Repeated Biodiesel Production from Waste Sewage Sludge Using a Cartridge Containing Commercial Acidic Polymer Catalysts

Biodiesel was produced from waste sewage sludge (WSS) using a one-step direct process (OSDP) that involves the simultaneous extraction of lipids from WSS and their transesterification with methanol in a single reactor.The sludge contained 16.1% lipids, with 55.5% of these being free fatty acids.Methanol and n-hexane were identified as the best solvent combination for this process.Indion 190, a styrenedivinylbenzene copolymer with sulfonic groups, was chosen as the most effective acid solid catalyst from the commercial polymer beads evaluated.A cartridge containing the catalyst was used in the OSDP to facilitate its reuse in repeated biodiesel production.To ensure complete mixing in the OSDP, a shaking speed of at least 200 rpm was required, and the optimal total volume of the solvent mixture was 9 mL/g-WSS, with a volume ratio of 33.3% methanol to 66.7% n-hexane.Under the optimal reaction conditions, which included 100 wt% catalyst concentration, a temperature of 60C, a reaction time of 6 hours, and a shaking speed of 200 rpm, 4.71% of biodiesel yield (g-biodiesel/g-WSS) was achieved.The acid solid catalysts lost efficacy after the third use, but their performance was restored to that of fresh catalysts through regeneration with sulfuric acid treatment.