Water purification apparatus, and a method for controlling a water purification apparatus

A water purification apparatus comprising:

• a reverse osmosis device comprising a reverse osmosis membrane;
• a feed pump arranged to receive inlet water and to direct feed water to an inlet of the reverse osmosis device, wherein the reverse osmosis device is configured and arranged to create permeate water and reject water from the feed water;
• a recirculation mechanism arranged to recirculate a portion of the reject water to the feed water;
• a temperature sensor device arranged to measure a temperature indicative of a temperature of the reverse osmosis membrane;
• a first flow rate sensor device arranged to measure a flow rate indicative of a permeate flow rate of the permeate water;
• a first conductivity cell arranged to measure a feed water conductivity indicative of a conductivity of the feed water;
• a second conductivity cell arranged to measure a permeate conductivity of the permeate water;
• a drain valve arranged to pass a portion of the reject water to a drain;
• and
• a control arrangement configured to:
• control recirculation of the portion of the reject water by means of the recirculation mechanism to achieve a predetermined recovery ratio of permeate flow rate to feed flow rate,
• control a feed pump rate, based on the measured temperature indicative of the temperature of the reverse osmosis membrane and a desired permeate conductivity, such that the permeate flow rate is at or within a predetermined margin of an energy efficient permeate flow rate, the energy efficient permeate flow rate determined based on a predetermined relation between the reverse osmosis membrane temperature, the permeate flow rate, the permeate conductivity of the permeate water and the feed water conductivity, and
• control the drain valve to pass a portion of the reject water to the drain to make the conductivity of the permeate water at or within a predetermined margin of the desired permeate conductivity.

A water purification apparatus comprising:

• a reverse osmosis device comprising a reverse osmosis membrane;
• a feed pump arranged to receive inlet water and to direct feed water to an inlet of the reverse osmosis device, wherein the reverse osmosis device is configured and arranged to create permeate water and reject water from the feed water;
• a recirculation mechanism arranged to recirculate a portion of the reject water to the feed water;
• a temperature sensor device arranged to measure a temperature indicative of a temperature of the reverse osmosis membrane;
• a first flow rate sensor device arranged to measure a flow rate indicative of a permeate flow rate of the permeate water;
• a first conductivity cell arranged to measure a feed water conductivity indicative of a conductivity of the feed water;
• and
• a control arrangement configured to:
• control recirculation of the portion of the reject water by means of the recirculation mechanism to achieve a predetermined recovery ratio of permeate flow rate to feed flow rate,
• control a feed pump rate based on the measured temperature indicative of the temperature of the reverse osmosis membrane and a desired permeate conductivity, such that the permeate flow rate is at or within a predetermined margin of an energy efficient permeate flow rate, the energy efficient permeate flow rate determined based on a predetermined relation between the reverse osmosis membrane temperature, the permeate flow rate, a permeate conductivity of the permeate water and the feed water conductivity, and
• provide an estimate of a feed flow rate Qf of the feed water, and calculate the predetermined recovery ratio as
• Y
• =
• Q
• p
• Q
• f
• ,
• wherein Y is the predetermined recovery ratio and Qp is the permeate flow rate.