“…PAA pretreatment significantly enriches functional microorganisms, i.e., those associated with hydrolysis, acidification, and CE, with their abundances rising from 18.3% to 39.7%. Paraclostridium , positively associated with substrate hydrolysis and MCFAs production [ 16 , 42 ], dominates in experimental groups, i.e., 12.2% for 20 mg PAA per g TSS and 12.9% for 25 mg PAA per g TSS, versus 0.5% in the control. Clostridium is a common SCFAs producer and a typical CE microorganism [ 43 ], whose abundance significantly increases with PAA dose, i.e., from 10.0% to 17.9%.…”