Book excerpt: Duckweed (L.gibba)-covered sewage lagoons (DSLs) are low cost treatment systems, especially suitable for warm climates, or in lands where there are warm seasons. This study attempts to assess DSL system as a new technology, contributing to the understanding of the different mechanisms in the system. Duckweed-covered sewage lagoons could either replace complete wastewater stabilization ponds (WSPs) or be introduced as a second stage in an integrated WSP-DSL treatment system, which could then be used for purifying municipal wastewater, achieving suitable effluent for reuse in agriculture. The duckweed harvested from DSL systems has, in itself, an intrinsic economic value.