Development of the “French system” vertical flow constructed wetland to treat raw domestic wastewater in India

The main aim of our study was to construct a two-stage vertical flow constructed wetland (VFCW) system to treat single household raw sewage water in India under tropical climate. For selecting the plant species different sets of lab experiments were carried out. Two different plant species (Typha angustata and Canna indica) were considered for their nutrient removal efficiency and biochemical methane potential (BMP) efficiency. Drum experiments were conducted to select the most suitable species for the constructed wetland. Batch assays were conducted in 100 ml bottles in order to determine BMP of plant biomass. The overall nutrient removal efficiency was the same in case of both the plant species that were tested. Typha angustata had been selected for planting in the single household wetland system as it is found in the natural wetlands of Goa and they have higher BMP than other species. The nutrient removal of pilot scale VFCW was monitored at two hydraulic loadings at 0.150 m/day and at 0.225 m/day. The removal of Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Total Kjeldahl Nitrogen (TKN), Ammoniacal Nitrogen (NH3-N), Total Phosphorous (TP), Total Dissolved Solid (TDS) and Total Volatile Solids (TVS) at 1st stage was 64%, 65%, 15%, 21%, 34% and 54% and for the 2nd stage reactor it is 90%, 88%, 50%,52%, 58% and 71% respectively on an average. After changing HLR (hydraulic loading rate) to 0.225 m/day the removal of COD, BOD, TDS, TVS, TKN and NH3-N at 1st stage was 61%, 62%, 33%, 40%, 35% and 58% and for the 2nd stage reactor it is 90%, 84%, 61%, 64%, 47% and 82% respectively on an average. As the loading rate increases there is no change in the treatment efficiency of TKN and NH3-N treatment efficiency increases. However marginal decrease in the treatment efficiency of COD and BOD of the system was observed. The overall footprint of the system got reduced from 1.5 m2 per person to 0.79 m2 per person under Goan climatic conditions.