ch. 1. Introduction -- ch. 2. The effect of baffles on algal-bacterial biofilm structure and composition of zooplankton in wastewater stabilization ponds -- ch. 3. Comparision of hydraulic flow patterns of four pilot scale baffled wastewater stabilization ponds -- ch. 4. Nitrification in bulk water and biofilms of algae wastewater stabilization ponds -- ch. 5. Nitrification rates of algal-bacterial biofilms in wastewater stabilization ponds under light and dark conditions -- ch. 6. Effect of operational conditions on the nitrogen removal in a pilot scale baffled wastewater stabilization ponds under tropical conditions -- ch. 7. Nitrogen mass balances for pilot scale biofilm stabilization ponds under tropical conditions.