Fresh Water Generation from Saline &Contaminated Textile Wastewater using an Active Solar Still Coupled with a Solar Pond System

Abstract

More than 70 % of the available water in Pakistan is unsafe for drinking purposes as per WHO guidelines. The situation is alarming in Sindh and southern Punjab, as the TDS level of more than 57% of raw water is greater than 3000 mg/L and 14.7 % have the TDS within the range of 1500-3000 mg/L. The unavailability of energy efficient water treatment technologies makes the water purification more difficult. Pakistan has an average of more than 10 hours of sunshine throughout the day of 5-7 kWh/m2 insulation. This study was conducted to harness the solar energy potential of Pakistan, using the solar stills coupled with a solar pond system, to device a reliable, clean and cheapest alternative technique to provide safe drinking water to the arid regions. For the designed system, the feed water having the TDS within the range of 1500-5000 mg/L showed an overall TDS removal efficiency of 99%. The coupling of the solar still with solar pond increased the yield by 45%, which was almost doubled when the temperature difference between the coolant and solar still was greater than 20˚C. A maximum yield of 16 liters per day of treated water was obtained which is equivalent to the requirements of a normal size household. In the solar pond, the feed water was pre-heated to a maximum of 37˚C using solar radiations. The solar pond was continuously run for a period of six weeks, using different composition of salts. Three thermal gradient layers were established using NaCl salt and a combination of NaCl & MgCl2. A combination of NaCl & MgCl2 pond was able to retain more thermal energy. The treatment performance of the proposed system was also monitored on the textile wastewater having the COD, BOD5, TSS and TDS of (1212, 658, 2218 and 268) mg/L respectively. A positive trend in the removal of all the parameters was observed, the COD dropped from 1212 to (42, 36 & 74) mg/L in three completed runs. An overall removal of 85% was observed in chlorides, 76% in fluorides, 95% in ammonia and no heavy metals were detected in both, the feed and product water.