The treatment of domestic wastewater and the improvement of our living environment is a matter of concern. Less costly methods are to be promoted because of the low financial power of the developing countries. In order to satisfy this requirement, here we have proposed an autonomous system for gray water treatment (SAUTEG) using the macrophytes Thalia geniculata plants. This system is composed of 75 plants/m ^² and purifying capacity EH equal to 8.7 x10 ^-3 equivalent-inhabitant. Using this system, gray water (catch water: EGo and collectors of wastewater: ECo) were collected and processed (EGT and ECT) and physicochemical parameters of the gray water were determined according to the French standard. There was a significant reduction in organic pollution at the level of EGT and ECT respectively (BOD ₅ : 93.49% - 99.04%, COD: 94.40% - 98.25%, MES: 99.99% - 99,98%), organoleptic parameters (color: 86.50% - 84.63%, Turb: 94.13% - 88.61%), trace metallic elements (Pb: 24.52% - 87.02%, Cd: 11.84% - 21.42%). There was also nutrients removal (NO ₃ ^- : 96.49% -19.04%, NTK: 94.94% - 100% and PO ₄ ^3- : 14.69% - 55.02%). The treated water was less turbid and lighter. There was a good performance of the system regarding biological parameters (E. coli: 100%; Enterococci: 100% and thermo-tolerant Coli: 99.99%). The values were close to those reported in the literature and some meet the standards of domestic wastewater treatment. Comparative study of the results revealed that the SAUTEG purified the waters from the collector better than the gray water. Thalia geniculata plants, in the system played an important role in the reduction of nitrates and lead in domestic wastewater. This system would therefore contribute to the improvement of the environment. We are looking forward to extending this study to other pollutants and to evaluating the saturation time of the system.

Background: Air pollution has caused health and environmental problems around the world. In this study we analysed the temporal evolution of air pollution in Cotonou regarding the standards of Benin and of World Health Organization (WHO). Design and methods: Solar-powered electrochemical sensors (CO: carbon monoxide, SO₂: sulphur dioxide, and O₃/NO₂: ozone/nitrogen dioxide) and photoionization detectors (for NMVOC: nonmethane volatile organic compounds) were permanently installed and monitored from June 2019 to March 2020 at Akpakpa PK3 (A) and Vèdokô Cica-Toyota (B) roundabouts. Results: CO and SO₂ concentrations at both roundabouts were significantly higher on weekends than on weekdays. The concentrations of NMVOC and O₃ / NO₂ on Sunday differed considerably from the other days of the week at A and B, respectively. There was a positive linear correlation between the concentrations of CO and SO₂, O₃ / NO₂ and SO₂, and CO O₃ / NO₂ to B, and only between CO and O₃ / NO₂, in A. At the two sites, the average of SO₂ concentrations (in μg/m³) were higher than the WHO standard (500) for an exposure of 10 minutes (2258 A and 2143 B) and the Benin standard (1300) for 1 hour exposure (2181 in A and 2092 in B). Conclusion: Air pollution varies in hours and days in Cotonou. Standards are respected, except for SO₂. Particular attention should be paid to the concentrations and the possible sources of gas. More sophisticated monitoring system should be put in place.

The rejection of untreated waste water in the nature decreases groundwater quality. Waste water treatment plants like activated sludge plant and stabilization pond plant built in Benin show their limits. Due to these problems, reed beds have to be experimented to bring a durable solution to waste water treatment problems in Benin. Compare to activated sludge plant and to stabilization pond plant, reed beds are the cheapest based on the technical and economical point of view. On addition to that, reed beds are easy to build and to maintain. The experiment plant is composed of four basins. The first basin is unplanted. The second basin is planted with Echinochloa pyramidalis. The third basin is planted with Panicum maximum and the last basin is planted with Typha domingensis. Each basin is a 1 m3 tank with drilled drain pipes. Three differentl ayers of gravel have been put on drilled drain pipes. Treated water analysis showed that the Typha domingensis basin has the best purfiying performances with final concentrations : 0 mg/L ; 21,10 mg/L ; 10 mg/L ; 0 mg/L et 12,20 mg/L respectively for TSS, COD, BOD5, TKN and TP. These final concentrations reached the discharge standards for municipal wastewater treatment plant in Benin. Consequently, Typha domingensis beds can be popularized by the beninese government to solve waste water treatment problems.