Drinking seawater: Investigations into desalination

Abstract

Water is essential to living organisms, yet only 0.02% of this natural resource is accessible as a direct source of fresh- and drinking water. South Africa, being a coastal country, is an ideal candidate for the use of treated sea water as an alternative source of fresh water. Desalination is the process in which dissolved salts are removed from saline water, forming fresh water. However, desalination processes are costly and are often energy and water intensive. This project considers the economic feasibility, environmental feasibility and viability of a differed distillation column that can be used as a desalination unit. A laboratory-scale distillation column was modified to provide energy to the unit with the purpose of decreasing the cost, time and energy requirements of the desalination (distillation) process. Current technologies such as Reverse Osmosis and Multi staged flash distillation are costly, time and energy intensive. In this work, the proposed desalination unit is a findenser in place of the traditional Liebig condenser to provide an environmentally friendly and cost effective alternative. It is also compact and portable which makes it favorable for domestic use. The small scale experiments performed using the Liebig condenser showed an average water recovery of 1.38 x 10-3 L/min and the scaled-up experiments show an average water recovery of 3.53 x 10-3 L/min, which resulted in an efficiency of 91% and 93%. Removal of salt water using the lab scale distillation unit requires 2 hours and 13 minutes to distil 500 mL. The salt solution reaches a maximum temperature of 105°C. The findenser is the more favourable cooling method due to its portability and conservation of water. Our results further show that the maximum capacity of this lab-scale unit is 3 liters of fresh water per day, over a 12 hour operational period.