Contribution and relationship between oxidative phosphorylation and photophosphorylation pathways in purple non-sulfur bacteria (PNSB) wastewater treatment under weak light-micro oxygen condition were studied quantitatively. Results showed that under weak light-anaerobic condition, PNSB followed photophosphorylation with the first-order degradation kinetic constant k(3) of 0.0585. Under dark-micro aerobic condition, it followed oxidative phosphorylation with k(2) of 0.0896. Under weak light-micro oxygen condition, both pathways existed with k(1) of 0.108. When light and oxygen both existed, oxidative phosphorylation had a strong competitiveness, it played a dominative role and counted for 92.7% in pollutants degradation, and meanwhile photophosphorylation was restrained by 81.6%. Theoretical analysis showed the common part from coenzyme Q(CoQ) to cytochrome c2 (Cyt c2) in both respiration and photosynthetic chains might cause the competition. When oxygen existed, respiration electron transport would be enhanced. Other potential explanations included that oxygen might damage the pigment and membrane system vital to photophosphorylation. (C) 2011 Elsevier Ltd. All rights reserved.