For　the　optimal　control　problem　of　predinitrification　wastewater　treatment　process,　a　Hopfield　neural　network　optimization　method　based　on　the　Lagrange　multiplier　is　proposed.　Firstly,　under　the　constrain　of　some　key　effluent　pollutant　qualities,　a　wastewater　treatment　optimization　objective　function　is　constructed　to　minimise　the　energy　consumption.　Then,　the　set　points　in　bioreactor　of　both　dissovled　oxygen　concentration　in　the　5th　compartment　and　nitrate　concentration　in　the　2nd　compartment　are　optimized　by　Hopfiled　neural　network,　respectively.　Both　concentrations　are　controlled　by　PID　controller.　Finally,　based　on　the　international　standard　benchmark,　the　simulation　results　show　that　through　the　optimization　of　Lagrange　multiplier　Hopfield　neural　network,　the　energy　consumption　of　wastewater　treatment　process　is　reduced　obviously　under　constraints　of　effluent　pollutant　qualities.　©,　2014,　Northeast　University.　All　right　reserved.