Membranes used in water treatment systems routinely get damaged, resulting in lower quality product water. In full-scale practices, once damage is detected, the filtration process needs to be interrupted to identify the location of the damage and replace the faulty membrane at the expense of significant downtime and higher maintenance cost. To address this issue, proof-of-concept of an innovative in situ healing technique was previously demonstrated on a simple, flat-sheet membrane using synthetic particles. The objective of this study was to test the efficacy of this chitosan-based in situ healing procedure to repair damaged hollow fiber membranes and restore near 6 log removal value (LRV) of viruses, under various damage size, pH, and foulant conditions. The performance of pristine, damaged, healed, and backwashed membranes was examined in terms of specific water flux, MS2 bacteriophage rejection, and synthetic nanoparticle rejection. The healing procedure effectively restored the performance of membranes with induced damages as large as 500 pm in length, even though there was a slight decrease in efficacy for larger damages. The presence of foulants did not interfere with the healing procedure. The results of this study collectively suggest high likelihood of success in real world systems, which will allow membrane filtration processes to be more durable, sustainable and cost-effective. (C) 2015 Elsevier B.V. All rights reserved.