THE EFFECT OF SUNLIGHT ON FECAL-COLIFORMS IN PONDS - IMPLICATIONS FOR RESEARCH AND DESIGN

Empirical and theoretical models of the effect of light on faecal coliforms (FC) in waste stabilization ponds are used to show that: (i) light can only have an impact on FC if complemented by high dissolved oxygen (DO) concentrations and a high pH; (ii) the tendency of algae to impede light penetration is offset by their ability to raise the pH and DO; and (iii) that visible light is more important than UV. Therefore the DO concentration and pH should be included in models of the effect of light in ponds. In the absence of light, pH values < 9.3 may have less impact than previously reported. The implications for design and research are discussed.