Water intake control of submerged ultrafiltration membrane system

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The main function of ultrafiltration technology is to trap small particles, reduce suspended matter and turbidity, remove bacteria and some organic pollutants, and achieve the purpose of improving and stabilizing water quality. The separation mechanism is as follows: the mechanical screening of the membrane surface aperture, the blocking effect of the membrane pore and the adsorption of impurities on the membrane surface and the membrane pore. This is not possible with traditional filtering. The use of ultrafiltration as reverse osmosis pretreatment process has been successfully applied in the reuse water treatment in many places in the country, effectively extending the cleaning cycle and service life of reverse osmosis membrane. After the ultrafiltration treatment, it can effectively remove the turbidity, chroma and part of COD in the wastewater, and ensure the stability of the subsequent reverse osmosis system operation.

 Submerged ultrafiltration membrane system
In the actual engineering design, the submerged ultrafiltration membrane system is generally run for multiple sets of membrane components at the same time, if conditions are available, it can also be considered spare, to meet the operating submerged ultrafiltration membrane if there is a need for reverse cleaning, chemical cleaning or accidents can be enabled spare membrane components to meet the actual processing capacity. When multiple submerged ultrafiltration membrane components are in operation at the same time, it is recommended that the submerged ultrafiltration membrane system distribute water through a distribution channel rather than using pipes to directly transport water. In addition to allowing multiple membrane pools to fill the same amount of water and keeping the liquid level of multiple membrane pools constant, the distribution channel can also reduce the capacity of front-end equipment, such as inlet pumps, self-cleaning filters, heat exchangers, etc.

At the same time, at the inlet of the membrane pool, a baffle device should also be set up to prevent excessive inlet flow rate from damaging the submerged ultrafiltration membrane. The main difference between the submerged ultrafiltration membrane and the ordinary ultrafiltration membrane is that the water of the submerged ultrafiltration membrane is first transported to multiple membrane pools by the distribution channel on average, and then the water in the membrane pool is pumped out from the membrane component through the liquid pump, so that the water passes through the submerged ultrafiltration membrane to achieve the filtration effect. During the operation of the submerged ultrafiltration membrane system, when the membrane pool is emptied after reverse cleaning, the membrane pool needs to be filled again as soon as possible to continue normal operation. Therefore, the water inlet equipment needs to increase part of the processing capacity to meet the program control time and the recovery rate that the submerged ultrafiltration membrane system needs to achieve.

Therefore, the treatment capacity of the inlet equipment is generally greater than the treatment capacity of the water producing equipment such as through the liquid pump. In the design process, the volume of the distribution channel usually needs to meet the following requirements: the amount of water injected into the membrane pool - the required inlet time after backwashing x the processing capacity of the inlet device - the amount of water generated by the drop of the remaining membrane pool level. It can also be seen from the above formula that the processing capacity of the inlet equipment is actually related to the inlet time, the volume of the distribution channel, the volume of the membrane pool and other aspects of the system design after the reverse cleaning of the submerged ultrafiltration membrane system. In the actual calculation process, the above multiple design conditions need to be checked according to the actual engineering situation. The optimal solution can only be obtained after many demonstration in many aspects such as land area and total project cost. After the optimal solution is obtained, the corresponding supporting equipment parameters need to be determined accordingly. For example, the inlet pipe and drainage pipe diameter of the membrane pool need to be determined according to the inlet time and empting time required by the system operation, rather than according to the flow rate and velocity of the pipe diameter in general engineering design.

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