1. Microbial contamination.
Microorganisms include bacteria, algae, bacteria and epidemics. Bacterial particles are very small, generally 0.5~1.0μm in diameter. Microbial contamination has at least two undesirable results for reverse osmosis element membrane
. The first is the proliferation and metabolism of microorganisms, which leads to a large amount of colloidal solution components, which leads to the clogging of reverse osmosis element membrane and the membrane flux is greatly reduced; the second is to increase the production of water. The number of bacteria.
The causes of microbial contamination generally include:
(1) Microorganisms with a higher total number of influents;
(2) The shutdown, maintenance, and flushing of the system are not stopped in strict accordance with the requirements of the technical guidelines;
(3) Water sterilization has not been terminated or the dosage of fungicides is too small;
(4) The intake water contains nutrients that are very easy to grow microorganisms, which leads to a large number of microorganisms growth;
(5) The pipeline is not sterilized on time. The surface of the membrane contaminated by microorganisms is very smooth and often has a pungent odor.
2. Organic matter and mineral oil pollution.
Membrane system problems caused by organic compounds account for 60%-80% of all system problems. The organic compounds in the influent water are adsorbed on the surface of reverse osmosis element membrane, which will damage the flux, especially in the first stage. In many cases, the adsorption layer formed on the surface of ro membrane element acts like another separation barrier layer to the melting salt in the water, blocking the membrane surface channel, resulting in an increase in the salt removal rate. Organic compounds with large molecular weights and hydrophobic functional groups tend to produce this effect, such as a small number of droplets.
3. Pollution caused by flocculants.
In the entire pretreatment process of reverse osmosis system, such as the air flotation or coagulation precipitation treatment module, a certain high-purity polyaluminum flocculant is added to remove the colloidal solution, particle residue and alcohol in the water.
The applications of flocculants are mainly divided into inorganic and organic types. Inorganic types are generally poly-iron and poly-aluminum, because inorganic flocculants are cheap and widely used. In order to avoid the iron ion pollution of reverse osmosis system, high-purity polyaluminum is generally used as the flocculant; the organic flocculant is generally polypropylene phthalamide and polypropylene salts. In the pretreatment module, inorganic and organic flocculants cooperate with each other, and the actual effect is good. However, in operation and application, according to different processes and water bodies, different water bodies should be selected through practical activities. In actual activities, the various and concentration values of flocculants will be determined by actual activities. Ifreverse osmosis element membrane enters water, too much flocculant will stay on the surface of the membrane for secondary precipitation, causing membrane fouling.
4. Pollution caused by fouling.
Scale is a kind of insoluble salt that precipitates solids on the surface of the membrane. The method to prevent scale is to ensure that the insoluble salt does not exceed the boundary of the saturated state. The precipitated scale is mainly inorganic components, mainly calcium bicarbonate. In addition to inorganic salts, many other inorganic acid salts also have lower saturation solubility. In order to prevent scale on the membrane area, an appropriate membrane scale inhibitor is generally added in front of the precision filter, which sometimes shows the interaction of different drugs added. Lead to the precipitation of insoluble components, thereby contaminating the membrane elements.
5. The colloidal solution is contaminated.
Colloidal solution is a kind of dust particles with a particle size of 1 nanometer (nm) to 1 μm, which is difficult to dissolve naturally like clay, and is usually negatively charged in water. Organic colloidal substances in wastewater, excess flocculant dosage, and hydroxide colloids formed by the hydrolysis of metal ions in sewage are common causes of colloidal pollution.