Membrane Cleaning and Storage

After the completion of the concentration operation a chemical clean was carried out for the MF and RO units. Flux was fuUy restored for both units by this cleaning step. 

For the MF unit, Memclean Ex A2, a commercial detergent supplied by Memtec, was used at a concentration of 5%w/w. The membranes are stored dry. 

The RO unit was cleaned with a 0.1%w/w KOFI solution (pH 12, max. 30 C) at a transmembrane pressure of 140 kPa. The membranes were then stored in 1% metabisulfite solution. 

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The process operation involves flve stages in a cycle that is to be completed in a total duration of 12 h which includes 10 h for the flve-stage operation, 1.5 h for reject recycle to feed tank, and 0.5 h for membrane cleaning and storage. The detailed explanation of the process in accordance is given below. 

Table 4.8 provides the complete operation and maintenance cost of RO system, which includes power, membrane module and micron filter cartridge re-plaeement costs, chemical consumption for cleaning and storage, etc. Feed capacity and recovery were assumed to be 2 m /h and 60%, respectively. The operational time for system was assumed to be 10 h per day in view of the fact that electric power supply in remote villages is restricted to a few hours per day. Depreciation costs were taken as 10% of the total capital investment while life of hardware is expected to be 10 years. Membrane life was foimd to be 3 years as per data collected at village sites where plants have been operated. 

This product is a colorless membrane filtered solution therefore, make sure that the storage tanks for solution are cleaned and free of any contamination. Use freshly boiled and cooled purified water for the manufacturing. Prepare approximately 2 L of freshly boiled and cooled purified water and store in a clean stainless steel storage vessel. 

Expert service More effective cleanings Documented results Higher cost Requires second set of membranes Membranes cleaned in situ—no need for replacement membranes Faster cleaning Less expensive Less efficient Capital outlay for cleaning skid Storage and handling of chemicals and waste... 

The hydrophilicity of the NH3 plasma-treated PP membranes increased with the increase in plasma treatment time and decreased with the increase in storage time (Yan et al. 2008). The adsorption of BSA on the modified membranes was lower than that on the unmodified-membrane surface and the flux recoveries after water and caustic cleaning for the NH3 plasma-treated membranes for 1 min were 51.1% and 60.7% higher than those for the unmodified membrane. However, the mechanical properties of the membranes decreased after prolonged plasma treatment, thus the optimal plasma treatment time for membrane modification was taken as 1 min. 

Membrane filtration utilizes cartridges that when properly cleaned and stored can be reused at a later date. For those cartridges that can be stored, it is common to thoroughly back-flush the membranes twice, first with cold water and then with warm water because the latter can bake-on macromolecules such as proteins. Membranes can be stored wet, most commonly in food-grade 95% v/v ethanol or a solution of citric (1200 mg/L) and SO2 (600mg/L). In all cases, the membrane manufacturer should be consulted for specific storage and back-flushing recommendations. 

Where membrane storage is required after cleaning, a 5% glycerol solution containing 0.5 to 1.0% weightformaldehyde often is employed. The membranes should be totally immersed, with all inlet and outlet valves closed. This solution should be changed every 30 days. 

The first aim of this work was to study the influence of an unwashed membrane filter on the cadmium, lead, and copper concentrations of filtered seawater samples. It was also desirable to ascertain whether, after passage of a reasonable quantity of water, the filter itself could be assumed to be clean so that subsequent portions of filtrate would be uncontaminated. If this were the case, it should be possible to eliminate the cleaning procedure and its contamination risks. The second purpose of the work was to test the possibility of long-term storage of samples at their natural pH (about 8) at 4 °C, kept in low-density polyethylene containers which have been cleaned with acid and conditioned with seawater. 

Peroxide or a combination of peroxide and peracetic acid is generally used to treat RO systems that are already contaminated with microbes. Due to its high ORP, however, a solution of only 0.2wt% peroxide is normally used (see Table 8.8). Temperature must be below 25°C and transition metals such as iron must be removed prior to treatment with peroxide to minimize oxidation of the membrane. Further, membrane should be cleaned free of deposits using an alkaline cleaner before peroxide is applied. Finally, a pH of 3 - 4 should be maintained and exposure limited to about 20 minutes for optimum result and maximum membrane life. Peroxide should not be used for storage of membrane modules. 

Sheet membrane linings are usually shipped in rolls. Exceptions include plasticized-unplasticized vinyl laminates, specially compounded asphalt and asphalt and rubber compounded sheets, usually shipped flat in cartons or boxes. These are applied to properly prepared surfaces with an adhesive that may be air-cured or heat-cured. At all events, so far as storage is concerned, temperatures above freezing and under 100°F are usually not matters of concern, unless the manufacturer or applicator so advises. Water and dirt, however, damage these materials so they should be stored in a clean storage area, off the ground and under cover. 

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