Feasibility of Using Treated Wastewater in Groundwater Aquifer Recharge in Abu Dhabi Emirate, UAE

Transcription

1 Feasibility of Using Treated Wastewater in Groundwater Aquifer Recharge in Abu Dhabi Emirate, UAE Dr. Mohamed A. Dawoud Water Resources Advisor Environment Agency Abu Dhabi, UAE

2 Overview Introduction Treated Wastewater Production in Abu Dhabi Present Status Future Predicted Treated Wastewater Production Treated Wastewater Reuse Options Reuse for Irrigation Reuse for Aquifer Recharge Reuse for Industrial and District Cooling Cost Benefit Analysis Estimation of Wastewater Treatment Costs Estimation of Conveyance Costs Estimation of Injection and Groundwater Monitoring Costs Results and Discussion

3 Introduction Depletion of freshwater supplies for potable and irrigation uses is a major challenge in Abu Dhabi. Wastewater reclamation and reuse has been recognized as a promising strategy to alleviating water scarcity and reducing the impacts on the environment Reuse of treated wastewater started in Abu Dhabi 20 years back Advanced wastewater treatment is required in order to maintain adequate levels of sustainable reuse. In Abu Dhabi all wastewater treated up to tertiary levels.

4 Treated Wastewater Production in Abu Dhabi Present Status 46% 54% Reused Discharge to Env. Region Daily Production (m 3 ) Daily Reuse (m 3 ) Daily Discharge to Environment (m 3 ) Abu Dhabi 689, , ,249 Eastern Region 185, ,957 8,208 Western Region 35,672 28,701 6,971 Total 299, , ,428

5 Treated Wastewater Production in Abu Dhabi Future Predicted Production ,435

6 Treated Wastewater Reuse Options Six key factors with gradual importance contribute to the success of a water reuse project: economic, financial, regulatory, psychological, organizational and technical factors as shown in Figure (4). The economic, financial and psychological factors depend on two main groups of parameters: (1) the internal motivation of the local water agencies and authorities to rapidly establish a meaningful economic analysis and a rigorous financial plan and to gain public acceptance and (2) external non-controlled parameters such as slow and heavy institutional decisionmaking process, politicians' subjectivity, stakeholders' personality. Technical Organizational Regulatory Psychological Economic/Financial

7 (1) Reuse for Irrigation Dubai road Project: Length is 45 Km Daily capacity of 140,000 cubic meters Cost estimate 220 Million Dirham Al Ain road Project: Length is 70 Km Daily capacity of 270,000 cubic meters Cost estimate 720 Million Dirham

8 (2) Reuse for Groundwater Aquifer Recharge Hydrogeologic Overview Map of the Emirate of Abu Dhabi Northern Emirates SA L Quaternary Aquifer / Aquitard units directly underlain by the Lower Fars Formation as basal unit (Regional Aquiclude). SA U Quaternary Sand and Gravel Aquifer underlain by the Upper Fars Formation as basal unit. SA S Coastal and Inland Sabkhas (derived form satelite image and Digital Elevation Model). SA M Quaternary Sand and Gravel Aquifer underlain by tectonically emplaced dark Marlstones and Shales as main basal unit. Occasional, discontinuous limestone layers and outcrops occur. SAJ Quaternary Sand and Gravel Aquifer east of Jebel Hafit (Al Jaww Plain) underlain by the Upper Fars and Lower Fars Formations as basal unit. Tm B Baynunah Formation: Continental Upper Miocene Sandstones and Conglomerates with gypsiferous cap-rocks that form small mesas. Underlain by the Lower Fars Formation as basal unit. Tm F Lower Fars Formation (Miocene mudstones and evaporites) outcropping, or near surface. Z Y X SA U W SA M Arabian Gulf V C SA U U SA M C A A' T S Tm B C R SAJ Tm B SA S SA S Q B B' Tm B Tm B P O SA L SA S N Limestone Ridges and Mountains M SA U L C SA L SA S Salt Diapir (Cambrian) K D' D J Thrust Faults (inferred from reprocessed seismic data) I H SA S G C C' D D' Profile Line of Cross-Sections (see Figure 21) F GWAP Exploration Well Sultanate of Oman E Kilometers D SA S C Kingdom of Saudi Arabia 0 Tm F B A

