Pretreating anaerobic fermentation liquid with calcium addition to improve short chain fatty acids extraction via in situ synthesis of layered double hydroxides.

•Adding calcium was proposed to improve SCFAs extraction from AFL via LDH synthesis.•The carbonate removal was up to 76.6% with 0.06 mol/L calcium addition at pH 12.•From SCFAs extraction view, the optimal SCFAs/Al3+ for SCFAs-LDH synthesis is 3.0.•Total SCFAs content in SCFAs-LDH with pretreatment was 4.5 times of the control.