Performance of surface-functionalized structured polypropylene fillers for toluene removal in biotrickling filters

Fillers significantly affect the efficient operation of biotrickling filters (BTFs). Herein, structured polypropylene fillers modified with polydopamine (PDA) and cationic polyacrylamide (CPAM) were developed to reduce pressure loss and shorten the start-up period. Based on thermodynamics and the extended Derjaguin–Landau–Verwey–Overbeek theory, both modified fillers could improve biocompatibility. BTF with CPAM-modified filler had a shorter start-up period than PDA-modified filler. The maximum elimination capacity of the BTFs packed with PDA and CPAM-modified filler was 75.52 g·m⁻³·h⁻¹ and 78.62 g·m⁻³·h⁻¹, respectively, at an inlet toluene loading rate of 97.26 g·m⁻³·h⁻¹ and an empty bed residence time of 33 s. CPAM-modified filler biofilms exhibited higher adhesion strength and extracellular polymeric substance content during early operation. Furthermore, coating differences affected the microbial community structure on the filler surface. The CPAM-modified filler demonstrated superior performance by enriching toluene-degrading bacteria and upregulating key catabolic genes during the start-up stage.