The　contributions　of　loosely　bound　extracellular　polymeric　substances　(LB-EPS),　tightly　bound　EPS　(TB-EPS),　residual　sludge　(the　sludge　left　after　EPS　extraction)　and　functional　groups　such　as　amine,　carboxyl,　phosphate　and　lipid　on　aerobic　granules　on　biosorption　of　four　different　dyes　(Reactive　Brilliant　Blue　KN-R　(KN-R),　Congo　Red　(CR),　Reactive　Brilliant　Red　K-2G　(RBR)　and　Malachite　Green　(MG))　were　investigated.　EPS　may　be　responsible　for　biosorption　of　cationic　dyes.　However,　residual　sludge　always　made　greater　contribution　than　that　of　EPS.　The　biosorption　mechanisms　were　dependent　on　the　functional　groups　on　aerobic　granules　and　dyes＇　chemical　structures.　The　lipid　and　phosphate　groups　might　be　the　main　binding　sites　for　KN-R　biosorption.　Amine,　carboxyl,　phosphate　and　lipid　were　all　responsible　for　the　binding　of　CR.　The　lipid　fractions　played　an　important　role　for　RBR　biosorption.　For　MG,　the　phosphate　groups　gave　the　largest　contribution.　(C)　2010　Elsevier　Ltd.　All　rights　reserved.