Performance and reliability comparison of French vertical flow treatment wetlands with other decentralized wastewater treatment technologies in tropical climates

When implementing a sanitation system, the selection of treatment process can be difficult. Beyond removal efficiency and effluent concentrations, reliability should be taken into account. This study compares reliability of French vertical flow treatment wetlands (F-VFTW) with the four main decentralized wastewater treatment technologies in small communities in the French Overseas Territories (FOT). Analysis of 963 regulatory self-monitoring sampling campaigns performed on 213 wastewater treatment plants show that operational disruptions due to sludge loss and loss of nitrification are often reported for activated sludge technology; rotating biological contactors often suffer from weak settlement; facultative pond removal is limited by algae; and F-VFTW fulfills all the French regulatory objectives at a frequency of 90 to 95%. In addition, the data from this study are compared to a similar database from Brazil using a statistical approach (coefficient of reliability). Amongst the eight decentralized wastewater treatment technologies evaluated, F-VFTW appears to be the most appropriate for achieving the discharge standard with a reliability close to 95%. Its reliability to face both environmental (rainfall) and social (maintenance capacities) constraints is a key parameter.