As　a　critical　component　of　the　biotrickling　filter　(BTF),　the　performance　of　fillers　is　vital　for　pollutant　purification.　A　novel　immobilized　filler　predominantly　composed　of　fly　ash　was　developed　to　enhance　the　BTF　performance　for　xylene　removal　while　promoting　the　comprehensive　utilization　of　solid　waste.　The　physical　and　chemical　properties　of　the　filler　and　the　performance　of　the　BTF　packed　with　the　fly　ash-based　composite　filler　were　investigated.　When　the　pH　of　the　nutrient　solution　was　below　7.4,　the　surface　of　the　filler　displayed　a　positive　charge,　which　facilitated　the　attachment　and　growth　of　microorganisms　Additionally,　the　formation　mechanisms　of　the　immobilized　fillers　and　their　nutrient　release　kinetics　were　elucidated　through　Fourier　transform　infrared　spectroscopy　and　nutrient　slow-release　kinetics　studies.　The　BTF　packed　with　the　composite　filler　achieved　complete　xylene　removal　at　an　inlet　concentration　of　300　mg/cm3　and　an　empty　bed　residence　time　of　30　s,　showcasing　its　superior　pollutant　removal　capabilities.　Moreover,　the　filler　demonstrated　robust　resilience　to　operational　interruptions.　The　BTF　packed　with　the　composite　filler　could　recover　rapidly　within　1　and　2　days　after　short-term　stagnation　periods　of　3　and　7　days,　respectively,　and　only　required　a　recovery　period　of　4　days　following　a　21-day　stagnation.　Throughout　the　195-day　operation,　the　system　maintained　a　pressure　drop　below　150　Pa,　effectively　avoiding　the　common　issue　of　swelling　often　associated　with　immobilized　fillers.　This　study　highlights　the　successful　application　of　fly　ash　in　creating　high-performance　immobilized　fillers　that　enhance　the　efficiency　of　biotrickling　filters　and　provide　significant　environmental　benefits.　©　2025　Elsevier　Ltd