Control of small reverse osmosis desalination plants with feed water bypass

Small reverse osmosis desalination plants without pH control normally use a feed water bypass to modify the permeate conductivity by mixing a little amount of feed water with the permeate. Plants with this characteristic have a different system configuration and the conductivity is usually not controlled. In this contribution, small plants with feed water bypass are studied from the dynamic point of view and a multivariable receding horizon controller is applied for the simultaneous control of permeate flow rate and conductivity. Results show the advantages of including the conductivity of permeate as well as the excellent performance of the designed controller.