Selective clogging of failed fibers

A method of selective clogging of failed hollow fibers of a membrane module comprising a pack or bundle of fibers in a shell-side and bore-side arrangement, the pack or bundle comprising failed fibers together with a plurality of non-failed fibers, the method comprising the steps of:

• clogging bores of all of the fibers at one end of the pack or bundle of the fibers;
• substantially evacuating the membrane module both at the shell-side and at the bore-side;
• filling the bore-side and the shell side with a non-permeant gas;
• subsequently holding the membrane module vertically, disconnecting the bore-side of the membrane module from a supply of the non-permeant gas and dipping another end of the membrane module opposite to the clogged end into a reservoir containing a liquid sealant;
• applying a reduced pressure to the shell-side for a period of time sufficient to permit suction of the liquid sealant into the bores of the failed fibers through a failure of which vacuum is applied to the bore-side;
• optionally, allowing the sealant to thicken, but not to solidify;
• filling the shell-side with a permeant gas, whereby to cause the permeant gas permeating to the bore-side to expel the sealant from the non-failed fibers, thus opening up the bores of the non-failed fibers;
• and allowing the sealant to solidify to clog the bores of the failed fibers.