An Advanced Technology for Groundwater Treatment in the Northern Aquifer of the State of Qatar

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1 An Advanced Technology for Groundwater Treatment in the Northern Aquifer of the State of Qatar Dr. Ahmed Abdel-Wahab Chemical Engineering Program Texas A&M University at Qatar

2 Outlines Groundwater quality in Qatar Problems of sulfate and silica UHLA treatment process Sulfate removal with UHLA Conclusions

3 Groundwater in Qatar Groundwater is the only source for agriculture in Qatar Two groundwater provinces: Northern province, where groundwater occurs as a freshwater 'floating lens' on brackish and saline water Southern province where water quality is generally brackish Most of the farms exist in the northern part

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5 Greenhouse Cooling Greenhouses are used for agriculture in Qatar Evaporative cooling is used for adjusting the temperature inside the greenhouse Pads are susceptible to clogging when the concentrations of scale-forming materials are high in the feed water.

6 Greenhouse Cooling (Cont.) Such clogging and scaling can: substantially decrease the heat transfer efficiency shorten the equipment life. In addition, the recycling of cooling water can be limited by decreased water quality. Sulfate and silica are the most common and aggressive scale forming materials.

7 Groundwater Quality Sulfate exists in high concentrations in the central and northern groundwater aquifers in Qatar. Affects the efficiency of the cooling system Limits water recovery in inland desalination systems Sulfate should be removed from the feed water Constituent Calcium Magnesium Sodium Potassium Total Carbonate Sulfate Chloride ph Raw water quality (mg/l)

8 Available Sulfate Removal Methods Reverse osmosis, ion exchange, or electrodialysis can be used to remove sulfate. However, these technologies are expensive and have operating problems. Additionally, theses technologies produce brine that needs to be disposed off.

9 Ultra-High Lime with Aluminum Process (UHLA) Aluminum Ca(OH)2 CaCO3 (s) Mg(OH)2 (s) MgH2SiO4 (s) Ca6Al2(SO4)3(OH)12 CO2 + Na2CO3 CaCO3 (s) CO2

10 Advantages of UHLA Ability to remove sulfate and silica Less expensive than other alternatives Same equipment of lime softening Alum sludge can be used as aluminum source Precipitated solids can be recycled

11 Applications of UHLA Recycled cooling water treatment Treatment of domestic and industrial wastewater before reuse or recycle Pretreatment before membranes Brine treatment in zero liquid discharge systems

12 Removal Mechanisms in UHLA Solid Phase: Calcium sulfoaluminate Calcium sulfoaluminate is a LDH [Ca2Al (OH)6]+ OH Ca OH OH Al Ca OH OH Ca OH [A, nh2o] SO4 2- OH 2- SO4 + A- = OH, Cl, Br, I, NO3, SO42, CO32,.

13 Kinetics of Sulfate Removal with UHLA 4000 Residual Sulfate concentration (mg/l) mM Sulfate mM Sulfate Time (Hr)

14 Effect of Chemical Doses on Sulfate Removal 100 Initial [SO4] = 10 mm Final [SO4] (mm) 90 Initial [SO4] = 50 mm 80 Initial [SO4] = 100 mm 70 Theoretical (ettringite) Lime dose (mm) 300 Aluminum dose = 50% of lime dose 400

15 Equilibrium Modeling Methodology Model was based on PHREEQC Precipitation is the controlling mechanism PHREEQC database was modified to include new solid phases and their solubility products Solid name Ettringite Monosulfate Tricalcium hydroxyaluminate Tetracalcium hydroxyaluminate Calcium sulfate Calcium hydroxide Aluminum hydroxide Log (Ksp) Source Damidot and Glasser (1993) Damidot and Glasser (1993) This work (Cl-OH data) This work (Cl-OH data) Stumm and Morgan (1996) Stumm and Morgan (1996) This work (Cl-OH data)

16 Precipitated Solids Formation of solid solution contains: Calcium sulfoaluminate (ettringite) (Ca6Al2(SO4)3(OH)12) Calcium monosulfate (Ca4Al2(SO4)(OH)12) Tricalcium hydroxyaluminate (Ca3Al2(OH)12) Tetracalcium hydroxyaluminate (Ca3Al2(OH)12 Ca(OH2)

17 Comparison between experimental data and model predictions 100 Initial [SO4] = 10 mm 90 Initial [SO4] = 50 mm 80 Initial [SO4] = 100 mm Final [SO4] (mm) Lime dose (mm)

18 XRDSO4 Intensity K F,C4 F,C4 Et Et K M Et C3,C4 Et 0 C3,C4 20 K 40 F,M M Theta Diffraction patterns for precipitated solids C3 = tricalcium hydroxyaluminate, C4 = tetracalcium hydroxyaluminate, Et = ettringite (calcium sulfoaluminate), and M = monosulfate (calcium monosulfoaluminate).

19 Fractions of precipitated solids Ettringite Tricalcium hydroxyaluminate Monosulfate Tetracalcium hydroxyaluminate 1 Initial [SO4] = 10 mm Initial [SO4] = 50 mm Initial [SO4] = 100 mm Fractions of solids in the solid solution Lime dose (mm)

20 Conclusions UHLA UHLA can can remove remove sulfate sulfate efficiently efficiently Sulfate Sulfate precipitates precipitates as as calcium calcium sulfoaluminate sulfoaluminate The The kinetics kinetics of of sulfate sulfate removal removal by by UHLA UHLA is is rapid rapid enough enough for for practical practical applications applications Deviation Deviation of of observed observed stoichiometry stoichiometry from from the the theoretical theoretical stoichiometry stoichiometry Formation Formation of of solid solid solution solution The The optimum optimum ratio ratio of of lime lime dose dose to to aluminum aluminum dose dose and and to to initial initial [SO [SO44]] was was Equilibrium Equilibrium model model was was developed developed and and itit accurately accurately predicted predicted the the experimental experimental results results

21 Acknowledgements Dr. Kamel Amer, DAWR Dr. Shamrukh Mahmoud, TAMUQ Department of Agricultural and Water Research (DAWR), MMAA, Doha, Qatar

22 Thank You SHOKRAN