Two-Stage Constructed Wetland for Treating Hospital Wastewater in Nepal

Abstract

To treat the wastewater of a hospital at Dhulikhel/Nepal, a two-stage constructed wetland was built with a settlement tank, a horizontal flow bed as first stage and a vertical flow bed as second stage. The plant is operated without electric power. The aim was the elimination of organic compounds, nitrification and a significant reduction of indicator bacteria. Different phases of operation (high and low water level within the soil profile, serial operation, one stage operation) were investigated, of which the serial operation with high water level in the horizontal flow bed and low water level in the vertical flow bed showed the best elimination performance. The areal removal rate constants (k-values) turned out to be very high (especially of the vertical flow bed) compared with literature values of other subsurface flow constructed wetlands. For the vertical flow bed kCOD was 0.22 m/d and kNH4-N was 0.85 m/d during serial operation. For kNH4-N a strong correlation with the hydraulic loading rate and the COD inlet concentration was found.