The effect of colloids on the occurrence, phase distribution and photolysis of twenty-seven emerging organic contaminants (EOCs) was studied in domestic and livestock wastewaters (DW and LW), respectively. Filtered water (<1 mu m) was separated into permeate (<1 kDa) and retentate (1 kDa-1 mu m) by cross flow ultrafiltration. Results indicated that total concentration of EOCs ranged from 1220 ng L-1 in permeate of DW to 5065 ng L-1 in retentate of LW. The average EOC fraction associated with colloids was 13.5% and 14.4% in OW and LW. Most of the EOCs exhibited pseudo-first-order degradation kinetics in all water samples. Control experiments using glass and quartz reactors showed that UV light was more effective on the photolysis of most EOCs. The EOCs photolysis in the three fractions of DW and LW could be accelerated or inhibited compared to ultrapure water with the enhancement factor ranging from -0.94 to 7.33. The impact of colloids on the photolysis of EOCs depended on the compound and the source of water. The photolysis of most EOCs in permeates and filtrates was generally accelerated, while inhibited in the retentates, which could be attributed to the relatively high dissolved organic carbon contents in retentates. (C) 2015 Elsevier B.V. All rights reserved.