Increasing long-chain dicarboxylic acid production by pretreating grease trap waste using ceramic ultrafiltration

Grease trap waste (GTW) is a lipid-rich, low-value waste stream that is a promising feedstock for the production of long-chain dicarboxylic acids (LCDAs) by Candida viswanathii. However, the presence of anionic surfactants and trace metals hinders this bioconversion process. This study evaluated the use of ceramic ultrafiltration as a pretreatment technology. A 3 nm ZrO₂ ceramic membrane removed approximately 90% of anionic surfactants and over 90% of Ni, Zn and Fe. Using a C1-grafted variant increased the flux sevenfold, to 2.3 L/(m².h), while retaining the same level of removal. Pretreating the GTW increased LCDA titres in shake flasks by up to sixfold compared to untreated feed. In fed-batch bioreactor runs, pretreated GTW yielded 43.5 g/L LCDA, which is a 25% improvement to the untreated GTW, with a final productivity of 0.46 g/(L.h) and a lipid-to-LCDA yield of 82%. However, biomass formation was lower with pretreated GTW, likely reflecting reduced levels of growth-promoting cofactors. Nevertheless, these results demonstrate that ceramic ultrafiltration enables robust LCDA production from GTW, supporting valorisation of lipid wastes.