EXPÉRIENCE D’ÉPURATION DES EAUX USÉES URBAINES PAR LAGUNAGE SOUS CLIMAT SAHÉLIEN (NIAMEY, NIGER) ET QUELQUES DONNÉES RÉCENTES SUR LA MISE EN PLACE DE CETTE TECHNIQUE DE TRAITEMENT SOUS CLIMAT SAHARIEN (CUVETTE DE OUARGLA, SAHARA SEPTENTRIONAL EST ALGÉRIEN)

Abstract

Treatment of wastewater from the city of Niamey Lagoon is a pilot facility that offers the possibility to carry out systematic comparisons between several channels and modes of treatment by lagooning (microphytic lagoon, lagoon to macrophytes) simultaneously and in the same operating conditions. This station was completed in 1998 with funding from the European Commission and technical assistance of the Belgian NGO AQUADEV. It is, with that of the IER (Interstate School of engineers of the Rural equipment of Ouargadougou), one of the few operational sites for research in West Africa. In the experiment described in this study, four courses of treatment were tested with the combination of three different systems of Lagoon: microphytic, rooted macrophytes (Echinocloa Stagnina) and floating macrophytes (Lemna minor) and Eichhornia crassipes. The performance of the four courses were assessed on the basis of comparison of the results. The combination between Eichhornia crassipes and Echinocloa Stagnina has proven to be the most powerful on the physico-chemical and biological parameters with 95% of discount on the, 94% on orthophosphates, 85% on cod and 80% for BOD5. The results showed, moreover, that, overall, there were no significant differences in treatment between the Lemna minor industry and the sector to microphytic natural lagoon. In other ecological context, the Algerian Sahara, awareness seems to see agenda for the use of the technique of the sewage treatment by lagooning, especially after the failures observed after the implementation of "sophisticated" methods of water treatment (primarily activated sludge) that proved very quickly maladjusted to the local context. We are for example the case of the station of lagunage aerated city of Ouargla which are still very recent. This development, in addition to the fact that it will allow a better support of the problem of the management of wastewater in the basin of Ouargla, will allow also to serve as a model of applied research for the treatment of wastewater lagoon in Saharan climate research hitherto little explored. This station, given his recent commissioning, has still not achieved stabilized operation plan (basin during filling, change important time flows arriving at the top of station, etc.) which could allow exploitation of the scientific results in a valid manner. Therefore, it will be, in this second part of the study, to carry out a description of the treatment site and present its main features