Control method for delaying nanofiltration membrane aluminum fouling of water treatment system

A control method for delaying nanofiltration membrane aluminum fouling of a water treatment system, the water treatment system comprising an ultrafiltration system, a nanofiltration system and a program control system;

• the ultrafiltration system comprising a first water supply sub-system, an ultrafiltration membrane group and a first water production sub-system sequentially in pipeline connection;
• a first dosing pipeline being provided between the first water supply sub-system and the ultrafiltration membrane group, and the first dosing pipeline being provided with a first dosing port for adding a first scale inhibitor and a second dosing port for adding a flocculant;
• the nanofiltration system comprising a second water supply sub-system, a nanofiltration membrane group and a second water production sub-system sequentially in pipeline connection;
• the second water supply sub-system being communicated with the first water production sub-system;
• a second dosing pipeline being provided between the second water supply sub-system and the nanofiltration membrane group, and the second dosing pipeline being provided with a third dosing port for adding a second scale inhibitor and a fourth dosing port for adding a reductant;
• each of the ultrafiltration system and the nanofiltration system having a water filtration function and a self-cleaning function;
• the program control system being configured to collect parameters of the water treatment system, and control operation of the ultrafiltration system and the nanofiltration system according to collected parameters;
• and
• the control method comprising:
• (1) detecting and recording the parameters of the water treatment system in real time;
• wherein the parameters of the water treatment system comprises temperature T of an influent of the nanofiltration system, conductivity E of the influent of the nanofiltration system, nanofiltration membrane flux J, nanofiltration recovery rate Y, pressure P1,1, pressure difference P2,1 and desalination rate η1,1 of the nanofiltration system at a certain moment within initial 5 min of a current filtration-flushing period, pressure P1,0, pressure difference P2.0 and desalination rate η1,0 of the nanofiltration system at a corresponding moment within initial 5min of a previous filtration-flushing period, wherein a pressure change amplitude is expressed as ΔP1=P1,1−P1,0, a pressure change rate is expressed as Δ1=ΔP1/P1,0, a pressure difference change amplitude is expressed as ΔP2=P2,1−P2,0, a pressure difference change rate is expressed as ΔP2=ΔP2/P2,0, and a desalination rate change amplitude is expressed as Δη1=η1,1−η1,0;
• (2) determining a total dosage C2 of the first scale inhibitor and the second scale inhibitor according to influent quality indexes and operating parameters of the nanofiltration system;
• wherein the influent quality indexes comprise the temperature T and the conductivity E, and the operating parameters comprise the nanofiltration membrane flux J and the nanofiltration recovery rate Y;
• and
• the total dosage C2 is calculated through the following equation:
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• wherein the total dosage C2 is in a range of 1.5-3.0 ppm, a1=(35−T)/23, b1=E/200−0.5, c1=0.5J−11, and d1=0.2Y−16;
• in a case where the temperature T is greater than or equal to 12° C., a2 is 1, otherwise a2 is 0;
• in a case where the conductivity E is lower than 300 μs/cm, b2 is 1, otherwise b2 is 0;
• in a case where the nanofiltration membrane flux J is 20-22 L/(m2·h), c2 is 1, otherwise c2 is 0;
• and in a case where the nanofiltration recovery rate Y is 80%-85%, d2 is 1, otherwise d2 is 0;
• (3) activating the water filtration function of the ultrafiltration system;
• (4) activating the water filtration function of the nanofiltration system;
• (5) determining whether there is aluminum fouling in the nanofiltration membrane group, wherein steps 1-5 are repeated when it is determined that there is no aluminum fouling;
• and when a condition where Δ1>0, Δ2>0 and Δη1>0 all occur lasts for 1 min, the nanofiltration membrane group is determined to suffer from aluminum fouling, and steps (6)-(8) are performed;
• (6) determining a dosage C3 of the first scale inhibitor and a dosage C4 of the second scale inhibitor;
• wherein the dosage C3 is calculated as C3=0.3+15Δη1, and is set to not exceed 0.5 ppm;
• and the dosage C4 is calculated as C4=C2−C3;
• and
• (7) adding the first scale inhibitor to the ultrafiltration system, and adding the second scale inhibitor to the nanofiltration system;
• and
• (8) when it is determined that there is aluminum fouling and after a filtration period is completed, activating the self-cleaning function of the ultrafiltration system to perform backwashing on the ultrafiltration membrane group, and activating the self-cleaning function of the nanofiltration system to flush the nanofiltration membrane group;
• wherein the first scale inhibitor is reacted with aluminum ions and the flocculant in sequence to form a colloidal precipitate, and the colloidal precipitate is intercepted on an upstream side of the ultrafiltration membrane group.