On-Site Wastewater Treatment System Design for a Marshy Urban Area in Nigeria
Oluwapelumi O. Ojuri
DOI: 10.2190/ES.31.2.e
Abstract
This research aims at evaluating the efficiency of soil-based wastewater treatment systems in developing countries and designing an on-site wastewater treatment system for a difficult local site condition. Information on wastewater flow and wastewater quality, transport and fate of typical pollutants, conventional systems and treatment options, and various other design considerations, was reviewed from relevant texts and publications. A site and soil evaluation was carried out in order to locate the area to be used for the absorption field and determine soil characteristics, percolation rate, restriction, and groundwater table. The on-site wastewater treatment and disposal system was sited such that its separation from building structures and boundaries permits repair, maintenance of required separation from wells and reduces undesirable effects of underground wastewater flow and dispersion. The absorption area was sized based on an estimation of the household's wastewater flow and daily loading rate, which corresponds to the percolation rate of the receiving soil surface. The on-site wastewater treatment system designed for Danjuma area, Odi-Olowo Street, Akure, Ondo State, Nigeria, is comprised of a septic tank, dosing chamber and a mound system, which house the absorption area (drain field). The design was based on the minimum standards for design and construction of on-site wastewater systems in the state of Kansas [1]. The septic tank (2 m x 1.5 m x 2 m) was sized based on the estimated wastewater flow of 2160 liters day-1 and the dosing chamber (1 m x 0.75 m x 1 m) has half the size of the septic tank. The mound system recommended for this site, which experiences seasonal high water tables and occasional floods, was raised using well-graded sand. The absorption area (10.5 m x 10.5 m) was sized based on an estimated wastewater flow of 2160 liters day-1 and a daily loading rate of 20 liters m-2 day-1, which corresponds to the obtained percolation rate of 18 mins cm-1 (0.056 cm min-1).
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