How elevation dictates technology selection in biological wastewater treatment

Abstract

Most wastewater treatment facilities are built using procedures from previous designs which are predominantly from sites and regions not located at high elevation. Recognizing this limitation, we assessed the effects of elevation above sea level on the suitability of process configurations and technologies as well as their associated energy costs. Using the International Water Association (IWA) benchmark simulation model No. 2 (modified Ludzack-Ettinger process layout) as a reference, we simulated scenarios including different activated sludge process configurations, operating under different environmental and process conditions. In order to include a wide sample of environmental conditions, data on atmospheric pressure, wastewater temperature, air temperature, and relative humidity (for average, warmest, and coldest months) were collected from municipal wastewater treatment plants located at different latitudes and elevations. The results confirm that elevation is a driver against the selection of diffused aeration technologies. Aeration costs for aerobic wastewater treatment are highly influenced by local project conditions, particularly by elevation and wastewater temperature, which together influence the driving force for oxygen transfer into water. When the driving force is low, operating costs are high. Recommendations for designing treatment processes effectively, including diffused aeration systems operating at high elevations above sea level, are proposed.