Abstract:The present drinking water purification system in Egypt uses surface water as a raw water supply without a preliminary filtration process. On the other hand, chlorine gas is added as a disinfectant agent in two steps, pre-and post-chlorination. Due to these reasons most of water treatment plants suffer low filtering effectiveness and produce the trihalomethane (THM) species as a chlorination by-product. The Ismailia Canal represents the most distal downstream of the main Nile River. Thus its water contains all the proceeded pollutants discharged into the Nile. In addition, the downstream reaches of the canal act as an agricultural drain during the closing period of the High Dam gates in January and February every year. Moreover, the wide industrial zone along the upstream course of the canal enriches the canal water with high concentrations of heavy metals. The obtained results indicate that the canal gains up to 24.06×10 6 m 3 of water from the surrounding shallow aquifer during the closing period of the High Dam gates, while during the rest of the year, the canal acts as an influent stream losing about 99.6×10 6 m 3 of its water budget. The reduction of total organic carbon (TOC) and suspended particulate matters (SPMs) should be one of the central goals of any treatment plan to avoid the disinfectants by-products. The combination of sedimentation basins, gravel pre-filtration and slow sand filtration, and underground passage with microbiological oxidation-reduction and adsorption criteria showed good removal of parasites and bacteria and complete elimination of TOC, SPM and heavy metals. Moreover, it reduces the use of disinfectants chemicals and lowers the treatment costs. However, this purification system under the arid climate prevailing in Egypt should be tested and modified prior to application.

Environmental isotope analyses in conjunction with the hydro-geochemical investigations and tentative reviewing of the paleoclimatic sea level changes are carried out to fingerprint the implications of climatic changes on the groundwater flow regime and geochemistry at the Nile Delta. Following up the footprints of groundwater flow history, it is observed that the Pleistocene, main groundwater aquifer of the Nile Delta was drained and refilled with Nile water several times due to the eustatic sea level propagations between dry and wet periods. Therefore, the present-day groundwater flow regime could be affected by the latest Holocene phase of climate changes during which no significant dramatic sea level changes were recorded. After the time slice of the Mediterranean humid phase, 8000-5500 BP, the sea level started to rise steeply from -15 m to the present-day level. Under this rising rate, the seawater invaded most of the northern delta lope and several 10 ths of kilometres inland via the mouths of the ancient Nile branches. During these arid conditions, deterioration of the Pleistocene unconfined aquifer could take place. This finding matches a famine and economic instabilities during the arid periods and flourishing and economic stabilities during the humid pluvial periods along the history of the ancient Egyptian civilization. In accordance to the latest active sea level rise stage in conjunction with the delta subsidence, a contagious groundwater level rise with a recent order of 3 cm/year is taking place leading to form several lake-like lagoons, water logging and soil salinization along the coastal plain and the eastern low lands. The Nile Delta is expected to suffer extreme soil salinization and gradual merging under the groundwater logging and seawater transgression especially, along the eastern coastal zone which suffers a high subsidence rate of about 5 mm/year. In contrast to previous studies, our findings show that, the present groundwater composition and salinity in the Nile Delta aquifers cannot be attributed to a recent seawater intrusion. The physico-chemical processes that explain this composition are combination of salt dissolution (mainly from Holocene fluviomarine aquifer), flushing by recent Nile water, ion exchange and evaporation.

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