Pollution Control Of Reverse Osmosis Membrane And Cleaning Scheme Optimization

Reverse osmosis(RO)technology is widely used in water treatment industry because of excellent desalination,but membrane fouling is the key to long-term stable operation of equipment.Different water sources and pretreatment processes will lead to different pollutant compositions.Therefore,water source and pretreatment must be studied before pollutant control schemes can be proposed to prevent membrane pollution.This paper is relies on the 500 t/h desalination project of Panjin Heyun Group.The project was put into operation in 2012.The reverse osmosis system was seriously polluted.The production capacity was reduced by nearly 50%,and the cleaning cycle was 1 month per time.In order to solve this problem,ROSA70 software is used to calculate the reverse osmosis system.The results show that 70% of the membrane area of group A is fouled up.When studying the composition of pollutants,dissecting membrane elements were used to obtain pollutant samples.Conventional titration and energy spectrometer(EDS)were used for qualitative analysis of pollutants.It was determined that the elements of pollutants consisted mainly of calcium,magnesium,titanium,iron,carbon and oxygen.The contents of calcium,magnesium,titanium and iron were 18.13%,8.75%,4.3% and 4.78%.In addition,the carbon and oxygen elements are 9.25% and 50.5%.The sludge density index(SDI),turbidity,colony number,productivity and desalination rate of different pretreatments were studied by means of comparative analysis.Finally,it was proved that ultrafiltration under this water source was the most suitable pretreatment technology.Ultrafiltration was used as pretreatment technology in the company's 1100 t/h desalination project,and the reverse osmosis cleaning cycle was 6 months after the project was put into operation.In addition,bactericidal treatment was applied to the UF water tank in terms of pretreatment adjustment,and the number of bacteria in the water tank was controlled from more than 1000 to 113.This measure improves the effect of pretreatment on microbial treatment.In terms of process improvement,the dosage of scale inhibitor was adjusted from 3 mg/L to 5 mg/L,the cleaning cycle of reverse osmosis membrane in 500 t/h project was extended from one month to two months.According to the composition of membrane pollutants,chemical cleaning formula was formulated.The influence of each cleaning agent was determined by range analysis of orthogonal experiment,and the recovery of membrane flux after cleaning was compared.The basic chemical cleaning formula was obtained as follows: 0.2% hydrochloric acid,2% citric acid,1% oxalic acid,0.2% sodium hydroxide,2% EDTA and 0.01% sodium tripolyphosphate.In order to improve the cleaning effect,AEO and Triton were compounded into a new formulation.The formulation is rich in isooctyl and phenyl functional groups,which can improve the combination and penetration of organic and metal ion pollutants.The polyoxyethylene functional group can increase the steric hindrance between fouling and prevent fouling from depositing on the membrane surface again during cleaning.The recipe cleaning solution can recover the reverse osmosis flux to 42%,which is more than 1 times higher than the conventional cleaning solution.The contact angle between surfactant and membrane surface was studied.It was proved that 0.2% AEO had the smallest contact angle of 44.4 degrees,and had the best wettability on the surface of cleaning products.