MOF-functionalized biochar for volatile fatty acid separation: Adsorption mechanism and sustainability evaluation

Ce-UiO-66 was anchored on biochar to fabricate hierarchical porous BC@UiO-66-MOF with abundant sites for selective VFA capture. • The composite selectively adsorbs short-chain VFAs via multilayer chemisorption and allows recovery by ethanol-water elution. • Fixed-bed tests verify superior separation capacity and renderability with 83% initial capacity retained after five adsorption-desorption cycles. • Aspen Plus simulation establishes an industrial VFA separation process, and optimized distillation enables 97-98% VFA purification. • LCA and economic analysis confirm the integrated process is eco-friendly, low-cost, and scalable for kitchen-waste recycling. Volatile fatty acids (VFAs) derived from anaerobic fermentation of kitchen waste represent valuable biobased building blocks, yet efficient separation and recovery of VFAs from complex aqueous fermentation liquors remain a persistent bottleneck. Adsorption serves as a promising route for bioproduct enrichment, but conventional adsorbents suffer from insufficient uptake capacity, low selectivity, or poor structural robustness. To overcome the weak mechanical stability of bare metal–organic frameworks and the lack of specific recognition toward target pollutants of pristine biochar, we rationally fabricate a Ce-UiO-66-functionalized biochar composite named BC@UiO-66-MOF for selective VFA capture. Response surface methodology (RSM) was employed to optimize adsorption operational parameters, while a suite of characterizations including SEM, BET, in situ FTIR, XPS, and XRD verified the successful immobilization of Ce-UiO-66-MOF moieties on biochar scaffolds. We systematically unravel the intrinsic adsorption mechanisms toward various VFAs and further assess the practical applicability of this composite for the treatment of authentic fermentation wastewater. The as-prepared BC@UiO-66-MOF integrates the complementary merits of biochar and Ce-UiO-66-MOF, delivering synergistically boosted structural stability, abundant pore channels, and enhanced adsorption capacity, alongside markedly improved VFA selectivity and cyclic reusability relative to unmodified biochar. Density functional theory (DFT) calculations disclose that acetic acid exhibits stronger, thermodynamically more spontaneous adsorption interactions in high-polarity aqueous media compared to ethanol, verifying ethanol as an ideal desorption eluent. Fixed-bed dynamic adsorption tests reveal that the BC@UiO-66-MOF packed column exhibits a 28% longer breakthrough duration and 72% greater saturated adsorption capacity than commercial biochar (BC), highlighting its outstanding performance under continuous-flow operation. Complementary Aspen Plus process simulation coupled with life cycle assessment (LCA) further substantiates the ecological sustainability and economic viability of the proposed VFA recovery workflow, underscoring the great industrial translation potential of the BC@UiO-66-MOF adsorbent for valorizing organic waste-derived VFAs. Schematic diagram of carbon-neutral circular system for VFA recovery from kitchen waste fermentation wastewater, with adsorption schematic shown on the right. Download: Download high-res image (309KB) Download: Download full-size image Carbon-neutral circular system for VFA recovery from kitchen waste fermentation wastewater and the VFA adsorption mechanism of BC@UiO-66-MOF.