and cationic polymer flocculants were insoluble in these solvents, remained in the residue, and did not contaminate the extracted lipids. Thus, the amphoteric flocculant KA305BH was found to be effective for lipid extraction with liquefied DME from <i>C. sorokiniana</i>. The proposed approach can facilitate the energy efficient production of biofuel from wet microalgae.