Author: Site Editor Publish Time: 2022-05-20 Origin: Site
In the process of using the equipment, in addition to the normal decay of performance, the decay of equipment performance due to pollution is more serious. The main types of contamination are chemical scale, organic and colloidal contamination, microbial contamination and so on. Different contaminants show different symptoms. The symptoms of membrane contamination also vary from one membrane company to another.
In the project we found that the length of contamination time is different, the symptoms are also different. Such as: membrane occurs calcium carbonate scale pollution, pollution time for a week, mainly manifested as a rapid decline in desalination rate, the pressure difference slowly increased, while the change in water production is not obvious, with citric acid cleaning can fully restore performance. Pollution time for a year (a pure water machine), salt flux from the initial 2mg / L rose to 37mg / L (the original water for 140mg / L ~ 160mg / L), water production from 230L / h down to 50L / h, with citric acid cleaning, salt flux down to 7mg / L, water production rose to 210L / h.
Furthermore contamination is often not homogeneous and the symptoms it presents vary somewhat, making the identification of contamination more difficult.
To identify the type of contamination, the raw water quality, design parameters, contamination indices, operating records, changes in equipment performance and microbiological indicators should be combined to determine.
(1) Colloidal contamination: When colloidal contamination occurs, it is usually accompanied by the following two characteristics: A. The microfilter clogs quickly in the pre-treatment, especially when the differential pressure increases quickly, and B. The SDI value is usually above 2.5.
(2) Microbiological contamination: When microbiological contamination occurs, the total number of bacteria in the permeated and concentrated water of the RO equipment is relatively high and must not normally be maintained and disinfected as required.
(3) Calcium scale: It can be judged according to the raw water quality and design parameters. For carbonate-type water, if the recovery rate is 75%, the LSI of the concentrate should be less than 1 if scale inhibitor is added during design; the LSI of the concentrate should be less than zero if scale inhibitor is not added, and calcium scale will not be produced in general.
(4) This can be judged by inserting a 1/4" PVC plastic pipe into the assembly to test the change in performance of different parts of the assembly.
(5) The type of contamination is determined by changes in the performance of the equipment.
(6) Acid washing (e.g. citric acid, dilute HCl) is available. Calcium scale is judged by the effectiveness of the cleaning and the cleaning solution, which is further confirmed by analysis of the cleaning solution composition.
(7) Chemical analysis of the cleaning solution: raw water, cleaning stock and cleaning solution are taken and three samples are analysed. After the type of contamination has been determined, the cleaning is carried out according to a specific method and then disinfected for use.
