JICA TRAINING COURSE ENVIRONMENT MANAGEMENT OF ENCLOSED COASTAL SEAS May 19- August 2 , 2008 ACTION PLAN IMPROVEMENT OF EBRIE LAGOON WATER QUALITY AT BANCO BAY BY BIOLOGICAL TREATMENT OF DOMESTIC WASTEWATER TONDOSSAMA KOROMORY BACTERIOLOGIST
INTRODUCTION The increasing world population in coastal zone, caused by industrialization and increasing urbanization is often associated with many environmental problems. Indeed Ebrie lagoon in coastal area at Abidjan, Cote d’Ivoire is nowadays subjected to different sources of pollution. Some of the causes of this pollution is discharge through different bays ,untreated domestic wastewater for lack of sewage treatment plan in Abidjan .Organic matters and nutrients leads to lagoon body eutrophication, depletion of oxygen, proliferation of harmful microorganisms, etc .Thus quality of marine organism and human health is threatened. To control Ebrie lagoon pollution ,Ivorian authorities must begin to treat domestic wastewater before discharge in to the lagoon body.
Ebrie lagoon LOCALIZATION OF EBRIE LAGOON COTE D’IVOIRE COASTAL Ebrié lagoon is one of the three big lagoon system of Cote d’Ivoire. Ebrié lagoon with a surface area of 566 km2, a length of 125 and a maximum width of 7 km, is the largest lagoon in West Africa. It receives freshwater from the Comoé, Agneby and La Mé rivers. This lagoon is connected to the ocean through the Vridi channel close to Abidjan and periodically through the Grand Bassam inlet in the eastern part.
GOAL AND OBJECTIF • The goal of this action plan is to improve Ebrie lagoon water quality at Banco bay by biological treatment of domestic wastewater in order to protect human health and conserve marine, and coastal environment in cote d’ivoire. • To achieve this goal of improvement Ebrie lagoon water quality, the following objective is suggested: Build wastewater treatment facility in which domestic wastewater of Attecoube and Adjame municipalities, will be treated by use of biological activated sludge process to reduce organic matter like COD, BOD, and nutrients like P, N ,before to be released into Banco bay.
DOMESTIC WASTEWATER • Domestic wastewater is the liquid component of waste removed from residences, businesses, and institutions. Essentially, water is considered drinking water or potable water before it is used; after it has been used and discarded it becomes wastewater. • Domestic wastewater generally includes material disposed of through toilets, sinks, tubs and showers, washing machines • Domestic wastewater must be treated and disposed of in a manner that minimizes potential for affecting public health, as well as minimizes the impact on the environment.
But this is not the case in Abidjan ,we have 70% of the population are connected to sewer network, which discharges its sewage into the Ebrie lagoon through the bay without any treatment( picture 1) . • Dufour and Slepoukha (1975) have provided data on sewage volume discharged to the Ebrié Lagoon compared with the volume of receiving waters. • In the area immediately around Abidjan, the volume of domestic sewage discharged each year was equivalent to about 18 % of the total lagoon volume (estimated to 2.6 x 109 m3). Domestic sewage accounts for just over half the total effluent volume.
Picture 1 : Sewer network in Attecoube municipality which discharges its sewage into Banco bay View of Banco bay
As consequence, the Ebrié lagoon has undergone eutrophication especially in the bays (Dufour and Slepoukha, 1975). Anthropogenic inputs of pollutants also contribute to the microbial contamination of lagoon waters and thereby increase the public health hazard (Kouassi et al., 1990). The Ebrié Lagoon waters have been considered as a “reservoir” of pathogenic micro-organisms, Vibrios, Salmonella and Shigella spp. are currently isolated from this environment (Dosso et al., 1984; Kouamé et al., 1979). Pollution may cause decline in biodiversity. There is also potential negative impacts to fisheries productivity as the major habitats, are impacted by pollution (Albaret and Charles-Dominiques, 1982).lastly ,wastewater affects Ebrie lagoon water quality through the production of taste, odor and malodorous gases ( case of banco bay, bietry bay)
For the aforementioned reasons, the immediate and nuisance-free removal of domestic wastewater from its sources of generation, succeeded by proper treatment and final disposal.
BIOLOGICAL TREATMENT OF DOMESTIC WASTERWATER Principle: Simple bacteria (cells) eat the organic material present in the wastewater. Through their metabolism, the organic material is transformed into cellular mass, which is no longer in solution but can be precipitated at the bottom of a settling tank or retained as slime on solid surfaces or vegetation in the system. The water exiting the system is then much clearer than it entered it. A key factor is the operation of any biological system is an adequate supply of oxygen. Indeed, cells need not only organic material as food but also oxygen to breathe, just like humans. Without an adequate supply of oxygen, the biological degradation of the waste is slowed down, thereby requiring a longer residency time of the water in the system. For a given flow rate of water to be treated, this translates into a system with a larger volume and thus taking more space.
Advantages: Like all biological systems, operation takes place at ambient temperature. There is no need to heat or cool the water, which saves on energy consumption. Because wastewater treatment operations take much space, they are located outdoor, and this implies that the system must be able to operate at seasonally varying temperatures. Cells come in a mix of many types, and accommodation to a temperature change is simply accomplished byself adaptation of the cell populationSimilarly, a change in composition of the organic material (due to people’s changing activities) leads to a spontaneous change in cell population, with the types best suited to digest the new material growing in larger numbers than other cell types.
Summary of sewage treatment operations • Primary treatment Separation removal is performed by letting solids and oils in the sewage settle out or float to the surface. In order to reduce the load for secondary treatment. this is usually done in a primary sedimentation tank at the treatment plant. • Secondary treatment The main secondary treatment processes in current use are the activated sludge process, the modified activated sludge process • Tertiary treatment it’s performed to bring water quality to a higher level than that attained in secondary treatment. it eliminates an additional portion of such factors as BOD, SS, N,P which secondary treatment cannot sufficiently remove
MERCI POUR VOTRE ATTENTION DOOMO ARIGATO GOZAIMASHITA