Ultrafiltration membrane technology in water treatment applications
Ultrafiltration method in water treatment and other industrial purification, concentration, separation process, can be used as the pretreatment of the process, but also can be used as the depth of processing of the process. Widely used in the water treatment process, often as a means of deep purification. According to the characteristics of the hollow fiber ultrafiltration membrane, the water supply before handling requirements. Because suspended solids, colloids, microorganisms and other impurities will be attached to the film surface, leaving the film contamination. Ultrafiltration membrane water flux trapped concentration of impurities on the surface of the membrane increases rapidly produce so-called concentration polarization phenomenon, the more serious is that some very small particles into the membrane pores and clogging water channel. In addition, microorganisms and their metabolites in water to generate viscous substances will be attached to the membrane surface. These factors will lead to a decline in the rate of change as well as the separation performance of the ultrafiltration membrane permeable. Ultrafiltration water supply temperature, PH value and the concentration at the same time the requirements of a certain limit. Appropriate pretreatment and adjust water quality, the ultrafiltration water supply must meet the water supply requirements of conditions, in order to extend the life of an ultrafiltration membrane, reducing the cost of water treatment.
A, in the killing of the microorganisms (bacteria, algae):
When the water contains microorganisms into the pre-treatment system, the part of the trapped microbes may adhere to the first processing system, such as multi-media filter medium surface. When adhering to the growth and reproduction of the ultrafiltration membrane surface, it is possible to make microporous completely clogged, or even completely blocked the lumen of the hollow fiber. The presence of micro-organisms on the dangers of the hollow fiber ultrafiltration membrane is extremely serious. Must pay attention to remove the raw water of microorganisms such as bacteria and algae. Usually by adding an oxidizing agent such as NaClO, O3, the concentration is generally from 1 to 5 mg / l in water treatment works. In addition, the UV light may be used. Sterilization of hollow fiber ultrafiltration membrane module in the lab, with hydrogen peroxide (H2O2) or potassium permanganate solution loop processing 30-60min. Kill microbial treatment can only kill microorganisms, but not removing microorganisms from the water, just to prevent the growth of microorganisms.
B, lower influent turbidity:
When water contains suspended solids, colloids, microorganisms and other impurities will cause the water to produce a certain degree of opacity, the turbidity of light will hinder, the number, size and shape of the optical effects and impurities. Measure water turbidity is generally said to eclipse degree, and provisions 1mg/lSiO2 turbidity, the greater the degree, the more trash content. Water supply turbidity in different areas have different requirements, for example, the general living water, turbidity should not be greater than 5 degrees. Since the turbidity measurements are to the light measured through the raw water by the particulate matter in the water reflecting the amount of light, the color, opacity, and the particle size, quantity and shape affect the relationship between the measured turbidity and suspended solids is random. For particles of less than several microns, turbidity, and can not be reflected.
The processing of the membrane, the precision of the micro-structure, the interception at the molecular level and even ion particles turbidity reflect the water quality is obviously inaccurate. In order to predict the tendency of the raw water pollution, the development of the SDI value test.
SDI value is mainly used to detect how much water colloidal and suspended matter particles, characterization of the the system influent water quality of important indicators. The SDI value determination method is generally a pore size of 0.45μm millipore 0.21MPa constant flow of water under pressure hydraulic first recording pass water to start filtration 500ml water sample required time T0, and then under the same conditions to continue to pass water 15min again recorded filtration 500ml water sample time required t15, and then calculated according to the following formula:
SDI = (1-t0/t15) × 100/15
The size of the value of water SDI colloids can be broadly reflect the degree of pollution. Well water SDI <3, 5 or more, surface water SDI, SDI limit of 6.66 ......, that need to be pretreated.
Ultrafiltration technology most effectively reduce the value of SDI, hollow fiber ultrafiltration membrane treated water SDI = 0, when the SDI is too large, especially the larger particles of the hollow fiber ultrafiltration membrane serious pollution in ultrafiltration process, must be pretreated, i.e. quartz sand, activated carbon, or are equipped with a variety of filter media filter, As to what kind of process is no fixed pattern, it is because the water from different sources, and thus the preprocessing method different.