Loose　nanofiltration　(NF)　membranes　are　an　attractive　avenue　in　effective　separation　of　organic　matters　and　salts　for　resource　recovery　from　highly-loaded　wastewater.　However,　membrane　fouling　remains　an　unclear　and　complex　factor　in　practical　applications.　In　this　work,　the　flux　of　a　loose　NF　membrane　fouled　by　humic　acid　at　various　solution　compositions　was　systematically　investigated.　The　strong　hydrophilicity　of　the　loose　NF　membrane　allows　for　slight　deposition　of　humic　acid　on　the　membrane　surface,　yielding　an　outstanding　antifouling　performance.　However,　a　moderate　flux　decline　was　observed　at　low　pH　and　high　ionic　strength,　due　to　reduction　in　charge　density　of　membrane　surface　for　formation　of　a　porous　foulant　layer.　At　higher　ionic　strength,　cake-enhanced　concentration　polarization　was　the　fouling　mechanism　that　dominates　the　membrane　flux.　The　presence　of　calcium　ions　induced　bridging　between　humic　acid　molecules　to　generate　a　compact　foulant　layer,　tremendously　deteriorating　the　membrane　flux.　Based　on　COMSOL　simulation　for　the　membrane　module,　the　hydrodynamics　near　the　membrane　surface　had　a　more　significant　effect　on　membrane　fouling　than　the　solution　chemistry,　which　is　consistent　with　scanning　electronic　microscopy　observation.　This　indicates　benign　hydrodynamic　condition　can　be　an　effective　strategy　to　fouling　control　for　loose　NF　membranes.　©　2018　Taiwan　Institute　of　Chemical　Engineers