French Type Constructed Wetlands for Sewage Treatment: Experiences from the Swings Prototype in India

Abstract

This study aimed to investigate the performance of the French Type Constructed Wetlands (FTCW) at a pilot scale level in real field conditions for sewage treatment in India. The pilot plant consisted of hybrid wetlands in two stages, vertical and horizontal sub-surface flow types. The first stage comprised three compartments, vegetated with three different native plants (phragmites australis, canna indica, and sagittaria), operated in parallel, and sequentially loaded. Each VSSF bed of 12.25m2 was fed with raw sewage directly for 3.5 days followed by twice the time resting period. The second stage consisted of one bed of an area of 45m2, planted with canna indica. The filter media used in stage 1 was a dual type (gravel and coarse sand) in three layers. The first stage was designed for the loadings of 33.75gBOD/m2d and 14.1 gNH4-N/m2d with the flexibility to operate at a variable hydraulic loading rate (HLR). Two years of monitoring data after the steady-state condition show variable performances at different hydraulic loading rates. Removal efficiencies of COD, BOD5, TSS, TN, and TP of the hybrid system at HLR of 0.4m/day were 87.1%, 87.3%, 84.6%, 67.93%, and 69.32% respectively. Doubling the HLR, the efficiency of the system decreased marginally for the same parameters. Out of the three vegetation, the bed planted with phragmites has shown the highest removal efficiency. The study has demonstrated that FTCW can be a suitable proposition as one of the potential methods for sewage treatment in India and similar regions.