Biological　activated　carbon　(BAC)　filtration,　both　alone　and　in　combination　with　ozone　pretreatment　(O3-BAC　filtration),　are　advanced　treatment　technologies　widely　employed　in　drinking　water　treatment　plants.　However,　the　impact　of　algal　organic　matter　(AOM)　on　their　performance　and　associated　microbial　communities　remained　inadequately　understood.　This　study　investigated　BAC　and　O3-BAC　filtration　using　columns　filled　with　two　types　of　granular　activated　carbon　(GAC)　and　fed　with　sand-filtered　water　spiked　with　AOM.　Microbial　communities　that　developed　on　GAC　were　subsequently　characterized.　The　results　indicated　that　AOM　significantly　reduced　the　removal　of　organic　matter　during　the　biodegradation　phase,　but　ozone　treatment　effectively　mitigated　this　reduction.　Excitation　and　emission　matrix　analysis　demonstrated　that　AOM　particularly　hindered　the　removal　of　non-terrestrial　humic　substances,　especially　tyrosine-like　substances,　whose　removal　was　further　diminished　by　ozone　oxidation.　Furthermore,　neither　biomass　nor　biological　activity　determined　BAC　performance.　AOM　and　ozone　oxidation　had　differential　impacts　on　bacterial　community　structures:　AOM　reduced　the　abundance　of　Proteobacteria　while　increasing　Bacteroidota　and　Chloroflexi,　whereas　ozone　promoted　Proteobacteria.　Positive　correlations　were　observed　between　Proteobacteria　and　UV254　removal　(p　Mn　removal　(p　3-BAC　filtration　systems.　©　2025　Elsevier　Ltd