Regional Conference on ‟Sustainable Integrated Wastewater Treatment and Reuse” Sharm El Sheikh - Egypt, 1-2 December, 2014 Tunisian Experience in Artificial Recharge using Treated Waste Water Habib CHAIEB CRDA of Siliana / Ministry of Agriculture - Tunisia 1 Introduction Rainfall : From 1500 mm in the north to less than 50 mm in the south. Average : 36 109 m3/y (11-90 109 m3) Available conventional water resources : 4.875 109 m3. - Surface water resources : 2.7 109 m3. Pop./2014: 10,982,754 - Underground water resources : 2.175 109 m3. Non renewable : 0.610 109 m3/y, Renewable : 1.6 109 m3/y. Ratio per capita : 440 m3 (2014) 350 m3 (2030) Available water resources : 4.275 109 m3. 91 overexploitation aquifers : 55 surface aquifers Withdrawals: 2.175 109 m3. (0.85 + 1.32) 36 deeper aquifers Boreholes /Phreatic or Surface aquifers (226) : 140000. Deep wells and springs / Deeper aquifers (343): 6255 (6167 + 88). Observation wells : 2159. Quality Network : 876. 2 Foreword Tunisia has 91/569 (16 %) overexploited aquifers at a rate of 146%. Renewable resources of these aquifers are estimated to 568 Mm3/year, more than 26% of the country's renewable resources (2175 m3/year). Water withdrawals from overexploited aquifers are evaluated at 829 Mm3/year, more than 38 % of the total (2175 m3/year). At this rate of withdrawals, the overexploitation could risk the pollution and the quantitative and qualitative degradation of groundwater resources. As a result of this overexploitation, signs of desertification have been observed in the region of the Eastern Coast of Cap Bon due to decline recorded in groundwater levels and a very high salinization (more than 20 g/l ) due to the seawater intrusion. So the significant increase in water POTENTIAL of TREATED WASTEWATER demand of different economic sectors and the availability of an increasingly - 2013 : 110 WWTP 240 Mm3/an important and permanent TWW potential, fact that the use of unconventional water - 2020 : 190 WWTP 300 Mm3/an resources becomes nowadays a Treated Wastewater Potential = 11 % strategic choice in the management of the country's water resources and a / GW Resources (2.2 billion m3/y). valorization of this kind water. 3 Case studies 1. Groundwater recharge from treated wastewater in Tunisia was observed in the first time in 1965 in Soukra aquifer after the creation of a public irrigated perimeter with treated wastewater product by Charguia WWTP. 2. In December 1986 and after the implementation of a project funded by the United Nations Development Program (UNDP, RAB080), an experimental station was built in the Souhil river basin to rechage Nabeul-Hammamet aquifer. 3. Since the creation of the public irrigated area of El Hajeb-Sidi Abid by treated wastewater from Sfax WWTP in 1995, significant rising of the piezometric groundwater levels were also observed, highlighting irrigation water percolation into the groundwater aquifer. 4. The landscaping of the river beds of Zrata and El Ayoun (Mahdia region) by infiltration facilities/structures, has allowed the aquifers of Boumerdes and Mahdia-Ksour Essef to benefit in 2005, from artificial recharge respectively with the treated wastewater of Boumerdes and El Jem WWTPs. 5. Finally, within the framework of the Investment Program in Water Sector (PISEAU), a new pilot site was built in 2008, in the region of Korba-El Mida aiming to recharge the groundwater aquifer of the Eastern Coast of Cap Bon region by treated wastewater from Korba WWTP. 4 Case study of Soukra aquifer Irrigated perimeter of Soukra The perimeter of Soukra is located at 8 km in north-east of the city of Tunis, bordering the sebkha of Ariana. It was created in 1964 and is equipped by an underground irrigation system. It covers an area of 1286 ha, divided into four sectors: Blue Sea Choutrana, soukra and Sidi Fredj. It is supplied by treated wastewater from the treatment plant ONAS Charguia. The treated effluent from the Charguia WWTP are pumped and repressed to the intermediate pump station of Ariana. Then the water is pumped to a storage tank located in the center of the perimeter and from which the water distribution is done by gravity. The objective of the reuse of treated wastewater was initially to save the orchards citrus region of Soukra where the groundwater Figure 1 : Carte de aquifer was suffering from substantial saltwater situation intrusion due to groundwater intensive withdrawals by surface wells and a few semi- deep wells in the surface/phreatic aquifer. 