| The technology of concentration reduction of pesticide waste liquid based on reverse osmosis technology has been successfully applied to engineering practice.However,during actual operation,it was found that the water production flux of the reverse osmosis system decreased rapidly.It can be foreseen that the pre-treated pesticide waste liquid still contains various components including endogenous inorganic salts,organic pesticides and exogenous coagulants.They gradually accumulate after entering the RO membrane system and are formed through various mechanisms.It caused irreversible severe membrane fouling.For this reason,it is necessary to classify and investigate the effect of representative components in pesticide waste liquid on RO membrane pollution under different operating conditions through simulation experiments,study the morphology,composition,and characteristics of polluted layers,and explore the formation mechanism of membrane pollution,providing theoretical basis for effective control of membrane pollution for similar projects.The aluminum salt was selected as the representative of the exogenous component,and the pollution characteristics of the RO membrane under different operating conditions were investigated.The experimental results showed that:(1)The high concentration of aluminum salt in the water quickly formed a dense colloid on the surface of the reverse osmosis membrane;(2)The effect of the p H of the inlet water on membrane pollution is most significant.Compared with the case where the p H of the feed water is acidic or alkaline,when the p H of the feed water is neutral,the membrane flux is the lowest,the rejection rate is the highest,the aluminum content in the membrane surface pollution layer is the highest,and the pollution degree is the most serious.Because the electrostatic effect between the membrane surface and the solute is opposite,the content of Al in the pollution layer of the membrane surface is lower than that of the acidic water during alkaline water inflow,and the degree of membrane pollution is the lowest;(3)When the p H of the water is the same,the membrane surface pollution The formation of the layer has a more significant effect on the concentration of aluminum in the influent,but a smaller effect on the operating pressure.Dimethyl tetrachloride(MCPA)was selected as a representative of the endogenous organic pesticide component,and its pollution characteristics to RO membranes under different operating conditions were investigated.The experimental results show that:(1)p H=8.7,methyl tetrachloride in the incoming water,a dense organic filter cake layer is formed on the surface of the reverse osmosis membrane,which causes the membraneflux to decrease;(2)p H=8.7,under high operating pressure,the rinsing effect is enhanced to slow down the rate of membrane fouling and the membrane flux is increased;(3)Dimethyl tetrachloride is a phenoxycarboxylic acid-based organic compound,which easily dissociates and carries a negative charge in an alkaline environment,and has electrostatic repulsion with the film surface.Under alkaline environment,it can effectively slow down the organic pollution caused by dimethyl tetrachloride.The simulated pretreatment process was used to prepare pesticide waste liquid,which contained various components such as inorganic salts,organic pesticides,and aluminum salts.The pollution characteristics of RO membranes under different operating conditions were investigated.The experimental results showed that:(1)The components form a dense contaminated layer of organic and inorganic mixture on the surface of the membrane,which causes the membrane flux to decrease;the main pollutions include: organic pollution caused by dimethyl tetrachloride,colloid pollution caused by aluminum,and inorganic scale pollution caused by calcium;(2)The contribution rate of each pollution effect under different p H of the feedwater is as follows: p H=5.5,organic C(25.56%)>Ca(20.44%)>Al(2.17%);p H=6.7,organic C(28.55%)>Ca(18.77%)>Al(3.18%);p H=8.7,Ca(24.59%)>Organic C(18.85%)>Al(2.97%).In acidic and neutral environments,organic pollution has the largest contribution rate and colloidal pollution has the lowest contribution rate;in alkaline environments,scale pollution contribution has the largest contribution rate,and colloidal pollution has the lowest contribution rate;(3)Organic pollution caused by dimethyl tetrachloride is about 35.60% and 51.46% higher than p H=8.7 at p H=5.5 and p H=6.7,respectively.It can be seen that increasing the p H can effectively reduce organic pollution;(4)p H=8.7,under the same Al concentration in the feed water,the membrane flux increases rapidly with increasing operating pressure.At low operating pressure,the organic pollution effect is strong;at high operating pressure,the inorganic scale pollution effect is strong;(5)p H=8.7,at the same operating pressure,with the increase of the concentration of aluminum salt in the water,the inorganic scale pollution effect has attenuated,at the same time,the colloidal pollution effect rises sharply.It is suggested that in the engineering practice,controlling the dosing amount of the external component aluminum salt and reducing the aluminum content entering the RO system as much as possible is of great significance for controlling membrane pollution.The pesticide waste liquid in actual engineering is usually in an alkaline environment.Through experimental research,it is found that the pollution effects in the alkaline environment have the following relationship: inorganic scale pollution(calcium)> organic pollution(pesticides)> colloid pollution(aluminum).For this reason,in the actual pesticide waste liquid concentration project,it is recommended that:(1)Use demineralized water to clean the reaction tank and container;(2)Accurately dose the aluminum salt coagulant in the pretreatment stage to adjust the pretreatment waste liquid p H to make it in an alkaline environment(8?9),complete coagulation and precipitation,reduce the concentration of aluminum salts and organic matter in the RO membrane influent water;at the same time,ensure that the ROmembrane influent water is in an alkaline environment to reduce colloid pollution caused by residual aluminum and organic pollution effects;(3)Keeping the operating pressure of the RO membrane system stable at an appropriate level is conducive to slowing down membrane pollution. |
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