Abstract
Constructed wetlands have recently received considerable attention as low cost and efficient means of cleaning up many different types of wastewaters at secondary and tertiary levels. This is an environmentally sound method of wastewater treatment that does not use hazardous chemicals, and is based on the high productivity and nutrient removal capability of the wetland that strongly relies on its intricate ecosystem structure and function. Research work was conducted on a tropical constructed wetland to establish its capability to treat wastewater during the dry season. A comparison of its efficacy with that of conventional wastewater treatment plants was made on the basis of the measured water quality parameters. Temperature, pH, dissolved oxygen, and conductivity were measured in situ. Total suspended solids (TSS), total dissolved solids (TDS), biochemical oxygen demand (BOD5), chemical oxygen demand (COD), phosphorus, ammonia, and nitrites were analyzed in the laboratory. Fecal coliforms were enumerated and Escherichia coli counts were determined. The TSS values reduced from a mean of 102 mg/l at the influent point to 16 mg/l at the effluent point, depicting a reduction of 84.3%. Influent TDS averaged 847 mg/l, while the effluent averaged 783 mg/l. Dry season BOD5 levels were reduced from an average of 286 at the inlet point to 11 mg/l at the outlet representing a reduction efficiency of 96.2%. COD levels were reduced from a mean of 2,002.5 to 47.5 mg/l depicting a removal efficiency of 97.6%. Phosphorus was reduced from a mean of 14 to 11 mg/l representing a percentage removal of 21.4%. Levels of ammonia reduced from a mean of 61 at the influent point to 36 mg/l at the effluent point representing a percent reduction of 41.0%. There was a 99.99% reduction for both the fecal coliforms and E. coli counts. Conductivity of wastewater increased from 1.08 to 1.98 mS, while the pH increased from 6.23 at the inlet point to 7.99 at the outlet of the system. Temperature and dissolved oxygen measurements showed a diurnal variation. The dry season wastewater heavy metal concentrations were in the following ranges: Pb (0.7–6.9 ppm), Cr (0.2–0.5 ppm), Zn (0.1–2.3 ppm), Ni (0.1–1.3 ppm) with Cd and Cu not being detected in the wastewater streams. Overall, tropical constructed wetlands are effective in treating wastewater streams and they perform a lot better than the popularly used waste stabilization ponds. This paper recommends that they can be widely used within the tropics.
Similar content being viewed by others
References
APHA. (1992). Standard methods for the examination of water and wastewater (16th ed.). Wahington DC: American Public Health Association.
Brix, H. (1997). Do macrophytes play a role in constructed treatment wetlands? Water Science and Technology, 35(5), 11–17.
Cowardin, L. M. V., Carter, V., Golet, F. C., & LaRoe, E. T. (1978). Classification of wetlands and deep water habitats of the US. FWS/OBS – 79/31 (p. 103). Washington, DC: US Fish and Wildlife Service Publication.
Hammer, D.A. (1989). Constructed wetlands for wastewater treatment. municipal, industrial and agricultural. Inc, USA. Lewis Publishers.
Hedmark, A., & Jonsson, M. (2008). Treatment of log yard runoff in a couch grass infiltration wetland in Sweden. International Journal of Environmental Studies, 65(2), 267–272.
Kadlec, R., & Knight, R. L. (1995). Treatment wetlands. Boca Raton: Lewis Publishers.
Khisa, K. (1997). The performance of a constructed wetland for treating wastewater at the Splash Water World, Nairobi; MPhil. Thesis; Moi University; Kenya.
Navid, D. (1989). The international law of migratory species: the Ramsar Convention. Natural Resources Journal, 29, 1001–1016.
Ng’weno, F. (1994). Seasonal wetlands in Nairobi. Rainbow Children’s Magazine. Nairobi, Kenya.
Shaw, S.P., & C.G. Fredine (1956). Wetlands of the United States, Their extent, and their value for water fowl and other wildlife (p 67). Washington, D.C.: US Department of the Interior, Fish and Wildlife Circular, Circular 39.
Scholz, M., & Lee, B.-H. (2005). Constructed wetlands: a review. International Journal of Environmental Studies, 62(4), 421–447.
Tarnocai, C. (1979). Canadian wetland registry. In: Proceedings of a workshop on Canadian wetlands environment, C.D.A. Ecological Land Classifiation Seres, 12, 9–38.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Kelvin, K., Tole, M. The Efficacy of a Tropical Constructed Wetland for Treating Wastewater During the Dry Season: The Kenyan Experience. Water Air Soil Pollut 215, 137–143 (2011). https://doi.org/10.1007/s11270-010-0465-2
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11270-010-0465-2