Capacitive deionisation for inland brackish groundwater desalination: A case study

Transcription

1 Capacitive deionisation for inland brackish groundwater desalination: A case study Dr. Wei Zhang, Mohamed Mossad and Prof. Linda Zou SA Water Centre for Water Management and Reuse, University of South Australia

2 Capacitive deionisation (CDI) Figure 1. Schematic diagram of the cell construction in the capacitive deionisation unit. Each cell assembly contained 200 sheets of activated carbon (100 cathodes and 100 anodes). The total mass of activated carbon was estimated to be 1,354 grams (g) with a specific area of 800 metres squared per gram (m 2 /g).

3 Figure 2. Schematic diagram of the capacitive deionisation (CDI) unit.

4 Testing site Figure 3. The location of the Wilora community in the Northern Territory, Australia, where the inset is a photograph of a local groundwater pipeline connection. The field test was carried out in October 2011, when the average temperature and humidity on-site were approximately 45 degrees Celsius ( C) and 80%, respectively.

5 Figure 4. Local water station at Wilora (left), front entrance (upper right) and CDI unit set up within the station (lower right)

6 TDS removal study Figure 5. Plot of TDS concentration as a function of time during the 90 s purification cycle for each flow rate, where the arrows indicate the appearance of lowest TDS concentration or highest TDS removal rate.

7 Figure 6. Highest TDS removal rate and treated TDS concentration over the target TDS concentration (500 mg/l) as a function of flow rate.

8 Energy efficiency study Table 1. Energy consumption (kwh/m 3 of treated water) and (Wh/g of salt removed) as a function of feed flow rate; Flow rate (L/min) Energy efficiency (kwh/m 3 ) Energy efficiency (Wh/g)

9 Figure 7. Times of increase of one working cycle energy consumption, treated water volume and electrosorptive loading of each flow rate compare to at flow rate of 1 L/min.

10 Ion selectivity study Table 2 Initial composition of the feed water at Wilora, Northern Territory, Australia. Ions Concentration (mg/l) ADWG Sodium Potassium 63 - Calcium Magnesium Iron Aluminium Copper Boron Arsenic Silica 88 - Nitrate Fluoride Chloride Iodide Sulphate Phosphorus Bicarbonate ph Turbidity 0.14 (NTU) 4 True colour 2.8 (CU) 15

11 Figure 8. The removal efficiency of different metal ions, where the error bars represent the three tests undertaken on different days under the same conditions.

12 Figure 9. the removal efficiency of different non-metal ions for each flow rate where the error bars represent the three tests undertaken on different days under the same conditions.

13 Lab scale study Figure 10. The electrosorption isotherm of sodium chloride onto activated carbon at the applied voltage of 1.5 V and a flow rate of 0.5 L/min.

14 Table 3 The fitting parameters of Langmuir and Freundlich isotherms and the regression coefficients. Isotherm Langmuir Freundlich Model equation Parameter Value R R

15 Figure 11. The electrosorption kinetics of sodium chloride onto capacitive deionisation electrodes at various feed concentrations.

16 Conclusions CDI technology offers a viable alternative solution to brackish water treatment, especially in communities in remote area where building a large and high-maintenance treatment plant is not practical. Using the current configuration and with the local water conditions, 7 L/min is recommended as the optimal operational flow rate for lowering the TDS level as close as to 500 mg/l. Energy consumption of CDI cells was approximately 0.76 kwh/m 3 of treated water in the optimal operating condition. The current CDI set-up has demonstrated a satisfactory overall hardness removal from the groundwater at Wilora at all flow rates. Long term operation showed little sign of performance reduction and is easy to maintain on-site using pre-formulated cleaning solution.

17 Acknowledgement LT Green Technology Thank you!