Combination of a well functioning constructed wetland with a pleasing landscape design in Nairobi, Kenya

摘要

The constructed wetland consists of a combination of a sub-surface horizontal flow system (VSB) planted with Typha, followed by a series of three pond systems planted with a variety of plants, including ornamental plants. The plant species include Typha, Cyperus latifolius, Cyperus papyrus, Hydrocotyle, Hydrocleis and Pontederia. The wetland is treating wastewater from a restaurant (The Carnivore) and a swimming pool resort with recreational facilities (Splash), both in Nairobi, Kenya. The wetland is designed to treat wastewater as well as to provide an aesthetically pleasing and environmentally sensitive landscape with ponds and ornamental plants for recreation. The 0.5 ha wetland is designed for 1,200 population equivalents, and has a high treatment efficiencies for BOD_5, SS, COD, faecal coliforms, Kj-N, NH_4-N and o-PO_4 of 98, 85, 96, 99, 90, 92 and 88% removal. An attempt has been made to determine a mass balance for the system. Most of the nitrogen and phosphorus is deposited in the soil of both the subsurface horizontal flow constructed wetland and the ponds. Some nitrogen is removed by denitrification, only 6% of it is retained by the plants. The sediments play therefore, a major role in the removal of the nutrients. The constructed wetland attacts many birds (128 bird species have been reported) and amphibians. The overall impression of the wetland is that the dual function of beauty and wastewater treatment is achieved.