The　organic　compound　composition　of　wastewater,　serves　as　a　crucial　indicator　for　the　operational　performance　of　activated　sludge　processes　and　has　a　major　influence　on　the　development　of　filamentous　bulking　in　activated　sludge.　This　study　focused　on　the　impact　of　typical　soluble　and　slowly-biodegradable　organic　compounds,　investigating　the　pathways　through　which　these　substrates　affect　the　occurrence　of　filamentous　bulking　in　systems　operated　under　both　high-　and　low-oxygen　conditions.　Results　showed　that　slowly-biodegradable　organic　compounds　lead　to　a　concentrated　distribution　of　microorganisms　within　flocs,　with　inward　growth　of　filamentous　bacteria.　Both　Tween-80　and　granular　starch　treated　systems　exhibited　a　significant　increase　in　protein　content.　The　glucose　system,　utilizing　soluble　substrates,　exhibited　a　markedly　higher　total　polysaccharide　content.　Microbial　communities　in　the　Tween-80　and　granular　starch　treated　systems　were　characterized　by　a　higher　abundance　of　bacteria　known　to　enhance　sludge　flocculation　and　settling,　such　as　Competibacter,　Xanthomonadaceae　and　Zoogloea.　These　findings　are　of　high　significance　for　controlling　the　operational　performance　and　stability　of　activated　sludge　systems,　deepening　our　understanding　and　providing　a　novel　perspective　for　the　improvement　of　wastewater　treatment　processes.　©　2024