Book excerpt: There is an urgent need to develop and improve low cost technologies for wastewater treatment. Simultaneously treating wastewater and producing duckweed in a pond system is, therefore, an attractive solution contributing to both environmental protection and food production. Duckweed has excellent qualities: a high protein content, a high growth rate and is an easy crop to handle. The small plant turns nitrogen from wastewater into a food source. This thesis reports on the effect of different operational variables, like anaerobic pre-treatment, the combination of algae and duckweed ponds and pond depth. Improved nitrogen removal was obtained through the combination of duckweed ponds with algae ponds. Duckweed pond systems could be designed with shallow depth without affecting nitrogen removal efficiency. This research is the result of the cooperative effort between the EIDENAR, Univalle, Cali, Colombia and the UNESCO-IHE Institute for Water Education in Delft, the Netherlands.