Towards an efficient and functional design of constructed wetlands systems for wastewater and sludge treatment in high altitude tropical regions

Abstract

The treatment of wastewater and sludge through decentralised natural systems, such as the French System, represents a sustainable and effective strategy. This system uses two stages of vertical flow constructed wetlands (VFCWs) to treat raw wastewater, eliminating sludge generation. Despite its extensive use in France, its application in Latin America, particularly in high-altitude Andean regions, has been limited. The main objective of this thesis was to investigate the feasibility of applying the French System for the treatment of domestic wastewater and septic sludge under the climatic conditions of the Andean Region, at 2500 meters above sea level, through a pilot study in Cuenca, Ecuador. Results showed that VFCWs can continuously handle extreme hydraulic loads of diluted wastewater, with proper feeding and resting periods, reducing the required treatment area and minimizing sludge accumulation. It was also determined that septic tanks remain common in both urban and rural areas, making the treatment of fecal sludge necessary. By using VFCWs for this type of sludge, it was observed that the use of multiple beds allows for adequate treatment, and that retaining the percolate for seven days significantly improves the removal of COD and TS without increasing the treatment area. The French System shows great potential for use in areas with climates similar to the Andean region for the treatment of domestic wastewater and septic sludge.