Concerns　of　quaternary　ammonium　compounds　(QACs)　and　microplastics　(MPs)　as　emerging　containments　accumulating　in　wastewater　treatment　plants　(WWTPs)　have　attracted　much　attention.　Plastisphere　with　distinctive　microbial　communities　might　also　be　the　repository　for　pathogens　and　resistance　genes　(RGs).　Thus,　the　effects　of　three　representative　QACs　with　different　concentrations　on　biofilm　and　plastisphere　were　studied　in　sulfur　autotrophic　denitrification　(SAD)　system.　Over　100　days,　1-5　mg/L　QACs　exerted　few　impacts　on　system　stability,　whereas　15　mg/L　QACs　seriously　lowered　the　microbial　activity　and　the　inhibitory　effects　ranked:　benzylalkyldimethylethyl　ammonium　compound　＞　dialkyldimethyl　ammonium　compound　＞　alkyltrimethyl　ammonium　compound.　Dosing　of　QACs　in　SAD　system　not　only　altered　the　microbial　community　structure　and　assembly,　but　also　induced　higher　levels　of　intracellular　RGs　and　extracellular　RGs　in　plastisphere　than　in　biofilm.　Although　the　free　RGs　abundances　in　water　slightly　lowered,　they　might　also　pose　great　ecological　risks.　Pathogens　identified　as　the　potential　hosts　of　RGs　were　more　prone　to　colocalizing　in　plastisphere.　Mobile　genetic　elements　directly　contributed　to　the　three-fraction　RGs　transmission　in　SAD　system.　This　study　offered　new　insights　into　the　differential　responses　of　biofilm　and　plastisphere　under　QACs　stress　and　guided　for　the　disinfectants　and　MPs　pollution　containment　in　WWTPs.