Pretreatment of Ultrafiltration Membrane System
Suspended solids, colloids, microorganisms and other impurities in the water will attach to the surface of the membrane, thereby fouling the membrane. Ultrafiltration Membrane has a relatively large water flux, and the concentration of trapped impurities on the membrane surface increases rapidly, resulting in concentration polarization. What is more serious is that some very small particles will enter the membrane pores and block the water channels. In addition, the viscous substances produced by microorganisms and their metabolites in the water will also adhere to the surface of the membrane. These factors will lead to a decrease in the water permeability of the ultrafiltration membrane and a change in the separation performance. Therefore, proper pretreatment of the ultrafiltration influent water must be carried out to meet the conditions of use of the ultrafiltration membrane, and to extend the service life of the ultrafiltration membrane.
1) The killing of microorganisms (bacteria, algae): When the water contains microorganisms, some of the trapped microorganisms may adhere to the media surface of the pre-treatment system such as the multi-media filter after entering the pre-treatment system. When microorganisms adhere to the surface of the ultrafiltration membrane system, growth and reproduction may completely block the micropores or even completely block the inner cavity of the hollow fiber membrane. The existence of microorganisms is extremely harmful to the hollow fiber ultrafiltration membrane. Therefore, it is necessary to pay attention to removing bacteria and algae in the raw water. Usually, adding NaClO, O3 and other oxidants in water treatment projects can effectively inhibit the reproduction of microorganisms, slow down membrane pollution, and extend the service life of membranes. In addition, UV sterilization can also be used.
2) Removal of suspended solids and colloidal substances: The suspended solids and colloidal substances in the water can be removed by using security filters, quartz sand filters, and activated carbon filters.
3) Removal of grease: After the secondary treatment, the oil content of oily sewage can reach below 10mg/L. If you want to enter the Ultrafiltration System, you must go through the tertiary treatment to meet the ultrafiltration water inlet requirements. The traditional three-stage deep degreasing process generally adopts activated carbon adsorption method and biological method, or a combination of the two methods and methods such as super oil-absorbing resin.
4) Hardness removal: For high-salinity raw water, it is necessary to add corresponding scale inhibitors to avoid scaling of membrane filaments.
5) Adjustment of inlet water temperature
The inlet water temperature of ultrafiltration can be selected according to the specific conditions of operation, so that the maximum economic water production of ultrafiltration can be achieved. If the water temperature is too low, the water production will decrease. In the actual application process, the temperature can be adjusted through the heat exchanger. accomplish. The energy consumption required for the adjustment of the water temperature should be balanced with the operating energy consumption of the Ultrafiltration Water System to achieve the best energy saving effect.
6) pH adjustment The pH value of the membrane module inlet water is in the range of 6-9. If the pH value of the inlet water exceeds this range, it can be adjusted to meet the inlet water requirements by adding acid or alkali. When adjusting the pH value, pay attention to the changes of other indicators in the water (such as hardness, etc.) to prevent damage to the membrane when adjusting the pH value.