The ultrafiltration membrane is the core element of the ultrafiltration equipment. Because it is a porous material and the impurities in the water are removed by physical interception, the ultrafiltration membrane should be cleaned regularly. The cleaning method is generally determined according to the nature of the membrane and the processing liquid. HONGTEK'S PVC Hollow Fiber UF Membrane Modules and PVDF Hollow Fiber UF Membrane Modules are cleaned by backwashing and the following backwash process for your reference:
1. Preparing liquid and low flow input cleaning fluid
First mix the cleaning fluid with the cleaning water pump, and preheat the cleaning fluid with a low flow rate. Then replace the raw water in the element with the lowest possible cleaning fluid pressure, and the pressure only needs to reach a pressure loss sufficient to replenish the incoming water to concentrated water. This operation can minimize the deposition of dirt on the membrane surface again.
2. Circulation and soaking
After raw water is replaced, the cleaning fluid should appear in the concentrated water pipeline, and circulate the cleaning fluid back to the cleaning water tank and keep the temperature of the cleaning fluid constant. Then stop the operation of the cleaning pump, and the membrane element is completely immersed in the cleaning solution. In order to maintain the temperature during soaking process, a very low circulation flow rate could be used.
3. High flow pump circulation
High flow can wash away contaminants that washed down by cleaning fluid. If the pollution is serious, using a larger flow rate will help clean. Under high flow conditions, there will be a problem of excessive high pressure drop, so the cleaning water flow should be determined according to the performance of the ultrafiltration membrane module, and not to exceed the limit.
Qualified pre-treated water can be used to flush the cleaning fluid in the system, unless there are corrosion problems(for example, still seawater will corrode stainless steel pipes). In order to prevent precipitation, the minimum rinse temperature is 20℃. During pickling process, the pH value of the cleaning solution should be checked at any time. When the pH of the cleaning solution increases by more than 0.5, acid should be added to the cleaning tank. What’s more, the total circulation time of the acidic cleaning solution should not exceed 20 minutes to prevent contaminants from re-depositing on the membrane surface. Then re-configure the cleaning fluid for the second acid cleaning operation.
Only when the ultrafiltration membrane is cleaned in time, it can maintain the permeation and life of membrane, and the correct cleaning method can save time and reduce the damage of the membrane element during the cleaning process. For different membrane modules, different cleaning method can be selected. For example, tubular modules can be mechanically cleaned with sponge balls, and hollow fiber modules can be backwashed.