The Influence Of Scale Inhibitor On Water Treatment Nanofiltration Process

As an advanced separation technology,nanofiltration?NF?is widely used in the treatment of water and wastewater.In the process of nanofiltration water treatment,scale inhibitors need to be added to the influent to prevent membrane fouling;when nanofiltration is used to treat the circulating cooling water discharge,the water also contains scale inhibitors.However,the influence of scale inhibitors on the performance of nanofiltration process is still lack of in-depth study.In this paper,the typical scale inhibitor aminotris?methylenephosphonic acid??ATMP?was selected.Through the experiments of nanofiltration membrane permeation experiment and scanning electron microscope?SEM?analysis,the effect of ATMP on the separation performance of nanofiltration and its inhibitory effect on the residual coagulant aluminum salt fouling membrane were investigated,and the nanofiltration process of sewage in circulating cooling water systems containing scale inhibitors was optimized.The main research contents and results are as follows:?1?The effect of scale inhibitor ATMP on nanofiltration separation performance was studied by experiments.The results showed that ATMP had significant effects on the Ca²⁺rejection rate and the p H of the experimental water sa mple.In general,as the concentration of ATMP increased,the p H of the experimental water sample decreased and the rejection rate of Ca²⁺by the nanofiltration membrane increased,but at the point of ATMP=10mg/L,the valley of the rejection rate and the peak of the permeation flux appeared.Further analysis showed that the main mechanism that ATMP affected the separation performance of nanofiltration membranes was not its chelation effect on calcium ions,but ATMP changed the p H value of the experimental water sample and caused the electrostatic effect to change.When the p H was lower than the isoelectric point?IEP?p H5.5?,the membrane was positively charged,and the electrostatic repulsion to calcium ions was enhanced,showing a higher re jection rate;after the p H was higher than the membrane isoelectric point,the membrane was negatively charged and the rejection rate was low when no ATMP-Ca insolubles presented.?2?Through nanofiltration experiment and SEM morphology analysis of the contaminated membrane,the mechanism of membrane contamination caused by residual aluminum and the inhibitory effect of ATMP on aluminum scale were investigated.The results showed that the membrane pollution increased with the increase of residual aluminum concentration and p H;the mechanism of membrane pollution caused by residual aluminum was that aluminum salt solution disintegrated to form a positively charged colloid,which easily aggregated with negatively charged membrane;after adding ATMP,it passed chelation and dispersion could significantly inhibit the accumulation of aluminum scale on the membrane surface,and increasing the ATMP concentration could effectively inhibit membrane contamination caused by residual aluminum.However,when the p H was higher,ATMP could form insoluble calcium salts with Ca,which reduces its scale inhibition performance.?3?The nanofiltration treatment process of sewage containing scale inhibitor was optimized.The sewage,which contains scale inhibitor,of the circulating cooling system was selected as the object of nanofiltration treatment.The stability of the water quality of the nanofiltration permeate and the up to standard of the coagulation treated of the nanofiltration concentrate were taken as the optimization goals.Partial nanofiltration pretreatment of raw water by-pass mixing nanofiltration membrane permeated water and coagulation treatment of total phosphorus?TP?in concentrated drainage were used as optimization methods to optimize the conventional full?inlet?nanofiltration system and experimental researches were carried out.When the recovery rate of nanofiltration was 70%,the nanofiltration treatment rate was0.72?0.78 and the Ryznar stability index?RSI?of total water production ranged from6.2 to 6.8,the water quality was stable.Economic evaluation of the optimized nanofiltration system was conducted.The results showed that compared with conventional full?inlet?nanofiltration system,the equipment investment and annual operating cost of the optimized nanofiltration system could be reduced by approximately 19.14%and 28.64%,respectively,making it more economical and practical.?4?In order to solve the problem of exceeding the standard of total phosphorus?TP?in nanofiltration sewage,the increased of coagulation to remove phosphorus had a good effect.At p H=7.0,the TP of nanofiltration concentrated drainage could be less than 0.5mg/L when the dosage of polyaluminum chloride?PAC l?reached more than120mg/L,which could meet the Grade A standard of the"Emission Standard for Pollutants in Urban Sewage Treatment Plants?GB18918-2002?".