Method of removing silicon dioxide from waste liquid, method of cleaning membrane tube and method of processing waste water

A method of cleaning a membrane tube for processing waste water, wherein the membrane tube contains residues of the waste water that include a first residue containing H2O2and a second residue containing silicon dioxide therein, the method comprising:

• conducting a first cleaning step to reduce a concentration of the first residue in the membrane tube to a first concentration;
• adding, at a temperature, a solution containing fluoride ions into the membrane tube to react with the second residue to form a reaction product;
• and
• conducting a second cleaning step to reduce the concentration of residual fluorine ions in the membrane tube to a second concentration.

A method for processing CMP waste water containing abrasive particles and an oxidant, comprising:

• filtering the CMP waste water with a membrane tube;
• and
• cleaning the membrane tube, comprising:
• conducting a first cleaning step to reduce a concentration of the oxidant in the waste water remaining in the membrane tube to a first concentration;
• adding, at a temperature, a reactive solution containing a reactive species into the membrane tube to react with the abrasive particles filtered from the CMP waste water to form a volatile compound;
• and
• conducting a second cleaning step to reduce the concentration of the reactive species remaining in the membrane tube to a second concentration.