In　order　to　analyze　and　verify　the　association　of　the　reverse　osmosis　(RO)　membrane　fouling　with　water　quality　in　full-scale　plants,　two　RO　systems　(40,　000　m(2)/d　and　20,　000　m(2)/d)　treating　different　secondary　effluents　were　operated　in　parallel.　The　quality　of　secondary　effluents　and　the　performance　of　RO　systems　were　monitored　over　12　months.　Difference　in　foulants　distribution　and　fouling　layer　composition　between　the　two　systems　were　evaluated　by　membrane　autopsy　and　foulants　characterization.　Results　verified　that:　1)　the　secondary　effluent　from　municipal　sewage　caused　more　serious　membrane　fouling;　2)　more　foulants　deposited　on　the　surface　of　leading　membrane　both　in　two　systems　(3.11　+/-　0.15　g/m(2)　and　2.93　+/-　0.13　g/m(2));　3)　the　microbial　community　on　the　RO　membrane　surface　contained　more　colonizing　bacteria　in　the　system　treating　municipal　sewage　secondary　effluent;　4)　organics　in　the　secondary　effluent　facilitated　biofouling　while　higher　ion　concentration　restrained　biofouling.　(C)　2019　Elsevier　B.V.　All　rights　reserved.