5 Wastewater treatment plant of Charguia Construction : 1940. Treatment capacity /secondary step (activated sludge and sedimentation): 30000 m3/d. Treated wastewater quality Salinity more than 1.6 to 2 g/l. Monthly average rate of dry residues ranged: 1.9- 3.9 g/l. Irrigation treated wastewater volume Irrigated area : 542.4 ha (Disserved Volume:5000 m3/ha/y, (≈2.7 Mm3/y). Irrigation impact on the aquifer Piezometric level evolution The piezometric fluctuations observed have confirmed the percolation of significant amounts of irrigation water into the aquifer with an average rise of 9 cm/y recorded between 1973 and 1998. Chemical impact Compared to 1973 situation, groundwater recorded in 1998 a significant quality improvement. The areas with high salinity which occupied 2/3 of the total area, were 6 significantly decreased in extension. Case study of Nabeul-Hammamet aquifer Wadi Souhil Site (Cap-Bon) Location: The phreatic aquifer of Wadi Souhil is located in the south-east of the Cap Bon Peninsula and belongs to the coastal aquifer system in the region of Nabeul-Hammamet, which extends as a whole on an area of ​​about 60 km2; Artificial recharge site location Water resources of Nabeul-Hammamet aquifer Average rainfall : 400 mm. renewable Resources : 12.5 106 m3. Salinity : 4 to 6 g/l. Exploitation : 15. 106 m3. Surface wells : 3930. Monitoring wells : 60. The downstream part of Nabeul-Hammamet aquifer was decreed since September 2, 1941 (Decree No. 105) as a prohibited area for new creation of wells intended to groundwater exploitation. 7 The recharge site The site reserved for the construction of the recharging device is located at 3 km from the Mediterranean Sea and 2.5 km north-west of the city of Nabeul. 4 infiltration basins (20 m side and 1.5 m to 1.7 m deep) with a total infiltration area of 1365 m². Recharge was done by a couple of basins by intermittence . While the first couple is functional, others are unemployed to permit aeration of the unsaturated zone and to preserve its purifying role and avoid the effects of overpressure. Thikness of the unsaturated zone : 12 m. Thikness of the aquifer between 2 and 3 m. Lithology is composed of coarse sand. Recharge site before Recharge site in service rehabilitation 8 Results Evolution of the TWW volume recharged in Wadi Souhil aquifer Chemical quality 0.3 0.279 0.238 0.246 0.25 Chemical analyzes done 0.191 before starting recharge, 0.2 ) 0.172 3 m show that groundwater was 0.151 6 0.147 0.133 10 0.15 0.113 0.118 contaminated by nitrates 0.104 0.095 0.091 0.1 (234-335 mg/l). 0.06 Volume Volume ( 0.043 0.042 0.05 After recharge, the 0 unsaturated zone has 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 improved the qualitative Recharge effect on the piezometric level in Wadi Souhil aquifer (Nabeul-Tunisia) situation of the groundwater, it has allowed the purification of the TWW that have diluted 03/01/1992 28/01/1992 18/02/1992 21/04/1992 02/06/1992 07/12/1992 17/11/1993 14/02/1994 07/05/1994 10/11/1994 14/06/1995 06/05/1996 09/01/1997 30/10/1997 24/04/1998 23/10/1998 31/04/1999 21/10/1999 27/04/2000 26/10/2000 01/04/2001 01/10/2001 01/04/2002 01/10/2002 01/04/2004 01/10/2004 7 groundwater around the site, 8 9 nitrate concentrations 10 decreases to 50 mg/l. 11 12 Water depth Waterdepth (m) 13 14 PZ1 PZ4bis PZ4 PZC1 PZ11 PZ14 9 Case study of El Hajeb-Sidi Abid aquifer (SFAX) Irrigated perimeter of El HAJEB / DATA • Startup: 1989 • Area: - 350 ha in 1989 - 450 ha in 2011 : Agricultural orientation : fodder crops 330 ha / intercropped with trees spaced 24 m x 24 m 120 ha bare land • Annual rainfall average (1950-2001): 212 mm • ETP annual average : 1195 mm • Source of water: Treated waste water plant Sfax SOUTH • Creation date in 1983: 47% domestic waste water, 21% industrial waste water, 20% parasite infiltration water and 10% collective water. • Before 2007, aerated lagoons : 24,000 m3 / d. • After 2007, low load activated sludge with denitrification in cascade 49500 m3/d. 10 El Hajeb-Sidi Abid aquifer /DATA Lenses of sand and gravel on low thickness (2-8 m), separated by clay and sand formations of 6 m thick. Exploitable resources are: 6.2 million m3/year; Withdrawals were made by 1245 wells. EvolutionFig N°12: of EvolutionTWW volume annuelle de volumeinfiltrated de recharge into the aquifer Volume (m3) 3500000 3000000 2500000 2000000 1500000 1000000 500000 0 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 YeaAnnée r Impact : The raising of level varies from 0.41 à 0.57 m (2005). Percolation to the phreatic aquifer : 0,1 Mm3 (5 % of the used TWW volume in irrigation). 11 Case study of Boumerdes aquifer (Mahdia) TWWP of Boumerdes / DATA • Starting : 2003 • Capacity : 700 m3/d • Treatment : Tertiary (Extended aeration) • Releases in the bed of the wadi Zrata / landscaped in storm water infiltration facilities/structures • Annual rainfall average : 301 mm Parameters DCO DBO5 SM (MES) Salinity (mgO²/l) (mgO²/l) (mg/l) (g/l) TWW Quality : Outlet 48 9 8 1.3 Standard 90