Urban Waste Water Collection And Treatment For Ganvié (Benin)

The project “Reinventing the Lake City of Ganvié" is part of the Government’s action plan as one of the top priority projects of Benin in the tourism sector. Nowadays, the city of Ganvié consists mainly of stilted houses with a population of around 37.000 inhabitants. The project’s objective is the identification of a wastewater treatment system with reference to the future scenario with a resident population of 73.000 inhabitants in 2038, along with a fluctuating tourist population estimated in approximately 11.000 people. The designed works are the following: Centralised Wastewater Treatment Plant (WWTP): complete treatment system (73.000 PE) with elimination of organic materials and nutrients and final disinfection in compliance with legally binding emission limits. The water line has been designed to minimize the energy consumption and the sludge production. It is structured as follows: Fine screening; Grit removal; Equalisation-homogenization and pumping; Anaerobic treatment UASB; Nitrification, denitrification and dephosphatising with activated sludge; Secondary sedimentation; Chemical disinfection. The sludge line is structured as follows: Pre-thickening; Anaerobic digestion; Post-thickening; Dehydration with belt filter press. The biogas generated through the anaerobic treatment UASB and through the anaerobic digestion of the activated sludge and of the sewage sludge is stored in a gasometer and, after a proper pre-treatment (elimination of humidity, hydrogen sulphide and siloxane), is used for energy recovery (production of electricity and heat) in a co-generation plant. Collective sanitation system: composed of main collection points (15) equipped with pumping stations which, through successive lifts, are capable to convey the wastewater to the WWTP. The collection points are designed so as to ensure easy construction and adequate integration in the typical local landscape. Phyto-purification system for individual treatment: including a pre-treatment unit (septic tank) and a treatment unit (phyto-purification with submerged flow, with filter beds or floating beds).