In　order　to　investigate　the　feasibility　of　biological　treatment　of　hypersaline　wastewater　produced　from　toilet　flushing　with　seawater　at　low　temperature,　pilot-scale　studies　were　established　with　plug-flow　activated　sludge　process　at　low　temperature　(5-9°C)　based　on　bench-scale　experiments.　The　critical　salinity　concentration　of　30　g/L,　which　resulted　from　the　cooperation　results　of　the　non-halophilic　bacteria　and　the　halophilic　bacteria,　was　drawn　in　bench-scale　experiment.　Pilot-scale　studies　showed　that　high　COD　removal　efficiency,　higher　than　85%,　was　obtained　at　low　temperature　when　30　percent　seawater　[seawater/(seawater　+　sewage)]　was　introduced.　The　salinity　improved　the　settleability　of　activated　sludge,　and　average　SV　dropped　down　from　38%　to　22.5%　after　adding　seawater.　Sludge　bulking　could　be　forborne　effectively　because　filamentous　bacteria　couldn＇t　subsist　under　high　salinity　concentration.