9 (2) Reuse for Groundwater Aquifer Recharge

10 (3) Reuse for Industrial and District Cooling The industrial and district cooling demands are very limited with a capacity of 25,000 m 3 /day. So covering these demands will not be enough to utilize all discharged treated wastewater to the environment. So, partially these demands can be covered with no impacts on the other two alternatives/options. Three factors are affecting the reuse of treated wastewater in industrial sector and district cooling including quantities, quality, regulations and the feasibility. Additional treatment facilities maybe needed which will be additional cost and affect the feasibility.

11 Cost Benefit Analysis Estimation of Wastewater Treatment Costs: The results indicating that the cost per unit treated wastewater ranges between 3 to 5 AED due to many factors affecting this cost Elevation Depth 140m+MSL 135m+MSL 110m+MSL 105m+MSL 100m+MSL 0m 5m 30m 35m 40m Cross Section Horizontal Exaggeration: 20fold 0m 0.1m 0.2m 0.3m 0.4m 0.5m 0.6m 0.7m 0.8m 0.9m 1m Top Hole Annulus-Sealing Compactonit 36 -Borehole Annulus-Cementation 30 -Steel Conductor Pipe 28 -Borehole Annulus Filling (Stone Chippings) 12 -PVC Blank Casing 2 -PVC Monitoring Pipe Static Groundwater Level Annulus-Sealing Compactonit 3 -PVC Monitoring Pipe (Screened Sections Filter-Gauze-Wrapped) Plan View Estimation of Conveyance Costs: High-density polyethylene pipe (HDPE) Diameters The average elevation change in Al Ain road project is estimated to be about 70 m and head losses due to pipe friction limit the overall head loss to no greater than 120 m. 95m+MSL 90m+MSL 85m+MSL 80m+MSL 75m+MSL 70m+MSL 45m 50m 55m 60m 65m 70m Filtersand-Packing (0.4mm - 0.8mm) Filtersand-Packing (0.7mm - 1.3mm) 12 -PVC Wire-wrapped Screen (0.3mm Openings) Centraliser (Production / Monitoring Casing) 4 -Steel Riser Pipe Centraliser (Riser Pipe / Monitoring Pipe) 65m+MSL 75m Submersible Pump Injection, recovery and Monitoring Costs: 60m+MSL 55m+MSL 80m 85m Cement-Plug 12¼ -Borehole (Pre-Drilling)

12 Results and Discussion Estimation of Conveyance Costs: High-density polyethylene pipe (HDPE) Diameters The average elevation change in Al Ain road project is estimated to be about 70 m and head losses due to pipe friction limit the overall head loss to no greater than 120 m. The market value for tertiary treated wastewater is set between $0.65 and $1.1 /m 3 without pumping and between $0.95 and $1.31 /m 3 with pumping Operation and maintenance cost for producing and transmission of the wastewater to the demand centers is about $0.16/m 3 without pumping and $0.16/m 3 with pumping. Reusing treated wastewater will reduce nutrient concentration which may detriment agricultural crops fertilization, although the negative economic impact figures vary from different studies between $-0.07/m 3 and $0.01/m 3. Aquifer recharge system with treated wastewater is inexpensive, efficient for pathogen removal, and is not highly technical to operate. Most of the cost associated with an SAT is for pumping the water from the recovery wells, which is usually $ USD per m3. In terms of reductions, SAT systems typically remove all BOD, TSS, and pathogenic organisms from the waste and tend to treat wastewater to a standard that would generally allow unrestricted irrigation.

13 Conclusion & Recommendations Treated wastewater can successfully replace potable desalinated water in district energy/power applications. However the present demands will not cover the available non-utilized and discharged treated wastewater. So their demands can be covered without impact on the other alternatives. Treated wastewater analyses over extended time frames indicated that the quality is suitable and no additional treatment is needed. The critical parameters of the treated wastewater include Cl, PO 4, NH 3, TOC, and TSS. There are some factors which should be taken into consideration for this option including design, materials, chemical, and the operational. Monitoring and control systems should be added.

14 Thanks