Method and system for liquid treatment

A method of treatment of liquid in a liquid treatment system comprising: at least one liquid treatment module including at least one membrane and having a feed liquid inlet at a feed side of said at least one membrane, a permeate outlet at a permeate side of said at least one membrane, and a concentrate outlet at a brine side of said at least one membrane; a high pressure pump operative for pressurizing feed liquid to be received at said feed liquid inlet; and a system controller for controlling operation of the system including providing instructions to operate said high pressure pump in one of at least two operation modes including: a first mode in which the high pressure pump maintains a fixed flow rate of the feed liquid at said feed liquid inlet or of a permeate liquid at said permeate outlet, while energy consumption of said high pressure pump being a function of variations of a first operational parameter measured in the system and indicative of salinity of liquid within said at least one liquid treatment module, and a second mode in which the high pressure pump maintains a flow rate of the feed liquid at said feed liquid inlet or of a permeate liquid at said permeate outlet, while energy consumption of said high pressure pump being a function of a second operational parameter determined so as to reduce energy consumption of the high pressure pump; said method being performed under control of said system controller and comprising steps of: pressurizing feed liquid by said high pressure pump in said first mode; circulating a concentrate from said concentrate outlet to said feed liquid inlet; providing to said system controller a third operational parameter measured in the system and indicative of salinity of liquid within said liquid treatment module; and upon detecting that a predetermined first threshold of said third operational parameter is reached, operating said high pressure pump in said second mode.