Investment, operation and maintenance costs (2012) for natural wastewater treatment systems in small communities in Colombia

A comparative analysis of investment, and operation and maintenance (O&M) costs, for natural wastewater treatment systems for small Colombian communities (500–30,000 capita) (Colombia, Ministerio de Desarrollo Económico, 2000) was performed, and a set of tools (equations, graphs and tables) were developed to estimate these costs as a support for decision making. This was achieved by a simulation where the climatic variables, water quality parameters, material, man labour and land costs were generated randomly, varying between the researched ranges for Colombia. These input variables were used to design 15 different combinations of natural treatment technologies, such as septic or sedimentation tanks, anaerobic, facultative and maturation ponds, free water surface wetlands and horizontal subsurface flow wetlands. For each one of these scenarios, an investment and O&M budget was estimated, uploading this information into a database performing one million iterations. Comparative cost graphs show the differences between combinations of technologies, influence of inlet principle variables on investment and O&M costs. The variation of O&M costs in natural treatment systems estimated for the different combinations was not significant, but the investment cost varies a lot. Land cost is one of the most important variables. Excavations and waterproofing were two construction activities with important influence on all the combinations. Conformation of wetlands was another construction activity that was significant in those that included wetland. Disinfection with maturation ponds is expensive especially in areas of high land cost.