Study On Reverse Osmosis Membrane Fouling And Cleaning In Pesticide Waste Liquid Treatment Process

The research object of this paper is taken from the reverse osmosis system in the pesticide waste liquid membrane concentration project of an agricultural pharmaceutical factory in Jiangsu province,which produces a large number of hazardous waste liquid in the process of pesticide production.In the process of waste liquid treatment,the pollution problem is obvious,and the blockage of the reverse osmosis system is especially serious.In this study,the membrane pollution of reverse osmosis system was analyzed and identified to find out the characteristic pollutants,and the optimal cleaning combination was explored through the cleaning test.In the end,it was applied to the engineering practice to save the cost.Firstly,the water quality of the reverse osmosis system was analyzed,and the inductively coupled plasma mass spectrometer was selected to quantitatively determine the ions of Yin and Yang,and COD and p H were determined by chemical method.According to the results of water quality analysis,the reverse osmosis system had a good treatment effect,with COD removal rate of 98.5%and TOC removal rate of98.7%.The COD of reverse osmosis effluent was 343ppm,and the TOC was 38ppm,which met the internal requirements of the enterprise.The removal rates of Na⁺and Ca²⁺in cations were 94.3%and 95.6%,respectively.The removal rates of SO₄^2-and CO₃^2-were 90.5%and 94%,respectively.The conductivity removal rate of reverse osmosis system was 95.2%,and the effluent conductivity was 99?s/cm,so the effluent quality was better.At the same time,this experiment laid a foundation for the next test of membrane fouling analysis and provided a theoretical basis.Apparent analysis,Loss on ignition,Scanning electron microscope and Energy dispersive spectrometer?SEM-EDS?,Fourier Infrared spectroscopy?FT-IR?and X-ray diffraction?XRD?were used to analyze and characterize reverse osmosis membrane.The experimental results showed that the membrane fouling was composed of organic pollution and inorganic pollution,and the organic pollution accounted for about 50%of the total pollution.Through SEM-EDS,FT-IR and XRD analysis,the composition of membrane contamination was determined to be organic pollution and inorganic pollution,without biological pollution.Inorganic pollution consisted of inorganic cation hydroxide?Ca?OH?₂,Mg?OH?₂?,Al?OH?₃,etc.),carbonate?Ca CO₃,Mg CO₃,etc.?,sulfate?Ca SO₄,Mg SO₄,etc.?and silicate(Si O₂,Ca Si O_3,etc.);organic pollution was the active ingredient of pesticide in the waste liquid of pesticide factory?dimethyl-pentamine,dimethyl-imide,pyrazole,etc.?.Cleaning experiment based on membrane fouling characteristics of both organic and inorganic pollution,took 0.2%hydrochloric acid,0.1%sodium hydroxide,0.025%sodium dodecylbenzenesulfonate,1:40 professional reverse osmosis acid cleaning solution and 1:30 professional reverse osmosis alkaline cleaning solution were selected as the cleaning liquid,comparing the cleaning fluid for reverse osmosis membrane cleaning effect and the impact of desalination rate,and determined the best membrane cleaning solution and reverse osmosis membrane fouling process.The test results showed that the cleaning solution above had an effect on the recovery of reverse osmosis membrane flux,but none could recover to the initial membrane flux,and the best cleaning effect was 1:30 professional reverse osmosis alkaline cleaning solution,the worst was 0.2%hydrochloric acid with the flux recovery rate of 56.8%and 41.3%,respectively.Combined cleaning effect was better than single cleaning;the optimal cleaning combination was 1:40 alkaline professional cleaning liquid plus 0.025%sodium dodecyl benzene sulfonate and plus 1:30 acid professional cleaning liquid,flux recovery rate up to 86%.After chemical cleaning of the reverse osmosis membrane,the desalination rate recovered to a certain extent,with the maximum desalination rate of98.8%,but it still could not recover to the desalination rate of 99.7%of the new membrane.It was speculated that the combination of pesticide active components and the reverse osmosis membrane produced irreversible contamination,resulting in a permanent reduction of the desalination rate.Different cleaning sequence led to different cleaning effects.According to the difference in effect?alkali before acid is better than acid before alkali?,it can be speculated that inorganic dirt was deposited on the surface of the membrane first,and then organic pollution began to affect the membrane flux.Four pesticide ingredients,sterilazole,enoylmorpholine,pyraclostrobin,and pendimethalin,were selected to investigate the effect of active ingredients on the reverse osmosis membrane,which all contain benzene rings.Among them,sterile azole and dimethyl-pentamine contain tertiary alcohols but no amides while pyrazole and sterilazole contain amides.The experimental results showed that the effective components of pesticide could indeed cause irreversible pollution to the reverse osmosis membrane.With the increase of soaking time,the pollution became more and more serious,and dimetovalin had the least impact on the membrane.The 30-days membrane flux ratio and desalination rate were 99.8%and 99.6%respectively.The possible reason was that dimetovalin only contains the aromatic structure similar to the membrane structure,but does not contain the amide-group characteristic of pyrazoles,which is an important component of reverse osmosis membrane.Through the research of this paper,the pollution of reverse osmosis system was found out,the mechanism of pollution was studied,the pollution process was speculated,and a feasible cleaning scheme was provided for the actual project,which saved more than 60,000 yuan of cost for the enterprise every year.It turned out to be a very meaningful research.