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Design of a Semi-Centralized Wastewater Treatment System for Developing Cities: The Case of Buea Municipality, Cameroon

Abstract

Ndam Yahaya David, Patamaken Aneck Simon Ndibnuh and Fredline Ilorme

The municipality of Buea currently lacks a conventional wastewater treatment system for domestic wastewater. The management of wastewater in the area under study is inadequate, making use of septic tanks, most of which are not constructed following standard norms, and are rarely emptied. The purpose of this work was to evaluate the current system for wastewater treatment and to propose a better conventional system capable of meeting environmental standards. The wastewater treatment system was designed using standard procedures and made use of the trickling filter technology for biological treatment. A gravity sewer was designed for the conveyance of wastewater, followed by primary and secondary settling tanks, and a biological treatment unit which is the trickling filter. The method used for this study involved carrying out a quantitative survey to gather relevant data needed to design the system, followed by the application of standard design procedures. The dimensions of the gravity sewer network made of polyvinyl chloride pipes ranged between diameters of 110 mm and 160 mm. The treatment system includes two primary settling tanks of diameters of 8 m and heights of 2.5 m, two trickling filters of diameter 26.4 m and height of 3.6 m, and two secondary settling tanks with a diameter 8m and height of 4.5 m. The theoretical performance of the system showed a Biochemical Oxygen demand reduction from 222 mg/L to 16.3 mg/L, Total Kjeldahl Nitrogen reduction from 55 mg/L to 22.5 mg/L and total Phosphorus reduction from 15 mg/L to 9.5 mg/L. The pollution reduction exhibited by the system enables the treated wastewater to meet the country’s environmental discharge standards. The design proposed with a cost estimate of about 1,528,023 USD (United States Dollar) is relatively low compared to constructing a septic tank for the households in the study area which costs about 4,183,041 USD. The system proposed is less costly at a city scale and more environmentally friendly compared to a standard septic tank. Hence such a system is recommended for developing cities especially Buea.