Cost Analysis of Trickling-filtration and Activated-sludge Plants for the Treatment of Municipal Wastewater

Cost estimation is an important consideration for the development and evaluation of wastewater treatment alternatives. This paper evaluates the most cost-effective treatment scheme among different plants employing two biological processes most commonly used for the treatment of municipal wastewater in Saudi Arabia, activated sludge and trickling filtration, by using a computer-based treatment cost estimating model. Project, and annual operation and maintenance (O & M) costs of trickling filtration (TF) are compared to those of two activated sludge (AS) systems: complete-mix and oxidation-ditch systems. Each system is a part of a complete treatment scheme for wastewater and sludge. The schemes are designed first on the basis of process variables and the reclaimed-water quality criteria for unrestricted irrigation specified by the Ministry of Water and Electricity, and then costed. In addition, cost effectiveness analysis is performed. For a flow of 200,000 m/day with BOD and SS of 300 mg/L and 400 mg/L, respectively, costs of treatment alternatives are evaluated in 2006 Saudi Riyals. Results reveal that project costs of the AS plants are more than that of the TF plant by about 12%-13%. The present worth costs of the former plants are also higher than that of the latter by about 18%-19%. Results also show that the annual O & M of the completely mixed and oxidation-ditch AS plants cost more than the TF plant by about 53% and 46%, respectively. The per unit cost of the TF plant is estimated at SR 1.06/m, while the costs for the complete-mix and oxidation ditch AS plants are respectively, SR 1.25/m and SR 1.23/m. Accordingly, the TF is obviously the most-cost effective treatment alternative.