pH-conditioning for simultaneous removal of arsenic and iron ions from groundwater

The effects of some commonly used pH conditioners, viz., lime, banana ash, the carbonate and the bicarbonate of sodium and potassium and their binary mixture, on simultaneous removal of arsenic and iron ions from water have been studied. KHCO₃ has been found to be the most suitable pH conditioner for the purpose. About 80 mg/L KHCO₃ can remove both arsenate and iron ions from initial 250 μg/L and 20 mg/L to below their respective guideline values of the WHO for drinking water, retaining the final pH in the acceptable range for drinking. The simultaneous removal of arsenate and iron by the pH-conditioners decreases in the order: Lime > KHCO₃ > NaHCO₃ > K₂CO₃ > Na₂CO₃ > ash. However, lime requires post-treatment correction of highly alkaline pH. The arsenate ion is removed predominantly through goethite or ferrihydrite in the presence of the bicarbonates and through ferric hydroxide in the presence of the more alkaline pH-conditioners. KHCO₃ is more advantageous over the more basic substances including NaHCO₃, because with it, one not only needs the smallest dose but also can avoid careful adjustment of the dose for regulating the initial and the final pH. The paper clearly demonstrates the potential of KHCO₃ to substitute the currently used pH-conditioners, viz., ash, lime and NaHCO₃ for simultaneous removal of arsenate and iron ions.     

Experimental investigation of the flow characteristics of jettisoning in a CO2 carrier

This experimental study was performed to investigate the flow characteristics in the jettisoning flow line of a liquid CO₂ carrier. When a pressurized liquid CO₂ container loses mechanical integrity, possibly by material or mechanical defects, the liquid inventory should be drained out rapidly for safety reasons using the so-called jettisoning process. In the course of jettisoning, the liquid CO₂ undergoes two phase change stages, from liquid to liquid + vapor and from liquid + vapor to solid + vapor. Consequently, the jettisoning release rate is affected by the characteristics of these phase changes. In this study, liquid CO₂ was discharged through a small tube, representing a jettisoning flow line. The temperature and pressure were measured along the tube, and the locations of the phase changes were inferred from the measured data. The experimental results showed that active nucleation occurred near the tube tip and that the phase change into solid and vapor occurred just after leaving the pipe, irrespective of the tube length in this study.