Producing　medium　chain　fatty　acids　(MCFAs)　from　waste　activated　sludge　(WAS)　is　crucial　for　sustainable　chemical　industries.　This　study　addressed　the　electron　donor　requirement　for　MCFAs　production　by　inoculating　Lactobacillus　at　varying　concentrations　(7.94　x　10(10),　3.18　x　10(11),　and　6.35　x　10(11)　cell/L)　to　supply　lactate　internally.　Interestingly,　the　highest　MCFAs　yield　(similar　to　2000　mg　COD/L)　occurred　at　the　lowest　Lactobacillus　inoculation.　Higher　inoculation　concentrations　redirected　more　carbon　from　WAS　towards　alcohols　production　rather　than　MCFAs　generation,　with　up　to　2852　mg　COD/L　alcohols　obtained　under　6.35　x　10(11)　cell/L　inoculation.　Clostridium　dominance　and　increased　genes　abundance　for　substrate　hydrolysis,　lactate　conversion,　and　MCFAs/alcohol　production　collectively　enhanced　WAS-derived　MCFAs　and　alcohols　synthesis　after　Lactobacillus　inoculation.　Overall,　the　strategy　of　Lactobacillus　inoculation　regulated　fermentation　outcomes　and　subsequent　carbon　recovery　in　WAS,　presenting　a　sustainable　technology　to　achieve　liquid　bio-energy　production　from　underutilized　wet　wastes.